1
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Silverman DN, Plante TB, Infeld MI, Juraschek SP, Dougherty G, Meyer MF. P1666Do beta-blockers increase the risk for hospitalizations in heart failure with preserved ejection fraction? A secondary analysis of beta-blocker use in the TOPCAT trial. Eur Heart J 2019. [DOI: 10.1093/eurheartj/ehz748.0424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Abstract
Background
The use of beta-blockers for treatment of heart failure (HF) with a reduced ejection fraction (EF) is unequivocally beneficial, but their role in the treatment of preserved EF (HFpEF) remains unclear.
Purpose
In a contemporary HFpEF cohort, we sought to assess the association of HF hospitalizations and the use of beta-blockers in patients with an EF above and below 50%.
Methods
The TOPCAT trial tested spironolactone vs. placebo among patients with HFpEF, including some with mild reductions in EF between 45–50%. The primary outcome was a composite of cardiovascular (CV) mortality, aborted cardiac arrest, or HF hospitalizations. Medication use, including beta-blockers, was reported at each visit and hospitalization. In the 1,761 participants from the Americas, we compared the association of beta-blocker use (vs. no use) and HF hospitalization or CV mortality using Cox proportional hazards models adjusted for baseline demographics, history of myocardial infarction, atrial fibrillation, chronic obstructive pulmonary disease, asthma, and hypertension. The analyses were repeated in the EF strata ≥50% and <50%.
Results
Among patients included in the current analysis (mean age 72 years, 50% female, 78% white), 1,496/1,761 (85%) received beta-blockers and 1,566/1,761 (89%) had an EF ≥50%. HF hospitalizations and CV mortality occurred in 399/1,761 (23%) and 223/1,761 (13%) of participants, respectively. Beta-blocker use was associated with an increase in risk of HF hospitalization among patients with preserved EF ≥50% [HR 1.56, (95% CI 1.09–2.24), p=0.01] and was associated with a reduction in risk of hospitalization in patients with an EF <50% [HR 0.42, (95% CI 0.18- 0.99), p<0.05]. We found a significant interaction for EF threshold and beta-blocker use on incident HF hospitalizations (p=0.01). There were no differences in CV mortality.
Figure 1. Kaplan Meier incidence plots
Conclusions
Beta-blocker use was associated with an increase in HF hospitalizations in patients with HFpEF (EF≥50%) but did not affect CV mortality. Further research is needed to confirm these findings and elucidate causality.
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Affiliation(s)
- D N Silverman
- University of Vermont Larner School of Medicine, Department of Medicine, Burlington, United States of America
| | - T B Plante
- University of Vermont Larner School of Medicine, Department of Medicine, Burlington, United States of America
| | - M I Infeld
- University of Vermont Larner School of Medicine, Department of Medicine, Burlington, United States of America
| | - S P Juraschek
- Beth Israel Deaconess Medical Center, Department of Medicine, Boston, United States of America
| | - G Dougherty
- Johns Hopkins Bloomberg School of Public Health, Baltimore, United States of America
| | - M F Meyer
- University of Vermont Larner School of Medicine, Department of Medicine, Burlington, United States of America
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2
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Andring JT, Lomelino CL, Tu C, Silverman DN, McKenna R, Swenson ER. Carbonic anhydrase II does not exhibit Nitrite reductase or Nitrous Anhydrase Activity. Free Radic Biol Med 2018; 117:1-5. [PMID: 29355738 DOI: 10.1016/j.freeradbiomed.2018.01.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/09/2017] [Revised: 01/09/2018] [Accepted: 01/13/2018] [Indexed: 01/25/2023]
Abstract
Carbonic anhydrase II (CA II) is a zinc metalloenzyme that catalyzes the reversible interconversion of water and CO2 to bicarbonate and a proton. CA II is abundant in most cells, and plays a role in numerous processes including gas exchange, epithelial ion transport, respiration, extra- and intracellular pH control, and vascular regulation. Beyond these CO2 and pH-linked roles, it has been postulated that CA II might also reduce nitrite (NO2-) to nitric oxide (NO), as bicarbonate and NO2- both exhibit sp2 molecular geometry and NO also plays an important role in vasodilation and regulation of blood pressure. Indeed, previous studies by Aamand et al. have shown that bovine CA II (BCA II) possesses nitrite dehydration activity and paradoxically demonstrated that CA inhibitors (CAIs) such as dorzolamide and acetazolamide significantly increased NO production (Aamand et al., 2009; Nielsen and Fago, 2015) [1,2]. Hence, the goal of this work was to revisit these studies using the same experimental conditions as Aamand et al. measuring NO generation by two methods, and to examine the structure of CA II in complex with NO2- in the presence and absence of dorzolamide. Our results contradict the previous findings and indicate that CA II does not exhibit nitrite reductase or dehydration activity, and that this is not enhanced in the presence of CA inhibitors. In addition, a structural examination of BCA II in complex with NO2- and superimposed with dorzolamide demonstrates that CA inhibitor binding at the active site to the zinc moiety blocks potential NO2- binding.
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Affiliation(s)
- Jacob T Andring
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL 32610, USA
| | - Carrie L Lomelino
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL 32610, USA
| | - Chingkuang Tu
- Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville, FL 32610, USA
| | - David N Silverman
- Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville, FL 32610, USA
| | - Robert McKenna
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL 32610, USA
| | - Erik R Swenson
- Medical Service, Veterans Affairs Puget Sound Health Care System, University of Washington, Seattle Washington 98108, USA.
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3
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Zhu W, Easthon LM, Reinhardt LA, Tu C, Cohen SE, Silverman DN, Allen KN, Richards NGJ. Substrate Binding Mode and Molecular Basis of a Specificity Switch in Oxalate Decarboxylase. Biochemistry 2016; 55:2163-73. [PMID: 27014926 PMCID: PMC4854488 DOI: 10.1021/acs.biochem.6b00043] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Oxalate
decarboxylase (OxDC) catalyzes the conversion of oxalate
into formate and carbon dioxide in a remarkable reaction that requires
manganese and dioxygen. Previous studies have shown that replacing
an active-site loop segment Ser161-Glu162-Asn163-Ser164 in the N-terminal domain of OxDC with
the cognate residues Asp161-Ala162-Ser-163-Asn164 of an evolutionarily related, Mn-dependent
oxalate oxidase gives a chimeric variant (DASN) that exhibits significantly
increased oxidase activity. The mechanistic basis for this change
in activity has now been investigated using membrane inlet mass spectrometry
(MIMS) and isotope effect (IE) measurements. Quantitative analysis
of the reaction stoichiometry as a function of oxalate concentration,
as determined by MIMS, suggests that the increased oxidase activity
of the DASN OxDC variant is associated with only a small fraction
of the enzyme molecules in solution. In addition, IE measurements
show that C–C bond cleavage in the DASN OxDC variant proceeds
via the same mechanism as in the wild-type enzyme, even though the
Glu162 side chain is absent. Thus, replacement of the loop
residues does not modulate the chemistry of the enzyme-bound Mn(II)
ion. Taken together, these results raise the possibility that the
observed oxidase activity of the DASN OxDC variant arises from an
increased level of access of the solvent to the active site during
catalysis, implying that the functional role of Glu162 is
to control loop conformation. A 2.6 Å resolution X-ray crystal
structure of a complex between oxalate and the Co(II)-substituted
ΔE162 OxDC variant, in which Glu162 has been deleted
from the active site loop, reveals the likely mode by which the substrate
coordinates the catalytically active Mn ion prior to C–C bond
cleavage. The “end-on” conformation of oxalate observed
in the structure is consistent with the previously published V/K IE data and provides an empty coordination
site for the dioxygen ligand that is thought to mediate the formation
of Mn(III) for catalysis upon substrate binding.
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Affiliation(s)
- Wen Zhu
- Department of Chemistry & Chemical Biology, Indiana University-Purdue University Indianapolis , Indianapolis, Indiana 46202, United States
| | - Lindsey M Easthon
- Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States
| | - Laurie A Reinhardt
- Department of Biochemistry, University of Wisconsin , Madison, Wisconsin 53726, United States
| | - Chingkuang Tu
- Department of Pharmacology & Therapeutics, University of Florida , Gainesville, Florida 32610, United States
| | - Steven E Cohen
- Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States
| | - David N Silverman
- Department of Pharmacology & Therapeutics, University of Florida , Gainesville, Florida 32610, United States
| | - Karen N Allen
- Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States
| | - Nigel G J Richards
- Department of Chemistry & Chemical Biology, Indiana University-Purdue University Indianapolis , Indianapolis, Indiana 46202, United States
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4
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Mahon BP, Díaz-Torres NA, Pinard MA, Tu C, Silverman DN, Scott KM, McKenna R. Activity and anion inhibition studies of the α-carbonic anhydrase from Thiomicrospira crunogena XCL-2 Gammaproteobacterium. Bioorg Med Chem Lett 2015; 25:4937-4940. [PMID: 25998503 PMCID: PMC5358508 DOI: 10.1016/j.bmcl.2015.05.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Revised: 04/28/2015] [Accepted: 05/01/2015] [Indexed: 11/29/2022]
Abstract
Thiomicrospira crunogena XCL-2 expresses an α-carbonic anhydrase (TcruCA). Sequence alignments reveal that TcruCA displays a high sequence identity (>30%) relative to other α-CAs. This includes three conserved histidines that coordinate the active site zinc, a histidine proton shuttling residue, and opposing hydrophilic and hydrophobic sides that line the active site. The catalytic efficiency of TcruCA is considered moderate relative to other α-CAs (k(cat)/K(M)=1.1×10(7) M(-1) s(-1)), being a factor of ten less efficient than the most active α-CAs. TcruCA is also inhibited by anions with Cl(-), Br(-), and I(-), all showing Ki values in the millimolar range (53-361 mM). Hydrogen sulfide (HS(-)) revealed the highest affinity for TcruCA with a Ki of 1.1 μM. It is predicted that inhibition of TcruCA by HS(-) (an anion commonly found in the environment where Thiomicrospira crunogena is located) is a way for Thiomicrospira crunogena to regulate its carbon-concentrating mechanism (CCM) and thus the organism's metabolic functions. Results from this study provide preliminary insights into the role of TcruCA in the general metabolism of Thiomicrospira crunogena.
