1
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Phillips RS, Bauer O. Characterization of aminoacrylate intermediates of pyridoxal-5'-phosphate dependent enzymes. Methods Enzymol 2023; 685:199-224. [PMID: 37245902 DOI: 10.1016/bs.mie.2023.03.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Pyridoxal-5'-phosphate (PLP) Schiff's bases of 2-aminoacrylate are intermediates in β-elimination and β-substitution reaction of PLP-dependent enzymes. These enzymes are found in two major families, the α-, or aminotransferase, superfamily, and the β-family. While the α-family enzymes primarily catalyze β-eliminations, the β-family enzymes catalyze both β-elimination and β-substitution reactions. Tyrosine phenol-lyase (TPL), which catalyzes the reversible elimination of phenol from l-tyrosine, is an example of an α-family enzyme. Tryptophan synthase catalyzes the irreversible formation of l-tryptophan from l-serine and indole, and is an example of a β-family enzyme. The identification and characterization of aminoacrylate intermediates in the reactions of both of these enzymes is discussed. The use of UV-visible absorption and fluorescence spectroscopy, X-ray and neutron crystallography, and NMR spectroscopy to identify aminoacrylate intermediates in these and other PLP enzymes is presented.
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Affiliation(s)
- Robert S Phillips
- Department of Chemistry, University of Georgia, Athens, GA, United States; Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, United States.
| | - Olivia Bauer
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, United States
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2
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Yang P, Xiao W, Lu S, Jiang S, Jiang S, Chen J, Wu W, Zheng Z, Jiang S. Characterization of a Trametes versicolor aflatoxin B1-degrading enzyme (TV-AFB1D) and its application in the AFB1 degradation of contaminated rice in situ. Front Microbiol 2022; 13:960882. [PMID: 36187979 PMCID: PMC9515612 DOI: 10.3389/fmicb.2022.960882] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Accepted: 08/24/2022] [Indexed: 11/13/2022] Open
Abstract
Aflatoxin B1 (AFB1) contaminates rice during harvest or storage and causes a considerable risk to human and animal health. In this study, Trametes versicolor AFB1–degrading enzyme (TV–AFB1D) gene recombinantly expressed in engineered E. coli BL21 (DE3) and Saccharomyces cerevisiae. The TV–AFB1D enzymatic characteristics and AFB1 degradation efficiency in contaminated rice were investigated. Results showed that the size of recombinant TV-AFB1D expressing in E. coli BL21 (DE3) and S. cerevisiae was appropriately 77 KDa. The kinetic equation of TV-AFB1D was y = 0.01671x + 1.80756 (R2 = 0.994, Km = 9.24 mM, and Vmax = 553.23 mM/min). The Kcat and Kcat/Km values of TV-AFB1D were 0.07392 (s−1) and 8 M−1 s−1, respectively. The AFB1 concentration of contaminated rice decreased from 100 μg/ml to 32.6 μg/ml after treatment at 32°C for 5 h under the catabolism of TV-AFB1D. S. cerevisiae engineered strains carrying aldehyde oxidase 1 (AOX1) and Cauliflower mosaic virus 35 S (CaMV 35 S) promoters caused the residual AFB1 contents, respectively, decreased to 3.4 and 2.9 μg/g from the initial AFB1 content of 7.4 μg/g after 24 h of fermentation using AFB1-contaminated rice as substrate. The AFB1 degradation rates of S. cerevisiae engineered strains carrying AOX1 and CaMV promoters were 54 and 61%, respectively. Engineered S. cerevisiae strains integrated with TV-AFB1D expression cassettes were developed to simultaneously degrade AFB1 and produce ethanol using AFB1-contaminated rice as substrate. Thus, TV-AFB1D has significant application potential in the AFB1 decomposition from contaminated agricultural products.
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Affiliation(s)
- Peizhou Yang
- College of Food and Biological Engineering, Anhui Key Laboratory of Intensive Processing of Agriculture Products, Hefei University of Technology, Hefei, China
- *Correspondence: Peizhou Yang, ,;
| | - Wei Xiao
- College of Food and Biological Engineering, Anhui Key Laboratory of Intensive Processing of Agriculture Products, Hefei University of Technology, Hefei, China
| | - Shuhua Lu
- College of Food and Biological Engineering, Anhui Key Laboratory of Intensive Processing of Agriculture Products, Hefei University of Technology, Hefei, China
| | - Shuying Jiang
- College of Food and Biological Engineering, Anhui Key Laboratory of Intensive Processing of Agriculture Products, Hefei University of Technology, Hefei, China
| | - Suwei Jiang
- Department of Biological, Food and Environment Engineering, Hefei University, Hefei, China
| | - Jianchao Chen
- College of Food and Biological Engineering, Anhui Key Laboratory of Intensive Processing of Agriculture Products, Hefei University of Technology, Hefei, China
| | - Wenjing Wu
- College of Food and Biological Engineering, Anhui Key Laboratory of Intensive Processing of Agriculture Products, Hefei University of Technology, Hefei, China
| | - Zhi Zheng
- College of Food and Biological Engineering, Anhui Key Laboratory of Intensive Processing of Agriculture Products, Hefei University of Technology, Hefei, China
| | - Shaotong Jiang
- College of Food and Biological Engineering, Anhui Key Laboratory of Intensive Processing of Agriculture Products, Hefei University of Technology, Hefei, China
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3
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Ghosh RK, Hilario E, Chang CEA, Mueller LJ, Dunn MF. Allosteric regulation of substrate channeling: Salmonella typhimurium tryptophan synthase. Front Mol Biosci 2022; 9:923042. [PMID: 36172042 PMCID: PMC9512447 DOI: 10.3389/fmolb.2022.923042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 08/11/2022] [Indexed: 11/13/2022] Open
Abstract
The regulation of the synthesis of L-tryptophan (L-Trp) in enteric bacteria begins at the level of gene expression where the cellular concentration of L-Trp tightly controls expression of the five enzymes of the Trp operon responsible for the synthesis of L-Trp. Two of these enzymes, trpA and trpB, form an αββα bienzyme complex, designated as tryptophan synthase (TS). TS carries out the last two enzymatic processes comprising the synthesis of L-Trp. The TS α-subunits catalyze the cleavage of 3-indole D-glyceraldehyde 3′-phosphate to indole and D-glyceraldehyde 3-phosphate; the pyridoxal phosphate-requiring β-subunits catalyze a nine-step reaction sequence to replace the L-Ser hydroxyl by indole giving L-Trp and a water molecule. Within αβ dimeric units of the αββα bienzyme complex, the common intermediate indole is channeled from the α site to the β site via an interconnecting 25 Å-long tunnel. The TS system provides an unusual example of allosteric control wherein the structures of the nine different covalent intermediates along the β-reaction catalytic path and substrate binding to the α-site provide the allosteric triggers for switching the αββα system between the open (T) and closed (R) allosteric states. This triggering provides a linkage that couples the allosteric conformational coordinate to the covalent chemical reaction coordinates at the α- and β-sites. This coupling drives the α- and β-sites between T and R conformations to achieve regulation of substrate binding and/or product release, modulation of the α- and β-site catalytic activities, prevention of indole escape from the confines of the active sites and the interconnecting tunnel, and synchronization of the α- and β-site catalytic activities. Here we review recent advances in the understanding of the relationships between structure, function, and allosteric regulation of the complex found in Salmonella typhimurium.
