1
|
Tripathi A, Dubey KD. The mechanistic insights into different aspects of promiscuity in metalloenzymes. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2024; 141:23-66. [PMID: 38960476 DOI: 10.1016/bs.apcsb.2023.12.022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/05/2024]
Abstract
Enzymes are nature's ultimate machinery to catalyze complex reactions. Though enzymes are evolved to catalyze specific reactions, they also show significant promiscuity in reactions and substrate selection. Metalloenzymes contain a metal ion or metal cofactor in their active site, which is crucial in their catalytic activity. Depending on the metal and its coordination environment, the metal ion or cofactor may function as a Lewis acid or base and a redox center and thus can catalyze a plethora of natural reactions. In fact, the versatility in the oxidation state of the metal ions provides metalloenzymes with a high level of catalytic adaptability and promiscuity. In this chapter, we discuss different aspects of promiscuity in metalloenzymes by using several recent experimental and theoretical works as case studies. We start our discussion by introducing the concept of promiscuity and then we delve into the mechanistic insight into promiscuity at the molecular level.
Collapse
Affiliation(s)
- Ankita Tripathi
- Department of Chemistry, School of Natural Science, Shiv Nadar Institution of Eminence, Greater Noida, Uttar Pradesh, India
| | - Kshatresh Dutta Dubey
- Department of Chemistry, School of Natural Science, Shiv Nadar Institution of Eminence, Greater Noida, Uttar Pradesh, India.
| |
Collapse
|
2
|
Yang Y, Liu Y, Zhao H, Liu D, Zhang J, Cheng J, Yang Q, Chu H, Lu X, Luo M, Sheng X, Zhang YHPJ, Jiang H, Ma Y. Construction of an artificial phosphoketolase pathway that efficiently catabolizes multiple carbon sources to acetyl-CoA. PLoS Biol 2023; 21:e3002285. [PMID: 37733785 PMCID: PMC10547157 DOI: 10.1371/journal.pbio.3002285] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Revised: 10/03/2023] [Accepted: 07/31/2023] [Indexed: 09/23/2023] Open
Abstract
The canonical glycolysis pathway is responsible for converting glucose into 2 molecules of acetyl-coenzyme A (acetyl-CoA) through a cascade of 11 biochemical reactions. Here, we have designed and constructed an artificial phosphoketolase (APK) pathway, which consists of only 3 types of biochemical reactions. The core enzyme in this pathway is phosphoketolase, while phosphatase and isomerase act as auxiliary enzymes. The APK pathway has the potential to achieve a 100% carbon yield to acetyl-CoA from any monosaccharide by integrating a one-carbon condensation reaction. We tested the APK pathway in vitro, demonstrating that it could efficiently catabolize typical C1-C6 carbohydrates to acetyl-CoA with yields ranging from 83% to 95%. Furthermore, we engineered Escherichia coli stain capable of growth utilizing APK pathway when glycerol act as a carbon source. This novel catabolic pathway holds promising route for future biomanufacturing and offering a stoichiometric production platform using multiple carbon sources.
Collapse
Affiliation(s)
- Yiqun Yang
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
| | - Yuwan Liu
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
- Haihe Laboratory of Synthetic Biology, Tianjin, China
| | - Haodong Zhao
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China
| | - Dingyu Liu
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
| | - Jie Zhang
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China
| | - Jian Cheng
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
| | - Qiaoyu Yang
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
| | - Huanyu Chu
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
| | - Xiaoyun Lu
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
| | - Mengting Luo
- School of Life Science and Technology, Wuhan Polytechnic University, Wuhan, China
| | - Xiang Sheng
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
| | - Yi-Heng P. J. Zhang
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
| | - Huifeng Jiang
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
- Haihe Laboratory of Synthetic Biology, Tianjin, China
| | - Yanhe Ma
- Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
- National Center of Technology Innovation for Synthetic Biology, Tianjin, China
| |
Collapse
|
3
|
Barreto MQ, Garbelotti CV, de Moura Soares J, Grandis A, Buckeridge MS, Leone FA, Ward RJ. Xylose isomerase from Piromyces sp. E2 is a promiscuous enzyme with epimerase activity. Enzyme Microb Technol 2023; 166:110230. [PMID: 36966679 DOI: 10.1016/j.enzmictec.2023.110230] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 03/15/2023] [Accepted: 03/18/2023] [Indexed: 04/03/2023]
Abstract
Xylose isomerase catalyzes the isomerization of D-xylose to D-xylulose with promiscuous activity for other saccharides including D-glucose, D-allose, and L-arabinose. The xylose isomerase from the fungus Piromyces sp. E2 (PirE2_XI) is used to engineer xylose usage by the fermenting yeast Saccharomyces cerevisiae, but its biochemical characterization is poorly understood with divergent catalytic parameters reported. We have measured the kinetic parameters of the PirE2_XI and analyzed its thermostability and pH-dependence towards different substrates. The PirE2_XI shows promiscuous activity towards D-xylose, D-glucose, D-ribose and L-arabinose with variable effects depending on different divalent ions and epimerizes D-xylose at C3 to produce D-ribulose in a substrate/product dependent ratio. The enzyme follows Michaelis-Menten kinetics for the substrates used and although KM values for D-xylose are comparable at 30 and 60 °C, the kcat/KM is three-fold greater at 60 °C. The purified PirE2_XI shows maximal activity at 65 °C in the pH range of 6.5-7.5 and is a thermostable enzyme, maintaining full activity over 48 h at 30 °C or 12 h at 60 °C. This is the first report demonstrating epimerase activity of the PirE2_XI and its ability to isomerize D-ribose and L-arabinose, and provides a comprehensive in vitro study of substrate specificity, effect of metal ions and temperature on enzyme activity and these findings advance the knowledge of the mechanism of action of this enzyme.