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Affiliation(s)
- Brian P Mahon
- Department of Biochemistry and Molecular Biology, University of Florida, College of Medicine, 100 Newell Dr LG-171, Gainesville, FL 32610, United States
| | - Natalia A Díaz-Torres
- Department of Biochemistry and Molecular Biology, University of Florida, College of Medicine, 100 Newell Dr LG-171, Gainesville, FL 32610, United States
| | - Melissa A Pinard
- Department of Biochemistry and Molecular Biology, University of Florida, College of Medicine, 100 Newell Dr LG-171, Gainesville, FL 32610, United States
| | - Chingkuang Tu
- Department of Biochemistry and Molecular Biology, University of Florida, College of Medicine, 100 Newell Dr LG-171, Gainesville, FL 32610, United States
| | - David N Silverman
- Department of Pharmacology and Therapeutics, University of Florida, College of Medicine, Gainesville, FL 32610, United States
| | - Kathleen M Scott
- Department of Integrated Biology, University of South Florida, Tampa, FL 33620, United States
| | - Robert McKenna
- Department of Biochemistry and Molecular Biology, University of Florida, College of Medicine, 100 Newell Dr LG-171, Gainesville, FL 32610, United States.
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5
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Shenderovich IG, Lesnichin SB, Tu C, Silverman DN, Tolstoy PM, Denisov GS, Limbach HH. NMR studies of active-site properties of human carbonic anhydrase II by using (15) N-labeled 4-methylimidazole as a local probe and histidine hydrogen-bond correlations. Chemistry 2014; 21:2915-29. [PMID: 25521423 DOI: 10.1002/chem.201404083] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 11/12/2014] [Indexed: 12/24/2022]
Abstract
By using a combination of liquid and solid-state NMR spectroscopy, (15) N-labeled 4-methylimidazole (4-MI) as a local probe of the environment has been studied: 1) in the polar, wet Freon CDF3 /CDF2 Cl down to 130 K, 2) in water at pH 12, and 3) in solid samples of the mutant H64A of human carbonic anhydrase II (HCA II). In the latter, the active-site His64 residue is replaced by alanine; the catalytic activity is, however, rescued by the presence of 4-MI. For the Freon solution, it is demonstrated that addition of water molecules not only catalyzes proton tautomerism but also lifts its quasidegeneracy. The possible hydrogen-bond clusters formed and the mechanism of the tautomerism are discussed. Information about the imidazole hydrogen-bond geometries is obtained by establishing a correlation between published (1) H and (15) N chemical shifts of the imidazole rings of histidines in proteins. This correlation is useful to distinguish histidines embedded in the interior of proteins and those at the surface, embedded in water. Moreover, evidence is obtained that the hydrogen-bond geometries of His64 in the active site of HCA II and of 4-MI in H64A HCA II are similar. Finally, the degeneracy of the rapid tautomerism of the neutral imidazole ring His64 reported by Shimahara et al. (J. Biol. Chem.- 2007, 282, 9646) can be explained with a wet, polar, nonaqueous active-site conformation in the inward conformation, similar to the properties of 4-MI in the Freon solution. The biological implications for the enzyme mechanism are discussed.
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Affiliation(s)
- Ilya G Shenderovich
- University of Regensburg, Universitätsstrasse 31, 93053 Regensburg (Germany).
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6
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West D, Pinard MA, Tu C, Silverman DN, McKenna R. Human carbonic anhydrase II-cyanate inhibitor complex: putting the debate to rest. Acta Crystallogr F Struct Biol Commun 2014; 70:1324-7. [PMID: 25286933 PMCID: PMC4188073 DOI: 10.1107/s2053230x14018135] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Accepted: 08/07/2014] [Indexed: 01/13/2024] Open
Abstract
The binding of anions to carbonic anhydrase II (CA II) has been attributed to high affinity for the active-site zinc. An anion of interest is cyanate, for which contrasting binding modes have been reported in the literature. Previous spectroscopic data have shown cyanate behaving as an inhibitor, directly binding to the zinc, in contrast to previous crystallographic data that implied that cyanate acts as a substrate mimic that is not directly bound to the zinc but overlaps with the binding site of the substrate CO2. Wild-type and the V207I variant of CA II have been expressed and X-ray crystal structures of their cyanate complexes have been determined to 1.7 and 1.5 Å resolution, respectively. The rationale for the V207I CA II variant was its close proximity to the CO2-binding site. Both structures clearly show that the cyanate binds directly to the zinc. In addition, inhibition constants (∼40 µM) were measured using (18)O-exchange mass spectrometry for wild-type and V207I CA II and were similar to those determined previously (Supuran et al., 1997). Hence, it is concluded that under the conditions of these experiments the binding of cyanate to CA II is directly to the zinc, displacing the zinc-bound solvent molecule, and not in a site that overlaps with the CO2 substrate-binding site.
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Affiliation(s)
- Dayne West
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
| | - Melissa A. Pinard
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
| | - Chingkuang Tu
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL 32610, USA
| | - David N. Silverman
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL 32610, USA
| | - Robert McKenna
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
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7
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Aggarwal M, Kondeti B, Tu C, Maupin CM, Silverman DN, McKenna R. Structural insight into activity enhancement and inhibition of H64A carbonic anhydrase II by imidazoles. IUCrJ 2014; 1:129-35. [PMID: 25075329 PMCID: PMC4062085 DOI: 10.1107/s2052252514004096] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/24/2013] [Accepted: 02/21/2014] [Indexed: 05/31/2023]
Abstract
Human carbonic anhydrases (CAs) are zinc metalloenzymes that catalyze the hydration and dehydration of CO2 and HCO3 (-), respectively. The reaction follows a ping-pong mechanism, in which the rate-limiting step is the transfer of a proton from the zinc-bound solvent (OH(-)/H2O) in/out of the active site via His64, which is widely believed to be the proton-shuttling residue. The decreased catalytic activity (∼20-fold lower with respect to the wild type) of a variant of CA II in which His64 is replaced with Ala (H64A CA II) can be enhanced by exogenous proton donors/acceptors, usually derivatives of imidazoles and pyridines, to almost the wild-type level. X-ray crystal structures of H64A CA II in complex with four imidazole derivatives (imidazole, 1--methylimidazole, 2--methylimidazole and 4-methylimidazole) have been determined and reveal multiple binding sites. Two of these imidazole binding sites have been identified that mimic the positions of the 'in' and 'out' rotamers of His64 in wild-type CA II, while another directly inhibits catalysis by displacing the zinc-bound solvent. The data presented here not only corroborate the importance of the imidazole side chain of His64 in proton transfer during CA catalysis, but also provide a complete structural understanding of the mechanism by which imidazoles enhance (and inhibit when used at higher concentrations) the activity of H64A CA II.
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Affiliation(s)
- Mayank Aggarwal
- Department of Biochemistry and Molecular Biology, University of Florida, PO Box 100245, Gainesville, FL 32610, USA
| | - Bhargav Kondeti
- Department of Biochemistry and Molecular Biology, University of Florida, PO Box 100245, Gainesville, FL 32610, USA
| | - Chingkuang Tu
- Department of Pharmacology and Therapeutics, University of Florida, PO Box 100247, Gainesville, FL 32610, USA
| | - C. Mark Maupin
- Department of Chemical and Biological Engineering, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401, USA
| | - David N. Silverman
- Department of Pharmacology and Therapeutics, University of Florida, PO Box 100247, Gainesville, FL 32610, USA
| | - Robert McKenna
- Department of Biochemistry and Molecular Biology, University of Florida, PO Box 100245, Gainesville, FL 32610, USA
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8
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Boone CD, Gill S, Tu C, Silverman DN, McKenna R. Structural, catalytic and stabilizing consequences of aromatic cluster variants in human carbonic anhydrase II. Arch Biochem Biophys 2013; 539:31-7. [PMID: 24036123 DOI: 10.1016/j.abb.2013.09.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Revised: 08/30/2013] [Accepted: 09/02/2013] [Indexed: 11/24/2022]
Abstract
The presence of aromatic clusters has been found to be an integral feature of many proteins isolated from thermophilic microorganisms. Residues found in aromatic cluster interact via π-π or C-H⋯π bonds between the phenyl rings, which are among the weakest interactions involved in protein stability. The lone aromatic cluster in human carbonic anhydrase II (HCA II) is centered on F226 with the surrounding aromatics F66, F95 and W97 located 12 Å posterior the active site; a location which could facilitate proper protein folding and active site construction. The role of F226 in the structure, catalytic activity and thermostability of HCA II was investigated via site-directed mutagenesis of three variants (F226I/L/W) into this position. The measured catalytic rates of the F226 variants via (18)O-mass spectrometry were identical to the native enzyme, but differential scanning calorimetry studies revealed a 3-4 K decrease in their denaturing temperature. X-ray crystallographic analysis suggests that the structural basis of this destabilization is via disruption and/or removal of weak C-H⋯π interactions between F226 to F66, F95 and W97. This study emphasizes the importance of the delicate arrangement of these weak interactions among aromatic clusters in overall protein stability.
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Affiliation(s)
- Christopher D Boone
- Biochemistry & Molecular Biology, University of Florida, P.O. Box 100245, Gainesville, FL 32610, United States
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9
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Boone CD, Habibzadegan A, Tu C, Silverman DN, McKenna R. Structural and catalytic characterization of a thermally stable and acid-stable variant of human carbonic anhydrase II containing an engineered disulfide bond. Acta Crystallogr D Biol Crystallogr 2013; 69:1414-22. [PMID: 23897465 DOI: 10.1107/s0907444913008743] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Accepted: 03/30/2013] [Indexed: 11/10/2022]
Abstract
The carbonic anhydrases (CAs) are a family of mostly zinc metalloenzymes that catalyze the reversible hydration of CO2 to bicarbonate and a proton. Recently, there has been industrial interest in utilizing CAs as biocatalysts for carbon sequestration and biofuel production. The conditions used in these processes, however, result in high temperatures and acidic pH. This unfavorable environment results in rapid destabilization and loss of catalytic activity in CAs, ultimately resulting in cost-inefficient high-maintenance operation of the system. In order to negate these detrimental industrial conditions, cysteines at residues 23 (Ala23Cys) and 203 (Leu203Cys) were engineered into a wild-type variant of human CA II (HCAII) containing the mutation Cys206Ser. The X-ray crystallographic structure of the disulfide-containing HCAII (dsHCAII) was solved to 1.77 Å resolution and revealed that successful oxidation of the cysteine bond was achieved while also retaining desirable active-site geometry. Kinetic studies utilizing the measurement of (18)O-labeled CO2 by mass spectrometry revealed that dsHCAII retained high catalytic efficiency, and differential scanning calorimetry showed acid stability and thermal stability that was enhanced by up to 14 K compared with native HCAII. Together, these studies have shown that dsHCAII has properties that could be used in an industrial setting to help to lower costs and improve the overall reaction efficiency.
