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Anderson AJ, Seebald LM, Arbour CA, Imperiali B. Probing Monotopic Phosphoglycosyl Transferases from Complex Cellular Milieu. ACS Chem Biol 2022; 17:3191-3197. [PMID: 36346917 PMCID: PMC9703085 DOI: 10.1021/acschembio.2c00648] [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] [Indexed: 11/09/2022]
Abstract
Monotopic phosphoglycosyl transferase enzymes (monoPGTs) initiate the assembly of prokaryotic glycoconjugates essential for bacterial survival and proliferation. MonoPGTs belong to an expansive superfamily with a diverse and richly annotated sequence space; however, the biochemical roles of most monoPGTs in glycoconjugate biosynthesis pathways remain elusive. To better understand these critical enzymes, we have implemented activity-based protein profiling (ABPP) probes as protein-centric, membrane protein compatible tools that lay the groundwork for understanding the activity and regulation of the monoPGT superfamily from a cellular proteome. With straightforward gel-based readouts, we demonstrate robust, covalent labeling at the active site of various representative monoPGTs from cell membrane fractions using 3-phenyl-2H-azirine probes.
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Affiliation(s)
- Alyssa J. Anderson
- Department of Biology and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Leah M. Seebald
- Department of Biology and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Christine A. Arbour
- Department of Biology and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Barbara Imperiali
- Department of Biology and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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2
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Blériot Y, Auberger N, Désiré J. Sugar-Derived Amidines and Congeners: Structures, Glycosidase Inhibition and Applications. Curr Med Chem 2021; 29:1271-1292. [PMID: 34951354 DOI: 10.2174/0929867329666211222164545] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 09/16/2021] [Accepted: 10/22/2021] [Indexed: 11/22/2022]
Abstract
Glycosidases, the enzymes responsible for the breakdown of glycoconjugates including di-, oligo- and polysaccharides are ubiquitous through all kingdoms of life. The extreme chemical stability of the glycosidic bond combined with the catalytic rates achieved by glycosidases makes them among the most proficient of all enzymes.
Given their multitude of roles in vivo, inhibition of these enzymes is highly attractive with potential in the treatment of a vast array of pathologies ranging from lysosomal storage and diabetes to viral infections. Therefore great efforts have been invested in the last three decades to design and synthesize inhibitors of glycosidases leading to a number of drugs currently on the market. Amongst the vast array of structures that have been disclosed, sugars incorporating an amidine moiety have been the focus of many research groups around the world because of their glycosidase transition state-like structure. In this review we report and discuss the structure, the inhibition profile and the use of these molecules including related structural congeners as transition state analogs.
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Affiliation(s)
- Yves Blériot
- Université de Poitiers, IC2MP, UMR CNRS 7285, Equipe "OrgaSynth", Groupe Glycochimie 4 rue Michel Brunet, 86073 Poitiers cedex 9. France
| | - Nicolas Auberger
- Université de Poitiers, IC2MP, UMR CNRS 7285, Equipe "OrgaSynth", Groupe Glycochimie 4 rue Michel Brunet, 86073 Poitiers cedex 9. France
| | - Jérôme Désiré
- Université de Poitiers, IC2MP, UMR CNRS 7285, Equipe "OrgaSynth", Groupe Glycochimie 4 rue Michel Brunet, 86073 Poitiers cedex 9. France
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3
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Quirke JCK, Crich D. Glycoside Hydrolases Restrict the Side Chain Conformation of Their Substrates To Gain Additional Transition State Stabilization. J Am Chem Soc 2020; 142:16965-16973. [PMID: 32877175 PMCID: PMC7544649 DOI: 10.1021/jacs.0c05592] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Carbohydrate side chain conformation confers a significant influence on reactivity during glycosylation and anomeric bond hydrolysis due to stabilization of the oxocarbenium-like transition state. By analysis of 513 pyranoside-bound glycoside hydrolase (GH) crystal structures, we determine that most glucosidases and β-mannosidases preferentially bind their substrates in the most reactive gauche,gauche (gg) conformation, thereby maximizing stabilization of the corresponding oxocarbenium ion-like transition state during hydrolysis. α-Galactoside hydrolases mostly show a preference for the second most activating gauche,trans (gt) conformation to avoid the energy penalty that would arise from imposing the gg conformation on galacto-configured ligands. These preferences stand in stark contrast to the side chain populations observed for these sugars both in free solution and bound to nonhydrolytic proteins, where for the most part a much greater diversity of side chain conformations is observed. Analysis of sequences of GH-ligand complexes reveals that side chain restriction begins with the enzyme-substrate complex and persists through the transition state until release of the hydrolysis product, despite changes in ring conformation along the reaction coordinate. This work will inform the design of new generations of glycosidase inhibitors with restricted side chains that confer higher selectivity and/or affinity.
