1
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Han SW, Jang Y, Kook J, Jang J, Shin JS. Reprogramming biocatalytic futile cycles through computational engineering of stereochemical promiscuity to create an amine racemase. Nat Commun 2024; 15:49. [PMID: 38169460 PMCID: PMC10761954 DOI: 10.1038/s41467-023-44218-7] [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: 05/22/2023] [Accepted: 12/05/2023] [Indexed: 01/05/2024] Open
Abstract
Repurposing the intrinsic properties of natural enzymes can offer a viable solution to current synthetic challenges through the development of novel biocatalytic processes. Although amino acid racemases are ubiquitous in living organisms, an amine racemase (AR) has not yet been discovered despite its synthetic potential for producing chiral amines. Here, we report the creation of an AR based on the serendipitous discovery that amine transaminases (ATAs) can perform stereoinversion of 2-aminobutane. Kinetic modeling revealed that the unexpected off-pathway activity results from stereochemically promiscuous futile cycles due to incomplete stereoselectivity for 2-aminobutane. This finding motivated us to engineer an S-selective ATA through in silico alanine scanning and empirical combinatorial mutations, creating an AR with broad substrate specificity. The resulting AR, carrying double point mutations, enables the racemization of both enantiomers of diverse chiral amines in the presence of a cognate ketone. This strategy may be generally applicable to a wide range of transaminases, paving the way for the development of new-to-nature racemases.
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Affiliation(s)
- Sang-Woo Han
- Department of Biotechnology, Yonsei University, 50 Yonsei-Ro, Seodaemun-Gu, Seoul, 03722, South Korea
- Department of Biotechnology, Konkuk University, Chungju, South Korea
| | - Youngho Jang
- Department of Biotechnology, Yonsei University, 50 Yonsei-Ro, Seodaemun-Gu, Seoul, 03722, South Korea
| | - Jihyun Kook
- Department of Biotechnology, Yonsei University, 50 Yonsei-Ro, Seodaemun-Gu, Seoul, 03722, South Korea
| | - Jeesu Jang
- Department of Biotechnology, Yonsei University, 50 Yonsei-Ro, Seodaemun-Gu, Seoul, 03722, South Korea
| | - Jong-Shik Shin
- Department of Biotechnology, Yonsei University, 50 Yonsei-Ro, Seodaemun-Gu, Seoul, 03722, South Korea.
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2
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Gao Y, Yang X, Hua L, Wang M, Ge Q, Wang W, Wang N, Ma J, Ge H. Crystal structure of an aspartate aminotransferase Lpg0070 from Legionella pneumophila. Biochem Biophys Res Commun 2023; 689:149230. [PMID: 37984176 DOI: 10.1016/j.bbrc.2023.149230] [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: 10/27/2023] [Revised: 11/01/2023] [Accepted: 11/06/2023] [Indexed: 11/22/2023]
Abstract
Legionella pneumophila aspartate aminotransferase (Lpg0070) is a member of the transaminase and belongs to the pyridoxal 5'-phosphate (PLP)-dependent superfamily. It is responsible for the transfer of α-amino between aspartate and α-ketoglutarate to form glutamate and oxaloacetate. Here, we report the crystal structure of Lpg0070 at the resolution of 2.14 Å and 1.7 Å, in apo-form and PLP-bound, respectively. Our structural analysis revealed the specific residues involved in the PLP binding and free form against PLP-bound supported conformational changes before substrate recognition. In vitro enzyme activity proves that the absence of the N-terminal arm reduces the enzyme activity of Lpg0070. These data provide further evidence to support the N-terminal arm plays a crucial role in catalytic activity.
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Affiliation(s)
- Yongshan Gao
- Institutes of Material Science and Information Technology, Anhui University, Hefei, 230601, China; School of Resources and Environmental Engineering, Anhui University, Hefei, 230601, China
| | - Xiaowen Yang
- Institutes of Material Science and Information Technology, Anhui University, Hefei, 230601, China
| | - Lan Hua
- Institutes of Material Science and Information Technology, Anhui University, Hefei, 230601, China
| | - Min Wang
- Institutes of Material Science and Information Technology, Anhui University, Hefei, 230601, China
| | - Qing Ge
- Institutes of Material Science and Information Technology, Anhui University, Hefei, 230601, China
| | - Weiqiang Wang
- Institutes of Material Science and Information Technology, Anhui University, Hefei, 230601, China
| | - Na Wang
- Institutes of Material Science and Information Technology, Anhui University, Hefei, 230601, China
| | - Jinming Ma
- Institutes of Material Science and Information Technology, Anhui University, Hefei, 230601, China.
| | - Honghua Ge
- Institutes of Material Science and Information Technology, Anhui University, Hefei, 230601, China.
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3
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Choi M, Rhee S. Structural and biochemical basis for the substrate specificity of Pad-1, an indole-3-pyruvic acid aminotransferase in auxin homeostasis. J Struct Biol 2022; 214:107857. [PMID: 35395410 DOI: 10.1016/j.jsb.2022.107857] [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: 12/17/2021] [Revised: 02/15/2022] [Accepted: 04/01/2022] [Indexed: 11/18/2022]
Abstract
Phytohormone indole-3-acetic acid (IAA) plays a vital role in regulating plant growth and development. Tryptophan-dependent IAA biosynthesis participates in IAA homeostasis by producing IAA via two sequential reactions, which involve a conversion of tryptophan to indole-3-pyruvic acid (IPyA) by tryptophan aminotransferase (TAA1) followed by the irreversible formation of IAA in the second reaction. Pad-1 from Solanaceae plants regulates IAA levels by catalyzing a reverse reaction of the first step of IAA biosynthesis. Pad-1 is a pyridoxal phosphate (PLP)-dependent aminotransferase, with IPyA as the amino acceptor and l-glutamine as the amino donor. Currently, the structural and functional basis for the substrate specificity of Pad-1 remains poorly understood. In this study, we carried out structural and kinetic analyses of Pad-1 from Solanum melongena. Pad-1 is a homodimeric enzyme, with coenzyme PLP present between a central large α/β domain and a protruding small domain. The active site of Pad-1 includes a vacancy near the phosphate group (P-side) and the 3'-O (O-side) of PLP. These features are distinct from those of TAA1, which is homologous in an overall structure with Pad-1 but includes only the P-side region in the active site. Kinetic analysis suggests that P-side residues constitute a binding pocket for l-glutamine, and O-side residues of Phe124 and Ile350 are involved in the binding of IPyA. These studies illuminate distinct differences in the active site between Pad-1 and TAA1, and provide structural and functional insights into the substrate specificity of Pad-1.
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Affiliation(s)
- Minyoung Choi
- Department of Agricultural Biotechnology, Seoul National University, Seoul, Republic of Korea
| | - Sangkee Rhee
- Department of Agricultural Biotechnology, Seoul National University, Seoul, Republic of Korea; Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul, Republic of Korea.
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4
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Dutta Banik S, Bankura A, Chandra A. A QM/MM simulation study of transamination reaction at the active site of aspartate aminotransferase: Free energy landscape and proton transfer pathways. J Comput Chem 2020; 41:2684-2694. [PMID: 32932551 DOI: 10.1002/jcc.26422] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Revised: 08/08/2020] [Accepted: 09/03/2020] [Indexed: 11/10/2022]
Abstract
Transaminase is a key enzyme for amino acid metabolism, which reversibly catalyzes the transamination reaction with the help of PLP (pyridoxal 5' -phosphate) as its cofactor. Here we have investigated the mechanism and free energy landscape of the transamination reaction involving the aspartate transaminase (AspTase) enzyme and aspartate-PLP (Asp-PLP) complex using QM/MM simulation and metadynamics methods. The reaction is found to follow a stepwise mechanism where the active site residue Lys258 acts as a base to shuttle a proton from α-carbon (CA) to imine carbon (C4A) of the PLP-Asp Schiff base. In the first step, the Lys258 abstracts the CA proton of the substrate leading to the formation of a carbanionic intermediate which is followed by the reprotonation of the Asp-PLP Schiff base at C4A atom by Lys258. It is found that the free energy barrier for the proton abstraction by Lys258 and that for the reprotonation are 17.85 and 3.57 kcal/mol, respectively. The carbanionic intermediate is 7.14 kcal/mol higher in energy than the reactant. Hence, the first step acts as the rate limiting step. The present calculations also show that the Lys258 residue undergoes a conformational change after the first step of transamination reaction and becomes proximal to C4A atom of the Asp-PLP Schiff base to favor the second step. The active site residues Tyr70* and Gly38 anchor the Lys258 in proper position and orientation during the first step of the reaction and stabilize the positive charge over Lys258 generated at the intermediate step.
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Affiliation(s)
- Sindrila Dutta Banik
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh, India
| | - Arindam Bankura
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh, India
| | - Amalendu Chandra
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh, India
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5
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Jeong SY, Jin H, Chang JH. Crystal structure of L-aspartate aminotransferase from Schizosaccharomyces pombe. PLoS One 2019; 14:e0221975. [PMID: 31465495 PMCID: PMC6715241 DOI: 10.1371/journal.pone.0221975] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2019] [Accepted: 08/18/2019] [Indexed: 01/01/2023] Open
Abstract
L-aspartate aminotransferase is a pyridoxal 5'-phosphate-dependent transaminase that catalyzes reversible transfer of an α-amino group from aspartate to α-ketoglutarate or from glutamate to oxaloacetate. L-aspartate aminotransferase not only mediates amino acid and carbohydrate metabolism but also regulates the cellular level of amino acids by catalyzing amino acid degradation and biosynthesis. To expand our structural information, we determined the crystal structure of L-aspartate aminotransferase from Schizosaccharomyces pombe at 2.1 Å resolution. A structural comparison between two yeast L-aspartate aminotransferases revealed conserved enzymatic mechanism mediated by the open-closed conformational change. Compared with higher eukaryotic species, L-aspartate aminotransferases showed distinguishable inter-subunit interaction between the N-terminal arm and a large domain of the opposite subunit. Interestingly, structural homology search showed varied conformation of the N-terminal arm among 71 structures of the family. Therefore, we classified pyridoxal 5'-phosphate-dependent enzymes into eight subclasses based on the structural feature of N-terminal arms. In addition, structure and sequence comparisons showed strong relationships among the eight subclasses. Our results may provide insights into structure-based evolutionary aspects of pyridoxal 5'-phosphate-dependent enzymes.
