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Conter C, Favretto F, Dominici P, Martinez-Cruz LA, Astegno A. Key substrate recognition residues in the active site of cystathionine beta-synthase from Toxoplasma gondii. Proteins 2023; 91:1383-1393. [PMID: 37163386 DOI: 10.1002/prot.26507] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Revised: 03/28/2023] [Accepted: 04/19/2023] [Indexed: 05/12/2023]
Abstract
Cystathionine β-synthase (CBS) catalyzes the condensation of l-serine and l-homocysteine to give l-cystathionine in the transsulfuration pathway. Recently, a few O-acetylserine (l-OAS)-dependent CBSs (OCBSs) have been found in bacteria that can exclusively function with l-OAS. CBS from Toxoplasma gondii (TgCBS) can efficiently use both l-serine and l-OAS to form l-cystathionine. In this work, a series of site-specific variants substituting S84, Y160, and Y246 with hydrophobic residues found at the same positions in OCBSs was generated to explore the roles of the hydroxyl moieties of these residues as determinants of l-serine/l-OAS preference in TgCBS. We found that the S84A/Y160F/Y246V triple mutant behaved like an OCBS in terms of both substrate requirements, showing β-replacement activity only with l-OAS, and pH optimum, which is decreased by ~1 pH unit. Formation of a stable aminoacrylate upon reaction with l-serine is prevented by the triple mutation, indicating the importance of the H-bonds between the hydroxyl groups of Y160, Y246, and S84 with l-serine in formation of the intermediate. Analysis of the independent effect of each mutation on TgCBS activity and investigation of the protein-aminoacrylate complex structure allowed for the conclusion that the hydroxyl group of Y246 has a major, but not exclusive, role in controlling the l-serine preference by efficiently stabilizing its leaving group. These studies demonstrate that differences in substrate specificity of CBSs are controlled by natural variations in as few as three residue positions. A better understanding of substrate specificity in TgCBS will facilitate the design of new antimicrobial compounds.
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Affiliation(s)
- Carolina Conter
- Department of Biotechnology, University of Verona, Verona, Italy
| | - Filippo Favretto
- Department of Biotechnology, University of Verona, Verona, Italy
| | - Paola Dominici
- Department of Biotechnology, University of Verona, Verona, Italy
| | - Luis Alfonso Martinez-Cruz
- Center for Cooperative Research in Biosciences (CIC bioGUNE), Basque Research and Technology Alliance (BRTA), Derio, Spain
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2
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Anufrieva NV, Morozova EA, Revtovich SV, Bazhulina NP, Timofeev V, Tkachev YV, Faleev N, Nikulin AD, Demidkina TV. Serine 339 in the Catalysis of γ- and β-Elimination Reactions. Acta Naturae 2022; 14:50-61. [PMID: 35923564 PMCID: PMC9307983 DOI: 10.32607/actanaturae.11242] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Accepted: 07/21/2021] [Indexed: 11/20/2022] Open
Abstract
Serine 339 of the active site of Citrobacter freundii
methionine γ-lyase (MGL) is a conserved amino acid in most
pyridoxal 5’-phosphate-dependent enzymes of the cystathionine
β-lyase subclass, to which MGL belongs. The reaction mechanism of the
MGL-catalyzed γ-elimination reaction is poorly explored. We replaced
serine 339 with alanine using site-directed mutagenesis. The replacement of
serine 339 with alanine led to a significant (by two orders of magnitude)
decrease in efficiency in the catalysis of the γ- and β-elimination
reactions by the mutant form of the enzyme. The exchange rates of the C-α-
and C-β-protons in the amino acids in complexes consisting of the enzyme
and competitive inhibitors decreased by one-two orders of magnitude. The
spectral characteristics of the mutant form indicated that the replacement did
not lead to significant changes in the conformation and tautomerism of MGL
internal aldimine. We crystallized the holoenzyme and determined its spatial
structure at 1.7 E resolution. The replacement of serine 339 with alanine did
not affect the overall course of the polypeptide chain of the MGL subunit and
the tetrameric enzyme structure. An analysis of the obtained kinetic and
spectral data, as well as the known spatial structures of C. freundii
MGL, indicates that serine 339 is necessary for efficient catalysis of
γ- and β-elimination reactions at the stage of C-α-proton
abstraction from the external aldimine, the γ-elimination reaction at the
stages of coenzyme C4’-atom protonation, and C-β-proton abstraction
from a ketimine intermediate.