Collapse
|
4
|
Miyamoto RY, de Melo RR, de Mesquita Sampaio IL, de Sousa AS, Morais ER, Sargo CR, Zanphorlin LM. Paradigm shift in xylose isomerase usage: a novel scenario with distinct applications. Crit Rev Biotechnol 2021; 42:693-712. [PMID: 34641740 DOI: 10.1080/07388551.2021.1962241] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Isomerases are enzymes that induce physical changes in a molecule without affecting the original molecular formula. Among this class of enzymes, xylose isomerases (XIs) are the most studied to date, partly due to their extensive application in industrial processes to produce high-fructose corn sirups. In recent years, the need for sustainable initiatives has triggered efforts to improve the biobased economy through the use of renewable raw materials. In this context, D-xylose usage is crucial as it is the second-most abundant sugar in nature. The application of XIs in biotransforming xylose, enabling downstream metabolism in several microorganisms, is a smart strategy for ensuring a low-carbon footprint and producing several value-added biochemicals with broad industrial applications such as in the food, cosmetics, pharmaceutical, and polymer industries. Considering recent advancements that have expanded the range of applications of XIs, this review provides a comprehensive and concise overview of XIs, from their primary sources to the biochemical and structural features that influence their mechanisms of action. This comprehensive review may help address the challenges involved in XI applications in different industries and facilitate the exploitation of xylose bioprocesses.
Collapse
Affiliation(s)
- Renan Yuji Miyamoto
- Brazilian Biorenewables National Laboratory (LNBR), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, Brazil.,Faculty of Pharmaceutical Sciences (FCF), State University of Campinas (UNICAMP), Campinas, Brazil
| | - Ricardo Rodrigues de Melo
- Brazilian Biorenewables National Laboratory (LNBR), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, Brazil
| | - Isabelle Lobo de Mesquita Sampaio
- Brazilian Biorenewables National Laboratory (LNBR), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, Brazil.,Faculty of Food Engineering (FEA), State University of Campinas (UNICAMP), Campinas, Brazil
| | - Amanda Silva de Sousa
- Brazilian Biorenewables National Laboratory (LNBR), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, Brazil
| | - Edvaldo Rodrigo Morais
- Brazilian Biorenewables National Laboratory (LNBR), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, Brazil.,Faculty of Food Engineering (FEA), State University of Campinas (UNICAMP), Campinas, Brazil
| | - Cintia Regina Sargo
- Brazilian Biorenewables National Laboratory (LNBR), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, Brazil
| | - Leticia Maria Zanphorlin
- Brazilian Biorenewables National Laboratory (LNBR), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, Brazil
| |
Collapse
|
5
|
Fernandez PL, Nagorski RW, Cristobal JR, Amyes TL, Richard JP. Phosphodianion Activation of Enzymes for Catalysis of Central Metabolic Reactions. J Am Chem Soc 2021; 143:2694-2698. [PMID: 33560827 PMCID: PMC7919737 DOI: 10.1021/jacs.0c13423] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
![]()
The activation barriers ΔG⧧ for
kcat/Km for the reactions of
whole substrates catalyzed by 6-phosphogluconate dehydrogenase, glucose 6-phosphate
dehydrogenase, and glucose 6-phosphate isomerase are reduced by 11–13 kcal/mol by
interactions between the protein and the substrate phosphodianion. Between 4 and 6
kcal/mol of this dianion binding energy is expressed at the transition state for
phosphite dianion activation of the respective enzyme-catalyzed reactions of truncated
substrates d-xylonate or d-xylose. These and earlier results from
studies on β-phosphoglucomutase, triosephosphate isomerase, and glycerol
3-phosphate dehydrogenase define a cluster of six enzymes that catalyze reactions in
glycolysis or of glycolytic intermediates, and which utilize substrate dianion binding
energy for enzyme activation. Dianion-driven conformational changes, which convert
flexible open proteins to tight protein cages for the phosphorylated substrate, have
been thoroughly documented for five of these six enzymes. The clustering of metabolic
enzymes which couple phosphodianion-driven conformational changes to enzyme activation
suggests that this catalytic motif has been widely propagated in the proteome.