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Affiliation(s)
- Soo Yeon Jeong
- Department of Biology Education, Kyungpook National University, Daegu, Republic of Korea
| | - Hyeonseok Jin
- Research Institute for Phylogenomics and Evolution, Kyungpook National University, Daegu, Republic of Korea
- * E-mail: (HJ); (JHC)
| | - Jeong Ho Chang
- Department of Biology Education, Kyungpook National University, Daegu, Republic of Korea
- Research Institute for Phylogenomics and Evolution, Kyungpook National University, Daegu, Republic of Korea
- * E-mail: (HJ); (JHC)
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6
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Cui X, Yu X, Cai W, Shao X. Water as a probe for serum-based diagnosis by temperature- dependent near-infrared spectroscopy. Talanta 2019; 204:359-366. [PMID: 31357305 DOI: 10.1016/j.talanta.2019.06.026] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Revised: 06/03/2019] [Accepted: 06/08/2019] [Indexed: 12/19/2022]
Abstract
Diagnosis based on the compositional variation of biological liquids such as serum has drawn much attention. For exploring the potential diagnostic information from serum samples, temperature-dependent near-infrared (NIR) spectroscopy was developed to obtain the spectral change of water reflecting the interactions in serum solution, and chemometric methods were employed to mine the information from the temperature-dependent NIR spectra. The spectra of 68 healthy controls, 42 patients with the type II diabetes and 16 patients with coronary heart disease were measured and analyzed by chemometric calculations. Continuous wavelet transform (CWT) was used to enhance the resolution of the spectra. From the processed spectra, the information of non-hydrogen-bonded (NHB), weakly hydrogen-bonded (WHB) and strongly hydrogen-bonded (SHB) water species was observed. For explaining the variation of the spectra with temperature, two-dimensional (2D) correlation analysis was adopted. A clear difference in SHB/NHB ratio in the synchronous maps was found between the spectra of the patients and the controls. 86.8% of the controls and 98.3% of the patients can be correctly identified. Furthermore, combining the maps of the synchronous and asynchronous analysis, the correlation between SHB and WHB water species was discovered to have an ability to discriminate the patients of diabetes and heart disease with an accuracy of 83.7% and 75.0%, respectively. Therefore, water may be a probe for providing diagnostic information by temperature-dependent NIR spectroscopy.
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Affiliation(s)
- Xiaoyu Cui
- Research Center for Analytical Sciences, College of Chemistry, Nankai University, Tianjin, 300071, China
| | - Xiaoming Yu
- Laboratory of Clinic, People's Hospital of Gaomi City, Gaomi, Shandong, 261000, China
| | - Wensheng Cai
- Research Center for Analytical Sciences, College of Chemistry, Nankai University, Tianjin, 300071, China
| | - Xueguang Shao
- Research Center for Analytical Sciences, College of Chemistry, Nankai University, Tianjin, 300071, China; Tianjin Key Laboratory of Biosensing and Molecular Recognition, Tianjin, 300071, China; State Key Laboratory of Medicinal Chemical Biology, Tianjin, 300071, China.
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7
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Soniya K, Awasthi S, Nair NN, Chandra A. Transimination Reaction at the Active Site of Aspartate Aminotransferase: A Proton Hopping Mechanism through Pyridoxal 5′-Phosphate. ACS Catal 2019. [DOI: 10.1021/acscatal.9b00834] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Kumari Soniya
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India
| | - Shalini Awasthi
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India
| | - Nisanth N. Nair
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India
| | - Amalendu Chandra
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India
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8
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Montioli R, Paiardini A, Giardina G, Zanzoni S, Cutruzzola F, Cellini B, Borri Voltattorni C. R180T variant of δ-ornithine aminotransferase associated with gyrate atrophy: biochemical, computational, X-ray and NMR studies provide insight into its catalytic features. FEBS J 2019; 286:2787-2798. [PMID: 30957963 DOI: 10.1111/febs.14843] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Revised: 02/21/2019] [Accepted: 04/05/2019] [Indexed: 02/01/2023]
Abstract
Among the over 50 gyrate atrophy-causing mutations of ornithine δ-aminotransferase (OAT), the R180T involves an active site residue located at the dimer interface, which in the crystal structure of OAT complexed with 5-fluoromethylornithine engages a salt bridge with the α-carboxylate of the substrate analogue. Starting from the previous finding that no transaminase activity was detected in CHO-K1 cells expressing the R180T variant, here we try to shed light at the protein level on the structural and/or functional defects of the R180T variant. To this aim, the variant has been cloned, expressed, purified and characterized by a combination of biochemical and structural studies. Although the R180T variant shares a similar overall conformation with the wild-type, its crystal structure solved at 1.8 Ǻ reveals slight structural alterations at the active site and at the dimeric interface. These changes are consistent with the spectroscopic and kinetic results, indicating that the variant, as compared with the wild-type OAT, shows (a) an increased Km value for l-ornithine (l-Orn), (b) an altered pyridoxal 5'-phosphate binding mode and affinity and (c) an increased thermostability. In addition, the R180T mutant exhibits a remarkable loss of catalytic activity and is endowed with the ability to catalyse not only the δ-transamination but also, albeit to a lesser extent, the α-transamination of l-Orn. Overall, these data indicate that the slight structural changes caused by the R180T mutation, preventing a proper collocation of l-Orn at the active site of OAT, are responsible for the notable reduction of the catalytic efficiency. ENZYMES: Ornithine aminotransferase EC 2.6.1.13. DATABASES: 6HX7.pdb.
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Affiliation(s)
- Riccardo Montioli
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Italy
| | - Alessandro Paiardini
- Department of Biochemical Sciences "A. Rossi Fanelli", Sapienza University of Rome, Italy
| | - Giorgio Giardina
- Department of Biochemical Sciences "A. Rossi Fanelli", Sapienza University of Rome, Italy
| | - Serena Zanzoni
- Centro Piattaforme Tecnologiche, University of Verona, Italy
| | - Francesca Cutruzzola
- Department of Biochemical Sciences "A. Rossi Fanelli", Sapienza University of Rome, Italy
| | - Barbara Cellini
- Department of Experimental Medicine, University of Perugia, Italy
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9
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Michiko N, Setyawan B, Sunaba-Mitsumasu S. Enzymatic reaction sites on a plane formed with four exon-junctions. J Theor Biol 2018; 457:51-56. [PMID: 30102888 DOI: 10.1016/j.jtbi.2018.08.011] [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: 05/08/2018] [Revised: 08/02/2018] [Accepted: 08/06/2018] [Indexed: 11/19/2022]
Abstract
Understanding the interaction of an enzyme with its substrate is important for the research of protein function. However, there is still no satisfactory explanation for protein folding, in spite of the continuous efforts by many excellent researchers. We present a novel approach for analysing enzyme-substrate complexes. Previously, we showed how four exon-junctions, in a domain of enzyme and carrier protein structures, form a plane around their respective ligands. Here, we report the formation of two planes by two combinations of four exon-junctions within the large enzyme, aspartate aminotransferase. Almost all the ligand atoms are located within one plane, while the other plane contains most linker-residue atoms of the coenzyme, suggesting that the former and latter planes serve as the enzyme reaction and support areas, respectively. Simulation results revealed that two-plane formation is possible in the enzyme with four random positions; however, the relationship between the coenzyme ligating substrate and the plane is significant and is biologically important. We describe the formation of such planes around the ligand, including the ligating residue for the coenzyme with no substrate.
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Affiliation(s)
- Nosaka Michiko
- Material and Biological Engineering, National Institute of Technology, Sasebo College, Sasebo, Japan.
| | - Budi Setyawan
- Material and Biological Engineering, National Institute of Technology, Sasebo College, Sasebo, Japan
| | - Syunya Sunaba-Mitsumasu
- Material and Biological Engineering, National Institute of Technology, Sasebo College, Sasebo, Japan
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10
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Holland CK, Berkovich DA, Kohn ML, Maeda H, Jez JM. Structural basis for substrate recognition and inhibition of prephenate aminotransferase from Arabidopsis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2018; 94:304-314. [PMID: 29405514 DOI: 10.1111/tpj.13856] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Revised: 01/25/2018] [Accepted: 01/29/2018] [Indexed: 05/23/2023]
Abstract
Aromatic amino acids are protein building blocks and precursors to a number of plant natural products, such as the structural polymer lignin and a variety of medicinally relevant compounds. Plants make tyrosine and phenylalanine by a different pathway from many microbes; this pathway requires prephenate aminotransferase (PAT) as the key enzyme. Prephenate aminotransferase produces arogenate, the unique and immediate precursor for both tyrosine and phenylalanine in plants, and also has aspartate aminotransferase (AAT) activity. The molecular mechanisms governing the substrate specificity and activation or inhibition of PAT are currently unknown. Here we present the X-ray crystal structures of the wild-type and various mutants of PAT from Arabidopsis thaliana (AtPAT). Steady-state kinetic and ligand-binding analyses identified key residues, such as Glu108, that are involved in both keto acid and amino acid substrate specificities and probably contributed to the evolution of PAT activity among class Ib AAT enzymes. Structures of AtPAT mutants co-crystallized with either α-ketoglutarate or pyridoxamine 5'-phosphate and glutamate further define the molecular mechanisms underlying recognition of keto acid and amino acid substrates. Furthermore, cysteine was identified as an inhibitor of PAT from A. thaliana and Antirrhinum majus plants as well as the bacterium Chlorobium tepidum, uncovering a potential new effector of PAT.
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Affiliation(s)
- Cynthia K Holland
- Department of Biology, Washington University in St Louis, St Louis, MO, 63130, USA
| | - Daniel A Berkovich
- Department of Biology, Washington University in St Louis, St Louis, MO, 63130, USA
| | - Madeleine L Kohn
- Department of Biology, Washington University in St Louis, St Louis, MO, 63130, USA
| | - Hiroshi Maeda
- Department of Botany, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Joseph M Jez
- Department of Biology, Washington University in St Louis, St Louis, MO, 63130, USA
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11
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Ginguay A, Cynober L, Curis E, Nicolis I. Ornithine Aminotransferase, an Important Glutamate-Metabolizing Enzyme at the Crossroads of Multiple Metabolic Pathways. BIOLOGY 2017; 6:biology6010018. [PMID: 28272331 PMCID: PMC5372011 DOI: 10.3390/biology6010018] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Revised: 02/23/2017] [Accepted: 02/24/2017] [Indexed: 02/06/2023]
Abstract
Ornithine δ-aminotransferase (OAT, E.C. 2.6.1.13) catalyzes the transfer of the δ-amino group from ornithine (Orn) to α-ketoglutarate (aKG), yielding glutamate-5-semialdehyde and glutamate (Glu), and vice versa. In mammals, OAT is a mitochondrial enzyme, mainly located in the liver, intestine, brain, and kidney. In general, OAT serves to form glutamate from ornithine, with the notable exception of the intestine, where citrulline (Cit) or arginine (Arg) are end products. Its main function is to control the production of signaling molecules and mediators, such as Glu itself, Cit, GABA, and aliphatic polyamines. It is also involved in proline (Pro) synthesis. Deficiency in OAT causes gyrate atrophy, a rare but serious inherited disease, a further measure of the importance of this enzyme.
