1
|
Herwig S, Kleinschmidt JH. The Formation of β-Strand Nine ( β9) in the Folding and Insertion of BamA from an Unfolded Form into Lipid Bilayers. MEMBRANES 2023; 13:247. [PMID: 36837750 PMCID: PMC9964827 DOI: 10.3390/membranes13020247] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/02/2023] [Revised: 02/10/2023] [Accepted: 02/14/2023] [Indexed: 06/18/2023]
Abstract
Transmembrane proteins span lipid bilayer membranes and serve essential functions in all living cells. Membrane-inserted domains are of either α-helical or β-barrel structure. Despite their biological importance, the biophysical mechanisms of the folding and insertion of proteins into membranes are not well understood. While the relative composition of the secondary structure has been examined by circular dichroism spectroscopy in folding studies for several outer membrane proteins, it is currently not known how individual β-strands fold. Here, the folding and insertion of the β-barrel assembly machinery protein A (BamA) from the outer membrane of Escherichia coli into lipid bilayers were investigated, and the formation of strand nine (β9) of BamA was examined. Eight single-cysteine mutants of BamA were overexpressed and isolated in unfolded form in 8 M urea. In each of these mutants, one of the residues of strand β9, from R572 to V579, was replaced by a cysteine and labeled with the fluorophore IAEDANS for site-directed fluorescence spectroscopy. Upon urea-dilution, the mutants folded into the native structure and were inserted into lipid bilayers of dilauroylphosphatidylcholine, similar to wild-type BamA. An aqueous and a membrane-adsorbed folding intermediate of BamA could be identified by strong shifts in the intensity maxima of the IAEDANS fluorescence of the labeled mutants of BamA towards shorter wavelengths, even in the absence of lipid bilayers. The shifts were greatest for membrane-adsorbed mutants and smaller for the inserted, folded mutants or the aqueous intermediates. The spectra of the mutants V573C-, L575C-, G577C-, and V579C-BamA, facing the lipid bilayer, displayed stronger shifts than the spectra recorded for the mutants R572C-, N574C-, T576C-, and K578C-BamA, facing the β-barrel lumen, in both the membrane-adsorbed form and the folded, inserted form. This alternating pattern was neither observed for the IAEDANS spectra of the unfolded forms nor for the water-collapsed forms, indicating that strand β9 forms in a membrane-adsorbed folding intermediate of BamA. The combination of cysteine scanning mutagenesis and site-directed fluorescence labeling is shown to be a valuable tool in examining the local secondary structure formation of transmembrane proteins.
Collapse
Affiliation(s)
- Sascha Herwig
- Institut für Biologie, FB 10 Mathematik und Naturwissenschaften, Universität Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel, Germany
| | - Jörg H. Kleinschmidt
- Institut für Biologie, FB 10 Mathematik und Naturwissenschaften, Universität Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel, Germany
- Center of Interdisciplinary Nanostructure Science and Technology, Universität Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel, Germany
| |
Collapse
|
2
|
Photophysical Properties of BADAN Revealed in the Study of GGBP Structural Transitions. Int J Mol Sci 2021; 22:ijms222011113. [PMID: 34681772 PMCID: PMC8540541 DOI: 10.3390/ijms222011113] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Revised: 10/06/2021] [Accepted: 10/09/2021] [Indexed: 01/14/2023] Open
Abstract
The fluorescent dye BADAN (6-bromoacetyl-2-dimetylaminonaphtalene) is widely used in various fields of life sciences, however, the photophysical properties of BADAN are not fully understood. The study of the spectral properties of BADAN attached to a number of mutant forms of GGBP, as well as changes in its spectral characteristics during structural changes in proteins, allowed to shed light on the photophysical properties of BADAN. It was shown that spectral properties of BADAN are determined by at least one non-fluorescent and two fluorescent isomers with overlapping absorbing bands. It was found that BADAN fluorescence is determined by the unsolvated "PICT" (planar intramolecular charge transfer state) and solvated "TICT" (twisted intramolecular charge transfer state) excited states. While "TICT" state can be formed both as a result of the "PICT" state solvation and as a result of light absorption by the solvated ground state of the dye. BADAN fluorescence linked to GGBP/H152C apoform is quenched by Trp 183, but this effect is inhibited by glucose intercalation. New details of the changes in the spectral characteristics of BADAN during the unfolding of the protein apo and holoforms have been obtained.
Collapse
|
3
|
Lux J, Azarkh M, Fitzner L, Keppler JK, Schwarz K, Drescher M, Steffen-Heins A. Amyloid aggregation of spin-labeled β-lactoglobulin. Part II: Identification of spin-labeled protein and peptide sequences after amyloid aggregation. Food Hydrocoll 2021. [DOI: 10.1016/j.foodhyd.2020.106174] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
|
4
|
Zhang Q, Zhang Y, Liu H, Chow HY, Tian R, Eva Fung YM, Li X. OPA-Based Bifunctional Linker for Protein Labeling and Profiling. Biochemistry 2020; 59:175-178. [PMID: 31657212 DOI: 10.1021/acs.biochem.9b00787] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Lysine residues have been considered as a routine conjugating site for protein chemical labeling and modification. The commercially available lysine-labeling agents have several limitations in labeling efficiency, stability, and cost. To pursue alternative protein lysine-labeling strategies, herein, we report the development of an ortho-phthalaldehyde (OPA)-based bifunctional linker suitable for protein chemical labeling and profiling. Among three designed OPA-based bifunctional linkers, OPA-NH-alkyne 5 was proved to be optimal for protein labeling with minimal protein turbidity. We further demonstrated OPA-NH-alkyne 5 was applicable for immediate capture of protein or proteome chemical labeling.