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Affiliation(s)
- Christopher D Boone
- Department of Biochemistry and Molecular Biology, University of Florida, PO Box 100245, Gainesville, FL 32610, USA
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10
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Aggarwal M, Boone CD, Kondeti B, Tu C, Silverman DN, McKenna R. Effects of cryoprotectants on the structure and thermostability of the human carbonic anhydrase II-acetazolamide complex. Acta Crystallogr D Biol Crystallogr 2013; 69:860-5. [PMID: 23633596 PMCID: PMC3640473 DOI: 10.1107/s0907444913002771] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2012] [Accepted: 01/28/2013] [Indexed: 11/10/2022]
Abstract
Protein X-ray crystallography has seen a progressive shift from data collection at cool/room temperature (277-298 K) to data collection at cryotemperature (100 K) because of its ease of crystal preparation and the lessening of the detrimental effects of radiation-induced crystal damage, with 20-25%(v/v) glycerol (GOL) being the preferred choice of cryoprotectant. Here, a case study of the effects of cryoprotectants on the kinetics of carbonic anhydrase II (CA II) and its inhibition by the clinically used inhibitor acetazolamide (AZM) is presented. Comparative studies of crystal structure, kinetics, inhibition and thermostability were performed on CA II and its complex with AZM in the presence of either GOL or sucrose. These results suggest that even though the cryoprotectant GOL was previously shown to be directly bound in the active site and to interact with AZM, it affects neither the thermostability of CA II nor the binding of AZM in the crystal structure or in solution. However, addition of GOL does affect the kinetics of CA II, presumably as it displaces the water proton-transfer network in the active site.
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Affiliation(s)
- Mayank Aggarwal
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, 1600 SW Archer Road, PO Box 100245, Gainesville, FL 32610, USA
| | - Christopher D. Boone
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, 1600 SW Archer Road, PO Box 100245, Gainesville, FL 32610, USA
| | - Bhargav Kondeti
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, 1600 SW Archer Road, PO Box 100245, Gainesville, FL 32610, USA
| | - Chingkuang Tu
- Department of Pharmacology, College of Medicine, University of Florida, 1600 SW Archer Road, PO Box 100245, Gainesville, FL 32610, USA
| | - David N. Silverman
- Department of Pharmacology, College of Medicine, University of Florida, 1600 SW Archer Road, PO Box 100245, Gainesville, FL 32610, USA
| | - Robert McKenna
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, 1600 SW Archer Road, PO Box 100245, Gainesville, FL 32610, USA
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11
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Mikulski R, West D, Sippel KH, Avvaru BS, Aggarwal M, Tu C, McKenna R, Silverman DN. Water networks in fast proton transfer during catalysis by human carbonic anhydrase II. Biochemistry 2012; 52:125-31. [PMID: 23215152 DOI: 10.1021/bi301099k] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Variants of human carbonic anhydrase II (HCA II) with amino acid replacements at residues in contact with water molecules in the active-site cavity have provided insights into the proton transfer rates in this protein environment. X-ray crystallography and (18)O exchange measured by membrane inlet mass spectrometry have been used to investigate structural and catalytic properties of variants of HCA II containing replacements of Tyr7 with Phe (Y7F) and Asn67 with Gln (N67Q). The rate constants for transfer of a proton from His64 to the zinc-bound hydroxide during catalysis were 4 and 9 μs(-1) for Y7F and Y7F/N67Q, respectively, compared with a value of 0.8 μs(-1) for wild-type HCA II. These higher values observed for Y7F and Y7F/N67Q HCA II could not be explained by differences in the values of the pK(a) of the proton donor (His64) and acceptor (zinc-bound hydroxide) or by the orientation of the side chain of the proton shuttle residue His64. They appeared to be associated with a reduced level of branching in the networks of hydrogen-bonded water molecules between proton shuttle residue His64 and the zinc-bound solvent molecule as observed in crystal structures at 1.5-1.6 Å resolution. Moreover, Y7F/N67Q HCA II is unique among the variants studied in having a direct, hydrogen-bonded chain of water molecules between the zinc-bound solvent and N(ε) of His64. This study provides the clearest example to date of the relevance of ordered water structure to rate constants for proton transfer in catalysis by carbonic anhydrase.
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Affiliation(s)
- Rose Mikulski
- Department of Pharmacology, University of Florida, Gainesville, FL 32610, USA
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12
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West D, Kim CU, Tu C, Robbins AH, Gruner SM, Silverman DN, McKenna R. Structural and kinetic effects on changes in the CO(2) binding pocket of human carbonic anhydrase II. Biochemistry 2012; 51:9156-63. [PMID: 23098192 DOI: 10.1021/bi301155z] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This work examines the effect of perturbing the position of bound CO(2) in the active site of human carbonic anhydrase II (HCA II) on catalysis. Variants of HCA II in which Val143 was replaced with hydrophobic residues Ile, Leu, and Ala were examined. The efficiency of catalysis in the hydration of CO(2) for these variants was characterized by (18)O exchange mass spectrometry, and their structures were determined by X-ray crystallography at 1.7-1.5 Å resolution. The most hydrophobic substitutions, V143I and V143L, showed decreases in the level of catalysis, as much as 20-fold, while the replacement by the smaller V143A mutation showed an only moderate 2-fold decrease in activity. Structural data for all three variants show no significant change in the overall position of amino acid side chains in the active site compared with the wild type. However, V143A HCA II showed additional ordered water molecules in the active site compared to the number for the wild type. To further investigate the decrease in the catalytic efficiency of V143I HCA II, an X-ray crystallographic CO(2) entrapment experiment was performed to 0.93 Å resolution. This structure revealed an unexpected shift in the CO(2) substrate toward the zinc-bound solvent, placing it ~0.3 Ǻ closer than previously observed in the wild type in conjunction with the observed dual occupancy of the product bicarbonate, presumably formed during the acquisition of data. These data suggest that the Ile substitution at position 143 reduced the catalytic efficiency, which is likely due to steric crowding resulting in destabilization of the transition state for conversion of CO(2) into bicarbonate and a decreased product dissociation rate.
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Affiliation(s)
- Dayne West
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, United States
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13
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Zimmerman S, Domsic JF, Tu C, Robbins AH, McKenna R, Silverman DN, Ferry JG. Role of Trp19 and Tyr200 in catalysis by the γ-class carbonic anhydrase from Methanosarcina thermophila. Arch Biochem Biophys 2012; 529:11-7. [PMID: 23111186 DOI: 10.1016/j.abb.2012.10.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2012] [Revised: 10/16/2012] [Accepted: 10/17/2012] [Indexed: 10/27/2022]
Abstract
Although widely distributed in Nature, only two γ class carbonic anhydrases are reported besides the founding member (Cam). Although roles for active-site residues important for catalysis have been identified in Cam, second shell residues have not been investigated. Two residues (Trp19 and Tyr200), positioned distant from the catalytic metal, were investigated by structural and kinetic analyses of replacement variants. Steady-state k(cat)/K(m) and k(cat) values decreased 3- to 10-fold for the Trp19 variants whereas the Y200 variants showed up to a 5-fold increase in k(cat). Rate constants for proton transfer decreased up to 10-fold for the Trp19 variants, and an increase of ~2-fold for Y200F. The pK(a) values for the proton donor decreased 1-2 pH units for Trp19 and Y200 variants. The variant structures revealed a loop composed of residues 62-64 that occupies a different conformation than previously reported. The results show that, although Trp19 and Y200 are non-essential, they contribute to an extended active-site structure distant from the catalytic metal that fine tunes catalysis. Trp19 is important for both CO(2)/bicarbonate interconversion, and the proton transfer step of catalysis.
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Affiliation(s)
- Sabrina Zimmerman
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA 16802, USA
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14
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Fisher SZ, Aggarwal M, Kovalevsky AY, Silverman DN, McKenna R. Neutron diffraction of acetazolamide-bound human carbonic anhydrase II reveals atomic details of drug binding. J Am Chem Soc 2012; 134:14726-9. [PMID: 22928733 DOI: 10.1021/ja3068098] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Carbonic anhydrases (CAs) catalyze the hydration of CO(2) forming HCO(3)(-) and a proton, an important reaction for many physiological processes including respiration, fluid secretion, and pH regulation. As such, CA isoforms are prominent clinical targets for treating various diseases. The clinically used acetazolamide (AZM) is a sulfonamide that binds with high affinity to human CA isoform II (HCA II). There are several X-ray structures available of AZM bound to various CA isoforms, but these complexes do not show the charged state of AZM or the hydrogen atom positions of the protein and solvent. Neutron diffraction is a useful technique for directly observing H atoms and the mapping of H-bonding networks that can greatly contribute to rational drug design. To this end, the neutron structure of H/D exchanged HCA II crystals in complex with AZM was determined. The structure reveals the molecular details of AZM binding and the charged state of the bound drug. This represents the first determined neutron structure of a clinically used drug bound to its target.
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Affiliation(s)
- S Zoë Fisher
- Bioscience Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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15
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Frost SC, Tu C, Silverman DN. Effect of Zinc on Carbonic Anhydrase IX Activity in MDA‐MB‐231 Breast Cancer Cells. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.966.6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Susan Cooke Frost
- Biochemistry and Molecular BiologyUniversity of FloridaGainesvilleFL
| | - Chingkuang Tu
- Pharmacology and TherapeuticsUniversity of FloridaGainesvilleFL
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16
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Tu C, Foster L, Alvarado A, McKenna R, Silverman DN, Frost SC. Role of zinc in catalytic activity of carbonic anhydrase IX. Arch Biochem Biophys 2012; 521:90-4. [PMID: 22465027 DOI: 10.1016/j.abb.2012.03.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2012] [Revised: 03/14/2012] [Accepted: 03/15/2012] [Indexed: 12/28/2022]
Abstract
The carbonic anhydrases (CAs) in the α class are zinc-dependent metalloenzymes. Previous studies have reported that recombinant forms of carbonic anhydrase IX (CAIX), a membrane-bound form of CA expressed in solid tumors, appear to be activated by low levels of zinc independent of its well-studied role at the catalytic site. In this study, we sought to determine if CAIX is stimulated by zinc in its native environment. MDA-MB-231 breast cancer cells express CAIX in response to hypoxia. We compared CAIX activity associated with membrane ghosts isolated from hypoxic cells with that in intact hypoxic cells. We measured CA activity directly using (18)O exchange from (13)CO(2) into water determined by membrane inlet mass spectrometry. In membrane ghosts, there was little effect of zinc at low concentrations on CAIX activity, although at high concentration zinc was inhibitory. In intact cells, zinc had no significant effect on CAIX activity. This suggests that there is an appreciable decrease in sensitivity to zinc when CAIX is in its natural membrane milieu compared to the purified forms.