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Affiliation(s)
- Antonin Ginguay
- Clinical Chemistry, Cochin Hospital, GH HUPC, AP-HP, 75014 Paris, France.
- Laboratory of Biological Nutrition, EA 4466 PRETRAM, Faculté de Pharmacie, Université Paris Descartes, 75006 Paris, France.
| | - Luc Cynober
- Clinical Chemistry, Cochin Hospital, GH HUPC, AP-HP, 75014 Paris, France.
- Laboratory of Biological Nutrition, EA 4466 PRETRAM, Faculté de Pharmacie, Université Paris Descartes, 75006 Paris, France.
| | - Emmanuel Curis
- Laboratoire de biomathématiques, plateau iB², Faculté de Pharmacie, Université Paris Descartes, 75006 Paris, France.
- UMR 1144, INSERM, Université Paris Descartes, 75006 Paris, France.
- UMR 1144, Université Paris Descartes, 75006 Paris, France.
- Service de biostatistiques et d'informatique médicales, hôpital Saint-Louis, Assistance publique-hôpitaux de Paris, 75010 Paris, France.
| | - Ioannis Nicolis
- Laboratoire de biomathématiques, plateau iB², Faculté de Pharmacie, Université Paris Descartes, 75006 Paris, France.
- EA 4064 "Épidémiologie environnementale: Impact sanitaire des pollutions", Faculté de Pharmacie, Université Paris Descartes, 75006 Paris, France.
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12
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Bujacz A, Rutkiewicz-Krotewicz M, Nowakowska-Sapota K, Turkiewicz M. Crystal structure and enzymatic properties of a broad substrate-specificity psychrophilic aminotransferase from the Antarctic soil bacterium Psychrobacter sp. B6. ACTA ACUST UNITED AC 2015; 71:632-45. [PMID: 25760611 DOI: 10.1107/s1399004714028016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Accepted: 12/23/2014] [Indexed: 12/20/2022]
Abstract
Aminotransferases (ATs) are enzymes that are commonly used in the chemical and pharmaceutical industries for the synthesis of natural and non-natural amino acids by transamination reactions. Currently, the easily accessible enzymes from mesophilic organisms are most commonly used; however, for economical and ecological reasons the utilization of aminotransferases from psychrophiles would be more advantageous, as their optimum reaction temperature is usually significantly lower than for the mesophilic ATs. Here, gene isolation, protein expression, purification, enzymatic properties and structural studies are reported for the cold-active aromatic amino-acid aminotransferase (PsyArAT) from Psychrobacter sp. B6, a psychrotrophic, Gram-negative strain from Antarctic soil. Preliminary computational analysis indicated dual functionality of the enzyme through the ability to utilize both aromatic amino acids and aspartate as substrates. This postulation was confirmed by enzymatic activity tests, which showed that it belonged to the class EC 2.6.1.57. The first crystal structures of a psychrophilic aromatic amino-acid aminotransferase have been determined at resolutions of 2.19 Å for the native enzyme (PsyArAT) and 2.76 Å for its complex with aspartic acid (PsyArAT/D). Both types of crystals grew in the monoclinic space group P21 under slightly different crystallization conditions. The PsyArAT crystals contained a dimer (90 kDa) in the asymmetric unit, which corresponds to the active form of this enzyme, whereas the crystals of the PsyArAT/D complex included four dimers showing different stages of the transamination reaction.
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Affiliation(s)
- Anna Bujacz
- Institute of Technical Biochemistry, Lodz University of Technology, Stefanowskiego 4/10, 90-924 Lodz, Poland
| | - Maria Rutkiewicz-Krotewicz
- Institute of Technical Biochemistry, Lodz University of Technology, Stefanowskiego 4/10, 90-924 Lodz, Poland
| | - Karolina Nowakowska-Sapota
- Institute of Technical Biochemistry, Lodz University of Technology, Stefanowskiego 4/10, 90-924 Lodz, Poland
| | - Marianna Turkiewicz
- Institute of Technical Biochemistry, Lodz University of Technology, Stefanowskiego 4/10, 90-924 Lodz, Poland
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13
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Dutta Banik S, Chandra A. A Hybrid QM/MM Simulation Study of Intramolecular Proton Transfer in the Pyridoxal 5′-Phosphate in the Active Site of Transaminase: Influence of Active Site Interaction on Proton Transfer. J Phys Chem B 2014; 118:11077-89. [DOI: 10.1021/jp506196m] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
| | - Amalendu Chandra
- Department of Chemistry, Indian Institute of Technology, Kanpur, India 208016
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14
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Lee H, Juncosa JI, Silverman RB. Ornithine aminotransferase versus GABA aminotransferase: implications for the design of new anticancer drugs. Med Res Rev 2014; 35:286-305. [PMID: 25145640 DOI: 10.1002/med.21328] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Ornithine aminotransferase (OAT) and γ-aminobutyric acid aminotransferase (GABA-AT) are classified under the same evolutionary subgroup and share a large portion of structural, functional, and mechanistic features. Therefore, it is not surprising that many molecules that bind to GABA-AT also bind well to OAT. Unlike GABA-AT, OAT had not been viewed as a potential therapeutic target until recently; consequently, the number of therapeutically viable molecules that target OAT is very limited. In this review the two enzymes are compared with respect to their active-site structures, catalytic and inactivation mechanisms, and selective inhibitors. Insight is offered that could aid in the design and development of new selective inhibitors of OAT for the treatment of cancer.
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Affiliation(s)
- Hyunbeom Lee
- Center for Molecular Innovation and Drug Discovery, Department of Chemistry, Chemistry of Life Processes Institute, Northwestern University, Evanston, Illinois
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15
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Pang J, Scrutton NS, Sutcliffe MJ. Quantum Mechanics/Molecular Mechanics Studies on the Mechanism of Action of Cofactor Pyridoxal 5′-Phosphate in Ornithine 4,5-Aminomutase. Chemistry 2014; 20:11390-401. [DOI: 10.1002/chem.201402759] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Indexed: 02/02/2023]
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16
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Peña-Soler E, Fernandez FJ, López-Estepa M, Garces F, Richardson AJ, Quintana JF, Rudd KE, Coll M, Vega MC. Structural analysis and mutant growth properties reveal distinctive enzymatic and cellular roles for the three major L-alanine transaminases of Escherichia coli. PLoS One 2014; 9:e102139. [PMID: 25014014 PMCID: PMC4094517 DOI: 10.1371/journal.pone.0102139] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Accepted: 06/13/2014] [Indexed: 12/17/2022] Open
Abstract
In order to maintain proper cellular function, the metabolism of the bacterial microbiota presents several mechanisms oriented to keep a correctly balanced amino acid pool. Central components of these mechanisms are enzymes with alanine transaminase activity, pyridoxal 5′-phosphate-dependent enzymes that interconvert alanine and pyruvate, thereby allowing the precise control of alanine and glutamate concentrations, two of the most abundant amino acids in the cellular amino acid pool. Here we report the 2.11-Å crystal structure of full-length AlaA from the model organism Escherichia coli, a major bacterial alanine aminotransferase, and compare its overall structure and active site composition with detailed atomic models of two other bacterial enzymes capable of catalyzing this reaction in vivo, AlaC and valine-pyruvate aminotransferase (AvtA). Apart from a narrow entry channel to the active site, a feature of this new crystal structure is the role of an active site loop that closes in upon binding of substrate-mimicking molecules, and which has only been previously reported in a plant enzyme. Comparison of the available structures indicates that beyond superficial differences, alanine aminotransferases of diverse phylogenetic origins share a universal reaction mechanism that depends on an array of highly conserved amino acid residues and is similarly regulated by various unrelated motifs. Despite this unifying mechanism and regulation, growth competition experiments demonstrate that AlaA, AlaC and AvtA are not freely exchangeable in vivo, suggesting that their functional repertoire is not completely redundant thus providing an explanation for their independent evolutionary conservation.
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Affiliation(s)
- Esther Peña-Soler
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (Spanish National Research Council, CSIC), Madrid, Spain
- Institute for Research in Biomedicine (IRB Barcelona), Barcelona, Spain
| | - Francisco J. Fernandez
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (Spanish National Research Council, CSIC), Madrid, Spain
| | - Miguel López-Estepa
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (Spanish National Research Council, CSIC), Madrid, Spain
| | - Fernando Garces
- The Scripps Research Institute, La Jolla, California, United States of America
| | - Andrew J. Richardson
- University of Miami Miller School of Medicine, Miami, Florida, United States of America
| | - Juan F. Quintana
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (Spanish National Research Council, CSIC), Madrid, Spain
| | - Kenneth E. Rudd
- University of Miami Miller School of Medicine, Miami, Florida, United States of America
| | - Miquel Coll
- Institute for Research in Biomedicine (IRB Barcelona), Barcelona, Spain
- Institut de Biologia Molecular de Barcelona (IBMB-CSIC), Barcelona, Spain
| | - M. Cristina Vega
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (Spanish National Research Council, CSIC), Madrid, Spain
- * E-mail:
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17
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Chan-Huot M, Dos A, Zander R, Sharif S, Tolstoy PM, Compton S, Fogle E, Toney MD, Shenderovich I, Denisov GS, Limbach HH. NMR Studies of Protonation and Hydrogen Bond States of Internal Aldimines of Pyridoxal 5′-Phosphate Acid–Base in Alanine Racemase, Aspartate Aminotransferase, and Poly-l-lysine. J Am Chem Soc 2013; 135:18160-75. [DOI: 10.1021/ja408988z] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Monique Chan-Huot
- Institut
für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany
- Ecole Normale Supérieure, Laboratoire des BioMolécules, 24 rue Lhomond, 75231 Cedex 05, Paris, France
| | - Alexandra Dos
- Institut
für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany
| | - Reinhard Zander
- Institut
für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany
| | - Shasad Sharif
- Institut
für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany
| | - Peter M. Tolstoy
- Institut
für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany
- Department
of Chemistry, St. Petersburg State University, Universitetskij pr. 26, 198504 St. Petersburg, Russian Federation
| | - Shara Compton
- Department
of Chemistry, University of California—Davis, One Shields Avenue, Davis, California 95616, United States
- Department
of Chemistry, Widener University, One University Place, Chester, Pennsylvania 19013, United States
| | - Emily Fogle
- Department
of Chemistry, University of California—Davis, One Shields Avenue, Davis, California 95616, United States
- Department of Chemistry & Biochemistry, CalPoly, San Luis Obispo, California 93407, United States
| | - Michael D. Toney
- Department
of Chemistry, University of California—Davis, One Shields Avenue, Davis, California 95616, United States
| | - Ilya Shenderovich
- Institut
für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany
- University of Regensburg, Universitätsstr.