Collapse
Affiliation(s)
- Qing Zhang
- Department of Chemistry, State Key Laboratory of Synthetic Chemistry , The University of Hong Kong , Hong Kong , People's Republic of China, SAR
| | - Yue Zhang
- Department of Chemistry, State Key Laboratory of Synthetic Chemistry , The University of Hong Kong , Hong Kong , People's Republic of China, SAR
| | - Heng Liu
- Department of Chemistry, State Key Laboratory of Synthetic Chemistry , The University of Hong Kong , Hong Kong , People's Republic of China, SAR
| | - Hoi Yee Chow
- Department of Chemistry, State Key Laboratory of Synthetic Chemistry , The University of Hong Kong , Hong Kong , People's Republic of China, SAR
| | - Ruijun Tian
- Department of Chemistry , Southern University of Science and Technology , Shenzhen , People's Republic of China
| | - Yi Man Eva Fung
- Department of Chemistry, State Key Laboratory of Synthetic Chemistry , The University of Hong Kong , Hong Kong , People's Republic of China, SAR
| | - Xuechen Li
- Department of Chemistry, State Key Laboratory of Synthetic Chemistry , The University of Hong Kong , Hong Kong , People's Republic of China, SAR
| |
Collapse
|
5
|
Mondal S, Chandra A, Venkatramani R, Datta A. Optically sensing phospholipid induced coil-helix transitions in the phosphoinositide-binding motif of gelsolin. Faraday Discuss 2019; 207:437-458. [PMID: 29363700 DOI: 10.1039/c7fd00197e] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
We present a systematic experimental and computational study of phospholipid induced peptide coil-helix transitions which are relevant in the context of proteins mediating cytoskeletal rearrangement via membrane binding. We developed a sensitive Förster resonance energy transfer (FRET) based assay to address whether coil-helix transitions in phospholipid binding motifs of actin-binding proteins can be induced by physiologically-relevant concentrations (1-20 μM) of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) phospholipids. Based on inter-residue distance constraints obtained from Molecular Dynamics (MD) simulations of a 20 residue peptide (Gel 150-169) from the actin-severing protein gelsolin, we synthetized and labeled the peptide with a tryptophan donor and IAEDANS acceptor pair. Upon addition of PI(4,5)P2 micelles and mixed vesicles containing PI(4,5)P2 and phosphatidylcholine to the peptide, we observed a decrease in the tryptophan emission intensity with increasing concentrations of PI(4,5)P2. The IAEDANS emission spectra showed a more complex profile exhibiting a blue shift of the emission peak and non-monotonic changes in the intensity profile with increasing concentrations of PI(4,5)P2. We showed that the IAEDANS acceptor emission response is a result of both intrinsic polarity sensitivity of the acceptor in the vicinity of the membrane surface and fluorescence energy transfer from the donor. Importantly, the fluorescence lifetime of the donor (tryptophan) showed a monotonous decrease with increasing mol% of PI(4,5)P2 from 1.13 ± 0.10 ns in the absence of phospholipids to 0.25 ± 0.03 ns in the presence of 100% PI(4,5)P2 micelles. We also showed a concomitant increase in FRET efficiency with increasing PI(4,5)P2 levels indicating a PI(4,5)P2 concentration dependent coil-helix transition. Our studies demonstrate that membrane PI(4,5)P2 concentrations as low as 2.5-5 μM can trigger helix-coil conformational changes in gelsolin relevant for triggering regulatory processes in the cell.
Collapse
Affiliation(s)
- Samsuzzoha Mondal
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India.
| | | | | | | |
Collapse
|
6
|
Fonin A, Kuznetsova I, Turoverov K. Spectral properties of BADAN in solutions with different polarities. J Mol Struct 2015. [DOI: 10.1016/j.molstruc.2015.01.038] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
|
7
|
Shabestari MH, Wolfs CJAM, Spruijt RB, van Amerongen H, Huber M. Exploring the structure of the 100 amino-acid residue long N-terminus of the plant antenna protein CP29. Biophys J 2014; 106:1349-58. [PMID: 24655510 DOI: 10.1016/j.bpj.2013.11.4506] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2013] [Revised: 11/14/2013] [Accepted: 11/27/2013] [Indexed: 12/01/2022] Open
Abstract
The structure of the unusually long (∼100 amino-acid residues) N-terminal domain of the light-harvesting protein CP29 of plants is not defined in the crystal structure of this membrane protein. We studied the N-terminus using two electron paramagnetic resonance (EPR) approaches: the rotational diffusion of spin labels at 55 residues with continuous-wave EPR, and three sets of distances with a pulsed EPR method. The N-terminus is relatively structured. Five regions that differ considerably in their dynamics are identified. Two regions have low rotational diffusion, one of which shows α-helical character suggesting contact with the protein surface. This immobile part is flanked by two highly dynamic, unstructured regions (loops) that cover residues 10-22 and 82-91. These loops may be important for the interaction with other light-harvesting proteins. The region around residue 4 also has low rotational diffusion, presumably because it attaches noncovalently to the protein. This section is close to a phosphorylation site (Thr-6) in related proteins, such as those encoded by the Lhcb4.2 gene. Phosphorylation might influence the interaction with other antenna complexes, thereby regulating the supramolecular organization in the thylakoid membrane.
Collapse
Affiliation(s)
| | - Cor J A M Wolfs
- Laboratory of Biophysics, Wageningen University, Wageningen, The Netherlands
| | - Ruud B Spruijt
- Laboratory of Biophysics, Wageningen University, Wageningen, The Netherlands
| | | | - Martina Huber
- Department of Molecular Physics, Leiden University, Leiden, The Netherlands.