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Affiliation(s)
- Chingkuang Tu
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL 32610, USA
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17
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Fisher Z, Kovalevsky AY, Mustyakimov M, Silverman DN, McKenna R, Langan P. Neutron structure of human carbonic anhydrase II: a hydrogen-bonded water network "switch" is observed between pH 7.8 and 10.0. Biochemistry 2011; 50:9421-3. [PMID: 21988105 DOI: 10.1021/bi201487b] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The neutron structure of wild-type human carbonic anhydrase II at pH 7.8 has been determined to 2.0 Å resolution. Detailed analysis and comparison to the previously determined structure at pH 10.0 show important differences in the protonation of key catalytic residues in the active site as well as a rearrangement of the H-bonded water network. For the first time, a completed H-bonded network stretching from the Zn-bound solvent to the proton shuttling residue, His64, has been directly observed.
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Affiliation(s)
- Zoë Fisher
- Bioscience Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87544, United States.
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18
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Mikulski R, Domsic JF, Ling G, Tu C, Robbins AH, Silverman DN, McKenna R. Structure and catalysis by carbonic anhydrase II: role of active-site tryptophan 5. Arch Biochem Biophys 2011; 516:97-102. [PMID: 22001224 DOI: 10.1016/j.abb.2011.09.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Revised: 09/27/2011] [Accepted: 09/28/2011] [Indexed: 11/25/2022]
Abstract
The tryptophan residue Trp5, highly conserved in the α class of carbonic anhydrases including human carbonic anhydrase II (HCA II), is positioned at the entrance of the active site cavity and forms a π-stacking interaction with the imidazole ring of the proton shuttle His64 in its outward orientation. We have observed that replacement of Trp5 in HCA II caused significant structural changes, as determined by X-ray diffraction, in the conformation of 11 residues at the N-terminus and in the orientation of the proton shuttle residue His64. Most significantly, two variants W5H and W5E HCA II had His64 predominantly outward in orientation, while W5F and wild type showed the superposition of both outward and inward orientations in crystal structures. Although Trp5 influences the orientation of the proton shuttle His64, this orientation had no significant effect on the rate constant for proton transfer near 1μs(-1), determined by exchange of (18)O between CO(2) and water measured by mass spectrometry. The apparent values of the pK(a) of the zinc-bound water and the proton shuttle residue suggest that different active-site conformations influence the two stages of catalysis, the proton transfer stage and the interconversion of CO(2) and bicarbonate.
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Affiliation(s)
- Rose Mikulski
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, United States
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19
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Moral MEG, Tu C, Richards NGJ, Silverman DN. Membrane inlet for mass spectrometric measurement of catalysis by enzymatic decarboxylases. Anal Biochem 2011; 418:73-7. [PMID: 21782782 DOI: 10.1016/j.ab.2011.06.031] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2011] [Revised: 05/17/2011] [Accepted: 06/23/2011] [Indexed: 01/20/2023]
Abstract
Membrane inlet mass spectrometry (MIMS) uses diffusion across a permeable membrane to detect in solution uncharged molecules of small molecular weight. We point out here the application of MIMS to determine catalytic properties of decarboxylases using as an example catalysis by oxalate decarboxylase (OxDC) from Bacillus subtilis. The decarboxylase activity generates carbon dioxide and formate from the nonoxidative reaction but is accompanied by a concomitant oxidase activity that consumes oxalate and oxygen and generates CO(2) and hydrogen peroxide. The application of MIMS in measuring catalysis by OxDC involves the real-time and continuous detection of oxygen and product CO(2) from the ion currents of their respective mass peaks. Steady-state catalytic constants for the decarboxylase activity obtained by measuring product CO(2) using MIMS are comparable to those acquired by the traditional endpoint assay based on the coupled reaction with formate dehydrogenase, and measuring consumption of O(2) using MIMS also estimates the oxidase activity. The use of isotope-labeled substrate ((13)C(2)-enriched oxalate) in MIMS provides a method to characterize the catalytic reaction in cell suspensions by detecting the mass peak for product (13)CO(2) (m/z 45), avoiding inaccuracies due to endogenous (12)CO(2).
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Affiliation(s)
- Mario E G Moral
- Department of Chemistry, University of Florida, Gainesville, FL 32610, USA
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20
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Cline MR, Tu C, Silverman DN, Toscano JP. Detection of nitroxyl (HNO) by membrane inlet mass spectrometry. Free Radic Biol Med 2011; 50:1274-9. [PMID: 21349325 DOI: 10.1016/j.freeradbiomed.2011.02.008] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2010] [Revised: 01/04/2011] [Accepted: 02/09/2011] [Indexed: 11/21/2022]
Abstract
Membrane inlet (or introduction) mass spectrometry (MIMS) was used to detect nitroxyl (HNO) in aqueous solution for the first time. The common HNO donors Angeli's salt (AS) and Piloty's acid (PA), along with a newly developed donor, 2-bromo-N-hydroxybenzenesulfonamide (2-bromo-Piloty's acid, 2BrPA), were examined by this technique. MIMS experiments revealed that under physiological conditions 2BrPA is an essentially pure HNO donor, but AS produces a small amount of nitric oxide (NO). In addition, MIMS experiments also confirmed that PA is susceptible to oxidation and NO production, but that 2BrPA is not as prone to oxidation.
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Affiliation(s)
- Meredith R Cline
- Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218, USA
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21
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Maupin CM, Castillo N, Taraphder S, Tu C, McKenna R, Silverman DN, Voth GA. Chemical rescue of enzymes: proton transfer in mutants of human carbonic anhydrase II. J Am Chem Soc 2011; 133:6223-34. [PMID: 21452838 PMCID: PMC4120857 DOI: 10.1021/ja1097594] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In human carbonic anhydrase II (HCA II), the mutation of position 64 from histidine to alanine (H64A) disrupts the rate limiting proton transfer (PT) event, resulting in a reduction of the catalytic activity of the enzyme as compared to the wild-type. Potential of mean force (PMF) calculations utilizing the multistate empirical valence bond (MS-EVB) methodology for H64A HCA II yields a PT free energy barrier significantly higher than that found in the wild-type enzyme. This high barrier, determined in the absence of exogenous buffer and assuming no additional ionizable residues in the PT pathway, indicates the likelihood of alternate enzyme pathways that utilize either ionizable enzyme residues (self-rescue) and/or exogenous buffers (chemical rescue). It has been shown experimentally that the catalytic activity of H64A HCA II can be chemically rescued to near wild-type levels by the addition of the exogenous buffer 4-methylimidazole (4MI). Crystallographic studies have identified two 4MI binding sites, yet site-specific mutations intended to disrupt 4MI binding have demonstrated these sites to be nonproductive. In the present work, MS-EVB simulations show that binding of 4MI near Thr199 in the H64A HCA II mutant, a binding site determined by NMR spectroscopy, results in a viable chemical rescue pathway. Additional viable rescue pathways are also identified where 4MI acts as a proton transport intermediary from the active site to ionizable residues on the rim of the active site, revealing a probable mode of action for the chemical rescue pathway.
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Affiliation(s)
- C. Mark Maupin
- Center for Biophysical Modeling and Simulation and Department of Chemistry, University of Utah, Salt Lake City, UT 84112
| | - Norberto Castillo
- Center for Biophysical Modeling and Simulation and Department of Chemistry, University of Utah, Salt Lake City, UT 84112
| | - Srabani Taraphder
- Center for Biophysical Modeling and Simulation and Department of Chemistry, University of Utah, Salt Lake City, UT 84112
- Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India
| | - Chingkuang Tu
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL 32610
| | - Robert McKenna
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610
| | - David N. Silverman
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL 32610
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610
| | - Gregory A. Voth
- Center for Biophysical Modeling and Simulation and Department of Chemistry, University of Utah, Salt Lake City, UT 84112
- Department of Chemistry, James Frank Institute, and Computation Institute, University of Chicago, 5735 S. Ellis Ave., Chicago, IL 60637
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22
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Frost SC, Li Y, Tu C, Silverman DN. Abstract 2056: Evidence against hypoxic-dependent activation of carbonic anhydrase IX in MDA-MB-231 breast cancer cells. Cancer Res 2011. [DOI: 10.1158/1538-7445.am2011-2056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Carbonic anhydrase IX (CAIX) is a membrane-bound, tumor-related enzyme the expression of which is often considered a marker for hypoxia, an indicator of poor prognosis, and associated with acidification of the tumor microenvironment. Many studies have shown that CAIX expression is induced by hypoxia exposing its catalytic domain to the interstitial milieu. Several recent studies have suggested that hypoxic conditions may also permit activation of CAIX, perhaps by causing a conformational change which exposes the catalytic pocket. Our goal was to assess the effect of anoxic conditions on CAIX activity in MDA-MB-231 cells, previously exposed to hypoxia which increases CAIX expression in the absence of other membrane-bound carbonic anhydrase (CA) family members.