31, 93040 Regensburg, Germany
| | - Gleb S. Denisov
- Institute
of Physics, St. Petersburg State University, 198504 St. Petersburg, Russian Federation
| | - Hans-Heinrich Limbach
- Institut
für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany
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18
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Toney MD. Aspartate aminotransferase: an old dog teaches new tricks. Arch Biochem Biophys 2013; 544:119-27. [PMID: 24121043 DOI: 10.1016/j.abb.2013.10.002] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Revised: 09/28/2013] [Accepted: 10/01/2013] [Indexed: 11/29/2022]
Abstract
Aspartate aminotransferase (AAT) is a prototypical pyridoxal 5'-phosphate (PLP) dependent enzyme that catalyzes the reversible interconversion of l-aspartate and α-ketoglutarate with oxalacetate and l-glutamate via a ping-pong catalytic cycle in which the pyridoxamine 5'-phosphate enzyme form is an intermediate. There is a bountiful literature on AAT that spans approximately 60years, and much fundamental mechanistic information on PLP dependent reactions has been gained from its study. Here, we review our recent work on AAT, where we again used it as a test bed for fundamental concepts in PLP chemistry. First, we discuss the role that coenzyme protonation state plays in controlling reaction specificity, then ground state destabilization via hyperconjugation in the external aldimine intermediate is examined. The third topic is light enhancement of catalysis of Cα-H deprotonation by PLP in solution and in AAT, which occurs through a triplet state of the external aldimine intermediate. Lastly, we consider recent advances in our analyses of enzyme multiple sequence alignments for the purpose of predicting mutations that are required to interconvert structurally similar but catalytically distinct enzymes, and the application of our program JANUS to the conversion of AAT into tyrosine aminotransferase.
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Affiliation(s)
- Michael D Toney
- Department of Chemistry, University of California, Davis, Davis, CA 95616, USA.
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19
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Walton CJ, Chica RA. A high-throughput assay for screening l- or d-amino acid specific aminotransferase mutant libraries. Anal Biochem 2013; 441:190-8. [DOI: 10.1016/j.ab.2013.07.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Revised: 06/29/2013] [Accepted: 07/02/2013] [Indexed: 10/26/2022]
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20
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Hammes GG, Benkovic SJ, Hammes-Schiffer S. Flexibility, diversity, and cooperativity: pillars of enzyme catalysis. Biochemistry 2011; 50:10422-30. [PMID: 22029278 PMCID: PMC3226911 DOI: 10.1021/bi201486f] [Citation(s) in RCA: 205] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This brief review discusses our current understanding of the molecular basis of enzyme catalysis. A historical development is presented, beginning with steady state kinetics and progressing through modern fast reaction methods, nuclear magnetic resonance, and single-molecule fluorescence techniques. Experimental results are summarized for ribonuclease, aspartate aminotransferase, and especially dihydrofolate reductase (DHFR). Multiple intermediates, multiple conformations, and cooperative conformational changes are shown to be an essential part of virtually all enzyme mechanisms. In the case of DHFR, theoretical investigations have provided detailed information about the movement of atoms within the enzyme-substrate complex as the reaction proceeds along the collective reaction coordinate for hydride transfer. A general mechanism is presented for enzyme catalysis that includes multiple intermediates and a complex, multidimensional standard free energy surface. Protein flexibility, diverse protein conformations, and cooperative conformational changes are important features of this model.
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Affiliation(s)
- Gordon G. Hammes
- Department of Biochemistry, Box 3711, Duke University, Durham, NC 27710
| | - Stephen J. Benkovic
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
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21
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Singh S, Banerjee R. PLP-dependent H(2)S biogenesis. BIOCHIMICA ET BIOPHYSICA ACTA 2011; 1814:1518-27. [PMID: 21315854 PMCID: PMC3193879 DOI: 10.1016/j.bbapap.2011.02.004] [Citation(s) in RCA: 141] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2010] [Revised: 01/11/2011] [Accepted: 02/01/2011] [Indexed: 12/15/2022]
Abstract
The role of endogenously produced H(2)S in mediating varied physiological effects in mammals has spurred enormous recent interest in understanding its biology and in exploiting its pharmacological potential. In these early days in the field of H(2)S signaling, large gaps exist in our understanding of its biological targets, its mechanisms of action and the regulation of its biogenesis and its clearance. Two branches within the sulfur metabolic pathway contribute to H(2)S production: (i) the reverse transsulfuration pathway in which two pyridoxal 5'-phosphate-dependent (PLP) enzymes, cystathionine β-synthase and cystathionine γ-lyase convert homocysteine successively to cystathionine and cysteine and (ii) a branch of the cysteine catabolic pathway which converts cysteine to mercaptopyruvate via a PLP-dependent cysteine aminotransferase and subsequently, to mercaptopyruvate sulfur transferase-bound persulfide from which H(2)S can be liberated. In this review, we present an overview of the kinetics of the H(2)S-generating reactions, compare the structures of the PLP-enzymes involved in its biogenesis and discuss strategies for their regulation. This article is part of a Special Issue entitled: Pyridoxal Phospate Enzymology.
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Affiliation(s)
- Sangita Singh
- Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109-5606
| | - Ruma Banerjee
- Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109-5606
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22
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Limbach HH, Chan-Huot M, Sharif S, Tolstoy PM, Shenderovich IG, Denisov GS, Toney MD. Critical hydrogen bonds and protonation states of pyridoxal 5'-phosphate revealed by NMR. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1814:1426-37. [PMID: 21703367 DOI: 10.1016/j.bbapap.2011.06.004] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 06/04/2011] [Accepted: 06/07/2011] [Indexed: 12/01/2022]
Abstract
In this contribution we review recent NMR studies of protonation and hydrogen bond states of pyridoxal 5'-phosphate (PLP) and PLP model Schiff bases in different environments, starting from aqueous solution, the organic solid state to polar organic solution and finally to enzyme environments. We have established hydrogen bond correlations that allow one to estimate hydrogen bond geometries from (15)N chemical shifts. It is shown that protonation of the pyridine ring of PLP in aspartate aminotransferase (AspAT) is achieved by (i) an intermolecular OHN hydrogen bond with an aspartate residue, assisted by the imidazole group of a histidine side chain and (ii) a local polarity as found for related model systems in a polar organic solvent exhibiting a dielectric constant of about 30. Model studies indicate that protonation of the pyridine ring of PLP leads to a dominance of the ketoenamine form, where the intramolecular OHN hydrogen bond of PLP exhibits a zwitterionic state. Thus, the PLP moiety in AspAT carries a net positive charge considered as a pre-requisite to initiate the enzyme reaction. However, it is shown that the ketoenamine form dominates in the absence of ring protonation when PLP is solvated by polar groups such as water. Finally, the differences between acid-base interactions in aqueous solution and in the interior of proteins are discussed. This article is part of a special issue entitled: Pyridoxal Phosphate Enzymology.
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Affiliation(s)
- Hans-Heinrich Limbach
- Institut für Chemie und Biochemie, Freie Universität Berlin, Takustraβe 3, D-14195, Germany.
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23
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Wrenger C, Müller IB, Schifferdecker AJ, Jain R, Jordanova R, Groves MR. Specific inhibition of the aspartate aminotransferase of Plasmodium falciparum. J Mol Biol 2010; 405:956-71. [PMID: 21087616 DOI: 10.1016/j.jmb.2010.11.018] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2010] [Revised: 11/05/2010] [Accepted: 11/09/2010] [Indexed: 10/18/2022]
Abstract
Aspartate aminotransferases (AspATs; EC 2.6.1.1) catalyze the conversion of aspartate and α-ketoglutarate into oxaloacetate and glutamate and are key enzymes in the nitrogen metabolism of all organisms. Recent findings suggest that the plasmodial enzyme [Plasmodium falciparum aspartate aminotransferase (PfAspAT)] may also play a pivotal role in energy metabolism and in the de novo biosynthesis of pyrimidines. However, while PfAspAT is a potential drug target, the high homology between the active sites of currently available AspAT structures hinders the development of specific inhibitors of these enzymes. In this article, we report the X-ray structure of the PfAspAT homodimer at a resolution of 2.8 Å. While the overall fold is similar to the currently available structures of other AspATs, the structure presented shows a significant divergence in the conformation of the N-terminal residues. Deletion of these divergent PfAspAT N-terminal residues results in a loss of activity for the recombinant protein, and addition of a peptide containing these 13 N-terminal residues results in inhibition both in vitro and in a lysate isolated from cultured parasites, while the activity of human cytosolic AspAT is unaffected. The finding that the divergent N-terminal amino acids of PfAspAT play a role in catalytic activity indicates that specific inhibition of the enzyme may provide a lead for the development of novel compounds in the treatment of malaria. We also report on the localization of PfAspAT to the parasite cytosol and discuss the implications of the role of PfAspAT in the supply of malate to the parasite mitochondria.
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Affiliation(s)
- Carsten Wrenger
- Department of Biochemistry, Bernhard Nocht Institute for Tropical Medicine, Bernhard Nocht Strasse 74, D-20359 Hamburg, Germany
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24
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Andréll J, Hicks MG, Palmer T, Carpenter EP, Iwata S, Maher MJ. Crystal Structure of the Acid-Induced Arginine Decarboxylase from Escherichia coli: Reversible Decamer Assembly Controls Enzyme Activity. Biochemistry 2009; 48:3915-27. [DOI: 10.1021/bi900075d] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Juni Andréll
- Division of Molecular Biosciences, Imperial College, London SW7 2AZ, U.K
| | | | | | | | - So Iwata
- Division of Molecular Biosciences, Imperial College, London SW7 2AZ, U.K
| | - Megan J. Maher
- Division of Molecular Biosciences, Imperial College, London SW7 2AZ, U.K
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25
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Cook PD, Holden HM. A structural study of GDP-4-keto-6-deoxy-D-mannose-3-dehydratase: caught in the act of geminal diamine formation. Biochemistry 2007; 46:14215-24. [PMID: 17997582 DOI: 10.1021/bi701686s] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Di- and trideoxysugars are an important class of carbohydrates synthesized by certain plants, fungi, and bacteria. Colitose, for example, is a 3,6-dideoxysugar found in the O-antigens of Gram-negative bacteria such as Escherichia coli, Salmonella enterica, Yersinia pseudotuberculosis, and Vibrio cholerae, among others. These types of dideoxysugars are thought to serve as antigenic determinants and to play key roles in bacterial defense and survival. Four enzymes are required for the biochemical synthesis of colitose starting from mannose-1-phosphate. The focus of this investigation, GDP-4-keto-6-deoxy-d-mannose-3-dehydratase (ColD), catalyzes the third step in the pathway, namely the PLP-dependent removal of the C3'-hydroxyl group from GDP-4-keto-6-deoxymannose. Whereas most PLP-dependent enzymes contain an active site lysine, ColD utilizes a histidine as its catalytic acid/base. The ping-pong mechanism of the enzyme first involves the conversion of PLP to PMP followed by the dehydration step. Here we present the three-dimensional structure of a site-directed mutant form of ColD whereby the active site histidine has been replaced with a lysine. The electron density reveals that the geminal diamine, a tetrahedral intermediate in the formation of PMP from PLP, has been trapped within the active site region. Functional assays further demonstrate that this mutant form of ColD cannot catalyze the dehydration reaction.
