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Drago VN, Devos JM, Blakeley MP, Forsyth VT, Parks JM, Kovalevsky A, Mueser TC. Neutron diffraction from a microgravity-grown crystal reveals the active site hydrogens of the internal aldimine form of tryptophan synthase. CELL REPORTS. PHYSICAL SCIENCE 2024; 5:101827. [PMID: 38645802 PMCID: PMC11027755 DOI: 10.1016/j.xcrp.2024.101827] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 04/23/2024]
Abstract
Pyridoxal 5'-phosphate (PLP), the biologically active form of vitamin B6, is an essential cofactor in many biosynthetic pathways. The emergence of PLP-dependent enzymes as drug targets and biocatalysts, such as tryptophan synthase (TS), has underlined the demand to understand PLP-dependent catalysis and reaction specificity. The ability of neutron diffraction to resolve the positions of hydrogen atoms makes it an ideal technique to understand how the electrostatic environment and selective protonation of PLP regulates PLP-dependent activities. Facilitated by microgravity crystallization of TS with the Toledo Crystallization Box, we report the 2.1 Å joint X-ray/neutron (XN) structure of TS with PLP in the internal aldimine form. Positions of hydrogens were directly determined in both the α- and β-active sites, including PLP cofactor. The joint XN structure thus provides insight into the selective protonation of the internal aldimine and the electrostatic environment of TS necessary to understand the overall catalytic mechanism.
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Affiliation(s)
- Victoria N. Drago
- Department of Chemistry and Biochemistry, University of Toledo, Toledo, OH 43606, USA
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Juliette M. Devos
- Life Sciences Group, Institut Laue–Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France
- Partnership for Structural Biology (PSB), 38000 Grenoble, France
| | - Matthew P. Blakeley
- Large Scale Structures Group, Institut Laue–Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France
| | - V. Trevor Forsyth
- Faculty of Medicine, Lund University, and LINXS Institute for Advanced Neutron and X-ray Science, Lund, Sweden
| | - Jerry M. Parks
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Andrey Kovalevsky
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Timothy C. Mueser
- Department of Chemistry and Biochemistry, University of Toledo, Toledo, OH 43606, USA
- Lead contact
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2
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Ito S, Yagi K, Sugita Y. Allosteric regulation of β-reaction stage I in tryptophan synthase upon the α-ligand binding. J Chem Phys 2023; 158:115101. [PMID: 36948822 DOI: 10.1063/5.0134117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023] Open
Abstract
Tryptophan synthase (TRPS) is a bifunctional enzyme consisting of α- and β-subunits that catalyzes the last two steps of L-tryptophan (L-Trp) biosynthesis. The first stage of the reaction at the β-subunit is called β-reaction stage I, which converts the β-ligand from an internal aldimine [E(Ain)] to an α-aminoacrylate [E(A-A)] intermediate. The activity is known to increase 3-10-fold upon the binding of 3-indole-D-glycerol-3'-phosphate (IGP) at the α-subunit. The effect of α-ligand binding on β-reaction stage I at the distal β-active site is not well understood despite the abundant structural information available for TRPS. Here, we investigate the β-reaction stage I by carrying out minimum-energy pathway searches based on a hybrid quantum mechanics/molecular mechanics (QM/MM) model. The free-energy differences along the pathway are also examined using QM/MM umbrella sampling simulations with QM calculations at the B3LYP-D3/aug-cc-pVDZ level of theory. Our simulations suggest that the sidechain orientation of βD305 near the β-ligand likely plays an essential role in the allosteric regulation: a hydrogen bond is formed between βD305 and the β-ligand in the absence of the α-ligand, prohibiting a smooth rotation of the hydroxyl group in the quinonoid intermediate, whereas the dihedral angle rotates smoothly after the hydrogen bond is switched from βD305-β-ligand to βD305-βR141. This switch could occur upon the IGP-binding at the α-subunit, as evidenced by the existing TRPS crystal structures.