We have taken advantage of membrane inlet mass spectrometry (MIMS) to directly analyze CA activity in intact cells by measuring the 18O exchange between CO2 and H2O. This method distinguishes between intracellular and extracellular CA activity. MDA-MB-231 cells were exposed to 1% oxygen for 16 hours after which they were isolated under normoxic or anoxic conditions. CA activity was then measured, again under normoxic or anoxic conditions. These data show biphasic depletion of 18O from CO2 under both normoxic and anoxic assay conditions. The first phase (which occurs over the first 20-40 seconds) represents a rapid diffusion of CO2 into cells where it is exposed to intracellular CAII. A catalytic cycle depletes 18O followed by efflux of CO2 from the cell. There was no difference in this phase between cells prepared and assayed under normoxic or anoxic conditions. The second phase (from 200-500 sec) is dominated by the hydration-dehydration reaction of CO2/HCO3− catalyzed by exofacial CA activity (CAIX). In cells exposed to anoxia, the slope of the second phase was greater than that observed with cells exposed to normoxic conditions indicating elevated CAIX activity. While this provided evidence that oxygen limitation might influence CAIX activity, the Ki values for two impermeant CA inhibitors, Cpd 5C and a polymeric sulfonamide, did not differ between anoxic and normoxic cells. We conclude from these data that the catalytic site of CAIX is exposed and functional under both anoxic or normoxic conditions.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2056. doi:10.1158/1538-7445.AM2011-2056
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Affiliation(s)
| | - Ying Li
- 1Univ. of Florida, Gainesville, FL
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23
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Frost SC, Li Y, Tu C, Wang H, Silverman DN. Catalysis of carbonic anhydrase IX and pH control in MDA‐MB‐231 breast cancer cells. FASEB J 2011. [DOI: 10.1096/fasebj.25.1_supplement.915.9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Ying Li
- Biochemistry and Molecular Biology
| | - Chingkuang Tu
- Pharmacology and TherapeuticsUniversity of FloridaGainesvilleFL
| | - Hai Wang
- Biochemistry and Molecular Biology
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24
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Li Y, Tu C, Wang H, Silverman DN, Frost SC. Catalysis and pH control by membrane-associated carbonic anhydrase IX in MDA-MB-231 breast cancer cells. J Biol Chem 2011; 286:15789-96. [PMID: 21454639 DOI: 10.1074/jbc.m110.188524] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Carbonic anhydrase IX (CAIX) is a membrane-bound, tumor-related enzyme whose expression is often considered a marker for hypoxia, an indicator of poor prognosis in the majority of cancer patients, and is associated with acidification of the tumor microenvironment. Here, we describe for the first time the catalytic properties of native CAIX in MDA-MB-231 breast cancer cells that exhibit hypoxia-inducible CAIX expression. Using (18)O exchange measured by membrane inlet mass spectrometry, we determined catalytic activity in membrane ghosts and intact cells. Exofacial carbonic anhydrase activity increases with exposure to hypoxia, an activity which is suppressed by impermeant sulfonamide CA inhibitors. Inhibition by sulfonamide inhibitors is not sensitive to reoxygenation. CAIX activity in intact cells increases in response to reduced pH. Data from membrane ghosts show that the increase in activity at reduced pH is largely due to an increase in the dehydration reaction. In addition, the kinetic constants of CAIX in membrane ghosts are very similar to our previous measurements for purified, recombinant, truncated forms. Hence, the activity of CAIX is not affected by the proteoglycan extension or membrane environment. These activities were measured at a total concentration for all CO(2) species at 25 mm and close to chemical equilibrium, conditions which approximate the physiological extracellular environment. Our data suggest that CAIX is particularly well suited to maintain the extracellular pH at a value that favors the survival fitness of tumor cells.
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Affiliation(s)
- Ying Li
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, USA
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25
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Moral MEG, Tu C, Imaram W, Angerhofer A, Silverman DN, Richards NGJ. Nitric oxide reversibly inhibits Bacillus subtilis oxalate decarboxylase. Chem Commun (Camb) 2011; 47:3111-3. [PMID: 21264418 DOI: 10.1039/c0cc04946h] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Membrane inlet mass spectrometry (MIMS) has been employed to assay the catalytic activity of oxalate decarboxylase (OxDC), allowing us to demonstrate that nitric oxide (NO) reversibly inhibits the enzyme under dioxygen-depleted conditions. X-band EPR measurements do not provide any direct evidence for the interaction of NO with either of the Mn(II) centers in OxDC raising the possibility that there is a separate dioxygen-binding pocket in the enzyme.
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Affiliation(s)
- Mario E G Moral
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
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26
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Fisher SZ, Kovalevsky AY, Domsic J, Mustyakimov M, Silverman DN, McKenna R, Langan P. Enzymes for carbon sequestration: neutron crystallographic studies of carbonic anhydrase. Acta Crystallogr D Biol Crystallogr 2010; 66:1178-83. [PMID: 21041933 PMCID: PMC2967421 DOI: 10.1107/s0907444910019700] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2010] [Accepted: 05/25/2010] [Indexed: 11/11/2022]
Abstract
Carbonic anhydrase (CA) is a ubiquitous metalloenzyme that catalyzes the reversible hydration of CO(2) to form HCO(3)(-) and H(+) using a Zn-hydroxide mechanism. The first part of catalysis involves CO(2) hydration, while the second part deals with removing the excess proton that is formed during the first step. Proton transfer (PT) is thought to occur through a well ordered hydrogen-bonded network of waters that stretches from the metal center of CA to an internal proton shuttle, His64. These waters are oriented and ordered through a series of hydrogen-bonding interactions to hydrophilic residues that line the active site of CA. Neutron studies were conducted on wild-type human CA isoform II (HCA II) in order to better understand the nature and the orientation of the Zn-bound solvent (ZS), the charged state and conformation of His64, the hydrogen-bonding patterns and orientations of the water molecules that mediate PT and the ionization of hydrophilic residues in the active site that interact with the water network. Several interesting and unexpected features in the active site were observed which have implications for how PT proceeds in CA.
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Affiliation(s)
- S Z Fisher
- Bioscience Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
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27
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Li Y, Wang H, Tu C, Shiverick KT, Silverman DN, Frost SC. Role of hypoxia and EGF on expression, activity, localization and phosphorylation of carbonic anhydrase IX in MDA-MB-231 breast cancer cells. Biochim Biophys Acta 2010; 1813:159-67. [PMID: 20920536 DOI: 10.1016/j.bbamcr.2010.09.018] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2010] [Revised: 09/24/2010] [Accepted: 09/27/2010] [Indexed: 12/12/2022]
Abstract
Carbonic anhydrase IX (CAIX) is a zinc metalloenzyme that catalyzes the reversible hydration of CO(2). CAIX is overexpressed in many types of cancer, including breast cancer, but is most frequently absent in corresponding normal tissues. CAIX expression is strongly induced by hypoxia and is significantly associated with tumor grade and poor survival. Herein, we show that hypoxia induces a significant increase in CAIX protein in MDA-MB-231 breast cancer cells. Using a unique mass spectrophotometric assay, we demonstrate that CAIX activity in plasma membranes isolated from MDA-MB-231 is correlated with CAIX content. We also show that CAIX exists predominantly as a dimeric, high-mannose N-linked glycoprotein. While there is some evidence that the dimeric form resides specifically in lipid rafts, our data do not support this hypothesis. EGF, alone, did not affect the distribution of CAIX into lipid rafts. However, acute EGF treatment in the context of hypoxia increased the amount of CAIX in lipid rafts by about 5-fold. EGF did not stimulate tyrosine phosphorylation of CAIX, although EGFR and down-stream signaling pathways were activated by EGF. Interestingly, hypoxia activated Akt independent of EGF action. Together, these data demonstrate that the active form of CAIX in the MDA-MB-231 breast cancer cell line is dimeric but that neither lipid raft localization nor phosphorylation are likely required for its dimerization or activity.
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Affiliation(s)
- Ying Li
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610-0267, USA
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28
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Domsic JF, Williams W, Fisher SZ, Tu C, Agbandje-McKenna M, Silverman DN, McKenna R. Structural and kinetic study of the extended active site for proton transfer in human carbonic anhydrase II. Biochemistry 2010; 49:6394-9. [PMID: 20578724 DOI: 10.1021/bi1007645] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The catalysis of CO(2) hydration by human carbonic anhydrase II (HCA II) is limited in maximal velocity by proton transfer from a zinc-bound water molecule to the proton shuttle His64. This proton transfer occurs along a hydrogen-bonded water network, leading to the proton shuttle residue His64, which in turn transfers the proton to bulk solvent. The side chain of His64 occupies two conformations in wild-type HCA II, pointing inward toward the zinc or outward toward bulk solvent. Previously, several studies have examined the roles of residues of the active site cavity that interact with the solvent-mediated hydrogen-bonded network between His64 and the zinc-bound water. Here these studies are extended to examine the effects on proton transfer by mutation at Lys170 (to Ala, Asp, Glu, and His), a residue located near the side chain of His64 but over 15 A away from the active site zinc. In all four variants, His64 is observed in the inward conformation associated with a decrease in the pK(a) of His64 by as much as 1.0 unit and an increase in the rate constant for proton transfer to as much as 4 micros(-1), approximately 5-fold larger than wild-type HCA II. The results show a significant extension of the effective active site of HCA II from the zinc-bound water at the base of the conical cavity in the enzyme to Lys170 near the rim of the cavity. These data emphasize that the active site of HCA II is extended to include residues that, at first glance, appear to be too far from the zinc to exert any catalytic effects.
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Affiliation(s)
- John F Domsic
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
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Avvaru BS, Arenas DJ, Tu C, Tanner DB, McKenna R, Silverman DN. Comparison of solution and crystal properties of Co(II)-substituted human carbonic anhydrase II. Arch Biochem Biophys 2010; 502:53-9. [PMID: 20637176 DOI: 10.1016/j.abb.2010.07.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2010] [Revised: 07/09/2010] [Accepted: 07/11/2010] [Indexed: 11/24/2022]
Abstract
The visible absorption of crystals of Co(II)-substituted human carbonic anhydrase II (Co(II)-HCA II) were measured over a pH range of 6.0-11.0 giving an estimate of pK(a) 8.4 for the ionization of the metal-bound water in the crystal. This is higher by about 1.2 pK(a) units than the pK(a) near 7.2 for Co(II)-CA II in solution. This effect is attributed to a nonspecific ionic strength effect of 1.4M citrate in the precipitant solution used in the crystal growth. A pK(a) of 8.3 for the aqueous ligand of the cobalt was measured for Co(II)-HCA II in solution containing 0.8M citrate. Citrate is not an inhibitor of the catalytic activity of Co(II)-HCA II and was not observed in crystal structures. The X-ray structures at 1.5-1.6A resolution of Co(II)-HCA II were determined for crystals prepared at pH 6.0, 8.5 and 11.0 and revealed no conformational changes of amino-acid side chains as a result of the use of citrate. However, the studies of Co(II)-HCA II did reveal a change in metal coordination from tetrahedral at pH 11 to a coordination consistent with a mixed population of both tetrahedral and penta-coordinate at pH 8.5 to an octahedral geometry characteristic of the oxidized enzyme Co(III)-HCA II at pH 6.0.
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Affiliation(s)
- Balendu Sankara Avvaru
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
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Fisher SZ, Kovalevsky AY, Domsic JF, Mustyakimov M, McKenna R, Silverman DN, Langan PA. Neutron structure of human carbonic anhydrase II: implications for proton transfer. Biochemistry 2010; 49:415-21. [PMID: 20025241 PMCID: PMC2893723 DOI: 10.1021/bi901995n] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Human carbonic anhydrase II (HCA II) catalyzes the reversible hydration of carbon dioxide to form bicarbonate and a proton. Despite many high-resolution X-ray crystal structures, mutagenesis, and kinetic data, the structural details of the active site, especially the proton transfer pathway, are unclear. A large HCA II crystal was prepared at pH 9.0 and subjected to vapor H-D exchange to replace labile hydrogens with deuteriums. Neutron diffraction studies were conducted at the Protein Crystallography Station at Los Alamos National Laboratory. The structure to 2.0 A resolution reveals several interesting active site features: (1) the Zn-bound solvent appearing to be predominantly a D(2)O molecule, (2) the orientation and hydrogen bonding pattern of solvent molecules in the active site cavity, (3) the side chain of His64 being unprotonated (neutral) and predominantly in an inward conformation pointing toward the zinc, and (4) the phenolic side chain of Tyr7 appearing to be unprotonated. The implications of these details are discussed, and a proposed mechanism for proton transfer is presented.