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Affiliation(s)
- Rittik K. Ghosh
- Department of Biochemistry, University of California, Riverside, Riverside, CA, United States
| | - Eduardo Hilario
- Department of Chemistry, University of California, Riverside, Riverside, CA, United States
| | - Chia-en A. Chang
- Department of Chemistry, University of California, Riverside, Riverside, CA, United States
| | - Leonard J. Mueller
- Department of Chemistry, University of California, Riverside, Riverside, CA, United States
- *Correspondence: Leonard J. Mueller, ; Michael F. Dunn,
| | - Michael F. Dunn
- Department of Biochemistry, University of California, Riverside, Riverside, CA, United States
- *Correspondence: Leonard J. Mueller, ; Michael F. Dunn,
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4
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Michalska K, Wellington S, Maltseva N, Jedrzejczak R, Selem-Mojica N, Rosas-Becerra LR, Barona-Gómez F, Hung DT, Joachimiak A. Catalytically impaired TrpA subunit of tryptophan synthase from Chlamydia trachomatis is an allosteric regulator of TrpB. Protein Sci 2021; 30:1904-1918. [PMID: 34107106 PMCID: PMC8376405 DOI: 10.1002/pro.4143] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 06/07/2021] [Accepted: 06/08/2021] [Indexed: 11/10/2022]
Abstract
Intracellular growth and pathogenesis of Chlamydia species is controlled by the availability of tryptophan, yet the complete biosynthetic pathway for l‐Trp is absent among members of the genus. Some representatives, however, preserve genes encoding tryptophan synthase, TrpAB – a bifunctional enzyme catalyzing the last two steps in l‐Trp synthesis. TrpA (subunit α) converts indole‐3‐glycerol phosphate into indole and glyceraldehyde‐3‐phosphate (α reaction). The former compound is subsequently used by TrpB (subunit β) to produce l‐Trp in the presence of l‐Ser and a pyridoxal 5′‐phosphate cofactor (β reaction). Previous studies have indicated that in Chlamydia, TrpA has lost its catalytic activity yet remains associated with TrpB to support the β reaction. Here, we provide detailed analysis of the TrpAB from C. trachomatis D/UW‐3/CX, confirming that accumulation of mutations in the active site of TrpA renders it enzymatically inactive, despite the conservation of the catalytic residues. We also show that TrpA remains a functional component of the TrpAB complex, increasing the activity of TrpB by four‐fold. The side chain of non‐conserved βArg267 functions as cation effector, potentially rendering the enzyme less susceptible to the solvent ion composition. The observed structural and functional changes detected herein were placed in a broader evolutionary and genomic context, allowing identification of these mutations in relation to their trp gene contexts in which they occur. Moreover, in agreement with the in vitro data, partial relaxation of purifying selection for TrpA, but not for TrpB, was detected, reinforcing a partial loss of TrpA functions during the course of evolution. PDB Code(s): 6V82;
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Affiliation(s)
- Karolina Michalska
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, Illinois, USA.,Structural Biology Center, X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, USA
| | - Samantha Wellington
- Department of Genetics, Broad Institute of MIT and Harvard, Cambridge, Massachusetts, USA
| | - Natalia Maltseva
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, Illinois, USA
| | - Robert Jedrzejczak
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, Illinois, USA
| | - Nelly Selem-Mojica
- Evolution of Metabolic Diversity Laboratory, Unidad de Genómica Avanzada (Langebio), Cinvestav, Mexico
| | - L Rodrigo Rosas-Becerra
- Evolution of Metabolic Diversity Laboratory, Unidad de Genómica Avanzada (Langebio), Cinvestav, Mexico
| | - Francisco Barona-Gómez
- Evolution of Metabolic Diversity Laboratory, Unidad de Genómica Avanzada (Langebio), Cinvestav, Mexico
| | - Deborah T Hung
- Department of Genetics, Broad Institute of MIT and Harvard, Cambridge, Massachusetts, USA
| | - Andrzej Joachimiak
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, Illinois, USA.,Structural Biology Center, X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, USA.,Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA
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5
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Alqarni MH, Foudah AI, Muharram MM, Budurian H, Labrou NE. Probing the Role of the Conserved Arg174 in Formate Dehydrogenase by Chemical Modification and Site-Directed Mutagenesis. Molecules 2021; 26:molecules26051222. [PMID: 33668802 PMCID: PMC7956174 DOI: 10.3390/molecules26051222] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2021] [Revised: 02/17/2021] [Accepted: 02/18/2021] [Indexed: 11/22/2022] Open
Abstract
The reactive adenosine derivative, adenosine 5′-O-[S-(4-hydroxy-2,3-dioxobutyl)]-thiophosphate (AMPS-HDB), contains a dicarbonyl group linked to the purine nucleotide at a position equivalent to the pyrophosphate region of NAD+. AMPS-HDB was used as a chemical label towards Candida boidinii formate dehydrogenase (CbFDH). AMPS-HDB reacts covalently with CbFDH, leading to complete inactivation of the enzyme activity. The inactivation kinetics of CbFDH fit the Kitz and Wilson model for time-dependent, irreversible inhibition (KD = 0.66 ± 0.15 mM, first order maximum rate constant k3 = 0.198 ± 0.06 min−1). NAD+ and NADH protects CbFDH from inactivation by AMPS-HDB, showing the specificity of the reaction. Molecular modelling studies revealed Arg174 as a candidate residue able to be modified by the dicarbonyl group of AMPS-HDB. Arg174 is a strictly conserved residue among FDHs and is located at the Rossmann fold, the common mononucleotide-binding motif of dehydrogenases. Arg174 was replaced by Asn, using site-directed mutagenesis. The mutant enzyme CbFDHArg174Asn was showed to be resistant to inactivation by AMPS-HDB, confirming that the guanidinium group of Arg174 is the target for AMPS-HDB. The CbFDHArg174Asn mutant enzyme exhibited substantial reduced affinity for NAD+ and lower thermostability. The results of the study underline the pivotal and multifunctional role of Arg174 in catalysis, coenzyme binding and structural stability of CbFDH.
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Affiliation(s)
- Mohammed Hamed Alqarni
- Department of Pharmacognosy, College of Pharmacy, Prince Sattam Bin Abdulaziz University, Alkharj 11942, Saudi Arabia;
- Correspondence: (M.H.A.); (N.E.L.)
| | - Ahmed Ibrahim Foudah
- Department of Pharmacognosy, College of Pharmacy, Prince Sattam Bin Abdulaziz University, Alkharj 11942, Saudi Arabia;
| | - Magdy Mohamed Muharram
- Department of Pharmaceutics, College of Pharmacy, Prince Sattam Bin Abdulaziz University, Alkharj 11942, Saudi Arabia;
- Department of Microbiology, College of Science, Al-Azhar University, Nasr City, Cairo 11884, Egypt
| | - Haritium Budurian
- Laboratory of Enzyme Technology, Department of Biotechnology, School of Food, Biotechnology and Development, Agricultural University of Athens, 75 Iera Odos Street, GR-11855 Athens, Greece;
| | - Nikolaos E. Labrou
- Laboratory of Enzyme Technology, Department of Biotechnology, School of Food, Biotechnology and Development, Agricultural University of Athens, 75 Iera Odos Street, GR-11855 Athens, Greece;
- Correspondence: (M.H.A.); (N.E.L.)
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6
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Phillips RS, Harris AP. Structural Basis of the Stereochemistry of Inhibition of Tryptophan Synthase by Tryptophan and Derivatives. Biochemistry 2021; 60:231-244. [PMID: 33428374 DOI: 10.1021/acs.biochem.0c00635] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have examined the reaction of Salmonella enterica serovar typhimurium tryptophan (Trp) synthase α2β2 complex with l-Trp, d-Trp, oxindolyl-l-alanine (OIA), and dioxindolyl-l-alanine (DOA) in the presence of disodium (dl)-α-glycerol phosphate (GP), using stopped-flow spectrophotometry and X-ray crystallography. All structures contained the d-isomer of GP bound at the α-active site. (3S)-OIA reacts with the pyridoxal-5'-phosphate (PLP) of Trp synthase to form a mixture of external aldimine and quinonoid complexes. The α-carboxylate of OIA rotates about 90° to become planar with the PLP when the quinonoid complex is formed, resulting in a conformational change in the loop of residues 110-115. The COMM domain of the Trp synthase-OIA complex is found as a mixture of two conformations. The (3R)-diastereomer of DOA binds about 5-fold more tightly than (3S)-OIA and also forms a mixture of aldimine and quinonoid complexes. DOA forms an additional H-bond between the 3-OH of DOA and βLys-87. l-Trp does not form a covalent complex with the PLP of Trp synthase. However, d-Trp forms a mixture of two external aldimine complexes which differ in the orientation of the α-carboxylate. In one conformation, the α-carboxylate is in the plane of the PLP, while in the other conformation, the α-carboxylate is perpendicular to the PLP plane. These results confirm that the stereochemistry of the transient indolenine quinonoid intermediate in the mechanism of Trp synthase is (3S) and demonstrate the linkage between aldimine and quinonoid reaction intermediates in the β-active site and allosteric communications with the α-active site.
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Affiliation(s)
- Robert S Phillips
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States.,Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602, United States
| | - Austin P Harris
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
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7
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Yang P, Wu Y, Jiang S, Zheng Z, Hou Z, Mu D, Xiao W, Jiang S, Yang YH. Effective Expression of the Serratia marcescens Phospholipase A1 Gene in Escherichia coli BL21(DE3), Enzyme Characterization, and Crude Rapeseed Oil Degumming via a Free Enzyme Approach. Front Bioeng Biotechnol 2019; 7:272. [PMID: 31681748 PMCID: PMC6811509 DOI: 10.3389/fbioe.2019.00272] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Accepted: 09/30/2019] [Indexed: 12/13/2022] Open
Abstract
Crude oil degumming by phospholipid removal is crucial to guarantee oil quality. Phospholipase degumming could produce green vegetable oil by reducing energy consumption and protecting the environment. To develop a novel phospholipase for oil degumming, we cloned the Serratia marcescens outer membrane phospholipase A gene (OM-PLA1) and expressed its 33 KDa protein in engineered Escherichia coli BL21(DE3). OM-PLA1 activity reached 18.9 U mL-1 with the induction of 0.6 mM isopropyl β-D-1-thiogalactopyranoside for 4 h. The optimum temperature and pH were 50°C and 7.5, respectively. Mg2+, Ca2+, Co2+, and Mn2+ at 0.1 mM L-1 significantly increased OM-PLA1 activity. The kinetic equations of OM-PLA1 and Lecitase Ultra were y = 13.7x+0.74 (Km = 18.53 mM, Vmax = 1.35 mM min-1) and y = 24.42x+0.58 (Km = 42.1 mM, Vmax = 1.72 mM min-1), respectively. The phosphorus content decreased from 22.6 to 9.3 mg kg-1 with the addition of 15 units of free recombinant OM-PLA1 into 150 g of crude rapeseed oil. OM-PLA1 has the close degumming efficiency with Lecitase Ultra. The S. marcescens outer membrane phospholipase gene (OM-PLA1) possessed higher substrate affinity and catalytic efficiency than Lecitase Ultra. This study provides an alternative approach to achieve crude vegetable oil degumming with enzymatic technology.
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Affiliation(s)
- Peizhou Yang
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Yun Wu
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Suwei Jiang
- Department of Biological, Food and Environment Engineering, Hefei University, Hefei, China
| | - Zhi Zheng
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Zhigang Hou
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Dongdong Mu
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Wei Xiao
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Shaotong Jiang
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Yung-Hun Yang
- Department of Biological Engineering, College of Engineering, Konkuk University, Seoul, South Korea
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8
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Buller AR, van Roye P, Cahn JK, Scheele RA, Herger M, Arnold FH. Directed Evolution Mimics Allosteric Activation by Stepwise Tuning of the Conformational Ensemble. J Am Chem Soc 2018; 140:7256-7266. [PMID: 29712420 PMCID: PMC5999571 DOI: 10.1021/jacs.8b03490] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Allosteric enzymes contain a wealth of catalytic diversity that remains distinctly underutilized for biocatalysis. Tryptophan synthase is a model allosteric system and a valuable enzyme for the synthesis of noncanonical amino acids (ncAA). Previously, we evolved the β-subunit from Pyrococcus furiosus, PfTrpB, for ncAA synthase activity in the absence of its native partner protein PfTrpA. However, the precise mechanism by which mutation activated TrpB to afford a stand-alone catalyst remained enigmatic. Here, we show that directed evolution caused a gradual change in the rate-limiting step of the catalytic cycle. Concomitantly, the steady-state distribution of the intermediates shifts to favor covalently bound Trp adducts, which have increased thermodynamic stability. The biochemical properties of these evolved, stand-alone TrpBs converge on those induced in the native system by allosteric activation. High-resolution crystal structures of the wild-type enzyme, an intermediate in the lineage, and the final variant, encompassing five distinct chemical states, show that activating mutations have only minor structural effects on their immediate environment. Instead, mutation stabilizes the large-scale motion of a subdomain to favor an otherwise transiently populated closed conformational state. This increase in stability enabled the first structural description of Trp covalently bound in a catalytically active TrpB, confirming key features of catalysis. These data combine to show that sophisticated models of allostery are not a prerequisite to recapitulating its complex effects via directed evolution, opening the way to engineering stand-alone versions of diverse allosteric enzymes.
