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Wang Y, Wang X, Niu S, Cheng W, Liu X, Min Y, Qiu Y, Ma L, Rao B, Zhu L. Improving the Activity of Tryptophan Synthetase via a Nucleic Acid Scaffold. Molecules 2023; 28:7272. [PMID: 37959692 PMCID: PMC10648251 DOI: 10.3390/molecules28217272] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2023] [Revised: 09/17/2023] [Accepted: 09/25/2023] [Indexed: 11/15/2023] Open
Abstract
Tryptophan synthetase (TSase), which functions as a tetramer, is a typical enzyme with a substrate channel effect, and shows excellent performance in the production of non-standard amino acids, histamine, and other biological derivatives. Based on previous work, we fused a mutant CE protein (colistin of E. coli, a polypeptide with antibacterial activity) sequence with the sequence of TSase to explore whether its catalytic activity could be enhanced, and we also analyzed whether the addition of a DNA scaffold was a feasible strategy. Here, dCE (CE protein without DNase activity) protein tags were constructed and fused to the TrapA and TrapB subunits of TSase, and the whole cell was used for the catalytic reaction. The results showed that after the dCE protein tag was fused to the TrapB subunit, its whole cell catalytic activity increased by 50%. Next, the two subunits were expressed separately, and the proteins were bound in vitro to ensure equimolar combination between the two subunits. After the dCE label was fused to TrapB, the activity of TSase assembled with TrapA also improved. A series of experiments revealed that the enzyme fused with dCE9 showed higher activity than the wild-type protein. In general, the activity of assembly TSase was optimal when the temperature was 50 °C and the pH was about 9.0. After a long temperature treatment, the enzyme maintained good activity. With the addition of exogenous nucleic acid, the activity of the enzyme increased. The maximum yield was 0.58 g/L, which was almost three times that of the wild-type TSase (0.21 g/L). The recombinant TSase constructed in this study with dCE fusion had the advantages of higher heat resistance and higher activity, and confirmed the feasibility of adding a nucleic acid scaffold, providing a new idea for the improvement of structurally similar enzymes.
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Affiliation(s)
- Yaping Wang
- Hubei Biopesticide Engineering Research Center, Hubei Academy of Agricultural Sciences, Biopesticide Branch of Hubei Innovation Centre of Agricultural Science and Technology, Wuhan 430064, China
- State Key Laboratory of Biocatalysis and Enzyme, Engineering Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Hubei Key Laboratory of Industrial Biotechnology, Biology Faculty of Hubei University, Hubei University, Wuhan 430062, China
| | - Xiangyi Wang
- Hubei Biopesticide Engineering Research Center, Hubei Academy of Agricultural Sciences, Biopesticide Branch of Hubei Innovation Centre of Agricultural Science and Technology, Wuhan 430064, China
- State Key Laboratory of Biocatalysis and Enzyme, Engineering Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Hubei Key Laboratory of Industrial Biotechnology, Biology Faculty of Hubei University, Hubei University, Wuhan 430062, China
| | - Shuhui Niu
- Hubei Biopesticide Engineering Research Center, Hubei Academy of Agricultural Sciences, Biopesticide Branch of Hubei Innovation Centre of Agricultural Science and Technology, Wuhan 430064, China
- State Key Laboratory of Biocatalysis and Enzyme, Engineering Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Hubei Key Laboratory of Industrial Biotechnology, Biology Faculty of Hubei University, Hubei University, Wuhan 430062, China
| | - Wei Cheng
- Hubei Biopesticide Engineering Research Center, Hubei Academy of Agricultural Sciences, Biopesticide Branch of Hubei Innovation Centre of Agricultural Science and Technology, Wuhan 430064, China
- State Key Laboratory of Biocatalysis and Enzyme, Engineering Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Hubei Key Laboratory of Industrial Biotechnology, Biology Faculty of Hubei University, Hubei University, Wuhan 430062, China
| | - Xiaoyan Liu
- Hubei Biopesticide Engineering Research Center, Hubei Academy of Agricultural Sciences, Biopesticide Branch of Hubei Innovation Centre of Agricultural Science and Technology, Wuhan 430064, China
| | - Yong Min
- Hubei Biopesticide Engineering Research Center, Hubei Academy of Agricultural Sciences, Biopesticide Branch of Hubei Innovation Centre of Agricultural Science and Technology, Wuhan 430064, China
| | - Yimin Qiu
- Hubei Biopesticide Engineering Research Center, Hubei Academy of Agricultural Sciences, Biopesticide Branch of Hubei Innovation Centre of Agricultural Science and Technology, Wuhan 430064, China
| | - Lixin Ma
- State Key Laboratory of Biocatalysis and Enzyme, Engineering Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Hubei Key Laboratory of Industrial Biotechnology, Biology Faculty of Hubei University, Hubei University, Wuhan 430062, China