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Affiliation(s)
- S Zoë Fisher
- Bioscience Division MS M888, Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA.
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Avvaru BS, Kim CU, Sippel KH, Gruner SM, Agbandje-McKenna M, Silverman DN, McKenna R. A short, strong hydrogen bond in the active site of human carbonic anhydrase II. Biochemistry 2010; 49:249-51. [PMID: 20000378 PMCID: PMC2810610 DOI: 10.1021/bi902007b] [Citation(s) in RCA: 125] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The crystal structure of human carbonic anhydrase II (HCA II) obtained at 0.9 A resolution reveals that a water molecule, termed deep water, Dw, and bound in a hydrophobic pocket of the active site forms a short, strong hydrogen bond with the zinc-bound solvent molecule, a conclusion based on the observed oxygen-oxygen distance of 2.45 A. This water structure has similarities with hydrated hydroxide found in crystals of certain inorganic complexes. The energy required to displace Dw contributes in significant part to the weak binding of CO(2) in the enzyme-substrate complex, a weak binding that enhances k(cat) for the conversion of CO(2) into bicarbonate. In addition, this short, strong hydrogen bond is expected to contribute to the low pK(a) of the zinc-bound water and to promote proton transfer in catalysis.
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Affiliation(s)
- Balendu Sankara Avvaru
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
| | - Chae Un Kim
- Department of Cornell High Energy Synchrotron Source (CHESS)Cornell University, Ithaca, NY 14853, USA
| | - Katherine H. Sippel
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
| | - Sol M. Gruner
- Department of Cornell High Energy Synchrotron Source (CHESS)Cornell University, Ithaca, NY 14853, USA
- Department of Physics, Cornell University, Ithaca, NY 14853, USA
| | - Mavis Agbandje-McKenna
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
| | - David N. Silverman
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
- Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
| | - Robert McKenna
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
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Mikulski R, Tu C, Swenson ER, Silverman DN. Reactions of nitrite in erythrocyte suspensions measured by membrane inlet mass spectrometry. Free Radic Biol Med 2010; 48:325-31. [PMID: 19913092 PMCID: PMC2818671 DOI: 10.1016/j.freeradbiomed.2009.11.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2009] [Revised: 10/28/2009] [Accepted: 11/05/2009] [Indexed: 10/20/2022]
Abstract
The reactions of nitrite with deoxygenated human erythrocytes were examined using membrane inlet mass spectrometry to detect the accumulation of NO in an extracellular solution. In this method an inlet utilizing a silicon rubber membrane is submerged in cell suspensions and allows NO to pass from the extracellular solution into the mass spectrometer. This provides a direct, continuous, and quantitative determination of nitric oxide concentrations over long periods without the necessity of purging the suspension with inert gas. We have not observed accumulation of NO compared with controls on a physiologically relevant time scale and conclude that, within the limitations of the mass spectrometric method and our experimental conditions, erythrocytes do not generate a net efflux of NO after the addition of millimolar concentrations of nitrite. Moreover, there was no evidence at the mass spectrometer of the accumulation of a peak at mass 76 that would indicate N(2)O(3), an intermediate that decays into NO and NO(2). Inhibition of red cell membrane anion exchangers and aquaporins did not affect these processes.
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Affiliation(s)
- Rose Mikulski
- Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville, FL 32610, USA
| | - Chingkuang Tu
- Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville, FL 32610, USA
| | - Erik R. Swenson
- Departments of Medicine and Physiology, Pulmonary Section, University of Washington, Seattle, WA 98108
| | - David N. Silverman
- Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville, FL 32610, USA
- Corresponding author: D. N. Silverman, Box 100267 Health Center, University of Florida, Gainesville, FL 32610-0267, USA. Fax: 352 392-9696.
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Maupin CM, Zheng J, Tu C, McKenna R, Silverman DN, Voth GA. Effect of active-site mutation at Asn67 on the proton transfer mechanism of human carbonic anhydrase II. Biochemistry 2009; 48:7996-8005. [PMID: 19634894 DOI: 10.1021/bi901037u] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The rate-limiting proton transfer (PT) event in the site-specific mutant N67L of human carbonic anhydrase II (HCA II) has been examined by kinetic, X-ray, and simulation approaches. The X-ray crystallography studies, which were previously reported, and molecular dynamics (MD) simulations indicate that the proton shuttling residue, His64, predominantly resides in the outward orientation with a significant disruption of the ordered water in the active site for the dehydration pathway. While disorder is seen in the active-site water, water cluster analysis indicates that the N67L mutant may form water clusters similar to those seen in the wild-type (WT). For the hydration pathway of the enzyme, the active site water cluster analysis reveals an inability of the N67L mutant to stabilize water clusters when His64 is in the inward orientation, thereby favoring PT when His64 is in the outward orientation. The preference of the N67L mutant to carry out the PT when His64 is in the outward orientation for both the hydration and dehydration pathway is reasoned to be the main cause of the observed reduction in the overall rate. To probe the mechanism of PT, solvent H/D kinetic isotope effects (KIEs) were experimentally studied with catalysis measured by the exchange of (18)O between CO(2) and water. The values obtained from the KIEs were determined as a function of the deuterium content of solvent, using the proton inventory method. No differences were detected in the overarching mechanism of PT between WT and N67L HCA II, despite changes in the active-site water structure and/or the orientation of His64.
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Affiliation(s)
- C Mark Maupin
- Center for Biophysical Modeling and Simulation and the Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA
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Avvaru BS, Busby SA, Chalmers MJ, Griffin PR, Venkatakrishnan B, Agbandje-McKenna M, Silverman DN, McKenna R. Apo-human carbonic anhydrase II revisited: implications of the loss of a metal in protein structure, stability, and solvent network. Biochemistry 2009; 48:7365-72. [PMID: 19583303 DOI: 10.1021/bi9007512] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Human carbonic anhydrase II (HCA II) is a monomeric zinc-containing metalloenzyme that catalyzes the hydration of CO(2) to form bicarbonate and a proton. The properties of the zinc have been extensively elucidated in catalysis but less well studied as a contributor to structure and stability. Apo-HCA II (without zinc) was prepared and compared to holo-HCA II: in crystallographic structural features, in backbone amide H/D exchange, and in thermal stability. The removal of zinc from the active site has no effect on either the topological fold of the enzyme or the ordered water network in the active site. However, the removal of the zinc alters the collective electrostatics of the apo-HCA II that result in the following differences from that of the holoenzyme: (1) the main thermal unfolding transition of the apo-HCA II is lowered by 8 degrees C, (2) the relative increase in thermal mobility of atoms of the apo-HCA II was not observed in the vicinity of the active site but manifested on the surface of the enzyme, and (3) the side chain of His 64, the proton shuttle residue that sits on the rim of the active site, is oriented outward and is associated with additional ordered "external" waters, as opposed to a near equal inward and outward orientation in the holo-HCA II.
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Affiliation(s)
- Balendu Sankara Avvaru
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, USA
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Mikulski RL, Silverman DN. Proton transfer in catalysis and the role of proton shuttles in carbonic anhydrase. Biochim Biophys Acta 2009; 1804:422-6. [PMID: 19679199 DOI: 10.1016/j.bbapap.2009.08.003] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2009] [Revised: 07/31/2009] [Accepted: 08/03/2009] [Indexed: 11/16/2022]
Abstract
The undisputed role of His64 in proton transfer during catalysis by carbonic anhydrases in the alpha class has raised questions concerning the details of its mechanism. The highly conserved residues Tyr7, Asn62, and Asn67 in the active-site cavity function to fine tune the properties of proton transfer by human carbonic anhydrase II (HCA II). For example, hydrophobic residues at these positions favor an inward orientation of His64 and a low pK(a) for its imidazole side chain. It appears that the predominant manner in which this fine tuning is achieved in rate constants for proton transfer is through the difference in pK(a) between His64 and the zinc-bound solvent molecule. Other properties of the active-site cavity, such as inward and outward conformers of His64, appear associated with the change in DeltapK(a); however, there is no strong evidence to date that the inward and outward orientations of His64 are in themselves requirements for facile proton transfer in carbonic anhydrase.
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Affiliation(s)
- Rose L Mikulski
- Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville, FL 32610-0267, USA
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Li Y, Wang H, Oosterwijk E, Tu C, Shiverick KT, Silverman DN, Frost SC. Expression and activity of carbonic anhydrase IX is associated with metabolic dysfunction in MDA-MB-231 breast cancer cells. Cancer Invest 2009; 27:613-23. [PMID: 19367501 DOI: 10.1080/07357900802653464] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The expression of carbonic anhydrase IX (CAIX), a marker for hypoxic tumors, is correlated with poor prognosis in breast cancer patients. We show herein that the MDA-MB-231 cells, a "triple-negative," basal B line, express exclusively CAIX, while a luminal cell line (T47D) expresses carbonic anhydrase XII (CAXII). CAIX expression in the basal B cells is both density- and hypoxia-dependent and is correlated with carbonic anhydrase activity. Evidence is provided that CAIX contributes to extracellular acidification through studies on pH, lactic acid production, and CAIX inhibition. Together, these studies suggest that CAIX expression and activity is associated with metabolic dysfunction in MDA-MB-231 cells.
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Affiliation(s)
- Ying Li
- Department of Biochemistry and Molecular Biology, University of Florida, College of Medicine, Gainesville, Florida 32610, USA
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Abstract
Human carbonic anhydrase II (HCA II) is one of the fastest known enzymes, which utilizes a rate-limiting proton transport (PT) step in its enzymatic reaction. To evaluate the PT event at an atomistic level, the multistate empirical valence bond (MS-EVB) method has been utilized in this work. It is observed that the PT event in HCA II exploits a transient active site water cluster to transport the excess proton between the catalytic zinc-bound water/hydroxide and the proton shuttling residue, His64. This PT event is found to be dependent on the enzyme's ability to form and stabilize the active site water cluster in addition to its ability to orient His64 in a favorable conformation. Evaluation of the PT free energy barrier for different orientations of His64 reveals this residue's vital role as a proton transporter and elucidates its direct effect on the barrier to PT through the active site water. It is suggested that the rate-limiting step oscillates between the active site water PT event to His64 and the de/protonation of His64 depending on the exogenous buffer concentration and the orientation of His64. In the absence of a PT acceptor/donor at position 64, it is found that the excess proton will utilize one of three distinct paths to enter/leave the active site. This latter result not only allows for an increased understanding of how enzymes capitalize on the protein/solvent interface to guide excess protons to/from areas of interest, it also provides valuable insight into the chemical rescue experiments on HCA II mutants.