Collapse
Affiliation(s)
- Patrick L Fernandez
- Department of Chemistry, University at Buffalo, SUNY, Buffalo, New York 14260-3000, United States
| | - Richard W Nagorski
- Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, United States
| | - Judith R Cristobal
- Department of Chemistry, University at Buffalo, SUNY, Buffalo, New York 14260-3000, United States
| | - Tina L Amyes
- Department of Chemistry, University at Buffalo, SUNY, Buffalo, New York 14260-3000, United States
| | - John P Richard
- Department of Chemistry, University at Buffalo, SUNY, Buffalo, New York 14260-3000, United States
| |
Collapse
|
6
|
Mehrabi P, Schulz EC, Agthe M, Horrell S, Bourenkov G, von Stetten D, Leimkohl JP, Schikora H, Schneider TR, Pearson AR, Tellkamp F, Miller RJD. Liquid application method for time-resolved analyses by serial synchrotron crystallography. Nat Methods 2019; 16:979-982. [DOI: 10.1038/s41592-019-0553-1] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Accepted: 08/06/2019] [Indexed: 01/01/2023]
|
7
|
Understanding xylose isomerase from Burkholderia cenocepacia: insights into structure and functionality for ethanol production. AMB Express 2019; 9:73. [PMID: 31127459 PMCID: PMC6534634 DOI: 10.1186/s13568-019-0795-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Accepted: 05/13/2019] [Indexed: 12/21/2022] Open
Abstract
The inability of the yeast Saccharomyces cerevisiae to produce ethanol from xylose has hampered the biofuel production from lignocellulosic biomass. However, prior studies reveal that functional expression of xylose isomerase (XI) from Burkholderia cenocepacia (XylABc) in S. cerevisiae has remarkably improved xylose consumption and ethanol productivity. Yet, little is known about kinetic and structural properties of this enzyme. Hereby, a purified recombinant XylA was assayed in vitro, showing optimal enzyme activity at 37 °C and pH 7.2. The Km of XylA for d-xylose was at least threefold lower than the Km results for any XI published to date (e.g. XylA from Piromyces sp.). In addition, oligomerization behavior as a tetramer was observed for XylA in solution. Functional and structural comparative analyses amongst three microbial XIs were further performed as theoretical models, showing that xylose orientation at the active site was highly conserved among the XIs. Mg2+ ions anchor the sugar and guide its pyranoside oxygen towards a histidine residue present at the active site, allowing an acid–base reaction, linearizing xylose. Electrostatic surface analyses showed that small variations in the net charge distribution and dipole moment could directly affect the way the substrate interacts with the protein, thus altering its kinetic properties. Accordingly, in silico modeling suggested the tetramer may be the major functional form. These analyses and the resulting model promote a better understanding of this protein family and pave the way to further protein engineering and application of XylA in the ethanol industry.
