1
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A colorimetric assay for the screening and kinetic analysis of nucleotide sugar 4,6-dehydratases. Anal Biochem 2022; 655:114870. [PMID: 36027972 DOI: 10.1016/j.ab.2022.114870] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2022] [Revised: 08/12/2022] [Accepted: 08/16/2022] [Indexed: 11/22/2022]
Abstract
Nucleotide sugar 4,6-dehydratases belong to the Short-chain Dehydrogenase/Reductase (SDR) superfamily and catalyze the conversion of an NDP-hexose to an NDP-4-keto-6-deoxy hexose, a key step in the biosynthesis of a plethora of deoxy and amino sugars. Here, we present a colorimetric assay for the detection of their reaction products (NDP-4-keto-6-deoxy hexoses) using concentrated sulfuric acid and an ethanolic resorcinol solution. Under these conditions, the keto-function of the dehydratase product reacts specifically with resorcinol to form an orange-red or pink complex for NDP-glucose/GDP-mannose and UDP-N-acetylglucosamine, respectively, with an absorption maximum at 510 nm. The presented assay allows reliable product detection at low concentrations and can be applied in microtiter plates. It thus allows the determination of kinetic enzyme parameters like the optimal temperature, pH, Vmax, KM and kcat, as well as the miniaturization for screening purposes with crude cell extracts. As such, this detection assay opens new possibilities for the characterization and screening of these dehydratases in 96-well plates for different research goals.
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2
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Wang Y, Li X, Wei J, Zhang X, Liu Y. Mechanism of Sugar Ring Contraction and Closure Catalyzed by UDP-d-apiose/UDP-d-xylose Synthase (UAXS). J Chem Inf Model 2022; 62:632-646. [PMID: 35043627 DOI: 10.1021/acs.jcim.1c01408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Uridine diphosphate (UDP)-apiose/UDP-xylose synthase (UAXS) is a member of the short-chain dehydrogenase/reductase superfamily (SDR), which catalyzes the ring contraction and closure of UDP-d-glucuronic acid (UDP-GlcA), affording UDP-apiose and UDP-xylose. UAXS is a special enzyme that integrates ring-opening, decarboxylation, rearrangement, and ring closure/contraction in a single active site. Recently, the ternary complex structure of UAXS was crystallized from Arabidopsis thaliana. In this work, to gain insights into the detailed formation mechanism of UDP-apiose and UDP-xylose, an enzyme-substrate reactant model has been constructed and quantum mechanical/molecular mechanical (QM/MM) calculations have been performed. Our calculation results reveal that the reaction starts from the C4-OH oxidation, which is accompanied by the conformational transformation of the sugar ring from chair type to boat type. The sugar ring-opening is prior to decarboxylation, and the deprotonation of the C2-OH group is the prerequisite for sugar ring-opening. Moreover, the keto-enol tautomerization of the decarboxylated intermediate is a necessary step for ring closure/contraction. Based on our calculation results, more UDP-apiose product was expected, which is in line with the experimental observation. Three titratable residues, Tyr185, Cys100, and Cys140, steer the reaction by proton transfer from or to UDP-GlcA, and Arg182, Glu141, and D337 constitute a proton conduit for sugar C2-OH deprotonation. Although Thr139 and Tyr105 are not directly involved in the enzymatic reaction, they are responsible for promoting the catalysis by forming hydrogen-bonding interactions with GlcA. Our calculations may provide useful information for understanding the catalysis of the SDR family.
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Affiliation(s)
- Yijing Wang
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Xinyi Li
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Jingjing Wei
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Xue Zhang
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Yongjun Liu
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
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3
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Jia T, Guo D, Han Y, Zhou D. Biosynthesis of UDP-2-acetamido-4-formamido-2,4,6-trideoxy-hexose by WekG, WekE, WekF, and WekD: Enzymes in the Wek pathway responsible for O-antigen Assembly in Escherichia coli O119. Carbohydr Res 2021; 507:108388. [PMID: 34271479 DOI: 10.1016/j.carres.2021.108388] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 06/28/2021] [Accepted: 06/28/2021] [Indexed: 11/15/2022]
Abstract
Considering the importance of bacterial glycoconjugates on virulence and host mimicry, there is a need to better understand the biosynthetic pathways of these unusual sugars to identify critical targets involved in bacterial pathogenesis. In this report, we describe the cloning, overexpression, purification, and biochemical characterization of the four central enzymes in the biosynthesis pathway for UDP-2-acetamido-4-formamido-2,4,6-trideoxy-hexose, WekG, WekE, WekF, and WekD. Product peaks from enzyme-substrate reactions were detected by using a combination of capillary electrophoresis (CE) and electrospray ionization-mass spectrometry (ESI-MS). Putative enzyme assignments were provided by protein sequence analysis. Combined with the mass spectrometric characterization of pathway intermediates, we propose a biosynthetic pathway for UDP-2-acetamido-4-formamido-2,4,6-trideoxy-hexose. This process involves C-4, C-6 dehydration, C-4 amination, and formylation. CID-ESI-MSn result confirmed that the final product is a 4 formamido derivative too rather than the 3 formamido derivatives as reported earlier.
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Affiliation(s)
- Tianyuan Jia
- TEDA Institute of Biological Sciences and Biotechnology, Nankai University, Tianjin, China; School of Medicine, Southern University of Science and Technology, Shenzhen, China; Key Laboratory of Microbial Functional Genomics, Tianjin, China; The Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, Nankai University, Tianjin, China
| | - Dan Guo
- TEDA Institute of Biological Sciences and Biotechnology, Nankai University, Tianjin, China; Key Laboratory of Microbial Functional Genomics, Tianjin, China; The Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, Nankai University, Tianjin, China
| | - Yanfang Han
- TEDA Institute of Biological Sciences and Biotechnology, Nankai University, Tianjin, China; Key Laboratory of Microbial Functional Genomics, Tianjin, China; The Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, Nankai University, Tianjin, China
| | - Dawei Zhou
- TEDA Institute of Biological Sciences and Biotechnology, Nankai University, Tianjin, China; Key Laboratory of Microbial Functional Genomics, Tianjin, China; The Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, Nankai University, Tianjin, China.
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4
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Abstract
The outer membrane (OM) of Gram-negative bacteria poses a barrier to antibiotic entry due to its high impermeability. Thus, there is an urgent need to study the function and biogenesis of the OM. In Enterobacterales, an order of bacteria with many pathogenic members, one of the components of the OM is enterobacterial common antigen (ECA). We have known of the presence of ECA on the cell surface of Enterobacterales for many years, but its properties have only more recently begun to be unraveled. ECA is a carbohydrate antigen built of repeating units of three amino sugars, the structure of which is conserved throughout Enterobacterales. There are three forms of ECA, two of which (ECAPG and ECALPS) are located on the cell surface, while one (ECACYC) is located in the periplasm. Awareness of the importance of ECA has increased due to studies of its function that show it plays a vital role in bacterial physiology and interaction with the environment. Here, we review the discovery of ECA, the pathways for the biosynthesis of ECA, and the interactions of its various forms. In addition, we consider the role of ECA in the host immune response, as well as its potential roles in host-pathogen interaction. Furthermore, we explore recent work that offers insights into the cellular function of ECA. This review provides a glimpse of the biological significance of this enigmatic molecule.