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Affiliation(s)
- C. Mark Maupin
- Center for Biophysical Modeling and Simulation and Department of Chemistry, UniVersity of Utah, Salt Lake City, Utah 84112
| | - Robert McKenna
- Department of Biochemistry and Molecular Biology, College of Medicine, UniVersity of Florida, GainesVille, Florida 32610
| | - David N. Silverman
- Department of Biochemistry and Molecular Biology, College of Medicine, UniVersity of Florida, GainesVille, Florida 32610
- Department of Pharmacology and Therapeutics, College of Medicine, UniVersity of Florida, GainesVille, Florida 32610
| | - Gregory A. Voth
- Center for Biophysical Modeling and Simulation and Department of Chemistry, UniVersity of Utah, Salt Lake City, Utah 84112
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Fisher SZ, Kovalevsky AY, Domsic JF, Mustyakimov M, Silverman DN, McKenna R, Langan P. Preliminary joint neutron and X-ray crystallographic study of human carbonic anhydrase II. Acta Crystallogr Sect F Struct Biol Cryst Commun 2009; 65:495-8. [PMID: 19407386 PMCID: PMC2675594 DOI: 10.1107/s1744309109013086] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2009] [Accepted: 04/06/2009] [Indexed: 11/10/2022]
Abstract
Carbonic anhydrases catalyze the interconversion of CO(2) to HCO(3)(-), with a subsequent proton-transfer (PT) step. PT proceeds via a proposed hydrogen-bonded water network in the active-site cavity that is stabilized by several hydrophilic residues. A joint X-ray and neutron crystallographic study has been initiated to determine the specific water network and the protonation states of the hydrophilic residues that coordinate it in human carbonic anhydrase II. Time-of-flight neutron crystallographic data have been collected from a large ( approximately 1.2 mm(3)) hydrogen/deuterium-exchanged crystal to 2.4 A resolution and X-ray crystallographic data have been collected from a similar but smaller crystal to 1.5 A resolution. Obtaining good-quality neutron data will contribute to the understanding of the catalytic mechanisms that utilize water networks for PT in protein environments.
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Affiliation(s)
- S Z Fisher
- Bioscience Division, Los Alamos National Laboratory, NM 87545, USA.
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Genis C, Sippel KH, Case N, Cao W, Avvaru BS, Tartaglia LJ, Govindasamy L, Tu C, Agbandje-McKenna M, Silverman DN, Rosser CJ, McKenna R. Design of a carbonic anhydrase IX active-site mimic to screen inhibitors for possible anticancer properties. Biochemistry 2009; 48:1322-31. [PMID: 19170619 PMCID: PMC2713499 DOI: 10.1021/bi802035f] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Recently, a convincing body of evidence has accumulated suggesting that the overexpression of carbonic anhydrase isozyme IX (CA IX) in some cancers contributes to the acidification of the extracellular matrix, which in turn promotes the growth and metastasis of the tumor. These observations have made CA IX an attractive drug target for the selective treatment of certain cancers. Currently, there is no available X-ray crystal structure of CA IX, and this lack of availability has hampered the rational design of selective CA IX inhibitors. In light of these observations and on the basis of structural alignment homology, using the crystal structure of carbonic anhydrase II (CA II) and the sequence of CA IX, a double mutant of CA II with Ala65 replaced by Ser and Asn67 replaced by Gln has been constructed to resemble the active site of CA IX. This CA IX mimic has been characterized kinetically using (18)O-exchange and structurally using X-ray crystallography, alone and in complex with five CA sulfonamide-based inhibitors (acetazolamide, benzolamide, chlorzolamide, ethoxzolamide, and methazolamide), and compared to CA II. This structural information has been evaluated by both inhibition studies and in vitro cytotoxicity assays and shows a correlated structure-activity relationship. Kinetic and structural studies of CA II and CA IX mimic reveal chlorzolamide to be a more potent inhibitor of CA IX, inducing an active-site conformational change upon binding. Additionally, chlorzolamide appears to be cytotoxic to prostate cancer cells. This preliminary study demonstrates that the CA IX mimic may provide a useful model to design more isozyme-specific CA IX inhibitors, which may lead to development of new therapeutic treatments of some cancers.
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Affiliation(s)
- Caroli Genis
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - Katherine H. Sippel
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - Nicolette Case
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - Wengang Cao
- Department of Urology, College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - Balendu Sankara Avvaru
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - Lawrence J. Tartaglia
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - Lakshmanan Govindasamy
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - Chingkuang Tu
- Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - Mavis Agbandje-McKenna
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - David N. Silverman
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL, 32610, USA,Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - Charles J. Rosser
- Department of Urology, College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - Robert McKenna
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL, 32610, USA,Corresponding Author: Phone: (352)-392-5696. Fax: (352) 392-3422. E-mail: (R.M.)
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Kantak KM, Mashhoon Y, Silverman DN, Janes AC, Goodrich CM. Role of the orbitofrontal cortex and dorsal striatum in regulating the dose-related effects of self-administered cocaine. Behav Brain Res 2009; 201:128-36. [PMID: 19428626 DOI: 10.1016/j.bbr.2009.02.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Revised: 01/29/2009] [Accepted: 02/02/2009] [Indexed: 11/25/2022]
Abstract
Little is known regarding which neural systems regulate dose-related changes in responses maintained by self-administered cocaine. This empirical question is important because elucidating neural systems engaged in this process could provide clues for effectively treating cocaine addiction. It has been suggested that different cocaine doses represent reinforcers of differing magnitudes, implicating the dorsal striatum or orbitofrontal cortex as important. Rats were trained to self-administer 1.0 mg/kg cocaine under a fixed-interval based second-order schedule. Next, cocaine unit doses (0.1-3.0 mg/kg) were each non-systematically available for a 5-day block of sessions. Tests (1h) were conducted on day 3 (vehicle) and day 5 (100 microg lidocaine) of each block. Lidocaine inactivation of the lateral dorsal striatum had no effect on dose-related responding or cocaine intake. In contrast, when doses along the ascending limb were available for self-administration, lidocaine inactivation of the lateral orbitofrontal cortex caused reductions in responding and cocaine intake, resulting in overall flattening of dose-response curves. This included reductions during the entire 1-h test sessions and during the interval immediately following the first cocaine infusion of test sessions. Lidocaine inactivation of the lateral orbitofrontal cortex did not alter responding during the first cocaine-free interval of test sessions, but increased the latency to the first infusion. Collectively, the findings suggest that when the amount of experience with different cocaine unit doses is limited to a few sessions, the lateral orbitofrontal cortex regulates the dose-related effects of self-administered cocaine, likely by processing information pertaining to the reinforcing value of each unit dose.
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Tu C, Mikulski R, Swenson ER, Silverman DN. Reactions of nitrite with hemoglobin measured by membrane inlet mass spectrometry. Free Radic Biol Med 2009; 46:14-9. [PMID: 18848984 PMCID: PMC2849169 DOI: 10.1016/j.freeradbiomed.2008.09.016] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2008] [Revised: 09/08/2008] [Accepted: 09/09/2008] [Indexed: 11/27/2022]
Abstract
Membrane inlet mass spectrometry was used to observe nitric oxide in the well-studied reaction of nitrite with hemoglobin. The membrane inlet was submerged in the reaction solutions and measured NO in solution via its flux across a semipermeable membrane leading to the mass spectrometer detecting the mass-to-charge ratio m/z 30. This method measures NO directly in solution and is an alternate approach compared with methods that purge solutions to measure NO. Addition to deoxy-Hb(Fe(II)) (near 38 microM heme concentration) of nitrite in a range of 80 microM to 16 mM showed no accumulation of either NO or N(2)O(3) on a physiologically relevant time scale with a sensitivity near 1 nM. The addition of nitrite to oxy-Hb(Fe(II)) and met-Hb(Fe(III)) did not accumulate free NO to appreciable extents. These observations show that for several minutes after mixing nitrite with hemoglogin, free NO does not accumulate to levels exceeding the equilibrium level of NO. The presence of cyanide ions did not alter the appearance of the data; however, the presence of 2 mM mercuric ions at the beginning of the experiment with deoxy-Hb(Fe(II)) shortened the initial phase of NO accumulation and increased the maximal level of free, unbound NO by about twofold. These experiments appear consistent with no role of met-Hb(Fe(III)) in the generation of NO and an increase in nitrite reductase activity caused by the presumed binding of mercuric to cysteine residues. These results raise questions about the ability of reduction of nitrite mediated by deoxy-Hb(Fe(II)) to play a role in vasodilation.
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Affiliation(s)
- Chingkuang Tu
- Department of Pharmacology and Therapeutics, College of Medicine, Box 100267 Health Center, University of Florida, Gainesville, FL 32610-0267, USA
| | - Rose Mikulski
- Department of Pharmacology and Therapeutics, College of Medicine, Box 100267 Health Center, University of Florida, Gainesville, FL 32610-0267, USA
| | - Erik R. Swenson
- Departments of Medicine and Physiology, Pulmonary Section, University of Washington, Seattle, WA 98108, USA
| | - David N. Silverman
- Department of Pharmacology and Therapeutics, College of Medicine, Box 100267 Health Center, University of Florida, Gainesville, FL 32610-0267, USA
- Corresponding author. Fax: +1 352 392 9696. (D.N. Silverman)
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Zheng J, Avvaru BS, Tu C, McKenna R, Silverman DN. Role of hydrophilic residues in proton transfer during catalysis by human carbonic anhydrase II. Biochemistry 2008; 47:12028-36. [PMID: 18942852 DOI: 10.1021/bi801473w] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Catalysis by the zinc metalloenzyme human carbonic anhydrase II (HCA II) is limited in maximal velocity by proton transfer between His64 and the zinc-bound solvent molecule. Asn62 extends into the active site cavity of HCA II adjacent to His64 and has been shown to be one of several hydrophilic residues participating in a hydrogen-bonded solvent network within the active site. We compared several site-specific mutants of HCA II with replacements at position 62 (Ala, Val, Leu, Thr, and Asp). The efficiency of catalysis in the hydration of CO 2 for the resulting mutants has been characterized by (18)O exchange, and the structures of the mutants have been determined by X-ray crystallography to 1.5-1.7 A resolution. Each of these mutants maintained the ordered water structure observed by X-ray crystallography in the active site cavity of wild-type HCA II; hence, this water structure was not a variable in comparing with wild type the activities of mutants at residue 62. Crystal structures of wild-type and N62T HCA II showed both an inward and outward orientation of the side chain of His64; however, other mutants in this study showed predominantly inward (N62A, N62V, N62L) or predominantly outward (N62D) orientations of His64. A significant role of Asn62 in HCA II is to permit two conformations of the side chain of His64, the inward and outward, that contributes to maximal efficiency of proton transfer between the active site and solution. The site-specific mutant N62D had a mainly outward orientation of His64, yet the difference in p K a between the proton donor His64 and zinc-bound hydroxide was near zero, as in wild-type HCA II. The rate of proton transfer in catalysis by N62D HCA II was 5% that of wild type, showing that His64 mainly in the outward orientation is associated with inefficient proton transfer compared with His64 in wild type which shows both inward and outward orientations. These results emphasize the roles of the residues of the hydrophilic side of the active site cavity in maintaining efficient catalysis by carbonic anhydrase.