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Affiliation(s)
- Shingo Ito
- Theoretical Molecular Science Laboratory, RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Kiyoshi Yagi
- Theoretical Molecular Science Laboratory, RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Yuji Sugita
- Theoretical Molecular Science Laboratory, RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
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3
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Maity AN, Chen JR, Li QY, Ke SC. The Nitrogen Atom of Vitamin B 6 Is Essential for the Catalysis of Radical Aminomutases. Int J Mol Sci 2022; 23:ijms23095210. [PMID: 35563602 PMCID: PMC9105233 DOI: 10.3390/ijms23095210] [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: 03/28/2022] [Revised: 05/03/2022] [Accepted: 05/04/2022] [Indexed: 11/16/2022] Open
Abstract
Radical aminomutases are pyridoxal 5'-phosphate (PLP, a B6 vitamer)-dependent enzymes that require the generation of a 5'-deoxyadenosyl radical to initiate the catalytic cycle, to perform a 1,2 amino group shift reaction. The role of the nitrogen atom of PLP in radical aminomutases has not been investigated extensively yet. We report an alternative synthetic procedure to provide easy access to 1-deazaPLP (dAPLP), an isosteric analog of PLP which acts as a probe for studying the role of the nitrogen atom. Our results revealed that lysine 5,6-aminomutase (5,6-LAM), a radical aminomutase, reconstituted with dAPLP cannot turn over a substrate, demonstrating that the nitrogen atom is essential for radical aminomutases. In contrast, biochemical and spectroscopic studies on the S238A variant reconstituted with PLP revealed a minuscule loss of activity. This apparent anomaly can be explained by a water-mediated rescue of activity in S238A, as if mimicking the active site of lysine 2,3-aminomutase. This study leads to a better comprehension of how enzymes harness the optimum capability of PLP to realize catalysis.
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Ito S, Yagi K, Sugita Y. Computational Analysis on the Allostery of Tryptophan Synthase: Relationship between α/β-Ligand Binding and Distal Domain Closure. J Phys Chem B 2022; 126:3300-3308. [PMID: 35446577 PMCID: PMC9083551 DOI: 10.1021/acs.jpcb.2c01556] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Tryptophan synthase (TRPS) is a bifunctional enzyme consisting of α and β-subunits and catalyzes the last two steps of l-tryptophan (L-Trp) biosynthesis, namely, cleavage of 3-indole-d-glycerol-3'-phosphate (IGP) into indole and glyceraldehyde-3-phosphate (G3P) in the α-subunit, and a pyridoxal phosphate (PLP)-dependent reaction of indole and l-serine (L-Ser) to produce L-Trp in the β-subunit. Importantly, the IGP binding at the α-subunit affects the β-subunit conformation and its ligand-binding affinity, which, in turn, enhances the enzymatic reaction at the α-subunit. The intersubunit communications in TRPS have been investigated extensively for decades because of the fundamental and pharmaceutical importance, while it is still difficult to answer how TRPS allostery is regulated at the atomic detail. Here, we investigate the allosteric regulation of TRPS by all-atom classical molecular dynamics (MD) simulations and analyze the potential of mean-force (PMF) along conformational changes of the α- and β-subunits. The present simulation has revealed a widely opened conformation of the β-subunit, which provides a pathway for L-Ser to enter into the β-active site. The IGP binding closes the α-subunit and induces a wide opening of the β-subunit, thereby enhancing the binding affinity of L-Ser to the β-subunit. Structural analyses have identified critical hydrogen bonds (HBs) at the interface of the two subunits (αG181-βS178, αP57-βR175, etc.) and HBs between the β-subunit (βT110 - βH115) and a complex of PLP and L-Ser (an α-aminoacrylate intermediate). The former HBs regulate the allosteric, β-subunit opening, whereas the latter HBs are essential for closing the β-subunit in a later step. The proposed mechanism for how the interdomain communication in TRPS is realized with ligand bindings is consistent with the previous experimental data, giving a general idea to interpret the allosteric regulations in multidomain proteins.