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Affiliation(s)
- Ashutosh K Rai
- Department of Biology, Texas A&M University, College Station, Texas, USA
| | - Angela M Mitchell
- Department of Biology, Texas A&M University, College Station, Texas, USA
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5
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Yan Y, Yang J, Wang L, Xu D, Yu Z, Guo X, Horsman GP, Lin S, Tao M, Huang SX. Biosynthetic access to the rare antiarose sugar via an unusual reductase-epimerase. Chem Sci 2020; 11:3959-3964. [PMID: 34122866 PMCID: PMC8152690 DOI: 10.1039/c9sc05766h] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Rubrolones, isatropolones, and rubterolones are recently isolated glycosylated tropolonids with notable biological activity. They share similar aglycone skeletons but differ in their sugar moieties, and rubterolones in particular have a rare deoxysugar antiarose of unknown biosynthetic provenance. During our previously reported biosynthetic elucidation of the tropolone ring and pyridine moiety, gene inactivation experiments revealed that RubS3 is involved in sugar moiety biosynthesis. Here we report the in vitro characterization of RubS3 as a bifunctional reductase/epimerase catalyzing the formation of TDP-d-antiarose by epimerization at C3 and reduction at C4 of the key intermediate TDP-4-keto-6-deoxy-d-glucose. These new findings not only explain the biosynthetic pathway of deoxysugars in rubrolone-like natural products, but also introduce RubS3 as a new family of reductase/epimerase enzymes with potential to supply the rare antiarose unit for expanding the chemical space of glycosylated natural products. Rubrolones, isarubrolones, and rubterolones are recently isolated glycosylated tropolonids with notable biological activity.![]()
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Affiliation(s)
- Yijun Yan
- State Key Laboratory of Phytochemistry and Plant Resources in West China, CAS Center for Excellence in Molecular Plant Sciences, Kunming Institute of Botany, Chinese Academy of Sciences Kunming 650201 China
| | - Jing Yang
- State Key Laboratory of Phytochemistry and Plant Resources in West China, CAS Center for Excellence in Molecular Plant Sciences, Kunming Institute of Botany, Chinese Academy of Sciences Kunming 650201 China
| | - Li Wang
- State Key Laboratory of Phytochemistry and Plant Resources in West China, CAS Center for Excellence in Molecular Plant Sciences, Kunming Institute of Botany, Chinese Academy of Sciences Kunming 650201 China
| | - Dongdong Xu
- State Key Laboratory of Phytochemistry and Plant Resources in West China, CAS Center for Excellence in Molecular Plant Sciences, Kunming Institute of Botany, Chinese Academy of Sciences Kunming 650201 China
| | - Zhiyin Yu
- State Key Laboratory of Phytochemistry and Plant Resources in West China, CAS Center for Excellence in Molecular Plant Sciences, Kunming Institute of Botany, Chinese Academy of Sciences Kunming 650201 China
| | - Xiaowei Guo
- State Key Laboratory of Phytochemistry and Plant Resources in West China, CAS Center for Excellence in Molecular Plant Sciences, Kunming Institute of Botany, Chinese Academy of Sciences Kunming 650201 China
| | - Geoff P Horsman
- Department of Chemistry & Biochemistry, Wilfrid Laurier University Waterloo ON N2L 3C5 Canada
| | - Shuangjun Lin
- State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University 800 Dongchuan Road Shanghai 200240 China
| | - Meifeng Tao
- State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University 800 Dongchuan Road Shanghai 200240 China
| | - Sheng-Xiong Huang
- State Key Laboratory of Phytochemistry and Plant Resources in West China, CAS Center for Excellence in Molecular Plant Sciences, Kunming Institute of Botany, Chinese Academy of Sciences Kunming 650201 China
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6
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A severe leakage of intermediates to shunt products in acarbose biosynthesis. Nat Commun 2020; 11:1468. [PMID: 32193369 PMCID: PMC7081202 DOI: 10.1038/s41467-020-15234-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Accepted: 02/23/2020] [Indexed: 11/08/2022] Open
Abstract
The α-glucosidase inhibitor acarbose, produced by Actinoplanes sp. SE50/110, is a well-known drug for the treatment of type 2 diabetes mellitus. However, the largely unexplored biosynthetic mechanism of this compound has impeded further titer improvement. Herein, we uncover that 1-epi-valienol and valienol, accumulated in the fermentation broth at a strikingly high molar ratio to acarbose, are shunt products that are not directly involved in acarbose biosynthesis. Additionally, we find that inefficient biosynthesis of the amino-deoxyhexose moiety plays a role in the formation of these shunt products. Therefore, strategies to minimize the flux to the shunt products and to maximize the supply of the amino-deoxyhexose moiety are implemented, which increase the acarbose titer by 1.2-fold to 7.4 g L−1. This work provides insights into the biosynthesis of the C7-cyclitol moiety and highlights the importance of assessing shunt product accumulation when seeking to improve the titer of microbial pharmaceutical products. Biosynthetic mechanism for the type 2 diabetes treatment drug acarbose is not fully revealed. Here, the authors show that shunt pathways and inefficient amino-deoxyhexose biosynthesis lead to 1-epi-valienol and valienol accumulation, and minimizing the flux to these shunt products can increase acarbose titer in Actinoplanes species.
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7
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Savino S, Borg AJE, Dennig A, Pfeiffer M, de Giorgi F, Weber H, Dubey KD, Rovira C, Mattevi A, Nidetzky B. Deciphering the enzymatic mechanism of sugar ring contraction in UDP-apiose biosynthesis. Nat Catal 2019; 2:1115-1123. [PMID: 31844840 PMCID: PMC6914363 DOI: 10.1038/s41929-019-0382-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
D-Apiose is a C-branched pentose sugar important for plant cell wall development. Its biosynthesis as UDP-D-apiose involves decarboxylation of the UDP-D-glucuronic acid precursor coupled to pyranosyl-to-furanosyl sugar ring contraction. This unusual multistep reaction is catalyzed within a single active site by UDP-D-apiose/UDP-D-xylose synthase (UAXS). Here, we decipher the UAXS catalytic mechanism based on crystal structures of the enzyme from Arabidopsis thaliana, molecular dynamics simulations expanded by QM/MM calculations, and mutational-mechanistic analyses. Our studies show how UAXS uniquely integrates a classical catalytic cycle of oxidation and reduction by a tightly bound nicotinamide coenzyme with retro-aldol/aldol chemistry for the sugar ring contraction. They further demonstrate that decarboxylation occurs only after the sugar ring opening and identify the thiol group of Cys100 in steering the sugar skeleton rearrangement by proton transfer to and from the C3’. The mechanistic features of UAXS highlight the evolutionary expansion of the basic catalytic apparatus of short-chain dehydrogenases/reductases for functional versatility in sugar biosynthesis.
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Affiliation(s)
- Simone Savino
- Department of Biology and Biotechnology, University of Pavia, Via Ferrata 1, 27100, Pavia, Italy.,Austrian Centre of Industrial Biotechnology, Petersgasse 14, 8010 Graz, Austria
| | - Annika J E Borg
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Petersgasse 12, 8010 Graz, Austria
| | - Alexander Dennig
- Austrian Centre of Industrial Biotechnology, Petersgasse 14, 8010 Graz, Austria.,Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Petersgasse 12, 8010 Graz, Austria
| | - Martin Pfeiffer
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Petersgasse 12, 8010 Graz, Austria
| | - Francesca de Giorgi
- Department of Biology and Biotechnology, University of Pavia, Via Ferrata 1, 27100, Pavia, Italy.,Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Petersgasse 12, 8010 Graz, Austria
| | - Hansjörg Weber
- Institute of Organic Chemistry, Graz University of Technology, NAWI Graz, Stremayrgasse 9, 8010 Graz, Austria
| | - Kshatresh Dutta Dubey
- Department of Inorganic and Organic Chemistry (Organic Chemistry Section) & Institute of Computational and Theoretical Chemistry (IQTCUB), University of Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain
| | - Carme Rovira
- Department of Inorganic and Organic Chemistry (Organic Chemistry Section) & Institute of Computational and Theoretical Chemistry (IQTCUB), University of Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain.,Catalan Institution for Advanced Studies (ICREA), Passeig Lluís Companys 23, 08010 Barcelona
| | - Andrea Mattevi
- Department of Biology and Biotechnology, University of Pavia, Via Ferrata 1, 27100, Pavia, Italy
| | - Bernd Nidetzky
- Austrian Centre of Industrial Biotechnology, Petersgasse 14, 8010 Graz, Austria.,Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Petersgasse 12, 8010 Graz, Austria
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8
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Pfeiffer M, Johansson C, Krojer T, Kavanagh KL, Oppermann U, Nidetzky B. A Parsimonious Mechanism of Sugar Dehydration by Human GDP-Mannose-4,6-dehydratase. ACS Catal 2019; 9:2962-2968. [PMID: 30984471 PMCID: PMC6454399 DOI: 10.1021/acscatal.9b00064] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Revised: 02/22/2019] [Indexed: 01/25/2023]
Abstract
![]()
Biosynthesis
of 6-deoxy sugars, including l-fucose, involves
a mechanistically complex, enzymatic 4,6-dehydration of hexose nucleotide
precursors as the first committed step. Here, we determined pre- and
postcatalytic complex structures of the human GDP-mannose 4,6-dehydratase
at atomic resolution. These structures together with results of molecular
dynamics simulation and biochemical characterization of wildtype and
mutant enzymes reveal elusive mechanistic details of water elimination
from GDP-mannose C5″ and C6″, coupled to NADP-mediated
hydride transfer from C4″ to C6″. We show that concerted
acid–base catalysis from only two active-site groups, Tyr179 and Glu157, promotes a syn 1,4-elimination
from an enol (not an enolate) intermediate. We also show that the
overall multistep catalytic reaction involves the fewest position
changes of enzyme and substrate groups and that it proceeds under
conserved exploitation of the basic (minimal) catalytic machinery
of short-chain dehydrogenase/reductases.