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Affiliation(s)
- Jiayin Zheng
- Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
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Domsic JF, Avvaru BS, Kim CU, Gruner SM, Agbandje-McKenna M, Silverman DN, McKenna R. Entrapment of carbon dioxide in the active site of carbonic anhydrase II. J Biol Chem 2008; 283:30766-71. [PMID: 18768466 DOI: 10.1074/jbc.m805353200] [Citation(s) in RCA: 165] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The visualization at near atomic resolution of transient substrates in the active site of enzymes is fundamental to fully understanding their mechanism of action. Here we show the application of using CO(2)-pressurized, cryo-cooled crystals to capture the first step of CO(2) hydration catalyzed by the zinc-metalloenzyme human carbonic anhydrase II, the binding of substrate CO(2), for both the holo and the apo (without zinc) enzyme to 1.1A resolution. Until now, the feasibility of such a study was thought to be technically too challenging because of the low solubility of CO(2) and the fast turnover to bicarbonate by the enzyme (Liang, J. Y., and Lipscomb, W. N. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 3675-3679). These structures provide insight into the long hypothesized binding of CO(2) in a hydrophobic pocket at the active site and demonstrate that the zinc does not play a critical role in the binding or orientation of CO(2). This method may also have a much broader implication for the study of other enzymes for which CO(2) is a substrate or product and for the capturing of transient substrates and revealing hydrophobic pockets in proteins.
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Affiliation(s)
- John F Domsic
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, USA
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Maupin CM, Saunders MG, Thorpe IF, McKenna R, Silverman DN, Voth GA. Origins of enhanced proton transport in the Y7F mutant of human carbonic anhydrase II. J Am Chem Soc 2008; 130:11399-408. [PMID: 18671353 PMCID: PMC2562593 DOI: 10.1021/ja802264j] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Human carbonic anhydrase II (HCA II), among the fastest enzymes known, catalyzes the reversible hydration of CO 2 to HCO 3 (-). The rate-limiting step of this reaction is believed to be the formation of an intramolecular water wire and transfer of a proton across the active site cavity from a zinc-bound solvent to a proton shuttling residue (His64). X-ray crystallographic studies have shown this intramolecular water wire to be directly stabilized through hydrogen bonds via a small well-defined set of amino acids, namely, Tyr7, Asn62, Asn67, Thr199, and Thr200. Furthermore, X-ray crystallographic and kinetic studies have shown that the mutation of tyrosine 7 to phenylalanine, Y7F HCA II, has the effect of increasing the proton transfer rate by 7-fold in the dehydration direction of the enzyme reaction compared to wild-type (WT). This increase in the proton transfer rate is postulated to be linked to the formation of a more directional, less branched, water wire. To evaluate this proposal, molecular dynamics simulations have been employed to study water wire formation in both the WT and Y7F HCA II mutant. These studies reveal that the Y7F mutant enhances the probability of forming small water wires and significantly extends the water wire lifetime, which may account for the elevated proton transfer seen in the Y7F mutant. Correlation analysis of the enzyme and intramolecular water wire indicates that the Y7F mutant significantly alters the interaction of the active site waters with the enzyme while occupancy data of the water oxygens reveals that the Y7F mutant stabilizes the intramolecular water wire in a manner that maximizes smaller water wire formation. This increase in the number of smaller water wires is likely to elevate the catalytic turnover of an already very efficient enzyme.
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Quint PS, Domsic JF, Cabelli DE, McKenna R, Silverman DN. Role of a Glutamate Bridge Spanning the Dimeric Interface of Human Manganese Superoxide Dismutase,. Biochemistry 2008; 47:4621-8. [DOI: 10.1021/bi7024518] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Patrick S. Quint
- Department of Pharmacology and Therapeutics and Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, and Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973
| | - John F. Domsic
- Department of Pharmacology and Therapeutics and Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, and Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973
| | - Diane E. Cabelli
- Department of Pharmacology and Therapeutics and Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, and Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973
| | - Robert McKenna
- Department of Pharmacology and Therapeutics and Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, and Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973
| | - David N. Silverman
- Department of Pharmacology and Therapeutics and Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, and Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973
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Barrese, AA, Genis C, Fisher SZ, Orwenyo JN, Kumara MT, Dutta SK, Phillips E, Kiddle JJ, Tu C, Silverman DN, Govindasamy L, Agbandje-McKenna M, McKenna R, Tripp BC. Inhibition of Carbonic Anhydrase II by Thioxolone: A Mechanistic and Structural Study. Biochemistry 2008; 47:3174-84. [DOI: 10.1021/bi702385k] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Albert A. Barrese,
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - Caroli Genis
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - S. Zoe Fisher
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - Jared N. Orwenyo
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - Mudalige Thilak Kumara
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - Subodh K. Dutta
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - Eric Phillips
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - James J. Kiddle
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - Chingkuang Tu
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - David N. Silverman
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - Lakshmanan Govindasamy
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - Mavis Agbandje-McKenna
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - Robert McKenna
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
| | - Brian C. Tripp
- Department of Biological Sciences, Mailstop 5410, College of Arts and Sciences, 1903 West Michigan Avenue, Western Michigan University, Kalamazoo, Michigan 49008-5410, Department of Biochemistry and Molecular Biology, College of Medicine, P.O. Box 100245, University of Florida, Gainesville, Florida 32610-0267, Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008-5410, and Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville,
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Abreu IA, Hearn A, An H, Nick HS, Silverman DN, Cabelli DE. The Kinetic Mechanism of Manganese-Containing Superoxide Dismutase from Deinococcus radiodurans: A Specialized Enzyme for the Elimination of High Superoxide Concentrations. Biochemistry 2008; 47:2350-6. [DOI: 10.1021/bi7016206] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Isabel A. Abreu
- Chemistry Department, Brookhaven National Laboratory, Building 555, Upton, New York 11973-5000, and Department of Pharmacology, University of Florida, Gainesville, Florida 32610
| | - Amy Hearn
- Chemistry Department, Brookhaven National Laboratory, Building 555, Upton, New York 11973-5000, and Department of Pharmacology, University of Florida, Gainesville, Florida 32610
| | - Haiqain An
- Chemistry Department, Brookhaven National Laboratory, Building 555, Upton, New York 11973-5000, and Department of Pharmacology, University of Florida, Gainesville, Florida 32610
| | - Harry S. Nick
- Chemistry Department, Brookhaven National Laboratory, Building 555, Upton, New York 11973-5000, and Department of Pharmacology, University of Florida, Gainesville, Florida 32610
| | - David N. Silverman
- Chemistry Department, Brookhaven National Laboratory, Building 555, Upton, New York 11973-5000, and Department of Pharmacology, University of Florida, Gainesville, Florida 32610
| | - Diane E. Cabelli
- Chemistry Department, Brookhaven National Laboratory, Building 555, Upton, New York 11973-5000, and Department of Pharmacology, University of Florida, Gainesville, Florida 32610
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Zheng J, Domsic JF, Cabelli D, McKenna R, Silverman DN. Structural and Kinetic Study of Differences between Human and Escherichia coli Manganese Superoxide Dismutases. Biochemistry 2007; 46:14830-7. [DOI: 10.1021/bi7014103] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jiayin Zheng
- Department of Pharmacology and Therapeutics and Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, and Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973
| | - John F. Domsic
- Department of Pharmacology and Therapeutics and Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, and Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973
| | - Diane Cabelli
- Department of Pharmacology and Therapeutics and Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, and Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973
| | - Robert McKenna
- Department of Pharmacology and Therapeutics and Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, and Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973
| | - David N. Silverman
- Department of Pharmacology and Therapeutics and Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, and Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973
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Abstract
We point out the advantages of membrane inlet mass spectrometry for the measurement of nitric oxide in aqueous solution. The membrane inlet probe was a 1.0-cm segment of Silastic tubing attached to the vacuum inlet leading to the ion source. Silastic is a semipermeable silicon rubber that allows flux of uncharged substances including nitric oxide (NO). The use of such an inlet to measure NO has several advantages that we demonstrate in this report. It provides a direct, continuous, and quantitative determination of dissolved nitric oxide concentrations over long periods of real time. The use of such an inlet in our system had a response time of 5 to 7 s and a detection lower limit with the current model of 1.0 nM. This apparatus was used to measure the generation of NO from solutions of nitrite, NONOates, and nitroprusside. The usefulness of such an inlet in measuring NO in physiological systems is discussed.
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Affiliation(s)
- Chingkuang Tu
- Department of Pharmacology and Therapeutics, College of Medicine, University of Florida, Gainesville, FL 32610, USA
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50
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Abstract
Considerable attention has been focused on proton transfer through intervening water molecules in complex macromolecules of biological interest, such as bacteriorhodopsin, cytochrome c oxidase, and many others. Proton transfer in catalysis by carbonic anhydrase provides a useful model for the study of the properties of such proton translocations. High-resolution X-ray crystallography in combination with measurements of catalysis have revealed new details of this process. A prominent proton shuttle residue His64 shows evidence of structural mobility, which appears to enhance proton transfer between the active site and bulk solvent. Moreover, the properties of the imidazole side chain of His64, including its conformations and pK(a), are finely tuned by surrounding residues of the active-site cavity. The structure of a network of ordered solvent molecules located between His64 and the active site are also sensitive to surrounding residues. These features combine to provide efficient proton-transfer rates as great as 10(6) s(-1) necessary to sustain rapid catalysis.
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Affiliation(s)
- David N Silverman
- Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville, Florida 32610, USA.
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