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Affiliation(s)
- Paul D Cook
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
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26
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Sharif S, Denisov GS, Toney MD, Limbach HH. NMR studies of coupled low- and high-barrier hydrogen bonds in pyridoxal-5'-phosphate model systems in polar solution. J Am Chem Soc 2007; 129:6313-27. [PMID: 17455937 DOI: 10.1021/ja070296+] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The 1H and 15N NMR spectra of several 15N-labeled pyridoxal-5'-phosphate model systems have been measured at low temperature in various aprotic and protic solvents of different polarity, i.e., dichloromethane-d2, acetonitrile-d3, tetrahydrofuran-d8, freon mixture CDF3/CDClF2, and methanol. In particular, the 15N-labeled 5'-triisopropyl-silyl ether of N-(pyridoxylidene)-tolylamine (1a), N-(pyridoxylidene)-methylamine (2a), and the Schiff base with 15N-2-methylaspartic acid (3a) and their complexes with proton donors such as triphenylmethanol, phenol, and carboxylic acids of increasing strength were studied. With the use of hydrogen bond correlation techniques, the 1H/15N chemical shift and scalar coupling data could be associated with the geometries of the intermolecular O1H1N1 (pyridine nitrogen) and the intramolecular O2H2N2 (Schiff base) hydrogen bonds. Whereas O1H1N1 is characterized by a series of asymmetric low-barrier hydrogen bonds, the proton in O2H2N2 faces a barrier for proton transfer of medium height. When the substituent on the Schiff base nitrogen is an aromatic ring, the shift of the proton in O1H1N1 from oxygen to nitrogen has little effect on the position of the proton in the O2H2N2 hydrogen bond. By contrast, when the substituent on the Schiff base nitrogen is a methyl group, a proton shift from O to N in O1H1N1 drives the tautomeric equilibrium in O2H2N2 from the neutral O2-H2...N2 to the zwitterionic O2-...H2-N(2+) form. This coupling is lost in aqueous solution where the intramolecular O2H2N2 hydrogen bond is broken by solute-solvent interactions. However, in methanol, which mimics hydrogen bonds to the Schiff base in the enzyme active site, the coupling is preserved. Therefore, the reactivity of Schiff base intermediates in pyridoxal-5'-phosphate enzymes can likely be tuned to the requirements of the reaction being catalyzed by differential protonation of the pyridine nitrogen.
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Affiliation(s)
- Shasad Sharif
- Institut für Chemie und Biochemie, Takustrasse 3, Freie Universität Berlin, D-14195 Berlin, Germany
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27
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Sharif S, Huot MC, Tolstoy PM, Toney MD, Jonsson KHM, Limbach HH. 15N nuclear magnetic resonance studies of acid-base properties of pyridoxal-5'-phosphate aldimines in aqueous solution. J Phys Chem B 2007; 111:3869-76. [PMID: 17388551 DOI: 10.1021/jp067334g] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
By use of 15N NMR spectroscopy, we have measured the pKa values of the aldimines 15N-(pyridoxyl-5'-phosphate-idine)-methylamine (2a), N-(pyridoxyl-5'-phosphate-15N-idine)-methylamine (2b), and 15N-(pyridoxyl-idine)-methylamine (3). These aldimines model the cofactor pyridoxal-5'-phosphate (PLP, 1) in a variety of PLP-dependent enzymes. The acid-base properties of the aldimines differ substantially from those of the free cofactor in the aldehyde form 1a or in the hydrated form 1b, which were also investigated using 15N NMR for comparison. All compounds contain three protonation sites, the pyridine ring, the phenol group, and the side chain phosphate (1, 2) or hydroxyl group (3). In agreement with the literature, 1a exhibits one of several pKas at 2.9 and 1b at 4.2. The 15N chemical shifts indicate that the corresponding deprotonation occurs partially in the pyridine and partially in the phenolic site, which compete for the remaining proton. The equilibrium constant of this ring-phenolate tautomerism was measured to be 0.40 for 1a and 0.06 for 1b. The tautomerism is essentially unaltered above pH 6.1, where the phosphate group is deprotonated to the dianion. This means that the pyridine ring is more basic than the phenolate group. Pyridine nitrogen deprotonation occurs at 8.2 for 1a and at 8.7 for 1b. By contrast, above pH 4 the phosphate site of 2 is deprotonated, while the pyridine ring pKa is 5.8. The Schiff base nitrogen does not deprotonate below pH 11.4. When the phosphate group is removed, the pKa of the Schiff base nitrogen decreases to 10.5. The phenol site cannot compete for the proton of the Schiff base nitrogen and is present in the entire pH range as a phenolate, preferentially hydrogen bonded to the solvent. The intrinsic 15N chemical shifts provide information about the hydrogen bond structures of the protonated and unprotonated species involved. Evidence is presented that the intramolecular OHN hydrogen bond of PLP aldimines is broken in aqueous solution. The coupling between the inter- and intramolecular OHN hydrogen bonds is also lost in this environment. The pyridine ring of the PLP aldimines is not protonated in aqueous solution near neutral pH. The basicity of the aldimine nitrogens would be even lower without the doubly negatively charged phosphate group. Protonation of both the Schiff base and pyridine nitrogens has been discussed as a prerequisite for catalytic activity, and the implications of the present findings for PLP catalysis are discussed.
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Affiliation(s)
- Shasad Sharif
- Institut für Chemie und Biochemie, Takustrasse 3, Freie Universität Berlin, D-14195 Berlin, Germany
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28
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Sharif S, Schagen D, Toney MD, Limbach HH. Coupling of Functional Hydrogen Bonds in Pyridoxal-5‘-phosphate−Enzyme Model Systems Observed by Solid-State NMR Spectroscopy. J Am Chem Soc 2007; 129:4440-55. [PMID: 17371021 DOI: 10.1021/ja066240h] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We present a novel series of hydrogen-bonded, polycrystalline 1:1 complexes of Schiff base models of the cofactor pyridoxal-5'-phosphate (PLP) with carboxylic acids that mimic the cofactor in a variety of enzyme active sites. These systems contain an intramolecular OHN hydrogen bond characterized by a fast proton tautomerism as well as a strong intermolecular OHN hydrogen bond between the pyridine ring of the cofactor and the carboxylic acid. In particular, the aldenamine and aldimine Schiff bases N-(pyridoxylidene)tolylamine and N-(pyridoxylidene)methylamine, as well as their adducts, were synthesized and studied using 15N CP and 1H NMR techniques under static and/or MAS conditions. The geometries of the hydrogen bonds were obtained from X-ray structures, 1H and 15N chemical shift correlations, secondary H/D isotope effects on the 15N chemical shifts, or directly by measuring the dipolar 2H-15N couplings of static samples of the deuterated compounds. An interesting coupling of the two "functional" OHN hydrogen bonds was observed. When the Schiff base nitrogen atoms of the adducts carry an aliphatic substituent such as in the internal and external aldimines of PLP in the enzymatic environment, protonation of the ring nitrogen shifts the proton in the intramolecular OHN hydrogen bond from the oxygen to the Schiff base nitrogen. This effect, which increases the positive charge on the nitrogen atom, has been discussed as a prerequisite for cofactor activity. This coupled proton transfer does not occur if the Schiff base nitrogen atom carries an aromatic substituent.
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Affiliation(s)
- Shasad Sharif
- Institut für Chemie und Biochemie, Takustrasse 3, Freie Universität Berlin, D-14195 Berlin, Germany
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29
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Cook PD, Thoden JB, Holden HM. The structure of GDP-4-keto-6-deoxy-D-mannose-3-dehydratase: a unique coenzyme B6-dependent enzyme. Protein Sci 2006; 15:2093-106. [PMID: 16943443 PMCID: PMC2242600 DOI: 10.1110/ps.062328306] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
L-colitose is a 3,6-dideoxysugar found in the O-antigens of some Gram-negative bacteria such as Escherichia coli and in marine bacteria such as Pseudoalteromonas tetraodonis. The focus of this investigation, GDP-4-keto-6-deoxy-D-mannose-3-dehydratase, catalyzes the third step in colitose production, which is the removal of the hydroxyl group at C3' of GDP-4-keto-6-deoxymannose. It is an especially intriguing PLP-dependent enzyme in that it acts as both a transaminase and a dehydratase. Here we present the first X-ray structure of this enzyme isolated from E. coli Strain 5a, type O55:H7. The two subunits of the protein form a tight dimer with a buried surface area of approximately 5000 A2. This is a characteristic feature of the aspartate aminotransferase superfamily. Although the PLP-binding pocket is formed primarily by one subunit, there is a loop, delineated by Phe 240 to Glu 253 in the second subunit, that completes the active site architecture. The hydrated form of PLP was observed in one of the enzyme/cofactor complexes described here. Amino acid residues involved in anchoring the cofactor to the protein include Gly 56, Ser 57, Asp 159, Glu 162, and Ser 183 from one subunit and Asn 248 from the second monomer. In the second enzyme/cofactor complex reported, a glutamate ketimine intermediate was found trapped in the active site. Taken together, these two structures, along with previously reported biochemical data, support the role of His 188 as the active site base required for catalysis.
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Affiliation(s)
- Paul D Cook
- Department of Biochemistry, University of Wisconsin-Madison, Wisconsin 53706, USA
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Golinelli-Pimpaneau B, Lüthi C, Christen P. Structural Basis for D-Amino Acid Transamination by the Pyridoxal 5′-Phosphate-dependent Catalytic Antibody 15A9. J Biol Chem 2006; 281:23969-77. [PMID: 16790434 DOI: 10.1074/jbc.m602184200] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Antibody 15A9, raised with 5'-phosphopyridoxyl (PPL)-N(epsilon)-acetyl-L-lysine as hapten, catalyzes the reversible transamination of hydrophobic D-amino acids with pyridoxal 5'-phosphate (PLP). The crystal structures of the complexes of Fab 15A9 with PPL-L-alanine, PPL-D-alanine, and the hapten were determined at 2.3, 2.3, and 2.5A resolution, respectively, and served for modeling the complexes with the corresponding planar imine adducts. The conformation of the PLP-amino acid adduct and its interactions with 15A9 are similar to those occurring in PLP-dependent enzymes, except that the amino acid substrate is only weakly bound, and, due to the immunization and selection strategy, the lysine residue that covalently binds PLP in these enzymes is missing. However, the N-acetyl-L-lysine moiety of the hapten appears to have selected for aromatic residues in hypervariable loop H3 (Trp-H100e and Tyr-H100b), which, together with Lys-H96, create an anion-binding environment in the active site. The structural situation and mutagenesis experiments indicate that two catalytic residues facilitate the transamination reaction of the PLP-D-alanine aldimine. The space vacated by the absent L-lysine side chain of the hapten can be filled, in both PLP-alanine aldimine complexes, by mobile Tyr-H100b. This group can stabilize a hydroxide ion, which, however, abstracts the C alpha proton only from D-alanine. Together with the absence of any residue capable of deprotonating C alpha of L-alanine, Tyr-H100b thus underlies the enantiomeric selectivity of 15A9. The reprotonation of C4' of PLP, the rate-limiting step of 15A9-catalyzed transamination, is most likely performed by a water molecule that, assisted by Lys-H96, produces a hydroxide ion stabilized by the anion-binding environment.