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Affiliation(s)
- Jonathan C K Quirke
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, 250 West Green Street, Athens, Georgia 30602, United States
- Department of Chemistry, University of Georgia, 140 Cedar Street, Athens, Georgia 30602, United States
- Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, Georgia 30602, United States
| | - David Crich
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, 250 West Green Street, Athens, Georgia 30602, United States
- Department of Chemistry, University of Georgia, 140 Cedar Street, Athens, Georgia 30602, United States
- Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, Georgia 30602, United States
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4
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Rovira C, Males A, Davies GJ, Williams SJ. Mannosidase mechanism: at the intersection of conformation and catalysis. Curr Opin Struct Biol 2019; 62:79-92. [PMID: 31891872 DOI: 10.1016/j.sbi.2019.11.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2019] [Revised: 10/06/2019] [Accepted: 11/15/2019] [Indexed: 12/17/2022]
Abstract
Mannosidases are a diverse group of enzymes that are important in the biological processing of mannose-containing polysaccharides and complex glycoconjugates. They are found in 12 of the >160 sequence-based glycosidase families. We discuss evidence that nature has evolved a small set of common mechanisms that unite almost all of these mannosidase families. Broadly, mannosidases (and the closely related rhamnosidases) perform catalysis through just two conformations of the oxocarbenium ion-like transition state: a B2,5 (or enantiomeric 2,5B) boat and a 3H4 half-chair. This extends to a new family (GT108) of GDPMan-dependent β-1,2-mannosyltransferases/phosphorylases that perform mannosyl transfer through a boat conformation as well as some mannosidases that are metalloenzymes and require divalent cations for catalysis. Yet, among this commonality lies diversity. New evidence shows that one unique family (GH99) of mannosidases use an unusual mechanism involving anchimeric assistance via a 1,2-anhydro sugar (epoxide) intermediate.
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Affiliation(s)
- Carme Rovira
- Departament de Química Inorgànica i Orgànica (Secció de Química Orgànica) & Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain; Institució Catalana de Recerca i Estudis Avançats (ICREA), Pg. Lluís Companys 23, 08010 Barcelona, Spain.
| | - Alexandra Males
- Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Gideon J Davies
- Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Spencer J Williams
- School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
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5
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Wang B, Olsen JI, Laursen BW, Navarro Poulsen JC, Bols M. Determination of protonation states of iminosugar-enzyme complexes using photoinduced electron transfer. Chem Sci 2017; 8:7383-7393. [PMID: 29163889 PMCID: PMC5672842 DOI: 10.1039/c7sc01540b] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Accepted: 08/29/2017] [Indexed: 12/16/2022] Open
Abstract
A series of N-alkylated analogues of 1-deoxynojirimycin containing a fluorescent 10-chloro-9-anthracene group in the N-alkyl substituent were prepared. The anthracene group acted as a reporting group for protonation at the nitrogen in the iminosugar because an unprotonated amine was found to quench fluorescence by photoinduced electron transfer. The new compounds were found to inhibit β-glucosidase from Phanerochaete chrysosporium and α-glucosidase from Aspergillus niger, with Ki values in the low micro- to nanomolar range. Fluorescence and inhibition versus pH studies of the β-glucosidase-iminosugar complexes revealed that the amino group in the inhibitor is unprotonated when bound, while one of the active site carboxylates is protonated.