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Affiliation(s)
- N. V. Anufrieva
- Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences, Moscow, 119991 Russia
| | - E. A. Morozova
- Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences, Moscow, 119991 Russia
| | - S. V. Revtovich
- Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences, Moscow, 119991 Russia
| | - N. P. Bazhulina
- Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences, Moscow, 119991 Russia
| | - V.P. Timofeev
- Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences, Moscow, 119991 Russia
| | - Ya. V. Tkachev
- Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences, Moscow, 119991 Russia
| | - N.G. Faleev
- Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences, Moscow, 119991 Russia
| | - A. D. Nikulin
- Institute of Protein Research of the Russian Academy of Sciences, Pushchino, Moscow Region, 142290 Russia
| | - T. V. Demidkina
- Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences, Moscow, 119991 Russia
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Soo VWC, Yosaatmadja Y, Squire CJ, Patrick WM. Mechanistic and Evolutionary Insights from the Reciprocal Promiscuity of Two Pyridoxal Phosphate-dependent Enzymes. J Biol Chem 2016; 291:19873-87. [PMID: 27474741 PMCID: PMC5025676 DOI: 10.1074/jbc.m116.739557] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2016] [Indexed: 11/06/2022] Open
Abstract
Enzymes that utilize the cofactor pyridoxal 5′-phosphate play essential roles in amino acid metabolism in all organisms. The cofactor is used by proteins that adopt at least five different folds, which raises questions about the evolutionary processes that might explain the observed distribution of functions among folds. In this study, we show that a representative of fold type III, the Escherichia coli alanine racemase (ALR), is a promiscuous cystathionine β-lyase (CBL). Furthermore, E. coli CBL (fold type I) is a promiscuous alanine racemase. A single round of error-prone PCR and selection yielded variant ALR(Y274F), which catalyzes cystathionine β-elimination with a near-native Michaelis constant (Km = 3.3 mm) but a poor turnover number (kcat ≈10 h−1). In contrast, directed evolution also yielded CBL(P113S), which catalyzes l-alanine racemization with a poor Km (58 mm) but a high kcat (22 s−1). The structures of both variants were solved in the presence and absence of the l-alanine analogue, (R)-1-aminoethylphosphonic acid. As expected, the ALR active site was enlarged by the Y274F substitution, allowing better access for cystathionine. More surprisingly, the favorable kinetic parameters of CBL(P113S) appear to result from optimizing the pKa of Tyr-111, which acts as the catalytic acid during l-alanine racemization. Our data emphasize the short mutational routes between the functions of pyridoxal 5′-phosphate-dependent enzymes, regardless of whether or not they share the same fold. Thus, they confound the prevailing model of enzyme evolution, which predicts that overlapping patterns of promiscuity result from sharing a common multifunctional ancestor.