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Affiliation(s)
- Béatrice Golinelli-Pimpaneau
- Laboratoire d'Enzymologie et Biochimie Structurales, CNRS Bât. 34, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France.
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31
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Sharif S, Denisov GS, Toney MD, Limbach HH. NMR Studies of Solvent-Assisted Proton Transfer in a Biologically Relevant Schiff Base: Toward a Distinction of Geometric and Equilibrium H-Bond Isotope Effects. J Am Chem Soc 2006; 128:3375-87. [PMID: 16522119 DOI: 10.1021/ja056251v] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The tautomeric equilibrium in a Schiff base, N-(3,5-dibromosalicylidene)-methylamine 1, a model for the hydrogen bonded structure of the cofactor pyridoxal-5'-phosphate PLP which is located in the active site of the enzyme, was measured by means of 1H and 15N NMR and deuterium isotope effects on 15N chemical shifts at variable temperature and in different organic solvents. The position of the equilibrium was estimated using the one-bond 1J(OHN) and vicinal 3J(H(alpha)CNH) scalar coupling constants. Additionally, DFT calculations of a series of Schiff bases, N-(R1-salicylidene)-alkyl(R2)amines, were performed to obtain the hydrogen bond geometries. The latter made it possible to investigate a broad range of equilibrium positions. The increase of the polarity of the aprotic solvent shifts the proton in the intramolecular OHN hydrogen bond closer to the nitrogen. The addition of methanol and of hexafluoro-2-propanol to 1 in aprotic solvents models the PLP-water interaction in the enzymatic active site. The alcohols, which vary in acidity and change the polarity around the hydrogen bond, also stabilize the equilibrium, so that the proton is shifted to the nitrogen.
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Affiliation(s)
- Shasad Sharif
- Institut für Chemie, Takustrasse 3, Freie Universität Berlin, D-14195 Berlin, Germany
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32
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Alaux S, Kusk M, Sagot E, Bolte J, Jensen AA, Bräuner-Osborne H, Gefflaut T, Bunch L. Chemoenzymatic synthesis of a series of 4-substituted glutamate analogues and pharmacological characterization at human glutamate transporters subtypes 1-3. J Med Chem 2006; 48:7980-92. [PMID: 16335922 DOI: 10.1021/jm050597z] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A series of nine L-2,4-syn-4-alkylglutamic acid analogues (1a-i) were synthesized in high yield and high enantiomeric excess (>99% ee) from their corresponding 4-substituted ketoglutaric acids (2a-i), using the enzyme aspartate aminotransferase (AAT) from pig heart or E. coli. The synthesized compounds were evaluated as potential ligands for the glutamate transporters EAAT1, EAAT2, and EAAT3 (excitatory amino acid transporter, subtypes 1-3) in the FLIPR membrane potential (FMP) assay. We found a distinct change in the pharmacological profile when the 4-methyl group (compound 1a, an EAAT1 substrate and EAAT2,3 inhibitor) was extended to a 4-ethyl group, compound 1b, as this analogue is an inhibitor at all three subtypes, EAAT1-3. Furthermore, we conclude that both large and bulky hydrophobic substituents in the 4-position of L-2,4-syn Glu are allowed by all three glutamate transporter subtypes EAAT1-3 while maintaining inhibitory activity.
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Affiliation(s)
- Sebastien Alaux
- Département de Chimie, Université Blaise Pascal, 63177 Aubière Cedex, France
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33
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Abstract
Pyridoxal 5'-phosphate-dependent aminotransferases reversibly catalyzes the transamination reaction in which the alpha-amino group of amino acid 1 is transferred to the 2-oxo acid of amino acid 2 (usually 2-oxoglutarate) to produce the 2-oxo acid of amino acid 1 and amino acid 2 (glutamate). An aminotransferase must thus be able to recognize and bind two kinds of amino acids (amino acids 1 and 2), the side chains of which are different in shape and properties, from among many other small molecules. The dual substrate recognition mechanism has been discovered based on three-dimensional structures of aromatic amino acids, histidinol phosphate, glutamine:phenylpyruvate, acetylornithine, and branched-chain amino acid aminotransferases. There are two representative strategies for dual substrate recognition. An aromatic amino acid aminotransferase prepares charged and neutral pockets for acidic and aromatic side chains, respectively, at the same place by a large-scale rearrangement of the hydrogen-bond network caused by the induced fit. In a branched-chain aminotransferase, the same hydrophobic cavity implanted with hydrophilic sites accommodates both hydrophobic and acidic side chains without side-chain rearrangements of the active-site residues, which is reminiscent of the lock and key mechanism. Dual substrate recognition in other aminotransferases is attained by combining the two representative methods.
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Affiliation(s)
- Ken Hirotsu
- Graduate School of Science, Osaka City University, Osaka 558-8585, Japan.
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Adams B, Lowpetch K, Thorndycroft F, Whyte SM, Young DW. Stereochemistry of reactions of the inhibitor/substrates l- and d-β-chloroalanine with β-mercaptoethanol catalysed by l-aspartate aminotransferase and d-amino acid aminotransferase respectively. Org Biomol Chem 2005; 3:3357-64. [PMID: 16132097 DOI: 10.1039/b508199h] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Two members of the alpha-family of PLP-dependent enzymes, L-aspartate aminotransferase and D-amino acid aminotransferase, have been shown to catalyse beta-substitution of L- and D-beta-chloroalanine respectively with beta-mercaptoethanol, reactions typical of the beta-family of PLP-dependent enzymes. The reaction catalysed by L-aspartate aminotransferase has been shown to occur with retention of stereochemistry, a typical outcome for reactions catalysed by beta-family enzymes. There are also indications that the reaction catalysed by D-amino acid aminotransferase may involve retention of stereochemistry. Both enzymes have been shown to catalyse exchange at C-3 when the appropriate enantiomer of beta-chloroalanine is the substrate.
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Affiliation(s)
- Benjamin Adams
- Department of Chemistry, University of Sussex, Falmer, Brighton, UK BN1 9QJ
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35
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Das K, Butler GH, Kwiatkowski V, Clark AD, Yadav P, Arnold E. Crystal structures of arginine deiminase with covalent reaction intermediates; implications for catalytic mechanism. Structure 2004; 12:657-67. [PMID: 15062088 DOI: 10.1016/j.str.2004.02.017] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2003] [Revised: 01/07/2004] [Accepted: 01/07/2004] [Indexed: 11/27/2022]
Abstract
Arginine deiminase (ADI), an enzyme that hydrolyzes arginine to generate energy in many parasitic microorganisms, has potent anticancer activities and can halt growth of solid tumors. We determined the crystal structure of ADI from Mycoplasma arginini in two different forms (1.6 and 2.0 A resolution) using multiple isomorphous replacement. ADI shares common structural features with the arginine-catabolizing enzymes Arg:Gly amidinotransferase and dimethylarginine dimethyl-aminohydrolase; ADI contains an additional domain of five helices. The scissile C-N bonds of the substrates and the catalytic triads (Cys398-His269-Glu213 of ADI) for the three enzymes superimpose on each other. The ADI structure from form I crystals corresponds to a tetrahedral intermediate with four heteroatoms (1S, 2N, 1O) covalently bonded to the reaction-center carbon. The structure from form II crystals represents an amidino-enzyme complex; the reaction-center carbon is covalently bonded to Cys398 sulfur and two nitrogens, and the reacting water molecule is only 2.54 A away.
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Affiliation(s)
- Kalyan Das
- Center for Advanced Biotechnology and Medicine (CABM) and Department of Chemistry and Chemical Biology, Rutgers University, 679 Hoes Lane, Piscataway, NJ 08854 USA
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36
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Pioselli B, Bettati S, Demidkina TV, Zakomirdina LN, Phillips RS, Mozzarelli A. Tyrosine phenol-lyase and tryptophan indole-lyase encapsulated in wet nanoporous silica gels: Selective stabilization of tertiary conformations. Protein Sci 2004; 13:913-24. [PMID: 15044726 PMCID: PMC2280055 DOI: 10.1110/ps.03492904] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The pyridoxal 5'-phosphate-dependent enzymes tyrosine phenol-lyase and tryptophan indole-lyase were encapsulated in wet nanoporous silica gels, a powerful method to selectively stabilize tertiary and quaternary protein conformations and to develop bioreactors and biosensors. A comparison of the enzyme reactivity in silica gels and in solution was carried out by determining equilibrium and kinetic parameters, exploiting the distinct spectral properties of catalytic intermediates and reaction products. The encapsulated enzymes exhibit altered distributions of ketoenamine and enolimine tautomers, increased values of inhibitors dissociation constants, slow attaining of steady-state in the presence of substrate and substrate analogs, modified steady-state distribution of catalytic intermediates, and a sixfold-eightfold decrease of specific activities. This behavior can be rationalized by a reduced conformational flexibility for the encapsulated enzymes and a selective stabilization of either the open (inactive) or the closed (active) form of the enzymes. Despite very similar structures and catalytic mechanisms, the influence of encapsulation is more pronounced for tyrosine phenol-lyase than tryptophan indole-lyase. This finding indicates that subtle structural and dynamic differences can lead to distinct interactions of the protein with the gel matrix.