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Affiliation(s)
- Shingo Ito
- Theoretical Molecular Science Laboratory, RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Kiyoshi Yagi
- Theoretical Molecular Science Laboratory, RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Yuji Sugita
- Theoretical Molecular Science Laboratory, RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.,Computational Biophysics Research Team, RIKEN Center for Computational Science, 7-1-26 Minatojima-Minamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan.,Laboratory for Biomolecular Function Simulation, RIKEN Center for Biosystems Dynamics Research, 1-6-5 Minatojima-Minamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan
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5
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Noguchi T, Isogai S, Terada T, Nishiyama M, Kuzuyama T. Cryptic Oxidative Transamination of Hydroxynaphthoquinone in Natural Product Biosynthesis. J Am Chem Soc 2022; 144:5435-5440. [PMID: 35293722 DOI: 10.1021/jacs.1c13074] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Pyridoxal 5'-phosphate (PLP)-dependent enzymes are a group of versatile enzymes that catalyze various reactions, but only a small number of them react with O2. Here, we report an unprecedented PLP-dependent enzyme, NphE, that catalyzes both transamination and two-electron oxidation using O2 as an oxidant. Our intensive analysis reveals that NphE transfers the l-glutamate-derived amine to 1,3,6,8-tetrahydroxynaphthalene-derived mompain to form 8-amino-flaviolin (8-AF) via a highly conjugated quinonoid intermediate that is reactive with O2. During the NphE reaction, O2 is reduced to yield H2O2. An integrated technique involving NphE structure prediction by AlphaFold v2.0 and molecular dynamics simulation suggested the O2-accessible cavity. Our in vivo results demonstrated that 8-AF is a genuine biosynthetic intermediate for the 1,3,6,8-tetrahydroxynaphthalene-derived meroterpenoid naphterpin without an amino group, which was supported by site-directed mutagenesis. This study clearly establishes the NphE reaction product 8-AF as a common intermediate with a cryptic amino group for the biosynthesis of terpenoid-polyketide hybrid natural products.
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Affiliation(s)
- Tomohiro Noguchi
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, JAPAN
| | - Shota Isogai
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, JAPAN
| | - Tohru Terada
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, JAPAN.,Collaborative Research Institute for Innovative Microbiology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, JAPAN
| | - Makoto Nishiyama
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, JAPAN.,Collaborative Research Institute for Innovative Microbiology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, JAPAN
| | - Tomohisa Kuzuyama
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, JAPAN.,Collaborative Research Institute for Innovative Microbiology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, JAPAN
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6
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Darbyshire AL, Mothersole RG, Wolthers KR. A Fold Type II PLP-Dependent Enzyme from Fusobacterium nucleatum Functions as a Serine Synthase and Cysteine Synthase. Biochemistry 2021; 60:524-536. [PMID: 33539704 DOI: 10.1021/acs.biochem.0c00902] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Serine synthase (SS) from Fusobacterium nucleatum is a fold type II pyridoxal 5'-phosphate (PLP)-dependent enzyme that catalyzes the β-replacement of l-cysteine with water to form l-serine and H2S. Herein, we show that SS can also function as a cysteine synthase, catalyzing the β-replacement of l-serine with bisulfide to produce l-cysteine and H2O. The forward (serine synthase) and reverse (cysteine synthase) reactions occur with comparable turnover numbers and catalytic efficiencies for the amino acid substrate. Reaction of SS with l-cysteine leads to transient formation of a quinonoid species, suggesting that deprotonation of the Cα and β-elimination of the thiolate group from l-cysteine occur via a stepwise mechanism. In contrast, the quinonoid species was not detected in the formation of the α-aminoacrylate intermediate following reaction of SS with l-serine. A key active site residue, D232, was shown to stabilize the more chemically reactive ketoenamine PLP tautomer and also function as an acid/base catalyst in the forward and reverse reactions. Fluorescence resonance energy transfer between PLP and W99, the enzyme's only tryptophan residue, supports ligand-induced closure of the active site, which shields the PLP cofactor from the solvent and increases the basicity of D232. These results provide new insight into amino acid metabolism in F. nucleatum and highlight the multiple catalytic roles of D232 in a new member of the fold type II family of PLP-dependent enzymes.