| |
Collapse
|
8
|
Chowdhury A, Choudhury A, Banerjee V, Banerjee R, Das KP. Spectroscopic studies of the unfolding of a multimeric protein α-crystallin. Biopolymers 2014; 101:549-60. [DOI: 10.1002/bip.22417] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Revised: 08/19/2013] [Accepted: 09/23/2013] [Indexed: 11/10/2022]
Affiliation(s)
- Aritra Chowdhury
- School of Chemistry; University of Manchester; Oxford Road, M13 9PL Manchester UK
- Dr. B. C. Guha Centre for Genetic Engineering and Biotechnology and Department of Biotechnology; Calcutta University; Ballygunge Circular Road Kolkata 700019 India
| | - Aparajita Choudhury
- Dr. B. C. Guha Centre for Genetic Engineering and Biotechnology and Department of Biotechnology; Calcutta University; Ballygunge Circular Road Kolkata 700019 India
| | - Victor Banerjee
- Department of Chemistry; Bose Institute; 93/1 A. P. C. Road Kolkata 700 009 India
| | - Rajat Banerjee
- Dr. B. C. Guha Centre for Genetic Engineering and Biotechnology and Department of Biotechnology; Calcutta University; Ballygunge Circular Road Kolkata 700019 India
| | - K. P. Das
- Department of Chemistry; Bose Institute; 93/1 A. P. C. Road Kolkata 700 009 India
| |
Collapse
|
9
|
Transient conformational remodeling of folding proteins by GroES-individually and in concert with GroEL. J Chem Biol 2013; 7:1-15. [PMID: 24386013 PMCID: PMC3877409 DOI: 10.1007/s12154-013-0106-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 09/18/2013] [Indexed: 11/24/2022] Open
Abstract
The commonly accepted dogma of the bacterial GroE chaperonin system entails protein folding mediated by cycles of several ATP-dependent sequential steps where GroEL interacts with the folding client protein. In contrast, we herein report GroES-mediated dynamic remodeling (expansion and compression) of two different protein substrates during folding: the endogenous substrate MreB and carbonic anhydrase (HCAII), a well-characterized protein folding model. GroES was also found to influence GroEL binding induced unfolding and compression of the client protein underlining the synergistic activity of both chaperonins, even in the absence of ATP. This previously unidentified activity by GroES should have important implications for understanding the chaperonin mechanism and cellular stress response. Our findings necessitate a revision of the GroEL/ES mechanism.
Collapse
|
10
|
Krepkiy D, Gawrisch K, Swartz KJ. Structural interactions between lipids, water and S1-S4 voltage-sensing domains. J Mol Biol 2012; 423:632-47. [PMID: 22858867 PMCID: PMC3616881 DOI: 10.1016/j.jmb.2012.07.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Revised: 07/17/2012] [Accepted: 07/20/2012] [Indexed: 10/28/2022]
Abstract
Membrane proteins serve crucial signaling and transport functions, yet relatively little is known about their structures in membrane environments or how lipids interact with these proteins. For voltage-activated ion channels, X-ray structures suggest that the mobile voltage-sensing S4 helix would be exposed to the membrane, and functional studies reveal that lipid modification can profoundly alter channel activity. Here, we use solid-state NMR to investigate structural interactions of lipids and water with S1-S4 voltage-sensing domains and to explore whether lipids influence the structure of the protein. Our results demonstrate that S1-S4 domains exhibit extensive interactions with lipids and that these domains are heavily hydrated when embedded in a membrane. We also find evidence for preferential interactions of anionic lipids with S1-S4 domains and that these interactions have lifetimes on the timescale of ≤ 10(-3)s. Arg residues within S1-S4 domains are well hydrated and are positioned in close proximity to lipids, exhibiting local interactions with both lipid headgroups and acyl chains. Comparative studies with a positively charged lipid lacking a phosphodiester group reveal that this lipid modification has only modest effects on the structure and hydration of S1-S4 domains. Taken together, our results demonstrate that Arg residues in S1-S4 voltage-sensing domains reside in close proximity to the hydrophobic interior of the membrane yet are well hydrated, a requirement for carrying charge and driving protein motions in response to changes in membrane voltage.
Collapse
Affiliation(s)
- Dmitriy Krepkiy
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892 USA
| | - Klaus Gawrisch
- Laboratory of Membrane Biochemistry and Biophysics, National Institute of Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892 USA
| | - Kenton J. Swartz
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892 USA
| |
Collapse
|
11
|
Huber T, Grama L, Hetényi C, Schay G, Fülöp L, Penke B, Kellermayer MSZ. Conformational dynamics of titin PEVK explored with FRET spectroscopy. Biophys J 2012; 103:1480-9. [PMID: 23062340 DOI: 10.1016/j.bpj.2012.08.042] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Revised: 08/03/2012] [Accepted: 08/09/2012] [Indexed: 01/05/2023] Open
Abstract
The proline-, glutamate-, valine-, and lysine-rich (PEVK) domain of the giant muscle protein titin is thought to be an intrinsically unstructured random-coil segment. Various observations suggest, however, that the domain may not be completely devoid of internal interactions and structural features. To test the validity of random polymer models for PEVK, we determined the mean end-to-end distances of an 11- and a 21-residue synthetic PEVK peptide, calculated from the efficiency of the fluorescence resonance energy transfer (FRET) between an N-terminal intrinsic tryptophan donor and a synthetically added C-terminal IAEDANS acceptor obtained in steady-state and time-resolved experiments. We find that the contour-length scaling of mean end-to-end distance deviates from predictions of a purely statistical polymer chain. Furthermore, the addition of guanidine hydrochloride decreased, whereas the addition of salt increased the FRET efficiency, pointing at the disruption of structure-stabilizing interactions. Increasing temperature between 10 and 50°C increased the normalized FRET efficiency in both peptides but with different trajectories, indicating that their elasticity and conformational stability are different. Simulations suggest that whereas the short PEVK peptide displays an overall random structure, the long PEVK peptide retains residual, loose helical configurations. Transitions in the local structure and dynamics of the PEVK domain may play a role in the modulation of passive muscle mechanics.