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Affiliation(s)
- Andrew R. Buller
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave, Madison, Wisconsin 53706, United States
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Paul van Roye
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Jackson K.B. Cahn
- Institute of Microbiology, Eidgenössische Technische Hochschule (ETH) Zürich, Vladimir-Prelog-Weg 4, Zurich 8093, Switzerland
| | - Remkes A. Scheele
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Michael Herger
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Frances H. Arnold
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
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9
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Romney DK, Murciano-Calles J, Wehrmüller JE, Arnold FH. Unlocking Reactivity of TrpB: A General Biocatalytic Platform for Synthesis of Tryptophan Analogues. J Am Chem Soc 2017; 139:10769-10776. [PMID: 28708383 DOI: 10.1021/jacs.7b05007/suppl_file/ja7b05007_si_002.pdf] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Derivatives of the amino acid tryptophan (Trp) serve as precursors for the chemical and biological synthesis of complex molecules with a wide range of biological properties. Trp analogues are also valuable as building blocks for medicinal chemistry and as tools for chemical biology. While the enantioselective synthesis of Trp analogues is often lengthy and requires the use of protecting groups, enzymes have the potential to synthesize such products in fewer steps and with the pristine chemo- and stereoselectivity that is a hallmark of biocatalysis. The enzyme TrpB is especially attractive because it can form Trp analogues directly from serine (Ser) and the corresponding indole analogue. However, many potentially useful substrates, including bulky or electron-deficient indoles, are poorly accepted. We have applied directed evolution to TrpB from Pyrococcus furiosus and Thermotoga maritima to generate a suite of catalysts for the synthesis of previously intractable Trp analogues. For the most challenging substrates, such as nitroindoles, the key to improving activity lay in the mutation of a universally conserved and mechanistically important residue, E104. The new catalysts express at high levels (>200 mg/L of Escherichia coli culture) and can be purified by heat treatment; they can operate up to 75 °C (where solubility is enhanced) and can synthesize enantiopure Trp analogues substituted at the 4-, 5-, 6-, and 7-positions, using Ser and readily available indole analogues as starting materials. Spectroscopic analysis shows that many of the activating mutations suppress the decomposition of the active electrophilic intermediate, an amino-acrylate, which aids in unlocking the synthetic potential of TrpB.
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Affiliation(s)
- David K Romney
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Javier Murciano-Calles
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Jöri E Wehrmüller
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Frances H Arnold
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
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10
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Romney DK, Murciano-Calles J, Wehrmüller JE, Arnold FH. Unlocking Reactivity of TrpB: A General Biocatalytic Platform for Synthesis of Tryptophan Analogues. J Am Chem Soc 2017; 139:10769-10776. [PMID: 28708383 PMCID: PMC5589443 DOI: 10.1021/jacs.7b05007] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
Derivatives
of the amino acid tryptophan (Trp) serve as precursors
for the chemical and biological synthesis of complex molecules with
a wide range of biological properties. Trp analogues are also valuable
as building blocks for medicinal chemistry and as tools for chemical
biology. While the enantioselective synthesis of Trp analogues is
often lengthy and requires the use of protecting groups, enzymes have
the potential to synthesize such products in fewer steps and with
the pristine chemo- and stereoselectivity that is a hallmark
of biocatalysis. The enzyme TrpB is especially attractive because
it can form Trp analogues directly from serine (Ser) and the corresponding
indole analogue. However, many potentially useful substrates, including
bulky or electron-deficient indoles, are poorly accepted. We have
applied directed evolution to TrpB from Pyrococcus furiosus and Thermotoga maritima to generate a suite of
catalysts for the synthesis of previously intractable Trp analogues.
For the most challenging substrates, such as nitroindoles, the key
to improving activity lay in the mutation of a universally conserved
and mechanistically important residue, E104. The new catalysts express
at high levels (>200 mg/L of Escherichia coli culture)
and can be purified by heat treatment; they can operate up to 75 °C
(where solubility is enhanced) and can synthesize enantiopure Trp
analogues substituted at the 4-, 5-, 6-, and 7-positions, using Ser
and readily available indole analogues as starting materials. Spectroscopic
analysis shows that many of the activating mutations suppress the
decomposition of the active electrophilic intermediate, an amino-acrylate,
which aids in unlocking the synthetic potential of TrpB.
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Affiliation(s)
- David K Romney
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Javier Murciano-Calles
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Jöri E Wehrmüller
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Frances H Arnold
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
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11
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Buller AR, van Roye P, Murciano-Calles J, Arnold FH. Tryptophan Synthase Uses an Atypical Mechanism To Achieve Substrate Specificity. Biochemistry 2016; 55:7043-7046. [PMID: 27935677 PMCID: PMC5207025 DOI: 10.1021/acs.biochem.6b01127] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Tryptophan synthase (TrpS) catalyzes the final steps in the biosynthesis of l-tryptophan from l-serine (Ser) and indole-3-glycerol phosphate (IGP). We report that native TrpS can also catalyze a productive reaction with l-threonine (Thr), leading to (2S,3S)-β-methyltryptophan. Surprisingly, β-substitution occurs in vitro with a 3.4-fold higher catalytic efficiency for Ser over Thr using saturating indole, despite a >82000-fold preference for Ser in direct competition using IGP. Structural data identify a novel product binding site, and kinetic experiments clarify the atypical mechanism of specificity: Thr binds efficiently but decreases the affinity for indole and disrupts the allosteric signaling that regulates the catalytic cycle.
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Affiliation(s)
- Andrew R. Buller
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Paul van Roye
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Javier Murciano-Calles
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Frances H. Arnold
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
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12
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Skopelitou K, Muleta AW, Papageorgiou AC, Chronopoulou E, Labrou NE. Catalytic features and crystal structure of a tau class glutathione transferase from Glycine max specifically upregulated in response to soybean mosaic virus infections. BIOCHIMICA ET BIOPHYSICA ACTA 2015; 1854:166-77. [PMID: 25479053 DOI: 10.1016/j.bbapap.2014.11.008] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2014] [Revised: 11/09/2014] [Accepted: 11/21/2014] [Indexed: 01/09/2023]
Abstract
The plant tau class glutathione transferases (GSTs) play important roles in biotic and abiotic stress tolerance in crops and weeds. In this study, we systematically examined the catalytic and structural features of a GST isoenzyme from Glycine max (GmGSTU10-10). GmGSTU10-10 is a unique isoenzyme in soybean that is specifically expressed in response to biotic stress caused by soybean mosaic virus (SMV) infections. GmGSTU10-10 was cloned, expressed in Escherichia coli, purified and characterized. The results showed that GmGSTU10-10 catalyzes several different reactions and exhibits wide substrate specificity. Of particular importance is the finding that the enzyme shows high antioxidant catalytic function and acts as hydroperoxidase. In addition, its Km for GSH is significantly lower, compared to other plant GSTs, suggesting that GmGSTU10-10 is able to perform efficient catalysis under conditions where the concentration of reduced glutathione is low (e.g. oxidative stress). The crystal structure of GmGSTU10-10 was solved by molecular replacement at 1.6Å resolution in complex with glutathione sulfenic acid (GSOH). Structural analysis showed that GmGSTU10-10 shares the same overall fold and domain organization as other plant cytosolic GSTs; however, major variations were identified in helix H9 and the upper part of helix H4 that affect the size of the active site pockets, substrate recognition and the catalytic mechanism. The results of the present study provide new information into GST diversity and give further insights into the complex regulation and enzymatic functions of this plant gene superfamily.
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Affiliation(s)
- Katholiki Skopelitou
- Laboratory of Enzyme Technology, Department of Biotechnology, School of Food, Biotechnology and Development, Agricultural University of Athens, 75 Iera Odos Street, GR-11855-Athens, Greece
| | - Abdi W Muleta
- Turku Centre for Biotechnology, University of Turku and Åbo Akademi University, Turku 20521, Finland
| | | | - Evangelia Chronopoulou
- Laboratory of Enzyme Technology, Department of Biotechnology, School of Food, Biotechnology and Development, Agricultural University of Athens, 75 Iera Odos Street, GR-11855-Athens, Greece
| | - Nikolaos E Labrou
- Laboratory of Enzyme Technology, Department of Biotechnology, School of Food, Biotechnology and Development, Agricultural University of Athens, 75 Iera Odos Street, GR-11855-Athens, Greece.