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Affiliation(s)
- Amanda L Darbyshire
- Department of Chemistry, University of British Columbia, Okanagan Campus, 3247 University Way, Kelowna, BC V1V 1V7, Canada
| | - Robert G Mothersole
- Department of Chemistry, University of British Columbia, Okanagan Campus, 3247 University Way, Kelowna, BC V1V 1V7, Canada
| | - Kirsten R Wolthers
- Department of Chemistry, University of British Columbia, Okanagan Campus, 3247 University Way, Kelowna, BC V1V 1V7, Canada
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7
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Borchert AJ, Ernst DC, Downs DM. Reactive Enamines and Imines In Vivo: Lessons from the RidA Paradigm. Trends Biochem Sci 2019; 44:849-860. [PMID: 31103411 PMCID: PMC6760865 DOI: 10.1016/j.tibs.2019.04.011] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Revised: 04/16/2019] [Accepted: 04/17/2019] [Indexed: 01/19/2023]
Abstract
Metabolic networks are webs of integrated reactions organized to maximize growth and replication while minimizing the detrimental impact that reactive metabolites can have on fitness. Enamines and imines, such as 2-aminoacrylate (2AA), are reactive metabolites produced as short-lived intermediates in a number of enzymatic processes. Left unchecked, the inherent reactivity of enamines and imines may perturb the metabolic network. Genetic and biochemical studies have outlined a role for the broadly conserved reactive intermediate deaminase (Rid) (YjgF/YER057c/UK114) protein family, in particular RidA, in catalyzing the hydrolysis of enamines and imines to their ketone product. Herein, we discuss new findings regarding the biological significance of enamine and imine production and outline the importance of RidA in controlling the accumulation of reactive metabolites.
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Affiliation(s)
- Andrew J Borchert
- Department of Microbiology, University of Georgia, Athens, GA 30602, USA
| | - Dustin C Ernst
- Current address: Center for Circadian Biology, University of California, San Diego, San Diego, CA 92161, USA
| | - Diana M Downs
- Department of Microbiology, University of Georgia, Athens, GA 30602, USA.
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8
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Graham DL, Beio ML, Nelson DL, Berkowitz DB. Human Serine Racemase: Key Residues/Active Site Motifs and Their Relation to Enzyme Function. Front Mol Biosci 2019; 6:8. [PMID: 30918891 PMCID: PMC6424897 DOI: 10.3389/fmolb.2019.00008] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Accepted: 02/12/2019] [Indexed: 01/06/2023] Open
Abstract
Serine racemase (SR) is the first racemase enzyme to be identified in human biology and converts L-serine to D-serine, an important neuronal signaling molecule that serves as a co-agonist of the NMDA (N-methyl-D-aspartate) receptor. This overview describes key molecular features of the enzyme, focusing on the side chains and binding motifs that control PLP (pyridoxal phosphate) cofactor binding as well as activity modulation through the binding of both divalent cations and ATP, the latter showing allosteric modulation. Discussed are catalytically important residues in the active site including K56 and S84—the si- and re-face bases, respectively,—and R135, a residue that appears to play a critical role in the binding of both negatively charged alternative substrates and inhibitors. The interesting bifurcated mechanism followed by this enzyme whereby substrate L-serine can be channeled either into D-serine (racemization pathway) or into pyruvate (β-elimination pathway) is discussed extensively, as are studies that focus on a key loop region (the so-called “triple serine loop”), the modification of which can be used to invert the normal in vitro preference of this enzyme for the latter pathway over the former. The possible cross-talk between the PLP enzymes hSR and hCBS (human cystathionine β-synthase) is discussed, as the former produces D-serine and the latter produces H2S, both of which stimulate the NMDAR and both of which have been implicated in neuronal infarction pursuant to ischemic stroke. Efforts to gain a more complete mechanistic understanding of these PLP enzymes are expected to provide valuable insights for the development of specific small molecule modulators of these enzymes as tools to study their roles in neuronal signaling and in modulation of NMDAR function.