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Affiliation(s)
- Martin Pfeiffer
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, 8010 Graz, Austria
| | - Catrine Johansson
- Structural Genomics Consortium, University of Oxford, Oxford OX3 7DQ, United Kingdom
- Botnar Research Centre, University of Oxford, Oxford OX3 7LD, United Kingdom
| | - Tobias Krojer
- Structural Genomics Consortium, University of Oxford, Oxford OX3 7DQ, United Kingdom
| | - Kathryn L Kavanagh
- Structural Genomics Consortium, University of Oxford, Oxford OX3 7DQ, United Kingdom
| | - Udo Oppermann
- Structural Genomics Consortium, University of Oxford, Oxford OX3 7DQ, United Kingdom
- Botnar Research Centre, University of Oxford, Oxford OX3 7LD, United Kingdom
- Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, 79085 Freiburg, Germany
| | - Bernd Nidetzky
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, 8010 Graz, Austria
- Austrian Centre of Industrial Biotechnology, 8010 Graz, Austria
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9
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Gokey T, Halavaty AS, Minasov G, Anderson WF, Kuhn ML. Structure of the Bacillus anthracis dTDP-l-rhamnose biosynthetic pathway enzyme: dTDP-α-d-glucose 4,6-dehydratase, RfbB. J Struct Biol 2018; 202:175-181. [PMID: 29331609 DOI: 10.1016/j.jsb.2018.01.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2017] [Revised: 01/08/2018] [Accepted: 01/09/2018] [Indexed: 11/27/2022]
Abstract
Many bacteria require l-rhamnose as a key cell wall component. This sugar is transferred to the cell wall using an activated donor dTDP-l-rhamnose, which is produced by the dTDP-l-rhamnose biosynthetic pathway. We determined the crystal structure of the second enzyme of this pathway dTDP-α-d-glucose 4,6-dehydratase (RfbB) from Bacillus anthracis. Interestingly, RfbB only crystallized in the presence of the third enzyme of the pathway RfbC; however, RfbC was not present in the crystal. Our work represents the first complete structural characterization of the four proteins of this pathway in a single Gram-positive bacterium.
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Affiliation(s)
- Trevor Gokey
- Department of Chemistry and Biochemistry, San Francisco State University, USA
| | - Andrei S Halavaty
- Department of Biochemistry and Molecular Genetics, Northwestern University Feinberg School of Medicine, USA; Center for Structural Genomics of Infectious Diseases (CSGID), USA
| | - George Minasov
- Department of Biochemistry and Molecular Genetics, Northwestern University Feinberg School of Medicine, USA; Center for Structural Genomics of Infectious Diseases (CSGID), USA
| | - Wayne F Anderson
- Department of Biochemistry and Molecular Genetics, Northwestern University Feinberg School of Medicine, USA; Center for Structural Genomics of Infectious Diseases (CSGID), USA
| | - Misty L Kuhn
- Department of Chemistry and Biochemistry, San Francisco State University, USA.
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10
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Standish AJ, Teh MY, Tran ENH, Doyle MT, Baker PJ, Morona R. Unprecedented Abundance of Protein Tyrosine Phosphorylation Modulates Shigella flexneri Virulence. J Mol Biol 2016; 428:4197-4208. [PMID: 27380737 DOI: 10.1016/j.jmb.2016.06.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Revised: 06/06/2016] [Accepted: 06/23/2016] [Indexed: 01/09/2023]
Abstract
Evidence is accumulating that protein tyrosine phosphorylation plays a crucial role in the ability of important human bacterial pathogens to cause disease. While most works have concentrated on its role in the regulation of a major bacterial virulence factor, the polysaccharide capsule, recent studies have suggested a much broader role for this post-translational modification. This prompted us to investigate protein tyrosine phosphorylation in the human pathogen Shigella flexneri. We first completed a tyrosine phosphoproteome, identifying 905 unique tyrosine phosphorylation sites on at least 573 proteins (approximately 15% of all proteins). This is the most tyrosine-phosphorylated sites and proteins in a single bacterium identified to date, substantially more than the level seen in eukaryotic cells. Most had not previously been identified and included proteins encoded by the virulence plasmid, which is essential for S. flexneri to invade cells and cause disease. In order to investigate the function of these phosphorylation sites in important virulence factors, phosphomimetic and ablative mutations were constructed in the type 3 secretion system ATPase Spa47 and the master virulence regulator VirB. This revealed that tyrosine residues phosphorylated in our study are critical for Spa47 and VirB activity, and tyrosine phosphorylation likely regulates their functional activity and subsequently the virulence of this major human pathogen. This study suggests that tyrosine phosphorylation plays a critical role in regulating a wide variety of virulence factors in the human pathogen S. flexneri and serves as a base for future studies defining its complete role.
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Affiliation(s)
- Alistair James Standish
- Research Centre for Infectious Diseases, Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia.
| | - Min Yan Teh
- Research Centre for Infectious Diseases, Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Elizabeth Ngoc Hoa Tran
- Research Centre for Infectious Diseases, Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Matthew Thomas Doyle
- Research Centre for Infectious Diseases, Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Paul J Baker
- Research Centre for Infectious Diseases, Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Renato Morona
- Research Centre for Infectious Diseases, Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
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11
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Tiwari P, Singh N, Dixit A, Choudhury D. Multivariate sequence analysis reveals additional function impacting residues in the SDR superfamily. Proteins 2014; 82:2842-56. [DOI: 10.1002/prot.24647] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2014] [Revised: 06/19/2014] [Accepted: 07/15/2014] [Indexed: 11/08/2022]
Affiliation(s)
- Pratibha Tiwari
- School of Biotechnology, Jawaharlal Nehru University; New Delhi 110 067 India
| | - Noopur Singh
- School of Biotechnology, Jawaharlal Nehru University; New Delhi 110 067 India
| | - Aparna Dixit
- School of Biotechnology, Jawaharlal Nehru University; New Delhi 110 067 India
| | - Devapriya Choudhury
- School of Biotechnology, Jawaharlal Nehru University; New Delhi 110 067 India
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12
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Ma G, Liu Y. The reaction mechanism of UDP-GlcNAc 5,6-dehydratase: a quantum mechanical/molecular mechanical (QM/MM) study. Theor Chem Acc 2014. [DOI: 10.1007/s00214-014-1524-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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13
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Ma G, Dong L, Liu Y. Insights into the catalytic mechanism of dTDP-glucose 4,6-dehydratase from quantum mechanics/molecular mechanics simulations. RSC Adv 2014. [DOI: 10.1039/c4ra04406a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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14
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Schwans JP, Sunden F, Gonzalez A, Tsai Y, Herschlag D. Uncovering the determinants of a highly perturbed tyrosine pKa in the active site of ketosteroid isomerase. Biochemistry 2013; 52:7840-55. [PMID: 24151972 PMCID: PMC3890242 DOI: 10.1021/bi401083b] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Within the idiosyncratic enzyme active-site environment, side chain and ligand pKa values can be profoundly perturbed relative to their values in aqueous solution. Whereas structural inspection of systems has often attributed perturbed pKa values to dominant contributions from placement near charged groups or within hydrophobic pockets, Tyr57 of a Pseudomonas putida ketosteroid isomerase (KSI) mutant, suggested to have a pKa perturbed by nearly 4 units to 6.3, is situated within a solvent-exposed active site devoid of cationic side chains, metal ions, or cofactors. Extensive comparisons among 45 variants with mutations in and around the KSI active site, along with protein semisynthesis, (13)C NMR spectroscopy, absorbance spectroscopy, and X-ray crystallography, was used to unravel the basis for this perturbed Tyr pKa. The results suggest that the origin of large energetic perturbations are more complex than suggested by visual inspection. For example, the introduction of positively charged residues near Tyr57 raises its pKa rather than lowers it; this effect, and part of the increase in the Tyr pKa from the introduction of nearby anionic groups, arises from accompanying active-site structural rearrangements. Other mutations with large effects also cause structural perturbations or appear to displace a structured water molecule that is part of a stabilizing hydrogen-bond network. Our results lead to a model in which three hydrogen bonds are donated to the stabilized ionized Tyr, with these hydrogen-bond donors, two Tyr side chains, and a water molecule positioned by other side chains and by a water-mediated hydrogen-bond network. These results support the notion that large energetic effects are often the consequence of multiple stabilizing interactions rather than a single dominant interaction. Most generally, this work provides a case study for how extensive and comprehensive comparisons via site-directed mutagenesis in a tight feedback loop with structural analysis can greatly facilitate our understanding of enzyme active-site energetics. The extensive data set provided may also be a valuable resource for those wishing to extensively test computational approaches for determining enzymatic pKa values and energetic effects.
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Affiliation(s)
- Jason P. Schwans
- Department of Biochemistry, Stanford University, Stanford, California 94305
| | - Fanny Sunden
- Department of Biochemistry, Stanford University, Stanford, California 94305
| | - Ana Gonzalez
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025
| | - Yingssu Tsai
- Department of Chemistry, Stanford University, Stanford, California 94305
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025
| | - Daniel Herschlag
- Department of Biochemistry, Stanford University, Stanford, California 94305
- Department of Chemistry, Stanford University, Stanford, California 94305
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15
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Cefalo AD, Broadbent JR, Welker DL. The Streptococcus thermophilus protein Wzh functions as a phosphotyrosine phosphatase. Can J Microbiol 2013; 59:391-8. [PMID: 23750953 DOI: 10.1139/cjm-2013-0094] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Amino acid residues that are important for metal binding and catalysis in Gram-positive phosphotyrosine phosphatases were identified in the Wzh protein of Streptococcus thermophilus MR-1C by using sequence comparisons. A His-tagged fusion Wzh protein was purified from Escherichia coli cultures and tested for phosphatase activity against synthetic phosphotyrosine and phosphoserine-threonine peptides. Purified Wzh released 2316.5 ± 138.7 pmol PO4·min(-1)·μg(-1) from phosphotyrosine peptide-1 and 2345.7 ± 135.2 pmol PO4·min(-1)·μg(-1) from phosphotyrosine peptide-2. The presence of the phosphotyrosine phosphatase inhibitor sodium vanadate decreased purified Wzh activity by 45%-50% at 1 mmol·L(-1), 74%-84% at 5 mmol·L(-1), and by at least 88% at 10 mmol·L(-1). Purified Wzh had no detectable activity against the phosphoserine-threonine peptide. These results clearly establish that S. thermophilus MR-1C Wzh functions as a phosphotyrosine phosphatase that could function to remove phosphate groups from proteins involved in exopolysaccharide biosynthesis, including the protein tyrosine kinase Wze and priming glycosyltransferase.