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Affiliation(s)
- Valerie W C Soo
- From the Institute of Natural and Mathematical Sciences, Massey University, Auckland 0632
| | - Yuliana Yosaatmadja
- the School of Biological Sciences, University of Auckland, Auckland 1142, and
| | | | - Wayne M Patrick
- the Department of Biochemistry, University of Otago, Dunedin 9054, New Zealand
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Anufrieva NV, Faleev NG, Morozova EA, Bazhulina NP, Revtovich SV, Timofeev VP, Tkachev YV, Nikulin AD, Demidkina TV. The role of active site tyrosine 58 in Citrobacter freundii methionine γ-lyase. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2015; 1854:1220-8. [PMID: 25584856 DOI: 10.1016/j.bbapap.2014.12.027] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2014] [Revised: 12/29/2014] [Accepted: 12/30/2014] [Indexed: 10/24/2022]
Abstract
In the spatial structure of methionine γ-lyase (MGL, EC 4.4.1.11) from Citrobacter freundii, Tyr58 is located at H-bonding distance to the oxygen atom of the phosphate "handle" of pyridoxal 5'-phosphate (PLP). It was replaced for phenylalanine by site-directed mutagenesis. The X-ray structure of the mutant enzyme was determined at 1.96Å resolution. Comparison of spatial structures and absorption spectra of wild-type and mutant holoenzymes demonstrated that the replacement did not result in essential changes of the conformation of the active site Tyr58Phe MGL. The Kd value of PLP for Tyr58Phe MGL proved to be comparable to the Kd value for the wild-type enzyme. The replacement led to a decrease of catalytic efficiencies in both γ- and β-elimination reactions of about two orders of magnitude as compared to those for the wild-type enzyme. The rates of exchange of C-α- and C-β- protons of inhibitors in D2O catalyzed by the mutant form are comparable with those for the wild-type enzyme. Spectral data on the complexes of the mutant form with the substrates and inhibitors showed that the replacement led to a change of rate the limiting step of the physiological reaction. The results allowed us to conclude that Tyr58 is involved in an optimal positioning of the active site Lys210 at some stages of γ- and β-elimination reactions. This article is part of a Special Issue entitled: Cofactor-dependent proteins: evolution, chemical diversity and bio-applications.
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Affiliation(s)
- Natalya V Anufrieva
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow 119991, Russia
| | - Nicolai G Faleev
- A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, ul. Vavilova 28, Moscow 117813, Russia
| | - Elena A Morozova
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow 119991, Russia
| | - Natalia P Bazhulina
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow 119991, Russia
| | - Svetlana V Revtovich
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow 119991, Russia
| | - Vladimir P Timofeev
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow 119991, Russia
| | - Yaroslav V Tkachev
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow 119991, Russia
| | - Alexei D Nikulin
- Institute of Protein Research, Russian Academy of Sciences, ul. Institutskaya 4, Pushchino, Moscow Region 142290, Russia
| | - Tatyana V Demidkina
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow 119991, Russia.
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A role for glutamate-333 of Saccharomyces cerevisiae cystathionine γ-lyase as a determinant of specificity. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2013; 1844:465-72. [PMID: 24291053 DOI: 10.1016/j.bbapap.2013.11.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Revised: 11/17/2013] [Accepted: 11/21/2013] [Indexed: 11/21/2022]
Abstract
Cystathionine γ-lyase (CGL) catalyzes the hydrolysis of l-cystathionine (l-Cth), producing l-cysteine (l-Cys), α-ketobutyrate and ammonia, in the second step of the reverse transsulfuration pathway, which converts l-homocysteine (l-Hcys) to l-Cys. Site-directed variants substituting residues E48 and E333 with alanine, aspartate and glutamine were characterized to probe the roles of these acidic residues, conserved in fungal and mammalian CGL sequences, in the active-site of CGL from Saccharomyces cerevisiae (yCGL). The pH optimum of variants containing the alanine or glutamine substitutions of E333 is increased by 0.4-1.2 pH units, likely due to repositioning of the cofactor and modification of the pKa of the pyridinium nitrogen. The pH profile of yCGL-E48A/E333A resembles that of Escherichia coli cystathionine β-lyase. The effect of substituting E48, E333 or both residues is the 1.3-3, 26-58 and 124-568-fold reduction, respectively, of the catalytic efficiency of l-Cth hydrolysis. The Km(l-Cth) of E333 substitution variants is increased ~17-fold, while Km(l-OAS) is within 2.5-fold of the wild-type enzyme, indicating that residue E333 interacts with the distal amine moiety of l-Cth, which is not present in the alternative substrate O-acetyl-l-serine. The catalytic efficiency of yCGL for α,γ-elimination of O-succinyl-l-homoserine (kcat/Km(l-OSHS)=7±2), which possesses a distal carboxylate, but lacks an amino group, is 300-fold lower than that of the physiological l-Cth substrate (kcat/Km(l-Cth)=2100±100) and 260-fold higher than that of l-Hcys (kcat/Km(l-Hcys)=0.027±0.005), which lacks both distal polar moieties. The results of this study suggest that the glutamate residue at position 333 is a determinant of specificity.