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13
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Axe JM, O'Rourke KF, Kerstetter NE, Yezdimer EM, Chan YM, Chasin A, Boehr DD. Severing of a hydrogen bond disrupts amino acid networks in the catalytically active state of the alpha subunit of tryptophan synthase. Protein Sci 2014; 24:484-94. [PMID: 25377949 DOI: 10.1002/pro.2598] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Revised: 10/31/2014] [Accepted: 10/31/2014] [Indexed: 12/22/2022]
Abstract
Conformational changes in the β2α2 and β6α6 loops in the alpha subunit of tryptophan synthase (αTS) are important for enzyme catalysis and coordinating substrate channeling with the beta subunit (βTS). It was previously shown that disrupting the hydrogen bond interactions between these loops through the T183V substitution on the β6α6 loop decreases catalytic efficiency and impairs substrate channeling. Results presented here also indicate that the T183V substitution decreases catalytic efficiency in Escherchia coli αTS in the absence of the βTS subunit. Nuclear magnetic resonance (NMR) experiments indicate that the T183V substitution leads to local changes in the structural dynamics of the β2α2 and β6α6 loops. We have also used NMR chemical shift covariance analyses (CHESCA) to map amino acid networks in the presence and absence of the T183V substitution. Under conditions of active catalytic turnover, the T183V substitution disrupts long-range networks connecting the catalytic residue Glu49 to the αTS-βTS binding interface, which might be important in the coordination of catalytic activities in the tryptophan synthase complex. The approach that we have developed here will likely find general utility in understanding long-range impacts on protein structure and dynamics of amino acid substitutions generated through protein engineering and directed evolution approaches, and provide insight into disease and drug-resistance mutations.
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Affiliation(s)
- Jennifer M Axe
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania, 16802
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14
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Hiyama T, Sato T, Imanaka T, Atomi H. The tryptophan synthase β-subunit paralogs TrpB1 and TrpB2 in Thermococcus kodakarensis are both involved in tryptophan biosynthesis and indole salvage. FEBS J 2014; 281:3113-25. [PMID: 24835339 DOI: 10.1111/febs.12845] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 05/01/2014] [Accepted: 05/13/2014] [Indexed: 11/26/2022]
Abstract
The last two steps of l-tryptophan (Trp) biosynthesis are catalyzed by Trp synthase, a heterotetramer composed of TrpA and TrpB. TrpB catalyzes the condensation of indole, synthesized by TrpA, and serine to Trp. In the hyperthermophilic archaeon Thermococcus kodakarensis, trpA and trpB (trpB1) are located adjacently in the trpCDEGFB1A operon. Interestingly, several organisms possess a second trpB gene (trpB2) encoding TrpB2, located outside of the trp operon in T. kodakarensis. Until now, the physiological function of trpB2 has not been examined genetically. In the present study, we report the biochemical and physiological analyses of TrpB2 from T. kodakarensis. Kinetic analysis indicated that TrpB2 catalyzed the TrpB reaction but did not interact with TrpA as in the case of TrpB1. When growth phenotypes were examined for gene disruption strains, the double-deletion mutant (ΔtrpB1ΔtrpB2) displayed Trp auxotrophy, whereas individual single mutants (ΔtrpB1 and ΔtrpB2 strains) did not. It has been proposed previously that, in Thermotoga maritima, TrpB2 provides an alternate route to generate Trp from serine and free indole (indole salvage). To accurately examine the capacity of TrpB1 and TrpB2 in Trp synthesis via indole salvage, we constructed ΔtrpEB1 and ΔtrpEB2 strains using strain KUW1 (ΔpyrFΔtrpE) as a host, eliminating the route for endogenous indole synthesis. Indole complemented the Trp auxotrophies of ΔtrpEB1 (ΔpyrFΔtrpEΔtrpB1) and ΔtrpEB2 (ΔpyrFΔtrpEΔtrpB2) to similar levels. The results indicate that TrpB1 and TrpB2 both contribute to Trp biosynthesis in T. kodakarensis and can utilize free indole, and that indole salvage does not necessarily rely on TrpB2 to a greater extent.
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Affiliation(s)
- Takayoshi Hiyama
- Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Japan
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15
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Masson P. Time-dependent kinetic complexities in cholinesterase-catalyzed reactions. BIOCHEMISTRY (MOSCOW) 2013; 77:1147-61. [PMID: 23157295 DOI: 10.1134/s0006297912100070] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Cholinesterases (ChEs) display a hysteretic behavior with certain substrates and inhibitors. Kinetic cooperativity in hysteresis of ChE-catalyzed reactions is characterized by a lag or burst phase in the approach to steady state. With some substrates damped oscillations are shown to superimpose on hysteretic lags. These time dependent peculiarities are observed for both butyrylcholinesterase and acetylcholinesterase from different sources. Hysteresis in ChE-catalyzed reactions can be interpreted in terms of slow transitions between two enzyme conformers E and E'. Substrate can bind to E and/or E', both Michaelian complexes ES and Ε'S can be catalytically competent, or only one of them can make products. The formal reaction pathway depends on both the chemical structure of the substrate and the type of enzyme. In particular, damped oscillations develop when substrate exists in different, slowly interconvertible, conformational, and/or micellar forms, of which only the minor form is capable of binding and reacting with the enzyme. Biphasic pseudo-first-order progressive inhibition of ChEs by certain carbamates and organophosphates also fits with a slow equilibrium between two reactive enzyme forms. Hysteresis can be modulated by medium parameters (pH, chaotropic and kosmotropic salts, organic solvents, temperature, osmotic pressure, and hydrostatic pressure). These studies showed that water structure plays a role in hysteretic behavior of ChEs. Attempts to provide a molecular mechanism for ChE hysteresis from mutagenesis studies or crystallographic studies failed so far. In fact, several lines of evidence suggest that hysteresis is controlled by the conformation of His438, a key residue in the catalytic triad of cholinesterases. Induction time may depend on the probability of His438 to adopt the operative conformation in the catalytic triad. The functional significance of ChE hysteresis is puzzling. However, the accepted view that proteins are in equilibrium between preexisting functional and non-functional conformers, and that binding of a ligand to the functional form shifts equilibrium towards the functional conformation, suggests that slow equilibrium between two conformational states of these enzymes may have a regulatory function in damping out the response to certain ligands and irreversible inhibitors. This is particularly true for immobilized (membrane bound) enzymes where the local substrate and/or inhibitor concentrations depend on influx in crowded organellar systems, e.g. cholinergic synaptic clefts. Therefore, physiological or toxicological relevance of the hysteretic behavior and damped oscillations in ChE-catalyzed reactions and inhibition cannot be ruled out.
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Affiliation(s)
- P Masson
- Institut de Recherches Biomédicales des Armées-CRSSA, La Tronche, Cedex 38702, France.
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16
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Miles EW. The tryptophan synthase α2β2 complex: a model for substrate channeling, allosteric communication, and pyridoxal phosphate catalysis. J Biol Chem 2013; 288:10084-10091. [PMID: 23426371 DOI: 10.1074/jbc.x113.463331] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
I reflect on my research on pyridoxal phosphate (PLP) enzymes over fifty-five years and on how I combined research with marriage and family. My Ph.D. research with Esmond E. Snell established one aspect of PLP enzyme mechanism. My postdoctoral work first with Hans L. Kornberg and then with Alton Meister characterized the structure and function of another PLP enzyme, l-aspartate β-decarboxylase. My independent research at the National Institutes of Health (NIH) since 1966 has focused on the bacterial tryptophan synthase α2β2 complex. The β subunit catalyzes a number of PLP-dependent reactions. We have characterized these reactions and the allosteric effects of the α subunit. We also used chemical modification to probe enzyme structure and function. Our crystallization of the tryptophan synthase α2β2 complex from Salmonella typhimurium led to the determination of the three-dimensional structure with Craig Hyde and David Davies at NIH in 1988. This landmark structure was the first structure of a multienzyme complex and the first structure revealing an intramolecular tunnel. The structure has provided a basis for exploring mechanisms of catalysis, channeling, and allosteric communication in the tryptophan synthase α2β2 complex. The structure serves as a model for many other multiprotein complexes that are important for biological processes in prokaryotes and eukaryotes.
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Affiliation(s)
- Edith Wilson Miles
- Laboratory of Biochemistry and Genetics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
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17
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Axe JM, Boehr DD. Long-range interactions in the α subunit of tryptophan synthase help to coordinate ligand binding, catalysis, and substrate channeling. J Mol Biol 2013; 425:1527-45. [PMID: 23376097 DOI: 10.1016/j.jmb.2013.01.030] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2012] [Revised: 01/23/2013] [Accepted: 01/23/2013] [Indexed: 10/27/2022]
Abstract
The α-subunit of tryptophan synthase (αTS) catalyzes the conversion of indole-3-glycerol phosphate to d-glyceraldehyde-3-phosphate and indole. We propose that allosteric networks intrinsic to αTS are modulated by the binding of the β-subunit to regulate αTS function. Understanding these long-range amino acid networks in αTS thus gives insight into the coordination of the two active sites within TS. In this study, we have used Ala residues as probes for structural and dynamic changes of αTS throughout its catalytic cycle, in the absence of the β-subunit. Projection analysis of the chemical shift changes by site-specific amino acid substitutions and ligand titrations indicates that αTS has three important conformational states: ligand-free, glyceraldehyde-3-phosphate-bound(like), and the active states. The amino acid networks within these conformations are different, as suggested by chemical shift correlation analysis. In particular, there are long-range connections, only in the active state, between Ala47, which reports on structural and dynamic changes associated with the general acid/base Glu49, and residues within the β2α2 loop, which contains the catalytically important Asp60 residue. These long-range interactions are likely important for coordinating chemical catalysis. In the free state, but not in the active state, there are connections between the β2α2 and β6α6 loops that likely help to coordinate substrate binding. Changes in the allosteric networks are also accompanied by protein dynamic changes. During catalytic turnover, the protein becomes more rigid on the millisecond timescale and the active-site dynamics are driven to a faster nanosecond timescale.