Collapse
Affiliation(s)
- Tamás Huber
- Department of Biophysics and Radiation Biology and MTA-SE Molecular Biophysics Research Group, Semmelweis University, Budapest, Hungary
| | | | | | | | | | | | | |
Collapse
|
12
|
Fyrner T, Magnusson K, Nilsson KPR, Hammarström P, Aili D, Konradsson P. Derivatization of a Bioorthogonal Protected Trisaccharide Linker—Toward Multimodal Tools for Chemical Biology. Bioconjug Chem 2012; 23:1333-40. [DOI: 10.1021/bc300160a] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Timmy Fyrner
- Division
of Chemistry and ‡Division of Molecular Physics, IFM, Linköping University, SE-581 83 Linköping, Sweden
| | - Karin Magnusson
- Division
of Chemistry and ‡Division of Molecular Physics, IFM, Linköping University, SE-581 83 Linköping, Sweden
| | - K. Peter R. Nilsson
- Division
of Chemistry and ‡Division of Molecular Physics, IFM, Linköping University, SE-581 83 Linköping, Sweden
| | - Per Hammarström
- Division
of Chemistry and ‡Division of Molecular Physics, IFM, Linköping University, SE-581 83 Linköping, Sweden
| | - Daniel Aili
- Division
of Chemistry and ‡Division of Molecular Physics, IFM, Linköping University, SE-581 83 Linköping, Sweden
| | - Peter Konradsson
- Division
of Chemistry and ‡Division of Molecular Physics, IFM, Linköping University, SE-581 83 Linköping, Sweden
| |
Collapse
|
13
|
Longhi S, Belle V, Fournel A, Guigliarelli B, Carrière F. Probing structural transitions in both structured and disordered proteins using site-directed spin-labeling EPR spectroscopy. J Pept Sci 2011; 17:315-28. [DOI: 10.1002/psc.1344] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2010] [Revised: 11/17/2010] [Accepted: 11/20/2010] [Indexed: 11/10/2022]
|
14
|
Liu Y, Chan YM, Wu J, Chen C, Benesi A, Hu J, Wang Y, Chen G. Chemical synthesis of a bisphosphorylated mannose-6-phosphate N-glycan and its facile monoconjugation with human carbonic anhydrase II for in vivo fluorescence imaging. Chembiochem 2011; 12:685-90. [PMID: 21404409 DOI: 10.1002/cbic.201000785] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2010] [Indexed: 12/11/2022]
Affiliation(s)
- Yunpeng Liu
- Department of Chemistry, The Pennsylvania State University, 104 Chemistry Building, University Park, PA 16802, USA
| | | | | | | | | | | | | | | |
Collapse
|
15
|
Owenius R, Jarl A, Jonsson BH, Carlsson U, Hammarström P. GroEL-induced topological dislocation of a substrate protein β-sheet core: a solution EPR spin-spin distance study. J Chem Biol 2010; 3:127-39. [PMID: 21479077 DOI: 10.1007/s12154-010-0038-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2010] [Accepted: 03/12/2010] [Indexed: 10/19/2022] Open
Abstract
The Hsp60-type chaperonin GroEL assists in the folding of the enzyme human carbonic anhydrase II (HCA II) and protects it from aggregation. This study was aimed to monitor conformational rearrangement of the substrate protein during the initial GroEL capture (in the absence of ATP) of the thermally unfolded HCA II molten-globule. Single- and double-cysteine mutants were specifically spin-labeled at a topological breakpoint in the β-sheet rich core of HCA II, where the dominating antiparallel β-sheet is broken and β-strands 6 and 7 are parallel. Electron paramagnetic resonance (EPR) was used to monitor the GroEL-induced structural changes in this region of HCA II during thermal denaturation. Both qualitative analysis of the EPR spectra and refined inter-residue distance calculations based on magnetic dipolar interaction show that the spin-labeled positions F147C and K213C are in proximity in the native state of HCA II at 20 °C (as close as ∼8 Å), and that this local structure is virtually intact in the thermally induced molten-globule state that binds to GroEL. In the absence of GroEL, the molten globule of HCA II irreversibly aggregates. In contrast, a substantial increase in spin-spin distance (up to >20 Å) was observed within minutes, upon interaction with GroEL (at 50 and 60 °C), which demonstrates a GroEL-induced conformational change in HCA II. The GroEL binding-induced disentanglement of the substrate protein core at the topological break-point is likely a key event for rearrangement of this potent aggregation initiation site, and hence, this conformational change averts HCA II misfolding.
Collapse
|
16
|
Krishnamurthy VM, Kaufman GK, Urbach AR, Gitlin I, Gudiksen KL, Weibel DB, Whitesides GM. Carbonic anhydrase as a model for biophysical and physical-organic studies of proteins and protein-ligand binding. Chem Rev 2008; 108:946-1051. [PMID: 18335973 PMCID: PMC2740730 DOI: 10.1021/cr050262p] [Citation(s) in RCA: 555] [Impact Index Per Article: 34.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Vijay M. Krishnamurthy
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138
| | - George K. Kaufman
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138
| | - Adam R. Urbach
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138
| | - Irina Gitlin
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138
| | - Katherine L. Gudiksen
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138
| | - Douglas B. Weibel
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138
| | - George M. Whitesides
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138
| |
Collapse
|
17
|
Site-directed fluorescence labeling of a membrane protein with BADAN: probing protein topology and local environment. Biophys J 2008; 94:3945-55. [PMID: 18234831 DOI: 10.1529/biophysj.107.125807] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The work presented here describes a new and simple method based on site-directed fluorescence labeling using the BADAN label that permits the examination of protein-lipid interactions in great detail. We applied this technique to a membrane-embedded, mainly alpha-helical reference protein, the M13 major coat protein. Using a high-throughput approach, 40 site-specific cysteine mutants were prepared of the 50-residues long protein. The steady-state fluorescence spectra were analyzed using a three-component spectral model that enabled the separation of Stokes shift contributions from water and internal label dynamics, and protein topology. We found that most of the fluorescence originated from BADAN labels that were hydrogen-bonded to water molecules even within the hydrophobic core of the membrane. Our spectral decomposition method revealed the embedment and topology of the labeled protein in the membrane bilayer under various conditions of headgroup charge and lipid chain length, as well as key characteristics of the membrane such as hydration level and local polarity, provided by the local dielectric constant.