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Affiliation(s)
- Danielle L Graham
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE, United States
| | - Matthew L Beio
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE, United States
| | - David L Nelson
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE, United States
| | - David B Berkowitz
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE, United States
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9
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Liang J, Han Q, Tan Y, Ding H, Li J. Current Advances on Structure-Function Relationships of Pyridoxal 5'-Phosphate-Dependent Enzymes. Front Mol Biosci 2019; 6:4. [PMID: 30891451 PMCID: PMC6411801 DOI: 10.3389/fmolb.2019.00004] [Citation(s) in RCA: 100] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2018] [Accepted: 01/25/2019] [Indexed: 12/23/2022] Open
Abstract
Pyridoxal 5′-phosphate (PLP) functions as a coenzyme in many enzymatic processes, including decarboxylation, deamination, transamination, racemization, and others. Enzymes, requiring PLP, are commonly termed PLP-dependent enzymes, and they are widely involved in crucial cellular metabolic pathways in most of (if not all) living organisms. The chemical mechanisms for PLP-mediated reactions have been well elaborated and accepted with an emphasis on the pure chemical steps, but how the chemical steps are processed by enzymes, especially by functions of active site residues, are not fully elucidated. Furthermore, the specific mechanism of an enzyme in relation to the one for a similar class of enzymes seems scarcely described or discussed. This discussion aims to link the specific mechanism described for the individual enzyme to the same types of enzymes from different species with aminotransferases, decarboxylases, racemase, aldolase, cystathionine β-synthase, aromatic phenylacetaldehyde synthase, et al. as models. The structural factors that contribute to the reaction mechanisms, particularly active site residues critical for dictating the reaction specificity, are summarized in this review.
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Affiliation(s)
- Jing Liang
- Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States
| | - Qian Han
- Laboratory of Tropical Veterinary Medicine and Vector Biology, Hainan Key Laboratory of Sustainable Utilization of Tropical Bioresources, Institute of Agriculture and Forestry, Hainan University, Haikou, China
| | - Yang Tan
- Institute of Synthetic Biology, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
| | - Haizhen Ding
- Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States
| | - Jianyong Li
- Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States
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10
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Controlling reaction specificity in pyridoxal phosphate enzymes. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1814:1407-18. [PMID: 21664990 DOI: 10.1016/j.bbapap.2011.05.019] [Citation(s) in RCA: 125] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Revised: 05/18/2011] [Accepted: 05/25/2011] [Indexed: 11/20/2022]
Abstract
Pyridoxal 5'-phosphate enzymes are ubiquitous in the nitrogen metabolism of all organisms. They catalyze a wide variety of reactions including racemization, transamination, decarboxylation, elimination, retro-aldol cleavage, Claisen condensation, and others on substrates containing an amino group, most commonly α-amino acids. The wide variety of reactions catalyzed by PLP enzymes is enabled by the ability of the covalent aldimine intermediate formed between substrate and PLP to stabilize carbanionic intermediates at Cα of the substrate. This review attempts to summarize the mechanisms by which reaction specificity can be achieved in PLP enzymes by focusing on three aspects of these reactions: stereoelectronic effects, protonation state of the external aldimine intermediate, and interaction of the carbanionic intermediate with the protein side chains present in the active site. This article is part of a Special Issue entitled: Pyridoxal Phosphate Enzymology.
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11
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Aitken SM, Lodha PH, Morneau DJK. The enzymes of the transsulfuration pathways: active-site characterizations. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1814:1511-7. [PMID: 21435402 DOI: 10.1016/j.bbapap.2011.03.006] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2010] [Revised: 03/03/2011] [Accepted: 03/09/2011] [Indexed: 11/19/2022]
Abstract
The diversity of reactions catalyzed by enzymes reliant on pyridoxal 5'-phosphate (PLP) demonstrates the catalytic versatility of this cofactor and the plasticity of the protein scaffolds of the major fold types of PLP-dependent enzymes. The enzymes of the transsulfuration (cystathionine γ-synthase and cystathionine β-lyase) and reverse transsulfuration (cystathionine β-synthase and cystathionine γ-lyase) pathways interconvert l-cysteine and l-homocysteine, the immediate precursor of l-methionine, in plants/bacteria and yeast/animals, respectively. These enzymes provide a useful model system for investigation of the mechanisms of substrate and reaction specificity in PLP-dependent enzymes as they catalyze distinct side chain rearrangements of similar amino acid substrates. Exploration of the underlying factors that enable enzymes to control the substrate and reaction specificity of this cofactor will enable the engineering of these properties and the development of therapeutics and antimicrobial compounds. Recent studies probing the role of active-site residues, of the enzymes of the transsulfuration pathways, as determinants of substrate and reaction specificity are the subject of this review. This article is part of a Special Issue entitled: Pyridoxal Phosphate Enzymology.
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Affiliation(s)
- Susan M Aitken
- Department of Biology, Carleton University, Ottowa, Canada.