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Affiliation(s)
- Angela D Cefalo
- Department of Biology, Utah State University, 5305 Old Main Hill, Logan, UT 84322, USA.
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16
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Beerens K, Soetaert W, Desmet T. Characterization and mutational analysis of the UDP-Glc(NAc) 4-epimerase from Marinithermus hydrothermalis. Appl Microbiol Biotechnol 2012; 97:7733-40. [DOI: 10.1007/s00253-012-4635-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2012] [Revised: 11/28/2012] [Accepted: 12/03/2012] [Indexed: 12/15/2022]
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17
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Singh S, Phillips GN, Thorson JS. The structural biology of enzymes involved in natural product glycosylation. Nat Prod Rep 2012; 29:1201-37. [PMID: 22688446 DOI: 10.1039/c2np20039b] [Citation(s) in RCA: 89] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The glycosylation of microbial natural products often dramatically influences the biological and/or pharmacological activities of the parental metabolite. Over the past decade, crystal structures of several enzymes involved in the biosynthesis and attachment of novel sugars found appended to natural products have emerged. In many cases, these studies have paved the way to a better understanding of the corresponding enzyme mechanism of action and have served as a starting point for engineering variant enzymes to facilitate to production of differentially-glycosylated natural products. This review specifically summarizes the structural studies of bacterial enzymes involved in biosynthesis of novel sugar nucleotides.
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Affiliation(s)
- Shanteri Singh
- Laboratory for Biosynthetic Chemistry, Pharmaceutical Sciences Division, School of Pharmacy, University of Wisconsin-Madison, 777 Highland Avenue, Madison, WI 53705, USA
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18
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Quantitative, directional measurement of electric field heterogeneity in the active site of ketosteroid isomerase. Proc Natl Acad Sci U S A 2012; 109:E299-308. [PMID: 22308339 DOI: 10.1073/pnas.1111566109] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Understanding the electrostatic forces and features within highly heterogeneous, anisotropic, and chemically complex enzyme active sites and their connection to biological catalysis remains a longstanding challenge, in part due to the paucity of incisive experimental probes of electrostatic properties within proteins. To quantitatively assess the landscape of electrostatic fields at discrete locations and orientations within an enzyme active site, we have incorporated site-specific thiocyanate vibrational probes into multiple positions within bacterial ketosteroid isomerase. A battery of X-ray crystallographic, vibrational Stark spectroscopy, and NMR studies revealed electrostatic field heterogeneity of 8 MV/cm between active site probe locations and widely differing sensitivities of discrete probes to common electrostatic perturbations from mutation, ligand binding, and pH changes. Electrostatic calculations based on active site ionization states assigned by literature precedent and computational pK(a) prediction were unable to quantitatively account for the observed vibrational band shifts. However, electrostatic models of the D40N mutant gave qualitative agreement with the observed vibrational effects when an unusual ionization of an active site tyrosine with a pK(a) near 7 was included. UV-absorbance and (13)C NMR experiments confirmed the presence of a tyrosinate in the active site, in agreement with electrostatic models. This work provides the most direct measure of the heterogeneous and anisotropic nature of the electrostatic environment within an enzyme active site, and these measurements provide incisive benchmarks for further developing accurate computational models and a foundation for future tests of electrostatics in enzymatic catalysis.
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19
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Gu X, Glushka J, Lee SG, Bar-Peled M. Biosynthesis of a new UDP-sugar, UDP-2-acetamido-2-deoxyxylose, in the human pathogen Bacillus cereus subspecies cytotoxis NVH 391-98. J Biol Chem 2010; 285:24825-33. [PMID: 20529859 DOI: 10.1074/jbc.m110.125872] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have identified an operon and characterized the functions of two genes from the severe food-poisoning bacterium, Bacillus cereus subsp. cytotoxis NVH 391-98, that are involved in the synthesis of a unique UDP-sugar, UDP-2-acetamido-2-deoxyxylose (UDP-N-acetyl-xylosamine, UDP-XylNAc). UGlcNAcDH encodes a UDP-N-acetyl-glucosamine 6-dehydrogenase, converting UDP-N-acetylglucosamine (UDP-GlcNAc) to UDP-N-acetyl-glucosaminuronic acid (UDP-GlcNAcA). The second gene in the operon, UXNAcS, encodes a distinct decarboxylase not previously described in the literature, which catalyzes the formation of UDP-XylNAc from UDP-GlcNAcA in the presence of exogenous NAD(+). UXNAcS is specific and cannot utilize UDP-glucuronic acid and UDP-galacturonic acid as substrates. UXNAcS is active as a dimer with catalytic efficiency of 7 mM(-1) s(-1). The activity of UXNAcS is completely abolished by NADH but unaffected by UDP-xylose. A real-time NMR-based assay showed unambiguously the dual enzymatic conversions of UDP-GlcNAc to UDP-GlcNAcA and subsequently to UDP-XylNAc. From the analyses of all publicly available sequenced genomes, it appears that UXNAcS is restricted to pathogenic Bacillus species, including Bacillus anthracis and Bacillus thuringiensis. The identification of UXNAcS provides insight into the formation of UDP-XylNAc. Understanding the metabolic pathways involved in the utilization of this amino-sugar may allow the development of drugs to combat and eradicate the disease.
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Affiliation(s)
- Xiaogang Gu
- Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602, USA
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20
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Huang RB, Du QS, Wang CH, Liao SM, Chou KC. A fast and accurate method for predicting pKa of residues in proteins. Protein Eng Des Sel 2010; 23:35-42. [PMID: 19926592 DOI: 10.1093/protein/gzp067] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Predicting the pH-activities of residues in proteins is an important problem in enzyme engineering and protein design. A novel predictor called 'Pred-pK(a)' was developed based on the physicochemical properties of amino acids and protein 3D structure. The Pred-pK(a) approach considers the influence of all other residues of the protein to predict the pK(a) value of an ionizable residue. An empirical equation was formulated, in which the pK(a) value was a distance-dependent function of physicochemical parameters of 20 amino acid types, describing their electrostatic and van der Waals interaction, as well as the effects of hydrogen bonds and solvation. Two sets of coefficients, {a(alpha)} and {b(l)}, were used in the predictor: {a(alpha)} is the weight factors of 20 amino acid types and {b(l)} is the weight factors of physicochemical properties of amino acids. An iterative double least square procedure was proposed to solve the two sets of weight factors alternately and iteratively in a training set. The two coefficient sets {a(alpha)} and {b(l)} thus obtained were used to predict the pK(a) values of residues in a protein. The average predictive error is +/-0.6 pH in less than a minute in common personal computer.
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Affiliation(s)
- Ri-Bo Huang
- Guangxi Academy of Sciences, 98 Daling Road, Nanning, Guangxi 530004, People's Republic of China
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21
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Hagelueken G, Huang H, Mainprize IL, Whitfield C, Naismith JH. Crystal structures of Wzb of Escherichia coli and CpsB of Streptococcus pneumoniae, representatives of two families of tyrosine phosphatases that regulate capsule assembly. J Mol Biol 2009; 392:678-88. [PMID: 19616007 PMCID: PMC2777267 DOI: 10.1016/j.jmb.2009.07.026] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2009] [Revised: 07/07/2009] [Accepted: 07/09/2009] [Indexed: 12/11/2022]
Abstract
Many Gram-positive and Gram-negative bacteria utilize polysaccharide surface layers called capsules to evade the immune system; consequently, the synthesis and export of the capsule are a potential therapeutic target. In Escherichia coli K-30, the integral membrane tyrosine autokinase Wzc and the cognate phosphatase Wzb have been shown to be key for both synthesis and assembly of capsular polysaccharides. In the Gram-positive bacterium Streptococcus pneumoniae, the CpsCD complex is analogous to Wzc and the phosphatase CpsB is the corresponding cognate phosphatase. The phosphatases are known to dephosphorylate their corresponding autokinases, yet despite their functional equivalence, they share no sequence homology. We present the structure of Wzb in complex with phosphate and high-resolution structures of apo-CpsB and a phosphate-complexed CpsB. We show that both proteins are active toward Wzc and thereby demonstrate that CpsB is not specific for CpsCD. CpsB is a novel enzyme and represents the first solved structure of a tyrosine phosphatase from a Gram-positive bacterium. Wzb and CpsB have completely different structures, suggesting that they must operate by very different mechanisms. Although the mechanism of Wzb can be inferred from previous studies, CpsB appears to have a tyrosine phosphatase mechanism not observed before. We propose a chemical mechanism for CpsB based on site-directed mutagenesis and structural data.