| | - Ben Rao
- Hubei Biopesticide Engineering Research Center, Hubei Academy of Agricultural Sciences, Biopesticide Branch of Hubei Innovation Centre of Agricultural Science and Technology, Wuhan 430064, China
| | - Lei Zhu
- Hubei Biopesticide Engineering Research Center, Hubei Academy of Agricultural Sciences, Biopesticide Branch of Hubei Innovation Centre of Agricultural Science and Technology, Wuhan 430064, China
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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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3
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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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Watkins-Dulaney E, Straathof S, Arnold F. Tryptophan Synthase: Biocatalyst Extraordinaire. Chembiochem 2021; 22:5-16. [PMID: 32677310 PMCID: PMC7935429 DOI: 10.1002/cbic.202000379] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Revised: 07/15/2020] [Indexed: 12/23/2022]
Abstract
Tryptophan synthase (TrpS) has emerged as a paragon of noncanonical amino acid (ncAA) synthesis and is an ideal biocatalyst for synthetic and biological applications. TrpS catalyzes an irreversible, C-C bond-forming reaction between indole and serine to make l-tryptophan; native TrpS complexes possess fairly broad specificity for indole analogues, but are difficult to engineer to extend substrate scope or to confer other useful properties due to allosteric constraints and their heterodimeric structure. Directed evolution freed the catalytically relevant TrpS β-subunit (TrpB) from allosteric regulation by its TrpA partner and has enabled dramatic expansion of the enzyme's substrate scope. This review examines the long and storied career of TrpS from the perspective of its application in ncAA synthesis and biocatalytic cascades.
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Affiliation(s)
- Ella Watkins-Dulaney
- Division of Biology and Biological Engineering, California Institute of Technology, MC 210-41, 1200 E. California Boulevard, Pasadena, CA 91125, USA
| | - Sabine Straathof
- Division of Chemistry and Chemical Engineering, California Institute of Technology, MC 210-41, 1200 E. California Boulevard, Pasadena, CA 91125, USA
| | - Frances Arnold
- Division of Biology and Biological Engineering, California Institute of Technology, MC 210-41, 1200 E. California Boulevard, Pasadena, CA 91125, USA
- Division of Chemistry and Chemical Engineering, California Institute of Technology, MC 210-41, 1200 E. California Boulevard, Pasadena, CA 91125, USA
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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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Amir-Heidari B, Thirlway J, Micklefield J. Stereochemical Course of Tryptophan Dehydrogenation during Biosynthesis of the Calcium-Dependent Lipopeptide Antibiotics. Org Lett 2007; 9:1513-6. [PMID: 17355143 DOI: 10.1021/ol0701619] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
[reaction: see text] Hydrogen atoms are abstracted from the C2' and C3'-pro-S positions of an (S)-tryptophanyl precursor, with overall syn stereochemistry, during the biosynthesis of the C-terminal Z-2',3'-dehydrotryptophan residue of the calcium-dependent lipopeptide antibiotics (CDAs) in Streptomyces coelicolor. The absence of beta-hydroxytryptophanyl, or other possible intermediates, further suggests a direct dehydrogenation mechanism similar to that proposed for the l-tryptophan 2',3'-oxidase from Chromobacterium violaceum.
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Affiliation(s)
- Bagher Amir-Heidari
- School of Chemistry and Manchester Interdisciplinary Biocentre, The University of Manchester, 131 Princess Street, Manchester M1 7ND, UK
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Jørgensen K, Rasmussen AV, Morant M, Nielsen AH, Bjarnholt N, Zagrobelny M, Bak S, Møller BL. Metabolon formation and metabolic channeling in the biosynthesis of plant natural products. CURRENT OPINION IN PLANT BIOLOGY 2005; 8:280-91. [PMID: 15860425 DOI: 10.1016/j.pbi.2005.03.014] [Citation(s) in RCA: 328] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Metabolon formation and metabolic channeling in plant secondary metabolism enable plants to effectively synthesize specific natural products and to avoid metabolic interference. Channeling can involve different cell types, take advantage of compartmentalization within the same cell or proceed directly within a metabolon. New experimental approaches document the importance of channeling in the synthesis of isoprenoids, alkaloids, phenylpropanoids, flavonoids and cyanogenic glucosides. Metabolon formation and metabolic channeling in natural-product synthesis facilitate attempts to genetically engineer new pathways into plants to improve their content of valuable natural products. They also offer the opportunity to introduce new traits by genetic engineering to produce plant cultivars that adhere to the principle of substantial equivalence.