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12
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Residue N84 of Yeast Cystathionine β-Synthase is a Determinant of Reaction Specificity. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2010; 1804:1424-31. [DOI: 10.1016/j.bbapap.2010.02.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2009] [Revised: 01/28/2010] [Accepted: 02/12/2010] [Indexed: 11/23/2022]
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13
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Fatmi MQ, Ai R, Chang CEA. Synergistic Regulation and Ligand-Induced Conformational Changes of Tryptophan Synthase. Biochemistry 2009; 48:9921-31. [DOI: 10.1021/bi901358j] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M. Qaiser Fatmi
- Department of Chemistry, University of California, Riverside, California 92521
| | - Rizi Ai
- Department of Chemistry, University of California, Riverside, California 92521
| | - Chia-en A. Chang
- Department of Chemistry, University of California, Riverside, California 92521
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14
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Quazi F, Aitken SM. Characterization of the S289A,D mutants of yeast cystathionine β-synthase. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2009; 1794:892-7. [DOI: 10.1016/j.bbapap.2009.02.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2008] [Revised: 02/17/2009] [Accepted: 02/18/2009] [Indexed: 10/21/2022]
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15
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Banerjee R, Zou CG. Redox regulation and reaction mechanism of human cystathionine-beta-synthase: a PLP-dependent hemesensor protein. Arch Biochem Biophys 2005; 433:144-56. [PMID: 15581573 DOI: 10.1016/j.abb.2004.08.037] [Citation(s) in RCA: 167] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2004] [Revised: 08/16/2004] [Indexed: 10/26/2022]
Abstract
Cystathionine beta-synthase in mammals lies at a pivotal crossroad in methionine metabolism directing flux toward cysteine synthesis and catabolism. The enzyme exhibits a modular organization and complex regulation. It catalyzes the beta-replacement of the hydroxyl group of serine with the thiolate of homocysteine and is unique in being the only known pyridoxal phosphate-dependent enzyme that also contains heme b as a cofactor. The heme functions as a sensor and modulates enzyme activity in response to redox change and to CO binding. Mutations in this enzyme are the single most common cause of hereditary hyperhomocysteinemia. Elucidation of the crystal structure of a truncated and highly active form of the human enzyme containing the heme- and pyridoxal phosphate binding domains has afforded a structural perspective on mechanistic and mutation analysis studies. The C-terminal regulatory domain containing two CBS motifs exerts intrasteric regulation and binds the allosteric activator, S-adenosylmethionine. Studies with mammalian cells in culture as well as with animal models have unraveled multiple layers of regulation of cystathionine beta-synthase in response to redox perturbations and reveal the important role of this enzyme in glutathione-dependent redox homestasis. This review discusses the recent advances in our understanding of the structure, mechanism, and regulation of cystathionine beta-synthase from the perspective of its physiological function, focusing on the clinically relevant human enzyme.
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Affiliation(s)
- Ruma Banerjee
- Department of Biochemistry, University of Nebraska, Lincoln, NE 68588-0664, USA.
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16
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Aitken SM, Kirsch JF. The enzymology of cystathionine biosynthesis: strategies for the control of substrate and reaction specificity. Arch Biochem Biophys 2005; 433:166-75. [PMID: 15581575 DOI: 10.1016/j.abb.2004.08.024] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2004] [Indexed: 11/29/2022]
Abstract
The ability of enzymes to catalyze specific reactions, while excluding others, is central to cellular metabolism. Control of reaction specificity is of particular importance for enzymes that employ catalytically versatile cofactors, of which pyridoxal 5'-phosphate is a prime example. Cystathionine gamma-synthase and cystathionine beta-synthase are the first enzymes in the transsulfuration and reverse transsulfuration pathways, respectively. Each of them occupies branch-point positions in amino acid metabolism and as such are subject to transcriptional and post-translational regulation. Both enzymes catalyze the pyridoxal 5'-phosphate-dependent formation of l-cystathionine; however, their substrate and reaction specificities are distinct. The mechanisms whereby these enzymes control the chemistry of the cofactor are the subject of this review.
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Affiliation(s)
- Susan M Aitken
- Department of Biology, Carleton University, Ottawa, Ontario, Canada K1S 5B6.