Collapse
|
8
|
Forbes CR, Sinha SK, Ganguly HK, Bai S, Yap GPA, Patel S, Zondlo NJ. Insights into Thiol-Aromatic Interactions: A Stereoelectronic Basis for S-H/π Interactions. J Am Chem Soc 2017; 139:1842-1855. [PMID: 28080040 PMCID: PMC5890429 DOI: 10.1021/jacs.6b08415] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Thiols can engage favorably with aromatic rings in S-H/π interactions, within abiological systems and within proteins. However, the underlying bases for S-H/π interactions are not well understood. The crystal structure of Boc-l-4-thiolphenylalanine tert-butyl ester revealed crystal organization centered on the interaction of the thiol S-H with the aromatic ring of an adjacent molecule, with a through-space Hthiol···Caromatic distance of 2.71 Å, below the 2.90 Å sum of the van der Waals radii of H and C. The nature of this interaction was further examined by DFT calculations, IR spectroscopy, solid-state NMR spectroscopy, and analysis of the Cambridge Structural Database. The S-H/π interaction was found to be driven significantly by favorable molecular orbital interactions, between an aromatic π donor orbital and the S-H σ* acceptor orbital (a π → σ* interaction). For comparison, a structural analysis of O-H/π interactions and of cation/π interactions of alkali metal cations with aromatic rings was conducted. Na+ and K+ exhibit a significant preference for the centroid of the aromatic ring and distances near the sum of the van der Waals and ionic radii, as expected for predominantly electrostatic interactions. Li+ deviates substantially from Na+ and K+. The S-H/π interaction differs from classical cation/π interactions by the preferential alignment of the S-H σ* toward the ring carbons and an aromatic π orbital rather than toward the aromatic centroid. These results describe a potentially broadly applicable approach to understanding the interactions of weakly polar bonds with π systems.
Collapse
Affiliation(s)
- Christina R. Forbes
- Department of Chemistry and Biochemistry, University of Delaware, Newark DE 19716, United States
| | | | | | - Shi Bai
- Department of Chemistry and Biochemistry, University of Delaware, Newark DE 19716, United States
| | - Glenn P. A. Yap
- Department of Chemistry and Biochemistry, University of Delaware, Newark DE 19716, United States
| | - Sandeep Patel
- Department of Chemistry and Biochemistry, University of Delaware, Newark DE 19716, United States
| | - Neal J. Zondlo
- Department of Chemistry and Biochemistry, University of Delaware, Newark DE 19716, United States
| |
Collapse
|
9
|
Waltman MJ, Yang ZK, Langan P, Graham DE, Kovalevsky A. Engineering acidic Streptomyces rubiginosus D-xylose isomerase by rational enzyme design. Protein Eng Des Sel 2014; 27:59-64. [PMID: 24402330 DOI: 10.1093/protein/gzt062] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
To maximize bioethanol production from lignocellulosic biomass, all sugars must be utilized. Yeast fermentation can be improved by introducing the d-xylose isomerase enzyme to convert the pentose sugar d-xylose, which cannot be fermented by Saccharomyces cerevisiae, into the fermentable ketose d-xylulose. The low activity of d-xylose isomerase, especially at the low pH required for optimal fermentation, limits its use. A rational enzyme engineering approach was undertaken, and seven amino acid positions were replaced to improve the activity of Streptomyces rubiginosus d-xylose isomerase towards its physiological substrate at pH values below 6. The active-site design was guided by mechanistic insights and the knowledge of amino acid protonation states at low pH obtained from previous joint X-ray/neutron crystallographic experiments. Tagging the enzyme with 6 or 12 histidine residues at the N-terminus resulted in a significant increase in the active-site affinity towards substrate at pH 5.8. Substituting an asparagine at position 215, which hydrogen bonded to the metal-bound Glu181 and Asp245, with an aspartate gave a variant with almost an order of magnitude lower KM than measured for the native enzyme, with a 4-fold increase in activity. Other studied variants showed similar (Asp57Asn, Glu186Gln/Asn215Asp), lower (Asp57His, Asn247Asp, Lys289His, Lys289Glu) or no (Gln256Asp, Asp287Asn, ΔAsp287) activity in acidic conditions relative to the native enzyme.
Collapse
Affiliation(s)
- Mary Jo Waltman
- Bioscience Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
| | | | | | | | | |
Collapse
|
10
|
Differential properties of native and tagged or untagged recombinant glucose isomerases of Streptomyces sp. SK and possible implication of the glycosylation. ACTA ACUST UNITED AC 2013. [DOI: 10.1016/j.molcatb.2013.05.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
|
11
|
Identification of critical residues for the activity and thermostability of Streptomyces sp. SK glucose isomerase. Appl Microbiol Biotechnol 2013; 97:9715-26. [PMID: 23463249 DOI: 10.1007/s00253-013-4784-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 02/13/2013] [Accepted: 02/15/2013] [Indexed: 10/27/2022]
Abstract
The role of residue 219 in the physicochemical properties of D-glucose isomerase from Streptomyces sp. SK strain (SKGI) was investigated by site-directed mutagenesis and structural studies. Mutants G219A, G219N, and G219F were generated and characterized. Comparative studies of their physicochemical properties with those of the wild-type enzyme highlighted that mutant G219A displayed increased specific activity and thermal stability compared to that of the wild-type enzyme, while for G219N and G219F, these properties were considerably decreased. A double mutant, SKGI F53L/G219A, displayed a higher optimal temperature and a higher catalytic efficiency than both the G219A mutant and the wild-type enzyme and showed a half-life time of about 150 min at 85 °C as compared to 50 min for wild-type SKGI. Crystal structures of SKGI wild-type and G219A enzymes were solved to 1.73 and 2.15 Å, respectively, and showed that the polypeptide chain folds into two structural domains. The larger domain consists of a (β/α)8 unit, and the smaller domain forms a loop of α helices. Detailed analyses of the three-dimensional structures highlighted minor but important changes in the active site region as compared to that of the wild-type enzyme leading to a displacement of both metal ions, and in particular that in site M2. The structural analyses moreover revealed how the substitution of G219 by an alanine plays a crucial role in improving the thermostability of the mutant enzyme.