Collapse
|
18
|
Almstedt K, Mårtensson LG, Carlsson U, Hammarström P. Thermodynamic interrogation of a folding disease. Mutant mapping of position 107 in human carbonic anhydrase II linked to marble brain disease. Biochemistry 2008; 47:1288-98. [PMID: 18189416 DOI: 10.1021/bi701720p] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
UNLABELLED Marble brain disease (MBD) also known as Guibaud-Vainsel syndrome is caused by autosomal recessive mutations in the human carbonic anhydrase II (HCA II) gene. HCA II is a 259 amino acid single domain enzyme and is dominated by a 10-stranded beta-sheet. One mutation associated with MBD entails the H107Y substitution where H107 is a highly conserved residue in the carbonic anhydrase protein family. We have previously demonstrated that the H107Y mutation is a remarkably destabilizing folding mutation [Almstedt et al. (2004) J. Mol. Biol. 342, 619-633]. Here, the exceptional destabilization by the H107Y mutation has been further investigated. A mutational survey of position H107 and a neighboring conserved position E117 has been performed entailing the mutants H107A, H107F, H107N, E117A and the double mutants H107A/E117A and H107N/E117A. All mutants were severely destabilized versus GuHCl and heat denaturation. Thermal denaturation and GuHCl phase diagram and ANS analyses showed that the mutants shifted HCA II toward populating ensembles of intermediates of molten globule type under physiological conditions. The native state stability of the mutants was in the following order: wt > H107N > E117A > H107A > H107F > H107Y > H107N/E117A > H107A/E117A. IN CONCLUSION (i) H107N is least destabilizing likely due to compensatory H-bonding ability of the introduced Asn residue. (ii) Double mutant cycles surprisingly reveal additive destabilization of H107N and E117A showing that H107 and E117 are independently stabilizing the folded protein. (iii) H107Y and H107F are exceptionally destabilizing due to bulkiness of the side chains whereas H107A is more accommodating, indicating long-range destabilizing effects of the natural pathogenic H107Y mutation.
Collapse
Affiliation(s)
- Karin Almstedt
- IFM-Department of Chemistry, Linköping University, 581 83 Linköping, Sweden
| | | | | | | |
Collapse
|
19
|
Silversmith RE, Levin MD, Schilling E, Bourret RB. Kinetic Characterization of Catalysis by the Chemotaxis Phosphatase CheZ. J Biol Chem 2008; 283:756-65. [DOI: 10.1074/jbc.m704400200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
|
20
|
Borbas KE, Kee HL, Holten D, Lindsey JS. A compact water-soluble porphyrin bearing an iodoacetamido bioconjugatable site. Org Biomol Chem 2008; 6:187-94. [DOI: 10.1039/b715072e] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
|
21
|
Swartz HM, Khan N, Khramtsov VV. Use of electron paramagnetic resonance spectroscopy to evaluate the redox state in vivo. Antioxid Redox Signal 2007; 9:1757-71. [PMID: 17678441 PMCID: PMC2702846 DOI: 10.1089/ars.2007.1718] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The aim of this article is to provide an overview of how electron paramagnetic resonance (EPR) can be used to measure redox-related parameters in vivo. The values of this approach include that the measurements are made under fully physiological conditions, and some of the measurements cannot be made by other means. Three complementary approaches are used with in vivo EPR: the rate of reduction or reactions of nitroxides, spin trapping of free radicals, and measurements of thiols. All three approaches already have produced unique and useful information. The measurement of the rate of decrease of nitroxides technically is the simplest, but difficult to interpret because the measured parameter, reduction in the intensity of the nitroxide signal, can occur by several different mechanisms. In vivo spin trapping can provide direct evidence for the occurrence of specific free radicals in vivo and reflect relative changes, but accurate absolute quantification remains challenging. The measurement of thiols in vivo also appears likely to be useful, but its development as an in vivo technique is at an early stage. It seems likely that the use of in vivo EPR to measure redox processes will become an increasingly utilized and valuable tool.
Collapse
Affiliation(s)
- Harold M Swartz
- Department of Radiology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
| | | | | |
Collapse
|
22
|
Abbyad P, Shi X, Childs W, McAnaney TB, Cohen BE, Boxer SG. Measurement of solvation responses at multiple sites in a globular protein. J Phys Chem B 2007; 111:8269-76. [PMID: 17592867 PMCID: PMC2507720 DOI: 10.1021/jp0709104] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Proteins respond to electrostatic perturbations through complex reorganizations of their charged and polar groups, as well as those of the surrounding media. These solvation responses occur both in the protein interior and on its surface, though the exact mechanisms of solvation are not well understood, in part because of limited data on the solvation responses for any given protein. Here, we characterize the solvation kinetics at sites throughout the sequence of a small globular protein, the B1 domain of streptococcal protein G (GB1), using the synthetic fluorescent amino acid Aladan. Aladan was incorporated into seven different GB1 sites, and the time-dependent Stokes shift was measured over the femtosecond to nanosecond time scales by fluorescence upconversion and time-correlated single photon counting. The seven sites range from buried within the protein core to fully solvent-exposed on the protein surface, and are located on different protein secondary structures including beta-sheets, helices, and loops. The dynamics in the protein sites were compared against the free fluorophore in buffer. All protein sites exhibited an initial, ultrafast Stokes shift on the subpicosecond time scale similar to that observed for the free fluorophore, but smaller in magnitude. As the probe is moved from the surface to more buried sites, the dynamics of the solvation response become slower, while no clear correlation between dynamics and secondary structure is observed. We suggest that restricted movements of the surrounding protein residues give rise to the observed long time dynamics and that such movements comprise a large portion of the protein's solvation response. The proper treatment of dynamic Stokes shift data when the time scale for solvation is comparable to the fluorescence lifetime is discussed.
Collapse
Affiliation(s)
- Paul Abbyad
- Department of Chemistry, Stanford University, Stanford, California 94305-5080
| | - Xinghua Shi
- Department of Chemistry, Stanford University, Stanford, California 94305-5080
| | - William Childs
- Department of Chemistry, Stanford University, Stanford, California 94305-5080
| | - Tim B. McAnaney
- Department of Chemistry, Stanford University, Stanford, California 94305-5080
| | - Bruce E. Cohen
- Biological Nanostructures Facility, The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
| | - Steven G. Boxer
- Department of Chemistry, Stanford University, Stanford, California 94305-5080
- To whom correspondence should be addressed, , Phone: (650)723-4482; fax (650)723-4817
| |
Collapse
|
23
|
Gitlin I, Gudiksen KL, Whitesides GM. Effects of Surface Charge on Denaturation of Bovine Carbonic Anhydrase. Chembiochem 2006; 7:1241-50. [PMID: 16847847 DOI: 10.1002/cbic.200600191] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
This work compares the denaturation of two proteins-bovine carbonic anhydrase II (BCA) and its derivative with all lysine groups acetylated (BCA-Ac(18))-by urea, guanidinium chloride (GuHCl), heat, and sodium dodecyl sulfate (SDS). It demonstrates that increasing the net negative charge of the protein by acetylation of lysines reduces its stability to urea, GuHCl, and heat, but increases its kinetic stability (its thermodynamic stability cannot be measured) towards denaturation by SDS. Increasing the ionic strength of the buffer improves the stability of BCA-Ac(18) to urea and heat, but still leaves it less stable than unacetylated BCA to those denaturants. In urea, the large change in electrostatic interactions not only modifies the free energy of denaturation, but also introduces a stable intermediate into the unfolding pathway. This work shows that modifications of charges on the surfaces of proteins can have a large effect--positive or negative, depending on the denaturant--on the stability of the proteins despite the exposure of these charges to high dielectric solvent and buffer ions.