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Affiliation(s)
- Gregor Hagelueken
- Centre for Biomolecular Sciences, The University of St. Andrews, Fife KY16 9RH, UK
| | - Hexian Huang
- Centre for Biomolecular Sciences, The University of St. Andrews, Fife KY16 9RH, UK
| | - Iain L. Mainprize
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
| | - Chris Whitfield
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
| | - James H. Naismith
- Centre for Biomolecular Sciences, The University of St. Andrews, Fife KY16 9RH, UK
- Corresponding author.
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22
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Chen YL, Chen YH, Lin YC, Tsai KC, Chiu HT. Functional characterization and substrate specificity of spinosyn rhamnosyltransferase by in vitro reconstitution of spinosyn biosynthetic enzymes. J Biol Chem 2009; 284:7352-63. [PMID: 19126547 DOI: 10.1074/jbc.m808441200] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Spinosyn, a potent insecticide, is a novel tetracyclic polyketide decorated with d-forosamine and tri-O-methyl-L-rhamnose. Spinosyn rhamnosyltransferase (SpnG) is a key biocatalyst with unique sequence identity and controls the biosynthetic maturation of spinosyn. The rhamnose is critical for the spinosyn insecticidal activity and cell wall biosynthesis of the spinosyn producer, Saccharopolyspora spinosa. In this study, we have functionally expressed and characterized SpnG and the three enzymes, Gdh, Epi, and Kre, responsible for dTDP-L-rhamnose biosynthesis in S. spinosa by purified enzymes from Escherichia coli. Most notably, the substrate specificity of SpnG was thoroughly characterized by kinetic and inhibition experiments using various NDP sugar analogs made by an in situ combination of NDP-sugar-modifying enzymes. SpnG was found to exhibit striking substrate promiscuity, yielding corresponding glycosylated variants. Moreover, the critical residues presumably involved in catalytic mechanism of Gdh and SpnG were functionally evaluated by site-directed mutagenesis. The information gained from this study has provided important insight into molecular recognition and mechanism of the enzymes, especially SpnG. The results have made possible the structure-activity characterization of SpnG, as well as the use of SpnG or its engineered form to serve as a combinatorial tool to make spinosyn analogs with altered biological activities and potency.
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Affiliation(s)
- Yi-Lin Chen
- Department of Biological Science and Technology, 75 Po-Ai St., National Chiao Tung University, Hsinchu 300, Taiwan
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23
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Theoretical calculations of the catalytic triad in short-chain alcohol dehydrogenases/reductases. Biophys J 2007; 94:1412-27. [PMID: 17981907 DOI: 10.1529/biophysj.107.111096] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Three highly conserved active site residues (Ser, Tyr, and Lys) of the family of short-chain alcohol dehydrogenases/reductases (SDRs) were demonstrated to be essential for catalytic activity and have been denoted the catalytic triad of SDRs. In this study computational methods were adopted to study the ionization properties of these amino acids in SDRs from Drosophila melanogaster and Drosophila lebanonensis. Three enzyme models, with different ionization scenarios of the catalytic triad that might be possible when inhibitors bind to the enzyme cofactor complex, were constructed. The binding of the two alcohol competitive inhibitors were studied using automatic docking by the Internal Coordinate Mechanics program, molecular dynamic (MD) simulations with the AMBER program package, calculation of the free energy of ligand binding by the linear interaction energy method, and the hydropathic interactions force field. The calculations indicated that deprotonated Tyr acts as a strong base in the binary enzyme-NAD(+) complex. Molecular dynamic simulations for 5 ns confirmed that deprotonated Tyr is essential for anchoring and orientating the inhibitors at the active site, which might be a general trend for the family of SDRs. The findings here have implications for the development of therapeutically important SDR inhibitors.
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24
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King JD, Harmer NJ, Preston A, Palmer CM, Rejzek M, Field RA, Blundell TL, Maskell DJ. Predicting protein function from structure--the roles of short-chain dehydrogenase/reductase enzymes in Bordetella O-antigen biosynthesis. J Mol Biol 2007; 374:749-63. [PMID: 17950751 PMCID: PMC2279256 DOI: 10.1016/j.jmb.2007.09.055] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2007] [Revised: 09/19/2007] [Accepted: 09/20/2007] [Indexed: 11/16/2022]
Abstract
The pathogenic bacteria Bordetella parapertussis and Bordetella bronchiseptica express a lipopolysaccharide O antigen containing a polymer of 2,3-diacetamido-2,3-dideoxy-l-galacturonic acid. The O-antigen cluster contains three neighbouring genes that encode proteins belonging to the short-chain dehydrogenase/reductase (SDR) family, wbmF, wbmG and wbmH, and we aimed to elucidate their individual functions. Mutation and complementation implicate each gene in O-antigen expression but, as their putative sugar nucleotide substrates are not currently available, biochemical characterisation of WbmF, WbmG and WbmH is impractical at the present time. SDR family members catalyse a wide range of chemical reactions including oxidation, reduction and epimerisation. Because they typically share low sequence conservation, however, catalytic function cannot be predicted from sequence analysis alone. In this context, structural characterisation of the native proteins, co-crystals and small-molecule soaks enables differentiation of the functions of WbmF, WbmG and WbmH. These proteins exhibit typical SDR architecture and coordinate NAD. In the substrate-binding domain, all three enzymes bind uridyl nucleotides. WbmG contains a typical SDR catalytic TYK triad, which is required for oxidoreductase function, but the active site is devoid of additional acid-base functionality. Similarly, WbmH possesses a TYK triad, but an otherwise feature-poor active site. Consequently, 3,5-epimerase function can probably be ruled out for these enzymes. The WbmF active site contains conserved 3,5-epimerase features, namely, a positionally conserved cysteine (Cys133) and basic side chain (His90 or Asn213), but lacks the serine/threonine component of the SDR triad and therefore may not act as an oxidoreductase. The data suggest a pathway for synthesis of the O-antigen precursor UDP-2,3-diacetamido-2,3-dideoxy-l-galacturonic acid and illustrate the usefulness of structural data in predicting protein function.
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Affiliation(s)
- Jerry D King
- Department of Veterinary Medicine, Madingley Road, University of Cambridge, Cambridge CB3 0ES, UK.
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25
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Steuber H, Czodrowski P, Sotriffer CA, Klebe G. Tracing changes in protonation: a prerequisite to factorize thermodynamic data of inhibitor binding to aldose reductase. J Mol Biol 2007; 373:1305-20. [PMID: 17905306 DOI: 10.1016/j.jmb.2007.08.063] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2007] [Revised: 08/25/2007] [Accepted: 08/29/2007] [Indexed: 11/17/2022]
Abstract
To prevent diabetic complications derived from enhanced glucose flux via the polyol pathway the development of aldose reductase inhibitors (ARIs) has been established as a promising therapeutic concept. Here, we study the binding process of inhibitors to aldose reductase (ALR2) with respect to changes of the protonation inventory upon complex formation. Knowledge of such processes is a prerequisite to factorize the binding free energy into enthalpic and entropic contributions on an absolute scale. Our isothermal titration calorimetry (ITC) measurements suggest a proton uptake upon complex formation with carboxylate-type inhibitors. As the protonation event will contribute strongly to the enthalpic signal recorded during ITC experiments, knowledge about the proton-accepting and releasing functional groups of the system is of utmost importance. However, this is intricate to retrieve, if, as in the present case, both, binding site and ligand possess several titratable groups. Here, we present pKa calculations complemented by mutagenesis and thermodynamic measurements suggesting a tyrosine residue located in the catalytic site (Tyr48) as a likely candidate to act as proton acceptor upon inhibitor binding, as it occurs deprotonated to a remarkable extent if only the cofactor NADP+ is bound. We furthermore provide evidence that the protonation state and binding thermodynamics depend strongly on the oxidation state of the cofactor;s nicotinamide moiety. Binding thermodynamics of IDD 388, IDD 393, tolrestat, sorbinil, and fidarestat are discussed in the context of substituent effects.