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Affiliation(s)
- Bo Wang
- Department of Chemistry , University of Copenhagen , Universitetsparken 5 , DK-2100 Copenhagen Ø , Denmark . ; Tel: +45 35320160
| | - Jacob Ingemar Olsen
- Department of Chemistry , University of Copenhagen , Universitetsparken 5 , DK-2100 Copenhagen Ø , Denmark . ; Tel: +45 35320160
| | - Bo W Laursen
- Department of Chemistry , University of Copenhagen , Universitetsparken 5 , DK-2100 Copenhagen Ø , Denmark . ; Tel: +45 35320160
| | - Jens Christian Navarro Poulsen
- Department of Chemistry , University of Copenhagen , Universitetsparken 5 , DK-2100 Copenhagen Ø , Denmark . ; Tel: +45 35320160
| | - Mikael Bols
- Department of Chemistry , University of Copenhagen , Universitetsparken 5 , DK-2100 Copenhagen Ø , Denmark . ; Tel: +45 35320160
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α-Geminal disubstituted pyrrolidine iminosugars and their C-4-fluoro analogues: Synthesis, glycosidase inhibition and molecular docking studies. Bioorg Med Chem 2017; 25:5148-5159. [DOI: 10.1016/j.bmc.2017.07.026] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 07/12/2017] [Accepted: 07/12/2017] [Indexed: 11/24/2022]
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7
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Balachandran N, To F, Berti PJ. Linear Free Energy Relationship Analysis of Transition State Mimicry by 3-Deoxy-d-arabino-heptulosonate-7-phosphate (DAHP) Oxime, a DAHP Synthase Inhibitor and Phosphate Mimic. Biochemistry 2017; 56:592-601. [PMID: 28045507 DOI: 10.1021/acs.biochem.6b01211] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Naresh Balachandran
- Department of Chemistry & Chemical Biology and ‡Department of Biochemistry & Biomedical Sciences, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1, Canada
| | - Frederick To
- Department of Chemistry & Chemical Biology and ‡Department of Biochemistry & Biomedical Sciences, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1, Canada
| | - Paul J. Berti
- Department of Chemistry & Chemical Biology and ‡Department of Biochemistry & Biomedical Sciences, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1, Canada
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8
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Colombo C, Bennet AJ. Probing Transition State Analogy in Glycoside Hydrolase Catalysis. ADVANCES IN PHYSICAL ORGANIC CHEMISTRY 2017. [DOI: 10.1016/bs.apoc.2017.09.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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9
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Borowski D, Zweiböhmer T, Ziegler T. 1,2-Annulated Sugars: Synthesis of Polyhydroxylated 2,10-Dioxadecalins with β-mannoConfiguration. European J Org Chem 2016. [DOI: 10.1002/ejoc.201601050] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Daniel Borowski
- Institute of Organic Chemistry; University of Tuebingen; Auf der Morgenstelle 18 72076 Tuebingen Germany
| | - Tobias Zweiböhmer
- Institute of Organic Chemistry; University of Tuebingen; Auf der Morgenstelle 18 72076 Tuebingen Germany
| | - Thomas Ziegler
- Institute of Organic Chemistry; University of Tuebingen; Auf der Morgenstelle 18 72076 Tuebingen Germany
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10
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Tankrathok A, Iglesias-Fernández J, Williams RJ, Pengthaisong S, Baiya S, Hakki Z, Robinson RC, Hrmova M, Rovira C, Williams SJ, Ketudat Cairns JR. A Single Glycosidase Harnesses Different Pyranoside Ring Transition State Conformations for Hydrolysis of Mannosides and Glucosides. ACS Catal 2015. [DOI: 10.1021/acscatal.5b01547] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Anupong Tankrathok
- School of Biochemistry, Institute of Science, and Center
for Biomolecular Structure, Function and Application, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand
- Department of Biotechnology, Faculty of Agro-Industrial
Technology, Rajamangala University of Technology, Isan, Kalasin Campus, Kalasin 46000, Thailand
| | - Javier Iglesias-Fernández
- Departament de Quı́mica
Orgànica/Institut de Quı́mica Teòrica i
Computacional (IQTCUB), Universitat de Barcelona, Martı́ i Franquès
1, 08028 Barcelona, Spain
| | - Rohan J. Williams
- School of Chemistry and Bio21 Molecular
Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Salila Pengthaisong
- School of Biochemistry, Institute of Science, and Center
for Biomolecular Structure, Function and Application, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand
| | - Supaporn Baiya
- School of Biochemistry, Institute of Science, and Center
for Biomolecular Structure, Function and Application, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand
| | - Zalihe Hakki
- School of Chemistry and Bio21 Molecular
Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Robert C. Robinson
- Institute of Molecular
and Cell Biology, A*STAR (Agency for Science, Technology and Research), Biopolis, Singapore 138673
- Department of Biochemistry, National University of Singapore, 8 Medical Drive, Singapore 117597
| | - Maria Hrmova
- School of Agriculture, Food and Wine, Australian
Centre for Plant Functional Genomics, University of Adelaide, Waite Campus, Glenn
Osmond, Australia
| | - Carme Rovira
- Departament de Quı́mica
Orgànica/Institut de Quı́mica Teòrica i
Computacional (IQTCUB), Universitat de Barcelona, Martı́ i Franquès
1, 08028 Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluı́s Companys, 23, 08018 Barcelona, Spain
| | - Spencer J. Williams
- School of Chemistry and Bio21 Molecular
Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - James R. Ketudat Cairns
- School of Biochemistry, Institute of Science, and Center
for Biomolecular Structure, Function and Application, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand
- Laboratory of Biochemistry, Chulabhorn Research Institute, Bangkok 10210, Thailand
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11
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Sørensen TH, Cruys-Bagger N, Borch K, Westh P. Free Energy Diagram for the Heterogeneous Enzymatic Hydrolysis of Glycosidic Bonds in Cellulose. J Biol Chem 2015; 290:22203-11. [PMID: 26183776 DOI: 10.1074/jbc.m115.659656] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Indexed: 01/25/2023] Open
Abstract
Kinetic and thermodynamic data have been analyzed according to transition state theory and a simplified reaction scheme for the enzymatic hydrolysis of insoluble cellulose. For the cellobiohydrolase Cel7A from Hypocrea jecorina (Trichoderma reesei), we were able to measure or collect relevant values for all stable and activated complexes defined by the reaction scheme and hence propose a free energy diagram for the full heterogeneous process. For other Cel7A enzymes, including variants with and without carbohydrate binding module (CBM), we obtained activation parameters for the association and dissociation of the enzyme-substrate complex. The results showed that the kinetics of enzyme-substrate association (i.e. formation of the Michaelis complex) was almost entirely entropy-controlled and that the activation entropy corresponded approximately to the loss of translational and rotational degrees of freedom of the dissolved enzyme. This implied that the transition state occurred early in the path where the enzyme has lost these degrees of freedom but not yet established extensive contact interactions in the binding tunnel. For dissociation, a similar analysis suggested that the transition state was late in the path where most enzyme-substrate contacts were broken. Activation enthalpies revealed that the rate of dissociation was far more temperature-sensitive than the rates of both association and the inner catalytic cycle. Comparisons of one- and two-domain variants showed that the CBM had no influence on the transition state for association but increased the free energy barrier for dissociation. Hence, the CBM appeared to promote the stability of the complex by delaying dissociation rather than accelerating association.
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Affiliation(s)
- Trine Holst Sørensen
- From Roskilde University, NSM, Research Unit for Functional Biomaterials, 1 Universitetsvej, Building 28, DK-4000 Roskilde, Denmark and
| | - Nicolaj Cruys-Bagger
- From Roskilde University, NSM, Research Unit for Functional Biomaterials, 1 Universitetsvej, Building 28, DK-4000 Roskilde, Denmark and
| | - Kim Borch
- Novozymes A/S, Krogshøjvej 36, DK-2880 Bagsværd, Denmark
| | - Peter Westh
- From Roskilde University, NSM, Research Unit for Functional Biomaterials, 1 Universitetsvej, Building 28, DK-4000 Roskilde, Denmark and
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12
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Kasture VM, Kalamkar NB, Nair RJ, Joshi RS, Sabharwal SG, Dhavale DD. Synthesis, conformational study, glycosidase inhibitory activity and molecular docking studies of dihydroxylated 4- and 5-amino-iminosugars. Carbohydr Res 2015; 408:25-32. [DOI: 10.1016/j.carres.2015.03.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Revised: 03/03/2015] [Accepted: 03/04/2015] [Indexed: 11/26/2022]
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13