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Jaworski AF, Aitken SM. Exploration of the six tryptophan residues of Escherichia coli cystathionine β-lyase as probes of enzyme conformational change. Arch Biochem Biophys 2013; 538:138-44. [DOI: 10.1016/j.abb.2013.07.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Revised: 07/06/2013] [Accepted: 07/08/2013] [Indexed: 10/26/2022]
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Characterization of C-S Lyase from C. diphtheriae: a possible target for new antimicrobial drugs. BIOMED RESEARCH INTERNATIONAL 2013; 2013:701536. [PMID: 24106714 PMCID: PMC3784150 DOI: 10.1155/2013/701536] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/05/2013] [Accepted: 07/16/2013] [Indexed: 12/28/2022]
Abstract
The emergence of antibiotic resistance in microbial pathogens requires the identification of new antibacterial drugs. The biosynthesis of methionine is an attractive target because of its central importance in cellular metabolism. Moreover, most of the steps in methionine biosynthesis pathway are absent in mammals, lowering the probability of unwanted side effects. Herein, detailed biochemical characterization of one enzyme required for methionine biosynthesis, a pyridoxal-5′-phosphate (PLP-) dependent C-S lyase from Corynebacterium diphtheriae, a pathogenic bacterium that causes diphtheria, has been performed. We overexpressed the protein in E. coli and analyzed substrate specificity, pH dependence of steady state kinetic parameters, and ligand-induced spectral transitions of the protein. Structural comparison of the enzyme with cystalysin from Treponema denticola indicates a similarity in overall folding. We used site-directed mutagenesis to highlight the importance of active site residues Tyr55, Tyr114, and Arg351, analyzing the effects of amino acid replacement on catalytic properties of enzyme. Better understanding of the active site of C. diphtheriae C-S lyase and the determinants of substrate and reaction specificity from this work will facilitate the design of novel inhibitors as antibacterial therapeutics.
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Exploration of structure–function relationships in Escherichia coli cystathionine γ-synthase and cystathionine β-lyase via chimeric constructs and site-specific substitutions. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2013; 1834:1044-53. [DOI: 10.1016/j.bbapap.2013.02.036] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Revised: 02/25/2013] [Accepted: 02/26/2013] [Indexed: 11/23/2022]
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Jaworski AF, Lodha PH, Manders AL, Aitken SM. Exploration of the active site of Escherichia coli cystathionine γ-synthase. Protein Sci 2013; 21:1662-71. [PMID: 22855027 DOI: 10.1002/pro.2135] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Cystathionine γ-synthase (CGS) catalyzes the condensation of O-succinyl-L-homoserine (L-OSHS) and L-cysteine (L-Cys), to produce L-cystathionine (L-Cth) and succinate, in the first step of the bacterial transsulfuration pathway. In the absence of L-Cys, the enzyme catalyzes the futile α,γ-elimination of L-OSHS, yielding succinate, α-ketobutyrate, and ammonia. A series of 16 site-directed variants of Escherichia coli CGS (eCGS) was constructed to probe the roles of active-site residues D45, Y46, R48, R49, Y101, R106, N227, E325, S326, and R361. The effects of these substitutions on the catalytic efficiency of the α,γ-elimination reaction range from a reduction of only ∼2-fold for R49K and the E325A,Q variants to 310- and 760-fold for R361K and R48K, respectively. A similar trend is observed for the k(cat) /K(m)(l-OSHS) of the physiological, α,γ-replacement reaction. The results of this study suggest that the arginine residues at positions 48, 106 and 361 of eCGS, conserved in bacterial CGS sequences, tether the distal and α-carboxylate moieties, respectively, of the L-OSHS substrate. In contrast, with the exception of the 13-fold increase observed for R106A, the K(m)(l-Cys) is not markedly affected by the site-directed replacement of the residues investigated. The decrease in k(cat) observed for the S326A variant reflects the role of this residue in tethering the side chain of K198, the catalytic base. Although no structures exist of eCGS bound to active-site ligands, the roles of individual residues is consistent with the structures inhibitor complexes of related enzymes. Substitution of D45, E325, or Y101 enables a minor transamination activity for the substrate L-Ala.
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