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Affiliation(s)
- Jennifer M Axe
- Department of Chemistry, Pennsylvania State University, 240 Chemistry Building, University Park, PA 16802, USA
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18
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Phillips RS, Wang AK, Marchal S, Lange R. Effects of Pressure and Osmolytes on the Allosteric Equilibria of Salmonella typhimurium Tryptophan Synthase. Biochemistry 2012; 51:9354-63. [DOI: 10.1021/bi301002q] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Robert S. Phillips
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602, United
States
| | - Alexandre Kim Wang
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - Stephane Marchal
- Inserm U710, Montpellier, F-34095 France, Université de Montpellier 2, Montpellier, F-34095 France, and EPHE, Paris, F-75007 France
| | - Reinhard Lange
- Inserm U710, Montpellier, F-34095 France, Université de Montpellier 2, Montpellier, F-34095 France, and EPHE, Paris, F-75007 France
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19
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Allosteric regulation of substrate channeling and catalysis in the tryptophan synthase bienzyme complex. Arch Biochem Biophys 2012; 519:154-66. [PMID: 22310642 DOI: 10.1016/j.abb.2012.01.016] [Citation(s) in RCA: 112] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2011] [Revised: 01/23/2012] [Accepted: 01/25/2012] [Indexed: 11/24/2022]
Abstract
The tryptophan synthase α2β2 bi-enzyme complex catalyzes the last two steps in the synthesis of l-tryptophan (l-Trp). The α-subunit catalyzes cleavage of 3-indole-d-glycerol 3'-phosphate (IGP) to give indole and d-glyceraldehyde 3'-phosphate (G3P). Indole is then transferred (channeled) via an interconnecting 25Å-long tunnel, from the α-subunit to the β-subunit where it reacts with l-Ser in a pyridoxal 5'-phosphate-dependent reaction to give l-Trp and a water molecule. The efficient utilization of IGP and l-Ser by tryptophan synthase to synthesize l-Trp utilizes a system of allosteric interactions that (1) function to switch the α-site on and off at different stages of the β-subunit catalytic cycle, and (2) prevent the escape of the channeled intermediate, indole, from the confines of the α- and β-catalytic sites and the interconnecting tunnel. This review discusses in detail the chemical origins of the allosteric interactions responsible both for switching the α-site on and off, and for triggering the conformational changes between open and closed states which prevent the escape of indole from the bienzyme complex.
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20
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Ehrmann A, Richter K, Busch F, Reimann J, Albers SV, Sterner R. Ligand-induced formation of a transient tryptophan synthase complex with αββ subunit stoichiometry. Biochemistry 2010; 49:10842-53. [PMID: 21090805 DOI: 10.1021/bi1016815] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The prototypical tryptophan synthases form a stable heterotetrameric αββα complex in which the constituting TrpA and TrpB1 subunits activate each other in a bidirectional manner. The hyperthermophilic archaeon Sulfolobus solfataricus does not contain a TrpB1 protein but instead two members of the phylogenetically distinct family of TrpB2 proteins, which are encoded within (sTrpB2i) and outside (sTrpB2a) the tryptophan operon. It has previously been shown that sTrpB2a does not functionally or structurally interact with sTrpA, whereas sTrpB2i substantially activates sTrpA in a unidirectional manner. However, in the absence of catalysis, no physical complex between sTrpB2i and sTrpA could be detected. In order to elucidate the structural requirements for complex formation, we have analyzed the interaction between sTrpA (α-monomer) and sTrpB2i (ββ-dimer) by means of spectroscopy, analytical gel filtration, and analytical ultracentrifugation, as well as isothermal titration calorimetry. In the presence of the TrpA ligand glycerol 3-phosphate (GP) and the TrpB substrate l-serine, sTrpA and sTrpB2i formed a physical complex with a thermodynamic dissociation constant of about 1 μM, indicating that the affinity between the α- and ββ-subunits is weaker by at least 1 order of magnitude than the affinity between the corresponding subunits of prototypical tryptophan synthases. The observed stoichiometry of the complex was 1 subunit of sTrpA per 2 subunits of sTrpB2i, which corresponds to a αββ quaternary structure and testifies to a strong negative cooperativity for the binding of the α-monomers to the ββ-dimer. The analysis of the interaction between sTrpB2i and sTrpA in the presence of several substrate, transition state, and product analogues suggests that the αββ complex remains stable during the whole catalytic cycle and disintegrates into α- and ββ-subunits upon the release of the reaction product tryptophan. The formation of a transient tryptophan synthase complex, together with the observed low affinity of sTrpB2i for l-serine, couples the rate of tryptophan biosynthesis in S. solfataricus to the cytosolic availability of l-serine.
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Affiliation(s)
- Alexander Ehrmann
- Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstrasse 31, D-93053 Regensburg, Germany
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21
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Phillips RS, Miles EW, McPhie P, Marchal S, Lange R, Holtermann G, Goody RS. Effects of hydrostatic pressure on the conformational equilibrium of tryptophan synthase from Salmonella typhimurium. Ann N Y Acad Sci 2010; 1189:95-103. [PMID: 20233374 DOI: 10.1111/j.1749-6632.2009.05201.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A wide range of parameters influence allosteric communications between the alpha- and beta-subunits of the Trp synthase alpha(2)beta(2) multienzyme complex with L-Ser, including monovalent cations, pH, temperature, ligands, organic solvents, and hydrostatic pressure. The conformational change from closed to open can be monitored either by absorbance at 423 nm or fluorescence at 495 nm from the pyridoxal-5'-phosphate-L-Ser complex. Pressure perturbation was used to quantify the effects of monovalent cations, ligands, and mutations on the conformational equilibrium of Trp synthase. P-jump kinetics in the presence of Na(+), NH(4) (+), and Na(+) together with benzimidazole were also examined. The plots of lnk versus P are nonlinear and require a compressibility (beta(double dagger) (o)) term to obtain a good fit. beta(double dagger) (o) is positive for the Na(+) enzyme but negative for NH(4) (+) and Na(+) with benzimidazole. These results suggest that there is a large contribution of solvation to the kinetics of the conformational change of Trp synthase. The relaxation kinetics are also different if the P-jumps are made by increasing or decreasing pressure, suggesting that the enzyme conformations are ensembles of microstates.
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22
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Fazary AE, Ismadji S, Ju YH. Studies on temperature dependent kinetics of Aspergillus awamori feruloyl esterase in water solutions. KINETICS AND CATALYSIS 2010. [DOI: 10.1134/s0023158410010064] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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23
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Raboni S, Bettati S, Mozzarelli A. Tryptophan synthase: a mine for enzymologists. Cell Mol Life Sci 2009; 66:2391-403. [PMID: 19387555 PMCID: PMC11115766 DOI: 10.1007/s00018-009-0028-0] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2009] [Revised: 03/30/2009] [Accepted: 03/31/2009] [Indexed: 01/12/2023]
Abstract
Tryptophan synthase is a pyridoxal 5'-phosphate-dependent alpha(2)beta(2) complex catalyzing the last two steps of tryptophan biosynthesis in bacteria, plants and fungi. Structural, dynamic and functional studies, carried out over more than 40 years, have unveiled that: (1) alpha- and beta-active sites are separated by about 20 A and communicate via the selective stabilization of distinct conformational states, triggered by the chemical nature of individual catalytic intermediates and by allosteric ligands; (2) indole, formed at alpha-active site, is intramolecularly channeled to the beta-active site; and (3) naturally occurring as well as genetically generated mutants have allowed to pinpoint functional and regulatory roles for several individual amino acids. These key features have made tryptophan synthase a text-book case for the understanding of the interplay between chemistry and conformational energy landscapes.
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Affiliation(s)
- Samanta Raboni
- Department of Biochemistry and Molecular Biology, University of Parma, Viale GP Usberti 23/A, 43100 Parma, Italy
- Present Address: CRIBI Biotechnology Centre, University of Padua, Padua, Italy
| | - Stefano Bettati
- Department of Biochemistry and Molecular Biology, University of Parma, Viale GP Usberti 23/A, 43100 Parma, Italy
- Italian National Institute of Biostructures and Biosystems, Parma, Italy
| | - Andrea Mozzarelli
- Department of Biochemistry and Molecular Biology, University of Parma, Viale GP Usberti 23/A, 43100 Parma, Italy
- Italian National Institute of Biostructures and Biosystems, Parma, Italy
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24
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Marchal S, Font J, Ribó M, Vilanova M, Phillips RS, Lange R, Torrent J. Asymmetric kinetics of protein structural changes. Acc Chem Res 2009; 42:778-87. [PMID: 19378977 DOI: 10.1021/ar800266r] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Thermodynamic and kinetic understanding of structural transformations in proteins is critical to new developments in medicine and biotechnology. These fields often require the design of mechanism-based modulators of protein function. Researchers increasingly consider these structural changes-such as folding/unfolding or shuttling between active and inactive states-within the energy landscape concept that supposes a high-dimensional, rugged conformational surface. The unevenness, or asperity, of this conformational surface results from energetic barriers and kinetic traps. However, for a large number of protein reactions, such as reversible folding/unfolding, the literature only reports simple two-state transitions, which calls into question the use of a more complex energy landscape model. The question is: are these reactions really that simple, or are we misled by a biased experimental approach? In this Account, we argue in favor of the latter possibility. Indeed, the frequently employed temperature-jump method only allows recording protein structure changes in the heating direction. Under those conditions, it might not be possible to detect other kinetic pathways that could have been taken in the cooling direction. Recently, however, we have developed bidirectional pressure- and temperature-jump methods, which can offer new insights. Here, we show the potential of these methods both for studying protein folding/unfolding reactions, taking ribonuclease A as model, and for studying functionally relevant protein conformational changes, using the open/closed allosteric transition of tryptophan synthase. For example, the heating and cooling temperature-jump induced kinetics involved in the folding/unfolding conformational surface of ribonuclease A is illustrated above. In both of our model systems, the kinetic transition states of several reaction steps were path-dependent, i.e. the rates and thermodynamic activation parameters depend on the direction of the applied pressure and temperature perturbation. This asymmetry suggests that proteins cope with external stress by adapting their structure to form different ensembles of conformational substates. These states are distinguished by their activation enthalpy and entropy barriers, which can be strongly negative in the folding direction. Based on our analysis of activation compressibility and heat capacity, hydration and packing defects of the kinetic transition states are also very important for determining the reaction path. We expect that a more generalized use of this experimental approach should allow researchers to obtain greater insight into the mechanisms of physiologically relevant protein structural changes.