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γ-Hydroxyethyl piperidine iminosugar and N-alkylated derivatives: A study of their activity as glycosidase inhibitors and as immunosuppressive agents. Bioorg Med Chem 2014; 22:5776-82. [DOI: 10.1016/j.bmc.2014.09.034] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Revised: 09/05/2014] [Accepted: 09/15/2014] [Indexed: 11/24/2022]
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14
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Jiang FX, Liu QZ, Zhao D, Luo CT, Guo CP, Ye WC, Luo C, Chen H. A concise synthesis of N-substituted fagomine derivatives and the systematic exploration of their α-glycosidase inhibition. Eur J Med Chem 2014; 77:211-22. [DOI: 10.1016/j.ejmech.2014.03.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Revised: 02/28/2014] [Accepted: 03/02/2014] [Indexed: 11/30/2022]
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15
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Ansari AA, Rajasekaran P, Khan MM, Vankar YD. Bicyclic Hybrid Sugars as Glycosidase Inhibitors: Synthesis and Comparative Study of Inhibitory Activities of Fused Oxa-Oxa, Oxa-Aza, and Oxa-Carbasugar Hybrid Molecules. J Org Chem 2014; 79:1690-9. [DOI: 10.1021/jo402574h] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Alafia A. Ansari
- Department
of Chemistry, Indian Institute of Technology, Kanpur, Uttar Pradesh 208016, India
| | - Parasuraman Rajasekaran
- Department
of Chemistry, Indian Institute of Technology, Kanpur, Uttar Pradesh 208016, India
| | - M. Musawwer Khan
- Department
of Chemistry, Aligarh Muslim University, Aligarh, Uttar Pradesh 202002, India
| | - Yashwant D. Vankar
- Department
of Chemistry, Indian Institute of Technology, Kanpur, Uttar Pradesh 208016, India
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16
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Rakic B, Rao FV, Freimann K, Wakarchuk W, Strynadka NCJ, Withers SG. Structure-based mutagenic analysis of mechanism and substrate specificity in mammalian glycosyltransferases: porcine ST3Gal-I. Glycobiology 2013; 23:536-45. [PMID: 23300007 DOI: 10.1093/glycob/cwt001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Sialyltransferases (STs) play essential roles in signaling and in the cellular recognition processes of mammalian cells by selectively installing cell-surface sialic acids in an appropriate manner both temporally and organ-specifically. The availability of the first three-dimensional structure of a mammalian (GT29) sialyltransferase has, for the first time, allowed quantitative structure/function analyses to be performed, thereby providing reliable insights into the roles of key active site amino acids. Kinetic analyses of mutants of ST3Gal-I, in conjunction with structural studies, have confirmed the mechanistic roles of His302 and His319 as general acid and base catalysts, respectively, and have quantitated other interactions with the cytosine monophosphate-N-acetyl β-neuraminic acid donor substrate. The contributions of side chains that provide key interactions with the acceptor substrate, defining its specificity, have also been quantitated. Particularly important transition-state interactions of 2.5 and 2.7 kcal mol(-1) are found between the acceptor axial 4-hydroxyl and the conserved side chains of Gln108 and Tyr269, respectively. These results provide a basis for the engineering of mammalian STs to accommodate non-natural substrate analogs that should prove valuable as chemical biological probes of sialyltransferase function.
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Affiliation(s)
- Bojana Rakic
- Department of Chemistry, University of British Columbia, Vancouver, BC, Canada
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17
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Development of inhibitors as research tools for carbohydrate-processing enzymes. Biochem Soc Trans 2012; 40:913-28. [DOI: 10.1042/bst20120201] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Carbohydrates, which are present in all domains of life, play important roles in a host of cellular processes. These ubiquitous biomolecules form highly diverse and often complex glycan structures without the aid of a template. The carbohydrate structures are regulated solely by the location and specificity of the enzymes responsible for their synthesis and degradation. These enzymes, glycosyltransferases and glycoside hydrolases, need to be functionally well characterized in order to investigate the structure and function of glycans. The use of enzyme inhibitors, which target a particular enzyme, can significantly aid this understanding, and may also provide insights into therapeutic applications. The present article describes some of the approaches used to design and develop enzyme inhibitors as tools for investigating carbohydrate-processing enzymes.