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Affiliation(s)
- Barbara Pioselli
- Department of Biochemistry and Molecular Biology, University of Parma, Via Parco delle Scienze 23/A, 43100 Parma, Italy
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37
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Schwarzenbacher R, Jaroszewski L, von Delft F, Abdubek P, Ambing E, Biorac T, Brinen LS, Canaves JM, Cambell J, Chiu HJ, Dai X, Deacon AM, DiDonato M, Elsliger MA, Eshagi S, Floyd R, Godzik A, Grittini C, Grzechnik SK, Hampton E, Karlak C, Klock HE, Koesema E, Kovarik JS, Kreusch A, Kuhn P, Lesley SA, Levin I, McMullan D, McPhillips TM, Miller MD, Morse A, Moy K, Ouyang J, Page R, Quijano K, Robb A, Spraggon G, Stevens RC, van den Bedem H, Velasquez J, Vincent J, Wang X, West B, Wolf G, Xu Q, Hodgson KO, Wooley J, Wilson IA. Crystal structure of an aspartate aminotransferase (TM1255) from Thermotoga maritima at 1.90 Å resolution. Proteins 2004; 55:759-63. [PMID: 15103638 DOI: 10.1002/prot.10646] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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38
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Rothman SC, Voorhies M, Kirsch JF. Directed evolution relieves product inhibition and confers in vivo function to a rationally designed tyrosine aminotransferase. Protein Sci 2004; 13:763-72. [PMID: 14767072 PMCID: PMC2286728 DOI: 10.1110/ps.03117204] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The Escherichia coli aspartate (AATase) and tyrosine (TATase) aminotransferases share 43% sequence identity and 72% similarity, but AATase has only 0.08% and 0.01% of the TATase activities (k(cat)/K(m)) for tyrosine and phenylalanine, respectively. Approximately 5% of TATase activity was introduced into the AATase framework earlier both by rational design (six mutations, termed HEX) and by directed evolution (9-17 mutations). The enzymes realized from the latter procedure complement tyrosine auxotrophy in TATase deficient E. coli. HEX complements even more poorly than does wild-type AATase, even though the (k(cat)/K(m)) value for tyrosine exhibited by HEX is similar to those of the enzymes found from directed evolution. HEX, however, is characterized by very low values of K(m) and K(D) for dicarboxylic ligands, and by a particularly slow release for oxaloacetate, the product of the reaction with aspartate and a TCA cycle intermediate. These observations suggest that HEX exists largely as an enzyme-product complex in vivo. HEX was therefore subjected to a single round of directed evolution with selection for complementation of tyrosine auxotrophy. A variant with a single amino acid substitution, A293D, exhibited substantially improved TATase function in vivo. The A293D mutation alleviates the tight binding to dicarboxylic ligands as K(m)s for aspartate and alpha-ketoglutarate are >20-fold higher in the HEX + A293D construct compared to HEX. This mutation also increased k(cat)/K(m)(Tyr) threefold. A second mutation, I73V, elicited smaller but similar effects. Both residues are in close proximity to Arg292 and the mutations may function to modulate the arginine switch mechanism responsible for dual substrate recognition in TATases and HEX.
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Affiliation(s)
- Steven C Rothman
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720-3206, USA
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39
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Omi R, Goto M, Miyahara I, Mizuguchi H, Hayashi H, Kagamiyama H, Hirotsu K. Crystal structures of threonine synthase from Thermus thermophilus HB8: conformational change, substrate recognition, and mechanism. J Biol Chem 2003; 278:46035-45. [PMID: 12952961 DOI: 10.1074/jbc.m308065200] [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
Threonine synthase, which is a PLP-dependent enzyme, catalyzes the beta,gamma-replacement reaction of l-homoserine phosphate to yield threonine and inorganic phosphate. The three-dimensional structures of the enzyme from Thermus thermophilus HB8 in its unliganded form and complexed with the substrate analogue 2-amino-5-phosphonopentanoic acid have been determined at 2.15 and 2.0 A resolution, respectively. The complexed form, assigned as an enamine, uncovered the interactions of the cofactor-analogue conjugate with the active site residues. The binding of the substrate analogue induces a large conformational change at the domain level. The small domain rotates by about 25 degrees and approaches the large domain to close the active site. The complicated catalytic process of the enzyme has been elucidated based on the complex structure to reveal the stereochemistry of the reaction and to present the released inorganic phosphate as a possible catalyst to carry a proton to the Cgamma atom of the substrate.
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Affiliation(s)
- Rie Omi
- Department of Chemistry, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan
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40
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Allert M, Baltzer L. Noncovalent binding of a reaction intermediate by a designed helix-loop-helix motif-implications for catalyst design. Chembiochem 2003; 4:306-18. [PMID: 12672110 DOI: 10.1002/cbic.200390051] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In our search for a catalyst for the transamination reaction of aspartic acid to form oxaloacetate, twenty-five forty-two-residue sequences were designed to fold into helix-loop-helix dimers and form binding sites for the key intermediate along the reaction pathway, the aldimine. This intermediate is formed from aspartic acid and the cofactor pyridoxal phosphate. The design of the binding sites followed a strategy in which exclusively noncovalent forces were used for binding the aldimine. Histidine residues were incorporated to catalyse the rate-limiting 1,3 proton transfer reaction that converts the aldimine into the ketimine, an intermediate that is subsequently hydrolysed to form oxaloacetate and pyridoxamine phosphate. The two most efficient catalysts, T-4 and T-16, selected from the pool of sequences by a simple screening procedure, were shown by CD and NMR spectroscopies to bind the aldimine intermediate with dissociation constants in the millimolar range. The mean residue ellipticity of T-4 in aqueous solution at pH 7.4 and a concentration of 0.75 mM was -18500 deg x cm(2) dmol(-1). Upon addition of 6 mm l-aspartic acid and 1.5 mM pyridoxal phosphate to form the aldimine, the mean residue ellipticity changed to -19900 deg x cm(2) dmol(-1). The corresponding mean residue ellipticities of T-16 were -21200 deg x cm(2) dmol(-1) and -24000 deg x cm(2) dmol(-1). These results show that the helical content increased in the presence of the aldimine, and that the folded polypeptides bound the aldimine. The (1)H NMR relaxation time of the imine CH proton of the aldimine was affected by the presence of T-4 as was the (31)P NMR resonance linewidth. The catalytic efficiencies of T-4 and T-16 were compared to that of imidazole and found to be more than three orders of magnitude larger. The designed binding sites were thus shown to be capable of binding the aldimine in close proximity to His residues, by noncovalent forces, into conformations that proved to be catalytically active. The results show for the first time the design of well-defined catalytic sites that bind a reaction intermediate with enzyme-like affinities under equilibrium conditions and represent an important advance in de novo catalyst design.
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Affiliation(s)
- Malin Allert
- Department of Chemistry, Organic Chemistry, Göteborg University 41296 Göteborg, Sweden
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41
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Hayashi H, Mizuguchi H, Miyahara I, Nakajima Y, Hirotsu K, Kagamiyama H. Conformational change in aspartate aminotransferase on substrate binding induces strain in the catalytic group and enhances catalysis. J Biol Chem 2003; 278:9481-8. [PMID: 12488449 DOI: 10.1074/jbc.m209235200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Aspartate aminotransferase has been known to undergo a significant conformational change, in which the small domain approaches the large domain, and the residues at the entrance of the active site pack together, on binding of substrates. Accompanying this conformational change is a two-unit increase in the pK(a) of the pyridoxal 5'-phosphate-Lys(258) aldimine, which has been proposed to enhance catalysis. To elucidate how the conformational change is coupled to the shift in the aldimine pK(a) and how these changes are involved in catalysis, we analyzed structurally and kinetically an enzyme in which Val(39) located at both the domain interface and the entrance of the active site was replaced with a bulkier residue, Phe. The V39F mutant enzyme showed a more open conformation, and the aldimine pK(a) was lowered by 0.7 unit compared with the wild-type enzyme. When Asn(194) had been replaced by Ala in advance, the V39F mutation did not decrease the aldimine pK(a), showing that the domain rotation controls the aldimine pK(a) via the Arg(386)-Asn(194)-pyridoxal 5'-phosphate linkage system. The maleate-bound V39F enzyme showed the aldimine pK(a) 0.9 unit lower than that of the maleate-bound wild-type enzyme. However, the positions of maleate, Asn(194), and Arg(386) were superimposable between the mutant and the wild-type enzymes; therefore, the domain rotation was not the cause of the lowered aldimine pK(a) value. The maleate-bound V39F enzyme showed an altered side-chain packing pattern in the 37-39 region, and the lack of repulsion between Gly(38) carbonyl O and Tyr(225) Oeta seemed to be the cause of the reduced pK(a) value. Kinetic analysis suggested that the repulsion increases the free energy level of the Michaelis complex and promotes the catalytic reaction.
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Affiliation(s)
- Hideyuki Hayashi
- Department of Biochemistry, Osaka Medical College, Takatsuki 569-8686, Japan
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42
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Abstract
Understanding the molecular mechanisms of enzyme catalysis and allosteric regulation has been a primary goal of biochemistry for many years. The dynamics of these processes, approached through a variety of kinetic methods, are discussed. The results obtained for many different enzymes suggest that multiple intermediates and conformations are general characteristics of the catalytic process and allosteric regulation. Ribonuclease, dihydrofolate reductase, chymotrypsin, aspartate aminotransferase, and aspartate transcarbamoylase are considered as specific examples. Typical and maximum rates of conformational changes and catalysis are also discussed, based on results obtained from model systems. The nature and rates of interconversion of the intermediates, along with structural information, can be used as the bases for understanding the incredible catalytic efficiency of enzymes. Potential roles of conformational changes in the catalytic process are discussed in terms of static and environmental effects, and in terms of dynamic coupling within the enzyme-substrate complex.
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Affiliation(s)
- Gordon G Hammes
- Department of Biochemistry, Box 3711, Duke University Medical Center, Durham, North Carolina 27710, USA
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43
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Deu E, Koch KA, Kirsch JF. The role of the conserved Lys68*:Glu265 intersubunit salt bridge in aspartate aminotransferase kinetics: multiple forced covariant amino acid substitutions in natural variants. Protein Sci 2002; 11:1062-73. [PMID: 11967363 PMCID: PMC2373551 DOI: 10.1110/ps.0200902] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
Abstract
The role of the Lys68*:Glu265 intersubunit salt bridge that is conserved (Csb) in all known aspartate aminotransferases (AATases), except those of animal cytosolic, Ac (His68*:Glu265), and plant mitochondrial, Pm (Met68*:Gln265), origins, was evaluated in the Escherichia coli AATase. Two double-mutant cycles, to K68M/E265Q and the charge reversed K68E/E265K, were characterized with the context dependence (C) and impact (I) formalism, previously defined for functional chimeric analysis. Mutations of Lys68* with Glu265 fixed are generally more deleterious than the converse mutations of Glu265 with Lys68* fixed, showing that buried negative charges have greater effects than buried positive charges in this context. Replacement of the charged Lys68*:Glu265 with the K68M/E265Q neutral pair introduces relatively small effects on the kinetic parameters. The differential sensitivity of k(cat)/K(M, L-Asp) and k(cat)/K(M, alpha-KG) to salt bridge mutagenic replacements is shown by a linear-free energy relationship, in which the logarithms of the latter second order rate constants are generally decreased by a factor of two more than are those of the former. Thus, k(cat)/K(M, L-Asp) and k(cat)/K(M, alpha-KG) are 133 and 442 mM(-1)s(-1) for the wild-type (WT) enzyme, respectively, but their relative order is reversed in the more severely compromised mutants (14.8 and 5.3 mM(-1)s(-1) for K68E). A Venn diagram illustrates apparent forced covariances of groups of amino acids that accompany the naturally occurring salt bridge replacements in the Pm and Ac classes. The more deeply rooted tree indicates that the Csb variant was the ancestral specie.