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Affiliation(s)
- Stéphane Marchal
- INSERM, U710, F-34095 Montpellier, France
- Université Montpellier 2, F-34095 Montpellier, France
- EPHE, 75007 Paris, France
| | - Josep Font
- School of Molecular and Microbial Biosciences, University of Sydney, NSW, 2006 Australia
| | - Marc Ribó
- Laboratori d’Enginyeria de Proteïnes, Dept. de Biologia, Fac. de Ciències, Universitat de Girona, Campus de Montilivi, 17071 Girona, Spain
| | - Maria Vilanova
- Laboratori d’Enginyeria de Proteïnes, Dept. de Biologia, Fac. de Ciències, Universitat de Girona, Campus de Montilivi, 17071 Girona, Spain
| | | | - Reinhard Lange
- INSERM, U710, F-34095 Montpellier, France
- Université Montpellier 2, F-34095 Montpellier, France
- EPHE, 75007 Paris, France
| | - Joan Torrent
- INSERM, U710, F-34095 Montpellier, France
- Université Montpellier 2, F-34095 Montpellier, France
- EPHE, 75007 Paris, France
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Phillips RS, Miles EW, McPhie P, Marchal S, Georges C, Dupont Y, Lange R. Pressure and temperature jump relaxation kinetics of the conformational change in Salmonella typhimurium tryptophan synthase L-serine complex: large activation compressibility and heat capacity changes demonstrate the contribution of solvation. J Am Chem Soc 2008; 130:13580-8. [PMID: 18795779 DOI: 10.1021/ja8018466] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Tryptophan synthase is an alpha2beta2 multienzyme complex that exhibits coupling of the alpha- and beta-subunit reactions by tightly controlled allosteric interactions. A wide range of parameters can affect the allosteric interactions, including monovalent cations, pH, alpha-site and beta-site ligands, temperature, and pressure. Rapid changes in hydrostatic pressure (P-jump) and temperature (T-jump) were used to examine the effects of pressure and temperature on the rates of the interconversion of external aldimine and aminoacrylate intermediates in the Tryptophan synthase-L-Ser complex. The intense fluorescence emission of the Tryptophan synthase L-Ser external aldimine complex at 495 nm, with 420 nm excitation, provides a probe of the conformational state of Trp synthase. P-jump measurements allowed the determination of rate constants for the reactions in the presence of Na(+), Na(+) with benzimidazole (BZI), and NH4(+). The data require a compressibility term, beta(o)(double dagger), to obtain good fits, especially for the NH4(+) and BZI/Na(+) data. The compressibility changes are consistent with changes in solvation in the transition state. The transition state for the relaxation is more similar in volume to the closed aminoacrylate complex in the presence of Na(+), while it is more similar to the open external aldimine in the presence of NH4(+). Differences between the relaxations for positive and negative P-jumps may arise from changing relative populations of microstates with pressure. T-jump experiments of the Na(+) form of the tryptophan synthase-L-Ser complex show large changes in rate and amplitude over the temperature range from 7 to 45 degrees C. The Arrhenius plots show strong curvature, and hence require a heat capacity term, DeltaC(p)(double dagger), to obtain good fits. The values of DeltaC(p)(double dagger) are very large and negative (-3.6 to -4.4 kJ mol(-1) K(-1)). These changes are also consistent with large changes in solvation in the transition state for interconversion of external aldimine and aminoacrylate intermediates in the Tryptophan synthase-L-Ser complex.
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Affiliation(s)
- Robert S Phillips
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA.
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Dunn MF, Niks D, Ngo H, Barends TR, Schlichting I. Tryptophan synthase: the workings of a channeling nanomachine. Trends Biochem Sci 2008; 33:254-64. [DOI: 10.1016/j.tibs.2008.04.008] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2008] [Revised: 04/07/2008] [Accepted: 04/08/2008] [Indexed: 01/25/2023]
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Tóth K, Sedlák E, Sprinzl M, Zoldák G. Flexibility and enzyme activity of NADH oxidase from Thermus thermophilus in the presence of monovalent cations of Hofmeister series. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2008; 1784:789-95. [PMID: 18339331 DOI: 10.1016/j.bbapap.2008.01.022] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2007] [Revised: 01/26/2008] [Accepted: 01/29/2008] [Indexed: 11/25/2022]
Abstract
Recently, we have shown that anions of Hofmeister series affect the enzyme activity through modulation of flexibility of its active site. The enzyme activity vs. anion position in Hofmeister series showed an unusual bell-shaped dependence. In the present work, six monovalent cations (Na(+), Gdm(+), NH(4)(+), Li(+), K(+) and Cs(+)) of Hofmeister series with chloride as a counterion have been studied in relation to activity and stability of flavoprotein NADH oxidase from Thermus thermophilus (NOX). With the exception of strongly chaotropic guanidinium cation, cations are significantly less effective in promoting the Hofmeister effect than anions mainly due to repulsive interactions of positive charges around the active site. Thermal denaturations of NOX reveal unfavorable electrostatic interaction at the protein surface that may be shielded to different extent by salts. Michaelis-Menten constants for NADH, accessibility of the active site as reflected by Stern-Volmer constants and activity of NOX at high cation concentrations (1-2 M) show bell-shaped dependences on cation position in Hofmeister series. Our analysis indicates that in the presence of kosmotropic cations the enzyme is more stable and possibly more rigid than in the presence of chaotropic cations. Molecular dynamic (MD) simulations of NOX showed that active site switches between open and closed conformations [J. Hritz, G. Zoldak, E. Sedlak, Cofactor assisted gating mechanism in the active site of NADH oxidase from Thermus thermophilus, Proteins 64 (2006) 465-476]. Enzyme activity, as well as substrate binding, can be regulated by the salt mediated perturbation of the balance between open and closed forms. We propose that compensating effect of accessibility and flexibility of the enzyme active site leads to bell-shaped dependence of the investigated parameters.
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Affiliation(s)
- Kamil Tóth
- Department of Biochemistry, Faculty of Sciences P. J. Safárik University, Kosice, Slovakia
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Quantitative effects of allosteric ligands and mutations on conformational equilibria in Salmonella typhimurium tryptophan synthase. Arch Biochem Biophys 2007; 470:8-19. [PMID: 18047826 DOI: 10.1016/j.abb.2007.11.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2007] [Revised: 11/07/2007] [Accepted: 11/08/2007] [Indexed: 11/21/2022]
Abstract
Allosteric communications are important in coordination of the reactions in the tryptophan (Trp) synthase alpha2beta2 multienzyme complex. We have measured the conformational equilibria of l-Ser and l-Trp complexes, using absorption and fluorescence spectrophotometry with hydrostatic pressure equilibrium perturbation. The effects of monovalent cations, disodium alpha-glycerophosphate (Na2GP), indoleacetylglycine (IAG), and benzimidazole (BZI), as well as of betaE109D and betaD305A mutations, on K(eq) for the conformational equilibria were determined. The l-Ser external aldimine-aminoacrylate equilibrium (K(eq)=[external aldimine]/[aminoacrylate]) has the largest value with Na+ (0.12), followed by K+ (0.04), Li+ (7.6 x 10(-4)), Rb+ (4.3 x 10(-4)), NH4+ (2.3 x 10(-4)), no cation (2.0 x 10(-4)) and Cs+ (1.6x10(-5)). alpha-Site ligands, Na(2)GP and IAG, have modest 3- to 40-fold effects on K(eq) in the direction of aminoacrylate, but BZI in the presence of Na+ gives a low value of K(eq) comparable to that obtained with Cs(+). There is no additivity of free energy for Na2GP and BZI, suggesting a common pathway for allosteric communications for both ligands. The values of DeltaV(o) range from -126 mL/mol for the Na+ complex to -204 mL/mol for the Na+ complex with BZI. The betaD305A mutation changes the K(eq) by a factor of at least 10(5) (26.7kJ/mol) and nearly abolishes allosteric communications. There are also dramatic decreases in the magnitude of both DeltaV(o) and DeltaS for the l-Ser external aldimine-aminoacrylate equilibrium for betaD305A Trp synthase, consistent with a large decrease in solvation accompanying the conformational change in betaD305A Trp synthase relative to wild-type Trp synthase. The betaE109D mutation has more modest but significant effects on K(eq), which differ with the ligand, ranging from 40-fold for GP to 2200-fold for BZI, even though betaGlu-109 is not directly involved in allosteric communications. The effect of GP on the external aldimine-quinonoid intermediate equilibrium of the Trp synthase-l-Trp complex is similar to that of GP on the Trp synthase-l-Ser external aldimine-aminoacrylate equilibrium. These results have allowed a quantitative comparison of the allosteric effects of ligand and mutations in Trp synthase. These allosteric effects are finely tuned to control the synthesis of l-Trp without resulting in substrate or product inhibition.
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Abstract
By far the largest proportion of the Earth's biosphere is comprised of organisms that thrive in cold environments (psychrophiles). Their ability to proliferate in the cold is predicated on a capacity to synthesize cold-adapted enzymes. These enzymes have evolved a range of structural features that confer a high level of flexibility compared to thermostable homologs. High flexibility, particularly around the active site, is translated into low-activation enthalpy, low-substrate affinity, and high specific activity at low temperatures. High flexibility is also accompanied by a trade-off in stability, resulting in heat lability and, in the few cases studied, cold lability. This review addresses the structure, function, and stability of cold-adapted enzymes, highlighting the challenges for immediate and future consideration. Because of the unique properties of cold-adapted enzymes, they are not only an important focus in extremophile biology, but also represent a valuable model for fundamental research into protein folding and catalysis.