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Affiliation(s)
- Kirsten Jørgensen
- Plant Biochemistry Laboratory, Department of Plant Biology, Royal Veterinary and Agricultural University, 40 Thorvaldsensvej, DK-1871 Frederiksberg C, Copenhagen, Denmark
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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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9
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Abstract
Typically differential equations are employed to simulate cellular dynamics. To develop a valid continuous model based on differential equations requires accurate parameter estimations; an accuracy which is often difficult to achieve, due to the lack of data. In addition, processes in metabolic pathways, e.g. metabolite channeling, seem to be of a rather qualitative and discrete nature. With respect to the available data and to the perception of the underlying system, a discrete rather than a continuous approach to modeling and simulation seems more adequate. A discrete approach does not necessarily imply a more abstract view on the system. If we move from macro to micro and multi-level modeling, aspects of subsystems and their interactions, which have been only implicitly represented, become an explicit part of the model. To start exploring discrete event phenomena within metabolite channeling we choose the tryptophan synthase. Based on a continuous macro model, a discrete event, multi-level model is developed which allows us to analyze the interrelation between structural and functional characteristics of the enzymes.
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Affiliation(s)
- Daniela Degenring
- Department of Computer Science, University of Rostock, Rostock D-18051, Germany
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10
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Osborne A, Teng Q, Miles EW, Phillips RS. Detection of open and closed conformations of tryptophan synthase by 15N-heteronuclear single-quantum coherence nuclear magnetic resonance of bound 1-15N-L-tryptophan. J Biol Chem 2003; 278:44083-90. [PMID: 12939261 DOI: 10.1074/jbc.m308276200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
1-15N-L-Tryptophan (1-15N-L-Trp) was synthesized from 15N-aniline by a Sandmeyer reaction, followed by cyclization to isatin, reduction to indole with LiAlH4, and condensation of the 15N-indole with L-serine, catalyzed by tryptophan synthase. 1-15N-L-Trp was complexed with wild-type tryptophan synthase and beta-subunit mutants, betaK87T, betaD305A, and betaE109D, in the absence or presence of the allosteric ligands sodium chloride and disodium alpha-glycerophosphate. The enzyme complexes were observed by 15N-heteronuclear single-quantum coherence nuclear magnetic resonance (15N-HSQC NMR) spectroscopy for the presence of 1-15N-L-Trp bound to the beta-active site. No 15N-HSQC signal was detected for 1-15N-L-Trp in 10 mm triethanolamine hydrochloride buffer at pH 8. 1-15N-L-Trp in the presence of wild-type tryptophan synthase in the absence or presence of 50 mm sodium chloride showed a cross peak at 10.25 ppm on the 1H axis and 129 ppm on the 15N axis as a result of reduced solvent exchange for the bound 1-15N-L-Trp, consistent with formation of a closed conformation of the active site. The addition of disodium alpha-glycerophosphate produced a signal twice as intense, suggesting that the equilibrium favors the closed conformation. 15N-HSQC NMR spectra of betaK87T and betaE109D mutant Trp synthase with 1-15N-L-Trp showed a similar cross peak either in the presence or absence of disodium alpha-glycerophosphate, indicating the preference for a closed conformation for these mutant proteins. In contrast, the betaD305A Trp synthase mutant only showed a 15N-HSQC signal in the presence of disodium alpha-glycerophosphate. Thus, this mutant Trp synthase favored an open conformation in the absence of disodium alpha-glycerophosphate but was able to form a closed conformation in the presence of disodium alpha-glycerophosphate. Our results demonstrate that the 15N-HSQC NMR spectra of 1-15N-L-Trp bound to Trp synthase can be used to determine the conformational state of mutant forms in solution rapidly. In contrast, UV-visible spectra of wild-type and mutant Trp synthase in the presence of L-Trp with NaCl and/or disodium alpha-glycerophosphate are more difficult to interpret in terms of altered conformational equilibria.
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Affiliation(s)
- Andrew Osborne
- Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, USA
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11
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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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Affiliation(s)
- K S Anderson
- Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520-8066, USA
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Affiliation(s)
- E W Miles
- Enzyme Structure and Function Section, Laboratory of Biochemistry and Genetics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
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Affiliation(s)
- P M Dewick
- School of Pharmaceutical Sciences, University of Nottingham, UK
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15
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Ahmed SA, McPhie P, Miles EW. Mechanism of activation of the tryptophan synthase alpha2beta2 complex. Solvent effects of the co-substrate beta-mercaptoethanol. J Biol Chem 1996; 271:29100-6. [PMID: 8910565 DOI: 10.1074/jbc.271.46.29100] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
To characterize the conformational transitions that lead to activation of catalysis by the tryptophan synthase alpha2beta2 complex, we have determined the solvent effects of a co-substrate, beta-mercaptoethanol, and of a model nonsubstrate, ethanol, on the catalytic and spectroscopic properties of the enzyme. Our results show that ethanol and beta-mercaptoethanol both alter the equilibrium distribution of pyridoxal 5'-phosphate intermediates formed in the reactions of L-serine at the beta site in the alpha2beta2 complex. Addition of increasing concentrations of ethanol increases the proportion of the external aldimine of L-serine and decreases the proportion of the external aldimine of aminoacrylate. Low concentrations of the co-substrate beta-mercaptoethanol (Kd = approximately 13 mM) decrease the proportion of the external aldimine of aminoacrylate and induce formation of the quinonoid of S-hydroxyethyl-L-cysteine. Higher concentrations of beta-mercaptoethanol decrease the concentration of the quinonoid intermediate and increase the proportion of the external aldimine of L-serine. Data analysis shows that beta-mercaptoethanol and ethanol both interact or bind preferentially with the conformer of the enzyme that predominates when the aldimine of L-serine is formed and shift the equilibrium in favor of this conformer. We propose that a nonpolar region of the beta subunit, possibly the hydrophobic indole tunnel, becomes less exposed to solvent in the conformational transition that activates the alpha2beta2 complex.