Collapse
|
12
|
Kovalevsky A, Hanson BL, Mason SA, Forsyth VT, Fisher Z, Mustyakimov M, Blakeley MP, Keen DA, Langan P. Inhibition of D-xylose isomerase by polyols: atomic details by joint X-ray/neutron crystallography. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2012; 68:1201-6. [PMID: 22948921 PMCID: PMC3489103 DOI: 10.1107/s0907444912024808] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Accepted: 05/30/2012] [Indexed: 11/10/2022]
Abstract
D-Xylose isomerase (XI) converts the aldo-sugars xylose and glucose to their keto analogs xylulose and fructose, but is strongly inhibited by the polyols xylitol and sorbitol, especially at acidic pH. In order to understand the atomic details of polyol binding to the XI active site, a 2.0 Å resolution room-temperature joint X-ray/neutron structure of XI in complex with Ni(2+) cofactors and sorbitol inhibitor at pH 5.9 and a room-temperature X-ray structure of XI containing Mg(2+) ions and xylitol at the physiological pH of 7.7 were obtained. The protonation of oxygen O5 of the inhibitor, which was found to be deprotonated and negatively charged in previous structures of XI complexed with linear glucose and xylulose, was directly observed. The Ni(2+) ions occupying the catalytic metal site (M2) were found at two locations, while Mg(2+) in M2 is very mobile and has a high B factor. Under acidic conditions sorbitol gains a water-mediated interaction that connects its O1 hydroxyl to Asp257. This contact is not found in structures at basic pH. The new interaction that is formed may improve the binding of the inhibitor, providing an explanation for the increased affinity of the polyols for XI at low pH.
Collapse
Affiliation(s)
- Andrey Kovalevsky
- Bioscience Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
| | | | | | | | | | | | | | | | | |
Collapse
|
13
|
Richard JP. A paradigm for enzyme-catalyzed proton transfer at carbon: triosephosphate isomerase. Biochemistry 2012; 51:2652-61. [PMID: 22409228 DOI: 10.1021/bi300195b] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Triosephosphate isomerase (TIM) catalyzes the stereospecific 1,2-proton shift at dihydroxyacetone phosphate (DHAP) to give (R)-glyceraldehyde 3-phosphate through a pair of isomeric enzyme-bound cis-enediolate phosphate intermediates. The chemical transformations that occur at the active site of TIM were well understood by the early 1990s. The mechanism for enzyme-catalyzed isomerization is similar to that for the nonenzymatic reaction in water, but the origin of the catalytic rate acceleration is not understood. We review the results of experimental work that show that a substantial fraction of the large 12 kcal/mol intrinsic binding energy of the nonreacting phosphodianion fragment of TIM is utilized to activate the active site side chains for catalysis of proton transfer. Evidence is presented that this activation is due to a phosphodianion-driven conformational change, the most dramatic feature of which is closure of loop 6 over the dianion. The kinetic data are interpreted within the framework of a model in which activation is due to the stabilization by the phosphodianion of a rare, desolvated, loop-closed form of TIM. The dianion binding energy is proposed to drive the otherwise thermodynamically unfavorable desolvation of the solvent-exposed active site. This reduces the effective local dielectric constant of the active site, to enhance stabilizing electrostatic interactions between polar groups and the anionic transition state, and increases the basicity of the carboxylate side chain of Glu-165 that functions to deprotonate the bound carbon acid substrate. A rebuttal is presented to the recent proposal [Samanta, M., Murthy, M. R. N., Balaram, H., and Balaram, P. (2011) ChemBioChem 12, 1886-1895] that the cationic side chain of K12 functions as an active site electrophile to protonate the carbonyl oxygen of DHAP.
Collapse
Affiliation(s)
- John P Richard
- Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260-3000, United States.
| |
Collapse
|