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Fujino A, Ose T, Yao M, Tokiwano T, Honma M, Watanabe N, Tanaka I. Structural and enzymatic properties of 1-aminocyclopropane-1-carboxylate deaminase homologue from Pyrococcus horikoshii. J Mol Biol 2004; 341:999-1013. [PMID: 15328614 DOI: 10.1016/j.jmb.2004.06.062] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2004] [Revised: 06/10/2004] [Accepted: 06/11/2004] [Indexed: 11/21/2022]
Abstract
1-Aminocyclopropane-l-carboxylate deaminase (ACCD) is a pyridoxal 5/-phosphate dependent enzyme that shows deaminase activity toward ACC, a precursor of plant hormone ethylene. ACCD from some soil bacteria has been reported to be able to break the cyclopropane ring of ACC to yield a-ketobutyrate and ammonia. We reported the crystal structure of ACCD from the yeast Hansenula saturnus in the absence/presence of substrate ACC, and proposed its ingenious reaction mechanisms. In order to study the enzyme further, we overexpressed the ACCD homologue protein (phAHP) from the fully decoded hyperthermophilic archearon, Pyrococcus horikoshii OT3. However, phAHP does not show ACCD activity at high temperature as well as at room temperature, though it has significant sequence similarity. Instead of ACCD activity, the GC-MS analysis and enzymatic method show that phAHP has deaminase activity toward L and D-serine. Here, we present the crystal structures of the native and ACC-complexed phAHP. The overall topology of the phAHP structure is very similar to that of ACCD; however, critical differences were observed around the active site. Here, the differences of enzymatic activity between phAHP and ACCD are discussed based on the structural differences of these two proteins. We suggest that the catalytic disagreement between these two enzymes comes from the difference of the residues near the pyridine ring of pyridoxal 5'-phosphate (PLP), not the difference of the catalytic residues themselves. We also propose a condition necessary in the primary sequence to have ACCD activity.
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Affiliation(s)
- Aiko Fujino
- Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan
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Ose T, Fujino A, Yao M, Watanabe N, Honma M, Tanaka I. Reaction intermediate structures of 1-aminocyclopropane-1-carboxylate deaminase: insight into PLP-dependent cyclopropane ring-opening reaction. J Biol Chem 2003; 278:41069-76. [PMID: 12882962 DOI: 10.1074/jbc.m305865200] [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 pyridoxal 5'-phosphate-dependent enzymes have been evolved to catalyze diverse substrates and to cause the reaction to vary. 1-Aminocyclopropane-1-carboxylate deaminase catalyzes the cyclopropane ring-opening reaction followed by deamination specifically. Since it was discovered in 1978, the enzyme has been widely investigated from the mechanistic and physiological viewpoints because the substrate is a precursor of the plant hormone ethylene and the enzymatic reaction includes a cyclopropane ring-opening. We have previously reported the crystal structure of the native enzyme. Here we report the crystal structures of the two reaction intermediates created by the mutagenesis complexed with the substrate. The substrate was validated in the active site of two forms: 1). covalent-bonded external aldimine with the coenzyme in the K51T form and 2). the non-covalent interaction around the coenzyme in the Y295F form. The orientations of the substrate in both structures were quite different form each other. In concert with other site-specific mutation experiments, this experiment revealed the ingenious and unique strategies that are used to achieve the specific activity. The substrate incorporated into the active site is reactivated by a two-phenol charge relay system to lead to the formation of a Schiff base with the coenzyme. The catalytic Lys51 residue may play a novel role to abstract the methylene proton from the substrate in cooperation with other factors, the carboxylate group of the substrate and the electron-adjusting apparatuses of the coenzyme.
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Affiliation(s)
- Toyoyuki Ose
- Division of Biological Science, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
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19
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Cook PF. Alpha,beta-elimination reaction of O-acetylserine sulfhydrylase. Is the pyridine ring required? BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1647:66-9. [PMID: 12686110 DOI: 10.1016/s1570-9639(03)00052-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
O-Acetylserine sulfhydrylase (OASS) catalyzes the elimination of acetate from O-acetyl-L-serine (OAS) followed by addition of bisulfide to give L-cysteine. Site-directed mutagenesis has been used to replace the active site serine, S272, which forms a hydrogen bond to N1 of pyridoxal 5'-phosphate (PLP) with alanine and aspartate. Based on UV-visible spectral and steady-state kinetic studies, both mutant enzymes catalyze the elimination reaction with an efficiency equal to that of the wild-type enzyme. Data are consistent with an anti-E(2) reaction proposed for the elimination reaction.