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Affiliation(s)
- Khawar Sohail Siddiqui
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW 2052, Australia.
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Kotzia GA, Labrou NE. L-Asparaginase from Erwinia Chrysanthemi 3937: cloning, expression and characterization. J Biotechnol 2006; 127:657-69. [PMID: 16984804 DOI: 10.1016/j.jbiotec.2006.07.037] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2005] [Revised: 05/19/2006] [Accepted: 07/31/2006] [Indexed: 11/25/2022]
Abstract
Bacterial L-asparaginases (L-ASNases) catalyze the conversion of L-asparagine to L-aspartate and ammonia. In the present work, we report the cloning and expression of L-asparaginase from Erwinia chrysanthemi 3937 (ErL-ASNase) in Escherichia coli BL21(DE3)pLysS. The enzyme was purified to homogeneity in a single-step procedure involving cation exchange chromatography on an S-Sepharose FF column. The enzymatic and structural properties of the recombinant enzyme were investigated and the kinetic parameters (K(m), k(cat)) for a number of substrates were determined. In addition, we found that the enzyme can be efficiently immobilized on epoxy-activated Sepharose CL-6B. The immobilized enzyme retains most of its activity (60%) and shows high stability at 4 degrees C. The approach offers the possibility of designing an ErL-ASNase bioreactor that can be operated over a long period of time with high efficiency, which can be used in leukaemia therapy.
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Affiliation(s)
- Georgia A Kotzia
- Laboratory of Enzyme Technology, Department of Agricultural Biotechnology, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece
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Spyrakis F, Raboni S, Cozzini P, Bettati S, Mozzarelli A. Allosteric communication between alpha and beta subunits of tryptophan synthase: modelling the open-closed transition of the alpha subunit. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2006; 1764:1102-9. [PMID: 16737856 DOI: 10.1016/j.bbapap.2006.03.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2006] [Revised: 03/16/2006] [Accepted: 03/16/2006] [Indexed: 12/12/2022]
Abstract
Ligand binding to the alpha-subunit of the alpha2beta2 complex of tryptophan synthase induces the alphaloop6 closure over the alpha-active site. This conformational change is associated with the formation of a hydrogen bond between alphaGly181 NH group and betaSer178 carbonyl oxygen, a key event for the triggering of intersubunit allosteric signals. Mutation of betaSer178 to Pro and alphaGly181 to Pro, Ala, Phe and Val abolishes the ligand-induced intersubunit communication. Molecular dynamics methods were applied to simulate the conformation of the highly flexible and crystallographically undetectable open state of alphaloop6 in the wild type and in the alpha181 mutants. The open conformation of alphaloop6 is favoured in the wild type enzyme in the absence of alpha-ligands, and in the alpha181 mutants both in the presence and absence of bound ligands. A very good correlation was found between the extent of limited tryptic proteolysis and both the hydrogen bond distance between alphaX181 and betaSer178, obtained from the molecular dynamics simulation, and the hydrogen bond strength, evaluated by HINT, an empirical force field that takes into account both enthalpic and entropic contributions. Comparison of the open and closed conformations of alphaloop6 suggests a pathway for substrate entrance into the alpha-active site and provides an explanation for the limited catalytic efficiency of the open state.
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Affiliation(s)
- Francesca Spyrakis
- Department of Biochemistry and Molecular Biology, University of Parma, 43100 Parma, Italy
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32
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Kotzia GA, Labrou NE. Cloning, expression and characterisation of Erwinia carotovora l-asparaginase. J Biotechnol 2005; 119:309-23. [PMID: 15951039 DOI: 10.1016/j.jbiotec.2005.04.016] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2004] [Revised: 04/08/2005] [Accepted: 04/19/2005] [Indexed: 11/28/2022]
Abstract
Bacterial L-asparaginases (E.C. 3.5.1.1) have been used as therapeutic agents in the treatment of acute childhood lymphoblastic leukaemia. L-asparaginase from Erwinia carotovora NCYC 1526 (ErA) was cloned and expressed in E. coli. The enzyme was purified to homogeneity by a two-step procedure comprising cation-exchange chromatography and affinity chromatography on immobilised L-asparagine. The enzymatic properties of the recombinant enzyme were investigated and the kinetic parameters (K(m), k(cat)) for a number of substrates were determined. Molecular modelling studies were also employed to create a model of ErA, based on the known structure of the Erwinia chrysanthemi enzyme. The molecular model was used to help interpret biochemical data concerning substrate specificity and catalytic mechanism of the enzyme. The kinetic parameters of selected substrates were determined at various pH values, and the pH-dependence profiles of V(max) and V(max)/K(m) were analyzed. The pH-dependence of V(max) shows one transition in the acidic pH range with pK(a)=5.4, and the pH-dependence of V(max)/K(m) exhibits two transitions with pK(a)=5.4 and 8.5. Based on analysis of alternative substrates and molecular modelling studies, it was concluded that the pK(a) at the acidic pH range corresponds to the active site residues Asp115 or Glu82, whereas the pK(a) observed at the alkaline pH range is not due to substrate amino group ionisation, but rather is the result of enzyme ionisation. The effect of temperature and viscosity on the catalytic activity of the enzyme was also investigated and it was concluded that the rate-limiting step of the catalytic reaction is relevant to structural transitions of the protein. Thermodynamic analysis of the activity data showed that the activation energies are dependent on the substrate, and entropy changes appear to be the main determinant contributing to substrate specificity.
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Affiliation(s)
- Georgia A Kotzia
- Laboratory of Enzyme Technology, Department of Agricultural Biotechnology, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece
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Raboni S, Bettati S, Mozzarelli A. Identification of the geometric requirements for allosteric communication between the alpha- and beta-subunits of tryptophan synthase. J Biol Chem 2005; 280:13450-6. [PMID: 15691828 DOI: 10.1074/jbc.m414521200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The pyridoxal 5'-phosphate-dependent tryptophan synthase alpha2beta2 complex is a paradigmatic protein for substrate channeling and allosteric regulation. The enzymatic activity is modulated by a ligand-mediated equilibrium between open (inactive) and closed (active) conformations of the alpha- and beta-subunit, predominantly involving the mobile alpha loop 6 and the beta-COMM domain that contains beta helix 6. The alpha ligand-triggered intersubunit communication seems to rely on a single hydrogen bond formed between the carbonyl oxygen of betaSer-178 of beta helix 6 and the NH group of alphaGly-181 of alpha loop 6. We investigated whether and to what extent mutations of alphaGly-181 and betaSer-178 affect allosteric regulation by the replacement of betaSer-178 with Pro or Ala and of alphaGly-181 with either Pro to remove the amidic proton that forms the hydrogen bond or Ala, Val, and Phe to analyze the dependence on steric hindrance of the open-closed conformational transition. The alpha and beta activity assays and the equilibrium distribution of beta-subunit catalytic intermediates indicate that mutations do not significantly influence the intersubunit catalytic activation but completely abolish ligand-induced alpha-to beta-subunit signaling, demonstrating distinct pathways for alpha-beta-site communication. Limited proteolysis experiments indicate that the removal of the interaction between betaSer-178 and alphaGly-181 strongly favors the more trypsin-accessible open conformation of the alpha-active site. When the hydrogen bond cannot be formed, the alpha-subunit is unable to attain the closed conformation, and consequently, the allosteric signal is aborted at the subunit interface.
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Affiliation(s)
- Samanta Raboni
- Department of Biochemistry and Molecular Biology, University of Parma, 43100 Parma, Italy
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Cash MT, Miles EW, Phillips RS. The reaction of indole with the aminoacrylate intermediate of Salmonella typhimurium tryptophan synthase: observation of a primary kinetic isotope effect with 3-[2H]indole. Arch Biochem Biophys 2004; 432:233-43. [PMID: 15542062 DOI: 10.1016/j.abb.2004.09.027] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2004] [Revised: 09/21/2004] [Indexed: 11/29/2022]
Abstract
The bacterial tryptophan synthase alpha(2)beta(2) complex catalyzes the final reactions in the biosynthesis of L-tryptophan. Indole is produced at the active site of the alpha-subunit and is transferred through a 25-30 A tunnel to the beta-active site, where it reacts with an aminoacrylate intermediate. Lane and Kirschner proposed a two-step nucleophilic addition-tautomerization mechanism for the reaction of indole with the aminoacrylate intermediate, based on the absence of an observed kinetic isotope effect (KIE) when 3-[(2)H]indole reacts with the aminoacrylate intermediate. We have now observed a KIE of 1.4-2.0 in the reaction of 3-[(2)H]indole with the aminoacrylate intermediate in the presence of monovalent cations, but not when an alpha-subunit ligand, disodium alpha-glycerophosphate (Na(2)GP), is present. Rapid-scanning stopped flow kinetic studies were performed of the reaction of indole and 3-[(2)H]indole with tryptophan synthase preincubated with L-serine, following the decay of the aminoacrylate intermediate at 350 nm, the formation of the quinonoid intermediate at 476 nm, and the formation of the L-Trp external aldimine at 423 nm. The addition of Na(2)GP dramatically slows the rate of reaction of indole with the alpha-aminoacrylate intermediate. A primary KIE is not observed in the reaction of 3-[(2)H]indole with the aminoacrylate complex of tryptophan synthase in the presence of Na(2)GP, suggesting binding of indole with tryptophan synthase is rate limiting under these conditions. The reaction of 2-methylindole does not show a KIE, either in the presence of Na(+) or Na(2)GP. These results support the previously proposed mechanism for the beta-reaction of tryptophan synthase, but suggest that the rate limiting step in quinonoid intermediate formation from indole and the aminoacrylate intermediate is deprotonation.