Collapse
Affiliation(s)
- Irina Gitlin
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA
| | | | | |
Collapse
|
24
|
Gangopadhyay JP, Ikemoto N. Role of the Met3534-Ala4271 region of the ryanodine receptor in the regulation of Ca2+ release induced by calmodulin binding domain peptide. Biophys J 2005; 90:2015-26. [PMID: 16387763 PMCID: PMC1386780 DOI: 10.1529/biophysj.105.074328] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
CaMBP, a peptide corresponding to the 3614-3643 calmodulin (CaM) binding region of the ryanodine receptor (RyR1), is known to activate RyR1 Ca2+ channel. To analyze the mechanism of channel regulation by the CaMBP-RyR1 interaction, we investigated a), CaMBP binding to RyR1, b), induced local conformational changes in the CaMBP binding region of RyR1 using the fluorescent conformational probe badan attached to CaMBP (CaMBP-badan), and c), effects of "a" and "b" on SR Ca2+ release. We also monitored the interaction of CaMBP-badan with CaM and a peptide corresponding to the Met3534-Ala4271 region of RyR1 (R3534-4271) as a control. At lower peptide concentrations (< or =15 microM), CaMBP binding to RyR1 increased the intensity of badan fluorescence emission at a shorter wavelength (the state resembling CaMBP-badan/Ca-CaM) and induced Ca2+ release. Further increase in CaMBP concentration (up to approximately 50 microM) produced more binding of CaMBP accompanied by further increase in the badan fluorescence emission but at a longer wavelength (the state resembling CaMBP-badan/apo-CaM) and inhibited Ca2+ release. Binding of CaMBP-badan to R3534-4271 increased the intensity of badan fluorescence, showing the similar concentration-dependent red-shift of the emission maximum. It is proposed that CaMBP interacts with two classes of binding sites located in the Met3534-Ala4271 region of RyR1, which activate and inhibit the Ca2+ channel, respectively.
Collapse
|
25
|
Lindgren M, Sörgjerd K, Hammarström P. Detection and characterization of aggregates, prefibrillar amyloidogenic oligomers, and protofibrils using fluorescence spectroscopy. Biophys J 2005; 88:4200-12. [PMID: 15764666 PMCID: PMC1305650 DOI: 10.1529/biophysj.104.049700] [Citation(s) in RCA: 259] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Transthyretin (TTR) is a protein linked to a number of different amyloid diseases including senile systemic amyloidosis and familial amyloidotic polyneuropathy. The transient nature of oligomeric intermediates of misfolded TTR that later mature into fibrillar aggregates makes them hard to study, and methods to study these species are sparse. In this work we explore a novel pathway for generation of prefibrillar aggregates of TTR, which provides important insight into TTR misfolding. Prefibrillar amyloidogenic oligomers and protofibrils of misfolded TTR were generated in vitro through induction of the molten globule type A-state from acid unfolded TTR through the addition of NaCl. The aggregation process produced fairly monodisperse oligomers (300-500 kD) within 2 h that matured after 20 h into larger spherical clusters (30-50 nm in diameter) and protofibrils as shown by transmission electron microscopy. Further maturation of the aggregates showed shrinkage of the spheres as the fibrils grew in length, suggesting a conformational change of the spheres into more rigid structures. The structural and physicochemical characteristics of the aggregates were investigated using fluorescence, circular dichroism, chemical cross-linking, and transmission electron microscopy. The fluorescent dyes 1-anilinonaphthalene-8-sulfonate (ANS), 4-4-bis-1-phenylamino-8-naphthalene sulfonate (Bis-ANS), 4-(dicyanovinyl)-julolidine (DCVJ), and thioflavin T (ThT) were employed in both static and kinetic assays to characterize these oligomeric and protofibrillar states using both steady-state and time-resolved fluorescence techniques. DCVJ, a molecular rotor, was employed for the first time for studies of an amyloidogenic process and is shown useful for detection of the early steps of the oligomerization process. DCVJ bound to the early prefibrillar oligomers (300-500 kD) with an apparent dissociation constant of 1.6 muM, which was slightly better than for ThT (6.8 muM). Time-resolved fluorescence anisotropy decay of ANS was shown to be a useful tool for giving further structural and kinetic information of the oligomeric aggregates. ThT dramatically increases its fluorescence quantum yield when bound to amyloid fibrils; however, the mechanism behind this property is unknown. Data from this work suggest that unbound ThT is also intrinsically quenched and functions similarly to a molecular rotor, which in combination with its environmental dependence provides a blue shift to the characteristic 482 nm wavelength when bound to amyloid fibrils.
Collapse
Affiliation(s)
- Mikael Lindgren
- Department of Physics, Norwegian University of Science and Technology, Trondheim
| | | | | |
Collapse
|
26
|
Karlsson M, Carlsson U. Protein adsorption orientation in the light of fluorescent probes: mapping of the interaction between site-directly labeled human carbonic anhydrase II and silica nanoparticles. Biophys J 2005; 88:3536-44. [PMID: 15731384 PMCID: PMC1305500 DOI: 10.1529/biophysj.104.054809] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Little is known about the direction and specificity of protein adsorption to solid surfaces, a knowledge that is of great importance in many biotechnological applications. To resolve the direction in which a protein with known structure and surface potentials binds to negatively charged silica nanoparticles, fluorescent probes were attached to different areas on the surface of the protein human carbonic anhydrase II. By this approach it was clearly demonstrated that the adsorption of the native protein is specific to limited regions at the surface of the N-terminal domain of the protein. Furthermore, the adsorption direction is strongly pH-dependent. At pH 6.3, a histidine-rich area around position 10 is the dominating adsorption region. At higher pH values, when the histidines in this area are deprotonated, the protein is also adsorbed by a region close to position 37, which contains several lysines and arginines. Clearly the adsorption is directed by positively charged areas on the protein surface toward the negatively charged silica surface at conditions when specific binding occurs.