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Affiliation(s)
- Edgar Deu
- Department of Molecular and Cell Biology, University of California-Berkeley, Berkeley, CA 94720-3206, USA
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44
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Metzler DE, Metzler CM, Sauke DJ. Coenzymes. Biochemistry 2001. [DOI: 10.1016/b978-012492543-4/50017-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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45
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Abstract
Crystal structures of reactive short-lived species, as occurring during chemical reactions, can be determined through time-resolved crystallography or trapping approaches. Prerequisite is the initiation and characterization of the reaction in the crystal. Ways to do this, recent results, caveats, and future prospects are discussed.
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Affiliation(s)
- I Schlichting
- Max Planck Institute for Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany
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46
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Use of inhibitors to study reactions catalyzed by enzymes requiring pyridoxal phosphate as coenzyme. PURE APPL CHEM 2000. [DOI: 10.1351/pac200072030373] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The stereochemistry of a variety of pyridoxal phosphate-mediated enzymic reactions has been studied using enzyme inhibitors that are stereospecifically labeled in the β-position with deuterium. A versatile synthesis has been developed to prepare a wide variety of stereospecifically labeled d- and l-amino acids and inhibitors. Investigation of the "turnover" of β-chloro-d-alanine and d- and l-serine-O-sulfate by d-amino acid aminotransferase and l-aspartate aminotransferase respectively has shown that reaction within the active site of the former enzyme occurs with retention of stereochemistry. Although l-aspartate aminotransferase is an enzyme of the α-family, when it was incubated with β-chloro-l-alanine in the presence of 2-mercaptoethanol, β-substitution occurred. This was shown to involve retention of stereochemistry, an outcome typical of reactions catalyzed by enzymes of the β-family that have little or no homology with enzymes of the α-family. Formation of the "Schnackerz intermediate" has been studied as has the d-amino acid oxidase catalyzed reaction of the naturally occurring inhibitor d-propargylglycine.
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Malashkevich VN, Strop P, Keller JW, Jansonius JN, Toney MD. Crystal structures of dialkylglycine decarboxylase inhibitor complexes. J Mol Biol 1999; 294:193-200. [PMID: 10556038 DOI: 10.1006/jmbi.1999.3254] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The crystal structures of four inhibitor complexes of dialkylglycine decarboxylase are reported. The enzyme does not undergo a domain closure, as does aspartate aminotransferase, upon inhibitor binding. Two active-site conformations have been observed in previous structures that differ in alkali metal ion content, and two active-site conformations have been shown to coexist in solution when a single type of metal ion is present. There is no indication of coexisting conformers in the structures reported here or in the previously reported structures, and the observed conformation is that expected based on the presence of potassium in the enzyme. Thus, although two active-site conformations coexist in solution, a single conformation, corresponding to the more active enzyme, predominates in the crystal. The structure of 1-aminocyclopropane-1-carboxylate bound in the active site shows the aldimine double bond to the pyridoxal phosphate cofactor to be fully out of the plane of the coenzyme ring, whereas the Calpha-CO2(-) bond lies close to it. This provides an explanation for the observed lack of decarboxylation reactivity with this amino acid. The carboxylate groups of both 1-aminocyclopropane-1-carboxylate and 5'-phosphopyridoxyl-2-methylalanine interact with Ser215 and Arg406 as previously proposed. This demonstrates structurally that alternative binding modes, which constitute substrate inhibition, occur in the decarboxylation half-reaction. The structures of d and l-cycloserine bound to the active-site show that the l-isomer is deprotonated at C(alpha), presumably by Lys272, while the d-isomer is not. This difference explains the approximately 3000-fold greater potency of the l versus the d-isomer as a competitive inhibitor of dialkylglycine decarboxylase.
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Affiliation(s)
- V N Malashkevich
- Department of Structural Biology, Biozentrum University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland.
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Kern AD, Oliveira MA, Coffino P, Hackert ML. Structure of mammalian ornithine decarboxylase at 1.6 A resolution: stereochemical implications of PLP-dependent amino acid decarboxylases. Structure 1999; 7:567-81. [PMID: 10378276 DOI: 10.1016/s0969-2126(99)80073-2] [Citation(s) in RCA: 122] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
BACKGROUND Pyridoxal-5'-phosphate (PLP) dependent enzymes catalyze a broad range of reactions, resulting in bond cleavage at C alpha, C beta, or C gamma carbons of D and L amino acid substrates. Ornithine decarboxylase (ODC) is a PLP-dependent enzyme that controls a critical step in the biosynthesis of polyamines, small organic polycations whose controlled levels are essential for proper growth. ODC inhibition has applications for the treatment of certain cancers and parasitic ailments such as African sleeping sickness. RESULTS The structure of truncated mouse ODC (mODC') was determined by multiple isomorphous replacement methods and refined to 1.6 A resolution. This is the first structure of a Group IV decarboxylase. The monomer contains two domains: an alpha/beta barrel that binds the cofactor, and a second domain consisting mostly of beta structure. Only the dimer is catalytically active, as the active sites are constructed of residues from both monomers. The interactions stabilizing the dimer shed light on its regulation by antizyme. The overall structure and the environment of the cofactor are compared with those of alanine racemase. CONCLUSIONS The analysis of the mODC' structure and its comparison with alanine racemase, together with modeling studies of the external aldimine intermediate, provide insight into the stereochemical characteristics of PLP-dependent decarboxylation. The structure comparison reveals stereochemical differences with other PLP-dependent enzymes and the bacterial ODC. These characteristics may be exploited in the design of new inhibitors specific for eukaryotic and bacterial ODCs, and provide the basis for a detailed understanding of the mechanism by which these enzymes regulate reaction specificity.
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Affiliation(s)
- A D Kern
- Department of Chemistry and Biochemistry, University of Texas at Austin 78712, USA
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Storici P, Capitani G, Müller R, Schirmer T, Jansonius JN. Crystal structure of human ornithine aminotransferase complexed with the highly specific and potent inhibitor 5-fluoromethylornithine. J Mol Biol 1999; 285:297-309. [PMID: 9878407 DOI: 10.1006/jmbi.1998.2289] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ornithine aminotransferase (l-ornithine:2-oxoacid delta-aminotransferase; EC 2.6.1.13), a pyridoxal-5'-phosphate-dependent mitochondrial enzyme controls the l-ornithine level in tissues by catalyzing the transfer of the delta-amino group of l-ornithine to 2-oxoglutarate, producing l-glutamate- gamma-semialdehyde and l-glutamate. (2S, 5S)-5-Fluoromethylornithine is the only inhibitor exclusively specific for ornithine aminotransferase known to date. Both in vitro and in vivo, it blocks the enzyme by a suicide reaction leading to a covalent adduct with the cofactor. The crystal structure of the enzyme-inhibitor complex was solved at a resolution of 1.95 A. No significant conformational changes compared with the native enzyme structure were observed. The structure reveals the atomic details of the cofactor-inhibitor adduct and its interactions with the active site of the enzyme. The main residues responsible for specific binding of the inhibitor are Arg180, which forms a strong salt bridge with the alpha-carboxylate and Tyr55, which is involved in a short hydrogen bond with the alpha-amino group. The experimental observation that in the racemic mixture, (2S, 5S)-5-fluoromethylornithine is exclusively responsible for the enzyme inhibition can be explained on the basis of the active site topology. Model building studies strongly suggest that the natural substrate l-ornithine, in its external aldimine adduct with the enzyme, makes use of the same recognition site as the inhibitor. It is proposed that the neutralization of the active site Arg413 by a salt bridge with Glu235 also plays an important role in productive binding of both 5-fluoromethylornithine and l-ornithine. Arg180 and Arg413 are believed to be instrumental in recognition of l-glutamate, by binding its gamma and alpha-carboxylate groups, respectively. This requires a different side-chain conformation of Glu235. Lys292 is the only obvious candidate for catalyzing the rate-limiting proton transfer steps in the transamination reaction.
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Affiliation(s)
- P Storici
- Division of Structural Biology Biozentrum, University of Basel, Klingelbergstrasse 70, Basel, CH-4056, Switzerland
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Mozzarelli A, Bettati S, Pucci AM, Burkhard P, Cook PF. Catalytic competence of O-acetylserine sulfhydrylase in the crystal probed by polarized absorption microspectrophotometry. J Mol Biol 1998; 283:135-46. [PMID: 9761679 DOI: 10.1006/jmbi.1998.2038] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The reactions of the pyridoxal 5'-phosphate-dependent enzyme O-acetylserine sulfhydrylase with the substrate O-acetyl-L-serine and substrate analogs have been investigated in the crystalline state by single-crystal polarized absorption microspectrophotometry. This approach has allowed us to examine the catalytic competence of the enzyme in different crystalline states, one of which was used to determine the three-dimensional structure; experimental conditions were defined for the accumulation of catalytic intermediates in the crystal suitable for crystallographic analyses.O-Acetyl-L-serine reacts with the enzyme in one of the crystal forms leading via a beta-elimination reaction to the accumulation of the alpha-aminoacrylate Schiff base, absorbing maximally at 320 and 470 nm, as in solution. The dissociation constant for the alpha-aminoacrylate Schiff base is in the millimolar range, 500-fold higher than in solution, suggesting that crystal lattice interactions may oppose functionally relevant conformational changes. The dissociation constant exhibits a bell-shaped dependence on pH centered at pH 7. At this pH the alpha-aminoacrylate species slowly decays with time (30% decrease in 24 hours). The alpha-aminoacrylate intermediate readily reacts with sodium azide, an analog of sulfide, the natural nucleophilic agent, to give a new amino acid and the native enzyme, indicating that the crystalline enzyme catalyzes the overall beta-replacement reaction as in solution. In other crystal forms, including that used for the X-ray investigation, O-acetyl-L-serine either has an even higher dissociation constant or causes crystal damage upon binding. When the crystalline enzyme reacts with either L-cysteine or L-serine, the external aldimine intermediate is formed. The dissociation constants for both substrate analogs are closer to those observed in solution and are modulated by pH as in solution. Findings demonstrate that O-acetylserine sulfhydrylase is catalytically competent in the crystal although some regions of the molecule, likely involved in an open-closed transition induced by O-acetyl-L-serine binding, may have a limited flexibility. The accumulation in the crystal of both the external aldimine and the alpha-aminoacrylate intermediate makes feasible their structural determination and, therefore, the elucidation of the catalytic pathway at the molecular level.
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Affiliation(s)
- A Mozzarelli
- Institute of Biochemical Sciences, Istituto Nazionale per la Fisica della Materia, University of Parma 43100 Parma, Italy
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