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Affiliation(s)
- Michael T Cash
- Department of Chemistry, Center for Metalloenzyme Studies, University of Georgia, Athens, GA 30602-2556, USA
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35
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36
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Hioki Y, Ogasahara K, Lee SJ, Ma J, Ishida M, Yamagata Y, Matsuura Y, Ota M, Ikeguchi M, Kuramitsu S, Yutani K. The crystal structure of the tryptophan synthase beta subunit from the hyperthermophile Pyrococcus furiosus. Investigation of stabilization factors. ACTA ACUST UNITED AC 2004; 271:2624-35. [PMID: 15206928 DOI: 10.1111/j.1432-1033.2004.04191.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The structure of the tryptophan synthase beta2 subunit (Pfbeta2) from the hyperthermophile, Pyrococcus furiosus, was determined by X-ray crystallographic analysis at 2.2 A resolution, and its stability was examined by DSC. This is the first report of the X-ray structure of the tryptophan synthase beta2 subunit alone, although the structure of the tryptophan synthase alpha2beta2 complex from Salmonella typhimurium has already been reported. The structure of Pfbeta2 was essentially similar to that of the beta2 subunit (Stbeta2) in the alpha2beta2 complex from S. typhimurium. The sequence alignment with secondary structures of Pfbeta and Stbeta in monomeric form showed that six residues in the N-terminal region and three residues in the C-terminal region were deleted in Pfbeta, and one residue at Pro366 of Stbeta and at Ile63 of Pfbeta was inserted. The denaturation temperature of Pfbeta2 was higher by 35 degrees C than the reported values from mesophiles at approximately pH 8. On the basis of structural information on both proteins, the analyses of the contributions of each stabilization factor indicate that: (a) the higher stability of Pfbeta2 is not caused by either a hydrophobic interaction or an increase in ion pairs; (b) the number of hydrogen bonds involved in the main chains of Pfbeta is greater by about 10% than that of Stbeta, indicating that the secondary structures of Pfbeta are more stabilized than those of Stbeta and (c) the sequence of Pfbeta seems to be better fitted to an ideally stable structure than that of Stbeta, as assessed from X-ray structure data.
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Affiliation(s)
- Yusaku Hioki
- Institute for Protein Research, Osaka University, Japan
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Zoldák G, Sprinzl M, Sedlák E. Modulation of activity of NADH oxidase from Thermus thermophilus through change in flexibility in the enzyme active site induced by Hofmeister series anions. ACTA ACUST UNITED AC 2004; 271:48-57. [PMID: 14686918 DOI: 10.1046/j.1432-1033.2003.03900.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The conformational dynamics of NADH oxidase from Thermus thermophilus was modulated by the Hofmeister series of anions (H2PO4-, SO42-, CH3COO-, Cl-, Br-, I-, ClO4-, SCN-) in the concentration range 0-3 M. Both chaotropic and kosmotropic anions, at high concentration, inhibit the enzyme by different mechanisms. Chaotropic anions increase the apparent Michaelis constant and decrease the activation barrier of the reaction. Kosmotropic anions have the opposite effect. Anions from the middle of the Hofmeister series do not significantly affect the enzyme activity even at high concentration. We detected no significant changes in ellipticity of the aromatic region in the presence of the anions studied. There is a decreased Stern-Volmer quenching constant for FAD fluorescence quenching in the presence of kosmotropic anions and an increased quenching constant in the presence of chaotropic anions. All of this indicates that active site flexibility is important in the function of the enzyme. The data demonstrate that both the high rigidity of the active site in the presence of kosmotropic anions, and its high flexibility in the presence of chaotropic anions have a decelerating effect on enzyme activity. The Hofmeister series of anions proved to be suitable agents for altering enzyme activity through changes in flexibility of the polypeptide chain, with potential importance in modulating extremozyme activity at room temperature.
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Affiliation(s)
- Gabriel Zoldák
- Department of Biochemistry, Faculty of Sciences, P. J. Safárik University, Kosice, Slovakia
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Szeltner Z, Rea D, Renner V, Juliano L, Fülop V, Polgár L. Electrostatic environment at the active site of prolyl oligopeptidase is highly influential during substrate binding. J Biol Chem 2003; 278:48786-93. [PMID: 14514675 DOI: 10.1074/jbc.m309555200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The positive electrostatic environment of the active site of prolyl oligopeptidase was investigated by using substrates with glutamic acid at positions P2, P3, P4, and P5, respectively. The different substrates gave various pH rate profiles. The pKa values extracted from the curves are apparent parameters, presumably affected by the nearby charged residues, and do not reflect the ionization of a simple catalytic histidine as found in the classic serine peptidases like chymotrypsin and subtilisin. The temperature dependence of kcat/Km did not produce linear Arrhenius plots, indicating different changes in the individual rate constants with the increase in temperature. This rendered it possible to calculate these constants, i.e. the formation (k1) and decomposition (k-1) of the enzyme-substrate complex and the acylation constant (k2), as well as the corresponding activation energies. The results have revealed the relationship between the complex Michaelis parameters and the individual rate constants. Structure determination of the enzyme-substrate complexes has shown that the different substrates display a uniform binding mode. None of the glutamic acids interacts with a charged group. We conclude that the specific rate constant is controlled by k1 rather than k2 and that the charged residues from the substrate and the enzyme can markedly affect the formation but not the structure of the enzyme-substrate complexes.
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Affiliation(s)
- Zoltán Szeltner
- Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, PO Box 7, H-1518 Budapest 112, Hungary
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Abstract
Tryptophan synthase is a classic enzyme that channels a metabolic intermediate, indole. The crystal structure of the tryptophan synthase alpha2beta2 complex from Salmonella typhimurium revealed for the first time the architecture of a multienzyme complex and the presence of an intramolecular tunnel. This remarkable hydrophobic tunnel provides a likely passageway for indole from the active site of the alpha subunit, where it is produced, to the active site of the beta subunit, where it reacts with L-serine to form L-tryptophan in a pyridoxal phosphate-dependent reaction. Rapid kinetic studies of the wild type enzyme and of channel-impaired mutant enzymes provide strong evidence for the proposed channeling mechanism. Structures of a series of enzyme-substrate intermediates at the alpha and beta active sites are elucidating enzyme mechanisms and dynamics. These structural results are providing a fascinating picture of loops opening and closing, of domain movements, and of conformational changes in the indole tunnel. Solution studies provide further evidence for ligand-induced conformational changes that send signals between the alpha and beta subunits. The combined results show that the switching of the enzyme between open and closed conformations couples the catalytic reactions at the alpha and beta active sites and prevents the escape of indole.
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Affiliation(s)
- E W Miles
- Section on Enzyme Structure and Function, Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda Maryland 20892-0830, USA.
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Hettwer S, Sterner R. A novel tryptophan synthase beta-subunit from the hyperthermophile Thermotoga maritima. Quaternary structure, steady-state kinetics, and putative physiological role. J Biol Chem 2002; 277:8194-201. [PMID: 11756459 DOI: 10.1074/jbc.m111541200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tryptophan synthase catalyzes the last two steps in the biosynthesis of the amino acid tryptophan. The enzyme is an alpha beta beta alpha complex in mesophilic microorganisms. The alpha-subunit (TrpA) catalyzes the cleavage of indoleglycerol phosphate to glyceraldehyde 3-phosphate and indole, which is channeled to the active site of the associated beta-subunit (TrpB1), where it reacts with serine to yield tryptophan. The TrpA and TrpB1 proteins are encoded by the adjacent trpA and trpB1 genes in the trp operon. The genomes of many hyperthermophilic microorganisms, however, contain an additional trpB2 gene located outside of the trp operon. To reveal the properties and potential physiological role of TrpB2, the trpA, trpB1, and trpB2 genes of Thermotoga maritima were expressed heterologously in Escherichia coli, and the resulting proteins were purified and characterized. TrpA and TrpB1 form the familiar alpha beta beta alpha complex, in which the two different subunits strongly activate each other. In contrast, TrpB2 forms a beta(2)-homodimer that has a high catalytic efficiency k(cat)/K(m)(indole) because of a very low K(m)(indole) but does not bind to TrpA. These results suggest that TrpB2 acts as an indole rescue protein, which prevents the escape of this costly hydrophobic metabolite from the cell at the high growth temperatures of hyperthermophiles.
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Affiliation(s)
- Stefan Hettwer
- Universität zu Köln, Institut für Biochemie, Otto-Fischer-Str. 12-14, D-50674 Köln, Germany
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Fan YX, McPhie P, Miles EW. Thermal repair of tryptophan synthase mutations in a regulatory intersubunit salt bridge. Evidence from arrhenius plots, absorption spectra, and primary kinetic isotope effects. J Biol Chem 2000; 275:20302-7. [PMID: 10801803 DOI: 10.1074/jbc.m001135200] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
This work is aimed at understanding how protein structure and conformation regulate activity and allosteric communication in the tryptophan synthase alpha(2)beta(2) complex from Salmonella typhimurium. Previous crystallographic and kinetic results suggest that both monovalent cations and a salt bridge between alpha subunit Asp(56) and beta subunit Lys(167) play allosteric roles. Here we show that mutation of either of these salt bridging residues produced deleterious effects that could be repaired by increased temperature in combination with CsCl or with NaCl plus an alpha subunit ligand, alpha-glycerol 3-phosphate. Arrhenius plots of the activity data under these conditions were nonlinear. The same conditions yielded temperature-dependent changes in the equilibrium distribution of enzyme-substrate intermediates and in primary kinetic isotope effects. We correlate the results with a model in which the mutant enzymes are converted by increased temperature from a low activity, "open" conformation to a high activity, "closed" conformation under certain conditions. The allosteric ligand and different monovalent cations affected the equilibrium between the open and closed forms. The results suggest that alpha subunit Asp(56) and beta subunit Lys(167) are not essential for catalysis and for allosteric communication between the alpha and beta subunits but that their mutual interaction is important in stabilization of the active, closed form of the alpha(2)beta(2) complex.
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Affiliation(s)
- Y X Fan
- Section on Enzyme Structure and Function, Laboratory of Biochemistry and Genetics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0830, USA
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