Collapse
Affiliation(s)
- Martin Karlsson
- IFM-Department of Chemistry, Linköping University, Linköping, Sweden
| | | |
Collapse
|
27
|
Almstedt K, Lundqvist M, Carlsson J, Karlsson M, Persson B, Jonsson BH, Carlsson U, Hammarström P. Unfolding a folding disease: folding, misfolding and aggregation of the marble brain syndrome-associated mutant H107Y of human carbonic anhydrase II. J Mol Biol 2004; 342:619-33. [PMID: 15327960 DOI: 10.1016/j.jmb.2004.07.024] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2004] [Revised: 07/01/2004] [Accepted: 07/12/2004] [Indexed: 11/23/2022]
Abstract
Most loss-of-function diseases are caused by aberrant folding of important proteins. These proteins often misfold due to mutations. The disease marble brain syndrome (MBS), known also as carbonic anhydrase II deficiency syndrome (CADS), can manifest in carriers of point mutations in the human carbonic anhydrase II (HCA II) gene. One mutation associated with MBS entails the His107Tyr substitution. Here, we demonstrate that this mutation is a remarkably destabilizing folding mutation. The loss-of-function is clearly a folding defect, since the mutant shows 64% of CO(2) hydration activity compared to that of the wild-type at low temperature where the mutant is folded. On the contrary, its stability towards thermal and guanidine hydrochloride (GuHCl) denaturation is highly compromised. Using activity assays, CD, fluorescence, NMR, cross-linking, aggregation measurements and molecular modeling, we have mapped the properties of this remarkable mutant. Loss of enzymatic activity had a midpoint temperature of denaturation (T(m)) of 16 degrees C for the mutant compared to 55 degrees C for the wild-type protein. GuHCl-denaturation (at 4 degrees C) showed that the native state of the mutant was destabilized by 9.2kcal/mol. The mutant unfolds through at least two equilibrium intermediates; one novel intermediate that we have termed the molten globule light state and, after further denaturation, the classical molten globule state is populated. Under physiological conditions (neutral pH; 37 degrees C), the His107Tyr mutant will populate the molten globule light state, likely due to novel interactions between Tyr107 and the surroundings of the critical residue Ser29 that destabilize the native conformation. This intermediate binds the hydrophobic dye 8-anilino-1-naphthalene sulfonic acid (ANS) but not as strong as the molten globule state, and near-UV CD reveals the presence of significant tertiary structure. Notably, this intermediate is not as prone to aggregation as the classical molten globule. As a proof of concept for an intervention strategy with small molecules, we showed that binding of the CA inhibitor acetazolamide increases the stability of the native state of the mutant by 2.9kcal/mol in accordance with its strong affinity. Acetazolamide shifts the T(m) to 34 degrees C that protects from misfolding and will enable a substantial fraction of the enzyme pool to survive physiological conditions.
Collapse
Affiliation(s)
- Karin Almstedt
- IFM-Department of Chemistry, Linköping University, 581 83 Linköping, Sweden
| | | | | | | | | | | | | | | |
Collapse
|
28
|
Gangopadhyay JP, Grabarek Z, Ikemoto N. Fluorescence probe study of Ca2+-dependent interactions of calmodulin with calmodulin-binding peptides of the ryanodine receptor. Biochem Biophys Res Commun 2004; 323:760-8. [PMID: 15381065 DOI: 10.1016/j.bbrc.2004.08.154] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2004] [Indexed: 11/25/2022]
Abstract
We have used a highly environment-sensitive fluorescent probe 6-bromoacetyl-2-dimethylaminonaphthalene (badan) to study the interaction between calmodulin (CaM) and a CaM-binding peptide of the ryanodine receptor (CaMBP) and its sub-fragments F1 and F4. Badan was attached to the Thr34Cys mutant of CaM (CaM-badan). Ca(2+) increase in a physiological range of Ca(2+) (0.1-2 microM) produced about 40 times increase in the badan fluorescence. Upon binding to CaMBP, the badan fluorescence of apo-CaM showed a small increase at a slow rate; whereas that of Ca-CaM showed a large decrease at a very fast rate. Upon binding of CaM to the badan-labeled CaMBP, the badan fluorescence showed a small and slow increase at low Ca(2+), and a large and fast increase at high Ca(2+). Thus, the badan probe attached to CaM Cys(34) can be used to monitor conformational changes occurring not only in CaM, but also those in the CaM-CaMBP interface. Based on our results we propose that both the interaction interface and the global conformation of the CaM-CaMBP complex are altered by calcium.
Collapse
|
29
|
Mårtensson LG, Karlsson M, Carlsson U. Dramatic stabilization of the native state of human carbonic anhydrase II by an engineered disulfide bond. Biochemistry 2002; 41:15867-75. [PMID: 12501217 DOI: 10.1021/bi020433+] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To find a disulfide pair that could stabilize the enzyme human carbonic anhydrase II (HCA II), we grafted the disulfide bridge from the related and unusually stable carbonic anhydrase form from Neisseria gonorrhoeae (NGCA) into the human enzyme. Thus, the two Cys residues at positions 23 and 203 were engineered into a pseudo-wild-type form of HCA II (C206S), giving the mutant C206S/A23C/L203C. The disulfide bond was not formed spontaneously. The native state of the reduced form of the mutant was markedly destabilized (2.9 kcal/mol) compared to that of HCA II. Formation of a disulfide bridge was achieved by treatment by oxidized glutathione. This led to a significant stabilization of the native conformation. Compared to HCA II the unfolding midpoint for the variant was increased from 0.9 to 1.7 M guanidine HCl, corresponding to a stabilization of 3.7 kcal/mol. This makes the human enzyme almost as stable as the model protein NGCA, for which the unfolding of the native state has a midpoint at 2.1 M guanidine HCl. The stabilized protein underwent, contrary to all other investigated variants of HCA II, an apparent two-state unfolding transition, as judged from intrinsic Trp fluorescence measurements. A molten-globule intermediate is nevertheless formed but is suppressed because of the high denaturant pressure it faces upon rupture of the native state.