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Affiliation(s)
- S A Ahmed
- Laboratory of Biochemical Pharmacology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA
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16
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Yee MC, Horn V, Yanofsky C. On the role of helix 0 of the tryptophan synthetase alpha chain of Escherichia coli. J Biol Chem 1996; 271:14754-63. [PMID: 8662916 DOI: 10.1074/jbc.271.25.14754] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The role of helix 0 of the alpha chain (TrpA) of the tryptophan synthetase alpha2beta2 multi-functional enzyme complex of Escherichia coli was examined by deleting amino-terminal residues 2-6, 2-11, or 2-19 of TrpA. Selected substitutions were also introduced at TrpA positions 2-6. The altered genes encoding these polypeptides were overexpressed from a foreign promoter on a multicopy plasmid and following insertion at their normal chromosomal location. Each deletion polypeptide was functional in vivo. However all appeared to be somewhat more labile and insoluble and less active enzymatically than wild type TrpA. The deletion polypeptides were overproduced and solubilized from cell debris by denaturation and refolding. Several were partially purified and assayed in various reactions in the presence of tryptophan synthetase beta2 (TrpB). The purified TrpADelta2-6 and TrpADelta2-11 deletion polypeptides had low activity in both the indole + serine --> tryptophan reaction and the indoleglycerol phosphate + serine --> tryptophan reaction. Poor activity in each reaction was partly due to reduced association of TrpA with TrpB. The addition of the TrpA ligands, alpha-glycerophosphate or indoleglycerol phosphate, during catalysis of the indole + serine --> tryptophan reaction increased association and activity. These findings suggest that removal of helix 0 of TrpA decreases TrpA-TrpB association as well as the activity of the TrpA active site. Alignment of the TrpA sequences from different species indicates that several lack part or all of helix 0. In some of these polypeptides, extra residues at the carboxyl end may substitute for helix 0.
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Affiliation(s)
- M C Yee
- Department of Biological Sciences, Stanford University, Stanford, California, 94305-5020, USA
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17
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Kong SK, Yim MB, Stadtman ER, Chock PB. Peroxynitrite disables the tyrosine phosphorylation regulatory mechanism: Lymphocyte-specific tyrosine kinase fails to phosphorylate nitrated cdc2(6-20)NH2 peptide. Proc Natl Acad Sci U S A 1996; 93:3377-82. [PMID: 8622943 PMCID: PMC39616 DOI: 10.1073/pnas.93.8.3377] [Citation(s) in RCA: 279] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
To determine if nitration of tyrosine residues by peroxynitrite (PN), which can be generated endogenously, can disrupt the phosphorylation of tyrosine residues in proteins involved in cell signaling networks, we studied the effect of PN-promoted nitration of tyrosine residues in a pentadecameric peptide, cdc2(6-20)NH2, on the ability of the peptide to be phosphorylated. cdc2(6-20)NH2 corresponds to the tyrosine phosphorylation site of p34cdc2 kinase, which is phosphorylated by lck kinase (lymphocyte-specific tyrosine kinase, p56lck). PN nitrates both Tyr-15 and Tyr-19 of the peptide in phosphate buffer (pH 7.5) at 37 degrees C. Nitration of Tyr-15. which is the phosphorylated amino acid residue, inhibits completely the phosphorylation of the peptide. The nitration reaction is enhanced by either Fe(III)EDTA or Cu(II)-Zn(II)-superoxide dismutase (Cu,Zn-SOD). The kinetic data are consistent with the view that reactions of Fe(111)EDTA or Cu,Zn-SOD with the cis form of PN yield complexes in which PN decomposes more slowly to form N02+, the nitrating agent. Thus, the nitration efficiency of PN is enhanced. These results are discussed from the point of view that PN-promoted nitration will result in permanent impairment of cyclic cascades that control signal transduction processes and regulate cell cycles.
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Affiliation(s)
- S K Kong
- Laboratory of Biochemistry, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
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