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Affiliation(s)
- Holger Steuber
- Department of Pharmaceutical Chemistry, Philipps-University Marburg, Marbacher Weg 6, 35032 Marburg, Germany
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26
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Ishiyama N, Creuzenet C, Miller WL, Demendi M, Anderson EM, Harauz G, Lam JS, Berghuis AM. Structural studies of FlaA1 from Helicobacter pylori reveal the mechanism for inverting 4,6-dehydratase activity. J Biol Chem 2006; 281:24489-95. [PMID: 16651261 DOI: 10.1074/jbc.m602393200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
FlaA1 from the human pathogen Helicobacter pylori is an enzyme involved in saccharide biosynthesis that has been shown to be essential for pathogenicity. Here we present five crystal structures of FlaA1 in the presence of substrate, inhibitors, and bound cofactor, with resolutions ranging from 2.8 to 1.9 A. These structures reveal that the enzyme is a novel member of the short-chain dehydrogenase/reductase superfamily. Additional electron microscopy studies show the enzyme to possess a hexameric doughnut-shaped quaternary structure. NMR analyses of "real time" enzyme-substrate reactions indicate that FlaA1 is a UDP-GlcNAc-inverting 4,6-dehydratase, suggesting that the enzyme catalyzes the first step in the biosynthetic pathway of a pseudaminic acid derivative, which is implicated in protein glycosylation. Guided by evidence from site-directed mutagenesis and computational simulations, a three-step reaction mechanism is proposed that involves Lys-133 functioning as both a catalytic acid and base.
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Affiliation(s)
- Noboru Ishiyama
- Department of Biochemistry and Department of Microbiology and Immunology, McGill University, Montreal, Quebec
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27
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Toseland CP, McSparron H, Davies MN, Flower DR. PPD v1.0--an integrated, web-accessible database of experimentally determined protein pKa values. Nucleic Acids Res 2006; 34:D199-203. [PMID: 16381845 PMCID: PMC1347398 DOI: 10.1093/nar/gkj035] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The Protein pK(a) Database (PPD) v1.0 provides a compendium of protein residue-specific ionization equilibria (pK(a) values), as collated from the primary literature, in the form of a web-accessible postgreSQL relational database. Ionizable residues play key roles in the molecular mechanisms that underlie many biological phenomena, including protein folding and enzyme catalysis. The PPD serves as a general protein pK(a) archive and as a source of data that allows for the development and improvement of pK(a) prediction systems. The database is accessed through an HTML interface, which offers two fast, efficient search methods: an amino acid-based query and a Basic Local Alignment Search Tool search. Entries also give details of experimental techniques and links to other key databases, such as National Center for Biotechnology Information and the Protein Data Bank, providing the user with considerable background information. The database can be found at the following URL: http://www.jenner.ac.uk/PPD.
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Affiliation(s)
| | | | | | - Darren R. Flower
- To whom correspondence should be addressed. Tel: +44 1635 577954; Fax: +44 1635 577901 577908;
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28
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Schroeder EK, Basso LA, Santos DS, de Souza ON. Molecular dynamics simulation studies of the wild-type, I21V, and I16T mutants of isoniazid-resistant Mycobacterium tuberculosis enoyl reductase (InhA) in complex with NADH: toward the understanding of NADH-InhA different affinities. Biophys J 2005; 89:876-84. [PMID: 15908576 PMCID: PMC1366637 DOI: 10.1529/biophysj.104.053512] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The increasing prevalence of tuberculosis in many areas of the world, associated with the rise in drug-resistant Mycobacterium tuberculosis (MTB) strains, presents a major threat to global health. InhA, the enoyl-ACP reductase from MTB, catalyzes the nicotinamide adenine dinucleotide (NADH)-dependent reduction of long-chain trans-2-enoyl-ACP fatty acids, an intermediate in mycolic acid biosynthesis. Mutations in the structural gene for InhA are associated with isoniazid resistance in vivo due to a reduced affinity for NADH, suggesting that the mechanism of drug resistance may be related to specific interactions between enzyme and cofactor within the NADH binding site. To compare the molecular events underlying ligand affinity in the wild-type, I21V, and I16T mutant enzymes and to identify the molecular aspects related to resistance, molecular dynamics simulations of fully solvated NADH-InhA (wild-type and mutants) were performed. Although very flexible, in the wild-type InhA-NADH complex, the NADH molecule keeps its extended conformation firmly bound to the enzyme's binding site. In the mutant complexes, the NADH pyrophosphate moiety undergoes considerable conformational changes, reducing its interactions with its binding site and probably indicating the initial phase of ligand expulsion from the cavity. This study should contribute to our understanding of specific molecular mechanisms of drug resistance, which is central to the design of more potent antimycobacterial agents for controlling tuberculosis.
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Affiliation(s)
- Evelyn Koeche Schroeder
- Laboratório de Bioinformática, Modelagem e Simulação de Biossistemas-LABIO, PPGCC, Faculdade de Informática, PUCRS, Porto Alegre, RS, Brazil
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29
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Abstract
The rapid progress in structural and molecular biology over the past fifteen years has allowed chemists to access the structures of enzymes, of their complexes and of mutants. This wealth of structural information has led to a surge in the interest in enzymes as elegant chemical catalysts. Enzymology is a distinguished field and has been making vital contributions to medicine and basic science long before structural biology. This review for the Colworth Medal Lecture discusses work from the author's laboratory. This work has been carried out in collaboration with many other laboratories. The work has mapped out the chemical mechanisms and structures of interesting novel enzymes. The review tries to highlight the interesting chemical aspects of the mechanisms involved and how structural analysis has provided a detailed insight. The review focuses on carbohydrate-processing pathways in bacteria, and includes some recent data on an integral membrane protein.
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Affiliation(s)
- J H Naismith
- Centre for Biomolecular Sciences, The University, St Andrews, KY16 9ST, UK.
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30
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Benach J, Winberg JO, Svendsen JS, Atrian S, Gonzàlez-Duarte R, Ladenstein R. Drosophila alcohol dehydrogenase: acetate-enzyme interactions and novel insights into the effects of electrostatics on catalysis. J Mol Biol 2005; 345:579-98. [PMID: 15581900 DOI: 10.1016/j.jmb.2004.10.028] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2004] [Revised: 09/29/2004] [Accepted: 10/11/2004] [Indexed: 11/19/2022]
Abstract
Drosophila alcohol dehydrogenase (DADH) is an NAD+-dependent enzyme that catalyzes the oxidation of alcohols to aldehydes/ketones and that is also able to further oxidize aldehydes to their corresponding carboxylic acids. The structure of the ternary enzyme-NADH-acetate complex of the slow alleloform of Drosophila melanogaster ADH (DmADH-S) was solved at 1.6 A resolution by X-ray crystallography. The coenzyme stereochemistry of the aldehyde dismutation reaction showed that the obtained enzyme-NADH-acetate complex reflects a productive ternary complex although no enzymatic reaction occurs. The stereochemistry of the acetate binding in the bifurcated substrate-binding site, along with previous stereochemical studies of aldehyde reduction and alcohol oxidation shows that the methyl group of the aldehyde in the reduction reaction binds to the R1 and in the oxidation reaction to the R2 sub-site. NMR studies along with previous kinetic studies show that the formed acetaldehyde intermediate in the oxidation of ethanol to acetate leaves the substrate site prior to the reduced coenzyme, and then binds to the newly formed enzyme-NAD+ complex. Here, we compare the three-dimensional structure of D.melanogaster ADH-S and a previous theoretically built model, evaluate the differences with the crystal structures of five Drosophila lebanonensis ADHs in numerous complexed forms that explain the substrate specificity as well as subtle kinetic differences between these two enzymes based on their crystal structures. We also re-examine the electrostatic influence of charged residues on the surface of the protein on the catalytic efficiency of the enzyme.
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Affiliation(s)
- Jordi Benach
- Center for Structural Biochemistry, Karolinska Institutet, 141 57 Huddinge, Sweden.
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31
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Webb NA, Mulichak AM, Lam JS, Rocchetta HL, Garavito RM. Crystal structure of a tetrameric GDP-D-mannose 4,6-dehydratase from a bacterial GDP-D-rhamnose biosynthetic pathway. Protein Sci 2004; 13:529-39. [PMID: 14739333 PMCID: PMC2286695 DOI: 10.1110/ps.03393904] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
d-Rhamnose is a rare 6-deoxy monosaccharide primarily found in the lipopolysaccharide of pathogenic bacteria, where it is involved in host-bacterium interactions and the establishment of infection. The biosynthesis of d-rhamnose proceeds through the conversion of GDP-d-mannose by GDP-d-mannose 4,6-dehydratase (GMD) to GDP-4-keto-6-deoxymannose, which is subsequently reduced to GDP-d-rhamnose by a reductase. We have determined the crystal structure of GMD from Pseudomonas aeruginosa in complex with NADPH and GDP. GMD belongs to the NDP-sugar modifying subfamily of the short-chain dehydrogenase/reductase (SDR) enzymes, all of which exhibit bidomain structures and a conserved catalytic triad (Tyr-XXX-Lys and Ser/Thr). Although most members of this enzyme subfamily display homodimeric structures, this bacterial GMD forms a tetramer in the same fashion as the plant MUR1 from Arabidopsis thaliana. The cofactor binding sites are adjoined across the tetramer interface, which brings the adenosyl phosphate moieties of the adjacent NADPH molecules to within 7 A of each other. A short peptide segment (Arg35-Arg43) stretches into the neighboring monomer, making not only protein-protein interactions but also hydrogen bonding interactions with the neighboring cofactor. The interface hydrogen bonds made by the Arg35-Arg43 segment are generally conserved in GMD and MUR1, and the interacting residues are highly conserved among the sequences of bacterial and eukaryotic GMDs. Outside of the Arg35-Arg43 segment, residues involved in tetrameric contacts are also quite conserved across different species. These observations suggest that a tetramer is the preferred, and perhaps functionally relevant, oligomeric state for most bacterial and eukaryotic GMDs.