Collapse
|
30
|
Teilum K, Maki K, Kragelund BB, Poulsen FM, Roder H. Early kinetic intermediate in the folding of acyl-CoA binding protein detected by fluorescence labeling and ultrarapid mixing. Proc Natl Acad Sci U S A 2002; 99:9807-12. [PMID: 12096190 PMCID: PMC125024 DOI: 10.1073/pnas.152321499] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Early conformational events during folding of acyl-CoA binding protein (ACBP), an 86-residue alpha-helical protein, were explored by using a continuous-flow mixing apparatus with a dead time of 70 micros to measure changes in intrinsic tryptophan fluorescence and tryptophan-dansyl fluorescence energy transfer. Although the folding of ACBP was initially described as a concerted two-state process, the tryptophan fluorescence measurements revealed a previously unresolved phase with a time constant tau = 80 micros, indicating formation of an intermediate with only slightly enhanced fluorescence of Trp-55 and Trp-58 relative to the unfolded state. To amplify this phase, a dansyl fluorophore was introduced at the C terminus by labeling an I86C mutant of ACBP with 5-IAEDANS [5-((((2-iodoacetyl)amino)ethyl)amino)naphthalene-1-sulfonic acid]. Continuous-flow refolding of guanidine HCl-denatured ACBP showed a major increase in tryptophan-dansyl fluorescence energy transfer, indicating formation of a partially collapsed ensemble of states on the 100-micros time scale. A subsequent decrease in dansyl fluorescence is attributed to intramolecular quenching of donor fluorescence on formation of the native state. The kinetic data are fully accounted for by three-state mechanisms with either on- or off-pathway intermediates. The intermediate accumulates to a maximum population of 40%, and its stability depends only weakly on denaturant concentration, which is consistent with a marginally stable ensemble of partially collapsed states with approximately 1/3 of the solvent-accessible surface buried. The findings indicate that ultrafast mixing methods combined with sensitive conformational probes can reveal transient accumulation of intermediate states in proteins with apparent two-state folding mechanisms.
Collapse
Affiliation(s)
- Kaare Teilum
- Department of Protein Chemistry, Institute of Molecular Biology, University of Copenhagen, DK-1353 Copenhagen K, Denmark
| | | | | | | | | |
Collapse
|
31
|
Huber M, Lindgren M, Hammarström P, Mårtensson LG, Carlsson U, Eaton GR, Eaton SS. Phase memory relaxation times of spin labels in human carbonic anhydrase II: pulsed EPR to determine spin label location. Biophys Chem 2001; 94:245-56. [PMID: 11804734 DOI: 10.1016/s0301-4622(01)00239-3] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Phase memory relaxation times (T(M) or T(2)) of spin labels in human carbonic anhydrase II (HCA II) are reported. Spin labels (N-(1-oxyl-2,2,5,5-tetramethyl-3-pyrrolidinyl)iodoacetamide, IPSL) were introduced at cysteines, by site-directed mutagenesis at seven different positions in the protein. By two pulse electron paramagnetic resonance (EPR), electron spin echo decays at 45 K are measured and fitted by stretched exponentials, resulting in relaxation parameters T(M) and x. T(M) values of seven positions are between 1.6 micros for the most buried residue (L79C) and 4.7 micros for a residue at the protein surface (W245C). In deuteriated buffer, longer T(M) are found for all but the most buried residues (L79C and W97C), and electron spin echo envelop modulation (ESEEM) of deuterium nuclei is observed. Different deuterium ESEEM patterns for W95C and W16C (surface residue) indicate differences in the local water concentration, or accessibility, of the spin label by deuterium. We propose T(M) as a parameter to determine the spin label location in proteins. Furthermore, these systems are interesting for studying the pertaining relaxation mechanism.
Collapse
Affiliation(s)
- M Huber
- Department of Molecular Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands.
| | | | | | | | | | | | | |
Collapse
|
32
|
Owenius R, Osterlund M, Svensson M, Lindgren M, Persson E, Freskgård PO, Carlsson U. Spin and fluorescent probing of the binding interface between tissue factor and factor VIIa at multiple sites. Biophys J 2001; 81:2357-69. [PMID: 11566805 PMCID: PMC1301706 DOI: 10.1016/s0006-3495(01)75882-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The specific complex between the extracellular part of tissue factor (sTF) and factor VIIa (FVIIa) was chosen as a model for studies of the binding interface between two interacting proteins. Six surface-exposed positions in sTF, residues known to contribute to the sTF-FVIIa interaction, were selected for cysteine mutation and site-directed labeling with spin and fluorescent probes. The binding interface was characterized by spectral data from electron paramagnetic resonance (EPR) and steady-state and time-domain fluorescence spectroscopy. The labels reported on compact local environments at positions 158 and 207 in the interface region between sTF and the gamma-carboxyglutamic acid (Gla) domain of FVIIa, and at positions 22 and 140 in the interface region between sTF and the first epidermal growth factor-like (EGF1) domain of FVIIa. The tightness of the local interactions in these parts of the interface is similar to that seen in the interior of globular proteins. This was further emphasized by the reduced local polarity detected by the fluorescent label upon FVIIa binding, especially in the sTF-Gla region. There were indications of structural rigidity also at positions 45 and 94 in the interface region between sTF and the protease domain (PD) of FVIIa, despite the perturbed cofactor function of these sTF variants. The results of the present study indicate that the multi-probing approach enables comparison of the tightness and characteristics of interaction along the binding interface of a protein complex. This approach also increases the probability of acquiring reliable structural data that are descriptive of the wild-type proteins.
Collapse
Affiliation(s)
- R Owenius
- IFM-Department of Chemical Physics, Linköping University, SE-581 83 Linköping, Sweden
| | | | | | | | | | | | | |
Collapse
|