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Affiliation(s)
- Paul F Cook
- Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, OK 73019, USA.
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Mehta PK, Christen P. The molecular evolution of pyridoxal-5'-phosphate-dependent enzymes. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2000; 74:129-84. [PMID: 10800595 DOI: 10.1002/9780470123201.ch4] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The pyridoxal-5-phosphate-dependent enzymes (B6 enzymes) that act on amino acid substrates are of multiple evolutionary origin. The numerous common mechanistic features of B6 enzymes thus are not historical traits passed on from a common ancestor enzyme but rather reflect evolutionary or chemical necessities. Family profile analysis of amino acid sequences supported by comparison of the available three-dimensional (3-D) crystal structures indicates that the B6 enzymes known to date belong to four independent evolutionary lineages of homologous (or more precisely paralogous) proteins, of which the alpha family is by far the largest. The alpha family (with aspartate aminotransferase as the prototype enzyme) includes enzymes that catalyze, with several exceptions, transformations of amino acids in which the covalency changes are limited to the same carbon atom that carries the amino group forming the imine linkage with the coenzyme (i.e., Calpha in most cases). Enzymes of the beta family (tryptophan synthase beta as the prototype enzyme) mainly catalyze replacement and elimination reactions at Cbeta. The D-alanine aminotransferase family and the alanine racemase family are the two other independent lineages, both with relatively few member enzymes. The primordial pyridoxal-5-phosphate-dependent enzymes apparently were regio-specific catalysts that first diverged into reaction-specific enzymes and then specialized for substrate specificity. Aminotransferases as well as amino acid decarboxylases are found in two different evolutionary lineages. Comparison of sequences from eukaryotic, archebacterial, and eubacterial species indicates that the functional specialization of most B6 enzymes has occurred already in the universal ancestor cell. The cofactor pyridoxal-5-phosphate must have emerged very early in biological evolution; conceivably, organic cofactors and metal ions were the first biological catalysts. In attempts to stimulate particular steps of molecular evolution, oligonucleotide-directed mutagenesis of active-site residues and directed molecular evolution have been applied to change both the substrate and reaction specificity of existent B6 enzymes. Pyridoxal-5-phosphate-dependent catalytic antibodies were elicited with a screening protocol that applied functional selection criteria as they might have been operative in the evolution of protein-assisted pyridoxal catalysis.
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Affiliation(s)
- P K Mehta
- Biochemisches Institut, Universität Zürich, Switzerland
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Ro HS, Miles EW. Structure and function of the tryptophan synthase alpha(2)beta(2) complex. Roles of beta subunit histidine 86. J Biol Chem 1999; 274:36439-45. [PMID: 10593940 DOI: 10.1074/jbc.274.51.36439] [Citation(s) in RCA: 5] [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
To probe the structural and functional roles of active-site residues in the tryptophan synthase alpha(2)beta(2) complex from Salmonella typhimurium, we have determined the effects of mutation of His(86) in the beta subunit. His(86) is located adjacent to beta subunit Lys(87), which forms an internal aldimine with the pyridoxal phosphate and catalyzes the abstraction of the alpha-proton of L-serine. The replacement of His(86) by leucine (H86L) weakened pyridoxal phosphate binding approximately 20-fold and abolished the circular dichroism signals of the bound coenzyme and of a reaction intermediate. Correlation of these results with previous crystal structures indicates that beta-His(86) plays a structural role in binding pyridoxal phosphate and in stabilizing the correct orientation of pyridoxal phosphate in the active site of the beta subunit. The H86L mutation also altered the pH profiles of absorbance and fluorescence signals and shifted the pH optimum for the synthesis of L-tryptophan from pH 7.5 to 8.8. We propose that the interaction of His(86) with the phosphate of pyridoxal phosphate and with Lys(87) lowers the pK(a) of Lys(87) in the wild-type alpha(2)beta(2) complex and thereby facilitates catalysis by Lys(87) in the physiological pH range.
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Affiliation(s)
- H S Ro
- Laboratory of Biochemistry and Genetics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0830, USA
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