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Affiliation(s)
- Nicole A Webb
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824-1319, USA
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Steckelbroeck S, Jin Y, Oyesanmi B, Kloosterboer HJ, Penning TM. Tibolone Is Metabolized by the 3α/3β-Hydroxysteroid Dehydrogenase Activities of the Four Human Isozymes of the Aldo-Keto Reductase 1C Subfamily: Inversion of Stereospecificity with a Δ5(10)-3-Ketosteroid. Mol Pharmacol 2004; 66:1702-11. [PMID: 15383625 DOI: 10.1124/mol.104.004515] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Tibolone is used to treat climacteric complaints and prevent osteoporosis. These beneficial effects are exerted via its 3alpha-and 3beta-hydroxymetabolites. Undesirable stimulation of the breast and endometrium is not apparent. Endometrial stimulation is prevented by the progestogenic activity of its Delta4-ene metabolite. The enzymes responsible for the formation of these active metabolites are unknown. Human aldo-keto reductase (AKR)1C isoforms have been shown to act as 3alpha/3beta-hydroxysteroid dehydrogenases (HSDs) on 5alpha-dihydrotestosterone (5alpha-DHT). We show that AKR1Cs also efficiently catalyze the reduction of the Delta(5(10))-3-ketosteroid tibolone to yield 3alpha- and 3beta-hydroxytibolone. Homogeneous recombinant AKR1C1, AKR1C3, and AKR1C4 gave similar catalytic profiles to those observed with 5alpha-DHT. AKR1C1 catalyzed exclusively the formation of 3beta-hydroxytibolone, AKR1C3 showed weak 3beta/3alpha-HSD activity, and AKR1C4 acted predominantly as a 3alpha-HSD. Whereas AKR1C2 acted as a 3alpha-HSD toward 5alpha-DHT, it functioned exclusively as a 3beta-HSD on tibolone. Furthermore, strong substrate inhibition was observed for the AKR1C2 catalyzed reduction of tibolone. Using NAD+, the 3-hydroxymetabolites were efficiently oxidized by homogeneous recombinant AKR1C2 and AKR1C4. However, because of potent inhibition of this activity by NADPH, AKR1Cs will probably act only as 3-ketosteroid reductases in vivo. Molecular docking simulations using crystal structures of AKR1C1 and AKR1C2 explained why AKR1C2 inverted its stereospecificity from a 3alpha-HSD with 5alpha-DHT to a 3beta-HSD with tibolone. The preference for AKR1C1 and AKR1C2 to form 3beta-hydroxytibolone, and the preference of the liver-specific AKR1C4 to form 3alpha-hydroxytibolone, may explain why 3beta-hydroxytibolone is the major metabolite in human target tissues and why 3alpha-hydroxytibolone is the major circulating metabolite.
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Affiliation(s)
- Stephan Steckelbroeck
- Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6084, USA
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Thomas JL, Duax WL, Addlagatta A, Kacsoh B, Brandt SE, Norris WB. Structure/function aspects of human 3beta-hydroxysteroid dehydrogenase. Mol Cell Endocrinol 2004; 215:73-82. [PMID: 15026177 DOI: 10.1016/j.mce.2003.11.018] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Separate genes encode the human type 1 (placenta, breast tumors, other peripheral tissues) and type 2 (gonad, adrenal) isoforms of 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD1, 3 beta-HSD2). Mutagenesis of 3 beta-HSD1 produced the Y154F, H156Y and K158Q mutant enzymes in the probable Y(154)-P-H(156)-S-K(158) catalytic motif. The H(156)Y mutant of the 3 beta-HSD1 created a chimera of the 3 beta-HSD2 motif (Y(154)-P-Y(156)-S-K(158)) in 3 beta-HSD1. The D241N, D257L, D258L and D265N mutants are in the potential isomerase site of the 3 beta-HSD1 enzyme. Homology modeling with UDP-galactose-4-epimerase predicted that Asp(36) in the Rossmann-fold domain is responsible for the NAD(H) specificity of human 3 beta-HSD1, and our D36A/K37R mutant tested that assignment. The H(156)Y mutant of the 3 beta-HSD1 enzyme shifted the substrate (DHEA) kinetics to the 14-fold higher K(m) value measured for the 3 beta-HSD2 activity. From Dixon analysis, epostane inhibited the 3 beta-HSD1 activity with 17-fold greater affinity compared to 3 beta-HSD2 and H(156)Y. The mutants of Tyr(154) and Lys(158) exhibited no dehydrogenase activity and appear to be catalytic 3 beta-HSD residues. The D257L and D258L mutations eliminated isomerase activity, suggesting that Asp(257) or Asp(258) may be catalytic residues for isomerase activity. The D36A/K37R mutant shifted the cofactor preference of both 3 beta-HSD and isomerase from NAD(H) to NADP(H). In addition to characterizing catalytic residues, these studies have identified the structural basis (His(156)) for an exploitable difference in the substrate and inhibition kinetics of 3 beta-HSD1 and 3 beta-HSD2. Hence, it may be possible to selectively inhibit human 3 beta-HSD1 to slow the growth of hormone-sensitive breast tumor cells and control placental steroidogenesis near term to prevent premature labor.
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Affiliation(s)
- James L Thomas
- Division of Basic Medical Sciences, Mercer University School of Medicine, Macon, GA, USA
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Meurisse R, Brasseur R, Thomas A. Aromatic side-chain interactions in proteins: Near- and far-sequence Tyr-X pairs. Proteins 2003; 54:478-90. [PMID: 14747996 DOI: 10.1002/prot.10582] [Citation(s) in RCA: 17] [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 the present study, an extensive analysis of the aromatic Tyr-X interactions is performed on a data set of 593 PDB structures, X being Phe, His, Tyr, and Trp. The nonredundant Tyr-X pairs (2645) were retained and separated by both the residue distance in the sequence and the secondary structures they bridge. Similar to the Phe-X and His-X pairs, the far-sequence Tyr-X pairs (X partner > five apart in the sequence: 74%) show comparable secondary structures and conformers for either type of X partner, in contrast with the near-sequence Tyr-X pairs (26%). As the Phe-X pairs, the near-sequence Tyr-X pairs stabilize secondary structures, mainly the alpha- helices (positions 1, 3, and 4) and the beta-strands (position 2). Like the Phe-X and His-X pairs, most far-sequence Tyr-X pairs (34%) bridge beta-strands and only 11% bridge helices. As for the Phe-X and the His-X pairs, the X partners of the far-sequence Tyr-X pairs are frequently "above" the tyrosine ring with tilted and normal rings, whereas the X partner of the near-sequence Tyr-X pairs gradually moves from the "aside" to the "above" location, together with a progressive decrease of normal and increase of parallel rings, respectively. Unlike the His-X pairs, the interactions of the hetroatom in Tyr-X pairs are only favored with a sequence position +4 and over, owing to the spatial accessibility of the heteroatom.
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Affiliation(s)
- Rita Meurisse
- Centre de Biophysique Moléculaire Numérique, Faculté Scientifique Agronomique de Gembloux, Gembloux, Belgium.
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35
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Allard STM, Cleland WW, Holden HM. High resolution X-ray structure of dTDP-glucose 4,6-dehydratase from Streptomyces venezuelae. J Biol Chem 2003; 279:2211-20. [PMID: 14570895 DOI: 10.1074/jbc.m310134200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Desosamine is a 3-(dimethylamino)-3,4,6-trideoxyhexose found in some macrolide antibiotics. In Streptomyces venezuelae, there are seven genes required for the biosynthesis of this unusual sugar. One of the genes, desIV, codes for a dTDP-glucose 4,6-dehydratase, which is referred to as DesIV. The reaction mechanisms for these types of dehydratases are quite complicated with proton abstraction from the sugar 4'-hydroxyl group and hydride transfer to NAD+, proton abstraction at C-5, and elimination of the hydroxyl group at C-6 of the sugar, and finally return of a proton to C-5 and a hydride from NADH to C-6. Here we describe the cloning, overexpression, and purification, and high resolution x-ray crystallographic analysis to 1.44 A of wild-type DesIV complexed with dTDP. Additionally, for this study, a double site-directed mutant protein (D128N/E129Q) was prepared, crystallized as a complex with NAD+ and the substrate dTDP-glucose and its structure determined to 1.35 A resolution. In DesIV, the phenolate group of Tyr(151) and O(gamma) of Thr(127) lie at 2.7 and 2.6 A, respectively from the 4'-hydroxyl group of the dTDP-glucose substrate. The side chain of Asp(128) is in the correct position to function as a general acid for proton donation to the 6'-hydroxyl group while the side chain of Glu(129) is ideally situated to serve as the general base for proton abstraction at C-5. This investigation provides further detailed information for understanding the exquisite chemistry that occurs in these remarkable enzymes.
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Affiliation(s)
- Simon T M Allard
- Department of Biochemistry, University of Wisconsin, Madison, WI 53706, USA
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36
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Thomas JL, Duax WL, Addlagatta A, Brandt S, Fuller RR, Norris W. Structure/function relationships responsible for coenzyme specificity and the isomerase activity of human type 1 3 beta-hydroxysteroid dehydrogenase/isomerase. J Biol Chem 2003; 278:35483-90. [PMID: 12832414 DOI: 10.1074/jbc.m304752200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human type 1 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD/isomerase) catalyzes the two sequential enzyme reactions on a single protein that converts dehydroepiandrosterone or pregnenolone to androstenedione or progesterone, respectively, in placenta, mammary gland, breast tumors, prostate, prostate tumors, and other peripheral tissues. Our earlier studies show that the two enzyme reactions are linked by the coenzyme product, NADH, of the 3 beta-HSD activity. NADH activates the isomerase activity by inducing a time-dependent conformational change in the enzyme protein. The current study tested the hypothesis that the 3 beta-HSD and isomerase activities shared a common coenzyme domain, and it characterized key amino acids that participated in coenzyme binding and the isomerase reaction. Homology modeling with UDP-galactose-4-epimerase predicts that Asp36 is responsible for the NAD(H) specificity of human 3 beta-HSD/isomerase and identifies the Rossmann-fold coenzyme domain at the amino terminus. The D36A/K37R mutant in the potential coenzyme domain and the D241N, D257L, D258L, and D265N mutants in the potential isomerase domain (previously identified by affinity labeling) were created, expressed, and purified. The D36A/K37R mutant shifts the cofactor preference of both 3 beta-HSD and isomerase from NAD(H) to NADP(H), which shows that the two activities utilize a common coenzyme domain. The D257L and D258L mutations eliminate isomerase activity, whereas the D241N and D265N mutants have nearly full isomerase activity. Kinetic analyses and pH dependence studies showed that either Asp257 or Asp258 plays a catalytic role in the isomerization reaction. These observations further characterize the structure/function relationships of human 3 beta-HSD/isomerase and bring us closer to the goal of selectively inhibiting the type 1 enzyme in placenta (to control the timing of labor) or in hormone-sensitive breast tumors (to slow their growth).
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Affiliation(s)
- James L Thomas
- Division of Basic Medical Sciences and Department of Obstetrics-Gynecology, Mercer University School of Medicine, Macon, Georgia 31207, USA.
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Bartlett GJ, Borkakoti N, Thornton JM. Catalysing new reactions during evolution: economy of residues and mechanism. J Mol Biol 2003; 331:829-60. [PMID: 12909013 DOI: 10.1016/s0022-2836(03)00734-4] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The diversity of function in some enzyme superfamilies shows that during evolution, enzymes have evolved to catalyse different reactions on the same structure scaffold. In this analysis, we examine in detail how enzymes can modify their chemistry, through a comparison of the catalytic residues and mechanisms in 27 pairs of homologous enzymes of totally different functions. We find that evolution is very economical. Enzymes retain structurally conserved residues to aid catalysis, including residues that bind catalytic metal ions and modulate cofactor chemistry. We examine the conservation of residue type and residue function in these structurally conserved residue pairs. Additionally, enzymes often retain common mechanistic steps catalyzed by structurally conserved residues. We have examined these steps in the context of their overall reactions.
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Affiliation(s)
- Gail J Bartlett
- Department of Biochemistry and Molecular Biology, University College London, Darwin Building, Gower Street, London WC1E 6BT, UK
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Abstract
Carbohydrates are highly abundant biomolecules found extensively in nature. Besides playing important roles in energy storage and supply, they often serve as essential biosynthetic precursors or structural elements needed to sustain all forms of life. A number of unusual sugars that have certain hydroxyl groups replaced by a hydrogen, an amino group, or an alkyl side chain play crucial roles in determining the biological activity of the parent natural products in bacterial lipopolysaccharides or secondary metabolite antibiotics. Recent investigation of the biosynthesis of these monosaccharides has led to the identification of the gene clusters whose protein products facilitate the unusual sugar formation from the ubiquitous NDP-glucose precursors. This review summarizes the mechanistic studies of a few enzymes crucial to the biosynthesis of C-2, C-3, C-4, and C-6 deoxysugars, the characterization and mutagenesis of nucleotidyl transferases that can recognize and couple structural analogs of their natural substrates and the identification of glycosyltransferases with promiscuous substrate specificity. Information gleaned from these studies has allowed pathway engineering, resulting in the creation of new macrolides with unnatural deoxysugar moieties for biological activity screening. This represents a significant progress toward our goal of searching for more potent agents against infectious diseases and malignant tumors.
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Affiliation(s)
- Xuemei M He
- Division of Medicinal Chemistry, College of Pharmacy, and Department of Chemistry and Biochemistry, University of Texas, Austin, Texas 78712, USA.
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39
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Abstract
In the past few years, significant progress has been made in our understanding of the biosynthesis of deoxyhexoses. Mechanistic studies have revealed how enzymes can cleave CbondO bonds of a hexose substrate to make unusual sugars. The increasing amount of knowledge about the biosynthesis of deoxysugars may allow the assembly of a repertoire of novel sugar structures through recruitment and collaborative action of genes from a variety of biosynthetic pathways to create diverse secondary metabolites in our search for novel antibiotic/antitumour agents.
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Affiliation(s)
- Xuemei He
- Division of Medicinal Chemistry, College of Pharmacy, Department of Chemistry and Biochemistry, University of Texas, Austin 78712, USA
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40
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Jeevarajah D, Patterson JH, McConville MJ, Billman-Jacobe H. Modification of glycopeptidolipids by an O-methyltransferase of Mycobacterium smegmatis. MICROBIOLOGY (READING, ENGLAND) 2002; 148:3079-3087. [PMID: 12368441 DOI: 10.1099/00221287-148-10-3079] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Glycopeptidolipids (GPLs) are a major component of the outer layers of the cell walls of several non-tuberculous mycobacteria. The Mycobacterium smegmatis GPLs consist of a diglycosylated lipopeptide core which is variably modified by acetylation and methylation. Analysis of a region of the M. smegmatis chromosome, upstream of the peptide synthetase gene, mps, revealed a GPL biosynthetic locus containing genes potentially involved in glycosylation, methylation, acetylation and transport of GPLs. Methyltransferases are required to modify rhamnose and the fatty acid of GPLs. Of the four methyltransferases encoded within the locus, one methyltransferase, Mtf2, was unlike sugar methyltransferases from other species. An mtf2 mutant was created and was shown to be unable to methylate the GPL fatty acids. Direct evidence is presented that Mtf2 is a methyltransferase that modifies the GPL fatty acid.
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Affiliation(s)
- Dharshini Jeevarajah
- Departments of Microbiology and Immunology1, and Biochemistry and Molecular Biology2, University of Melbourne, Victoria 3010, Australia
| | - John H Patterson
- Departments of Microbiology and Immunology1, and Biochemistry and Molecular Biology2, University of Melbourne, Victoria 3010, Australia
| | - Malcolm J McConville
- Departments of Microbiology and Immunology1, and Biochemistry and Molecular Biology2, University of Melbourne, Victoria 3010, Australia
| | - Helen Billman-Jacobe
- Departments of Microbiology and Immunology1, and Biochemistry and Molecular Biology2, University of Melbourne, Victoria 3010, Australia
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41
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Allard STM, Beis K, Giraud MF, Hegeman AD, Gross JW, Wilmouth RC, Whitfield C, Graninger M, Messner P, Allen AG, Maskell DJ, Naismith JH. Toward a structural understanding of the dehydratase mechanism. Structure 2002; 10:81-92. [PMID: 11796113 DOI: 10.1016/s0969-2126(01)00694-3] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
dTDP-D-glucose 4,6-dehydratase (RmlB) was first identified in the L-rhamnose biosynthetic pathway, where it catalyzes the conversion of dTDP-D-glucose into dTDP-4-keto-6-deoxy-D-glucose. The structures of RmlB from Salmonella enterica serovar Typhimurium in complex with substrate deoxythymidine 5'-diphospho-D-glucose (dTDP-D-glucose) and deoxythymidine 5'-diphosphate (dTDP), and RmlB from Streptococcus suis serotype 2 in complex with dTDP-D-glucose, dTDP, and deoxythymidine 5'-diphospho-D-pyrano-xylose (dTDP-xylose) have all been solved at resolutions between 1.8 A and 2.4 A. The structures show that the active sites are highly conserved. Importantly, the structures show that the active site tyrosine functions directly as the active site base, and an aspartic and glutamic acid pairing accomplishes the dehydration step of the enzyme mechanism. We conclude that the substrate is required to move within the active site to complete the catalytic cycle and that this movement is driven by the elimination of water. The results provide insight into members of the SDR superfamily.
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Affiliation(s)
- Simon T M Allard
- Centre for Biomolecular Sciences, North Haugh, The University, St. Andrews, Fife KY16 9ST, Scotland, United Kingdom
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