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18
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Kang Y, Terrier P, Ding C, Douglas DJ. Solution and gas-phase H/D exchange of protein-small-molecule complexes: Cex and its inhibitors. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:57-67. [PMID: 22006406 DOI: 10.1007/s13361-011-0263-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2011] [Revised: 09/20/2011] [Accepted: 09/23/2011] [Indexed: 05/31/2023]
Abstract
The properties of noncovalent complexes of the enzyme exo-1,4-β-D-glycanase ("Cex") with three aza-sugar inhibitors, deoxynojirimycin (X(2)DNJ), isofagomine lactam (X(2)IL), and isofagomine (X(2)IF), have been studied with solution and gas-phase hydrogen deuterium exchange (H/Dx) and measurements of collision cross sections of gas-phase ions. In solution, complexes have lower H/Dx levels than free Cex because binding the inhibitors blocks some sites from H/Dx and reduces fluctuations of the protein. In mass spectra of complexes, abundant Cex ions are seen, which mostly are formed by dissociation of complexes in the ion sampling interface. Both complex ions and Cex ions formed from a solution containing complexes have lower cross sections than Cex ions from a solution of Cex alone. This suggests the Cex ions formed by dissociation "remember" their solution conformations. For a given charge, ions of the complexes have greater gas-phase H/Dx levels than ions of Cex. Unlike cross sections, H/Dx levels of the complexes do not correlate with the relative gas-phase binding strengths measured by MS/MS. Cex ions from solutions with or without inhibitors, which have different cross sections, show the same H/Dx level after 15 s, indicating the ions may fold or unfold on the seconds time scale of the H/Dx experiment. Thus, cross sections show that complexes have more compact conformations than free protein ions on the time scale of ca. 1 ms. The gas-phase H/Dx measurements show that at least some complexes retain different conformations from the Cex ions on a time scale of seconds.
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Affiliation(s)
- Yang Kang
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T 1Z1, Canada
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19
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Goddard-Borger ED, Fiege B, Kwan EM, Withers SG. Glycosynthase-Mediated Assembly of Xylanase Substrates and Inhibitors. Chembiochem 2011; 12:1703-11. [DOI: 10.1002/cbic.201100229] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Indexed: 11/09/2022]
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20
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Guce AI, Clark NE, Salgado EN, Ivanen DR, Kulminskaya AA, Brumer H, Garman SC. Catalytic mechanism of human alpha-galactosidase. J Biol Chem 2010; 285:3625-3632. [PMID: 19940122 PMCID: PMC2823503 DOI: 10.1074/jbc.m109.060145] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2009] [Revised: 11/06/2009] [Indexed: 11/06/2022] Open
Abstract
The enzyme alpha-galactosidase (alpha-GAL, also known as alpha-GAL A; E.C. 3.2.1.22) is responsible for the breakdown of alpha-galactosides in the lysosome. Defects in human alpha-GAL lead to the development of Fabry disease, a lysosomal storage disorder characterized by the buildup of alpha-galactosylated substrates in the tissues. alpha-GAL is an active target of clinical research: there are currently two treatment options for Fabry disease, recombinant enzyme replacement therapy (approved in the United States in 2003) and pharmacological chaperone therapy (currently in clinical trials). Previously, we have reported the structure of human alpha-GAL, which revealed the overall structure of the enzyme and established the locations of hundreds of mutations that lead to the development of Fabry disease. Here, we describe the catalytic mechanism of the enzyme derived from x-ray crystal structures of each of the four stages of the double displacement reaction mechanism. Use of a difluoro-alpha-galactopyranoside allowed trapping of a covalent intermediate. The ensemble of structures reveals distortion of the ligand into a (1)S(3) skew (or twist) boat conformation in the middle of the reaction cycle. The high resolution structures of each step in the catalytic cycle will allow for improved drug design efforts on alpha-GAL and other glycoside hydrolase family 27 enzymes by developing ligands that specifically target different states of the catalytic cycle. Additionally, the structures revealed a second ligand-binding site suitable for targeting by novel pharmacological chaperones.
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Affiliation(s)
- Abigail I Guce
- Departments of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003
| | - Nathaniel E Clark
- From the Departments of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003
| | - Eric N Salgado
- From the Departments of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003
| | - Dina R Ivanen
- the Molecular and Radiation Biophysics Division, Petersburg Nuclear Physics Institute, Russian Academy of Science, Orlova Roscha, Gatchina 188300, Leningrad District, Russia, and
| | - Anna A Kulminskaya
- the Molecular and Radiation Biophysics Division, Petersburg Nuclear Physics Institute, Russian Academy of Science, Orlova Roscha, Gatchina 188300, Leningrad District, Russia, and
| | - Harry Brumer
- the Department of Biotechnology, Royal Insitute of Technology (KTH), 10691 Stockholm, Sweden
| | - Scott C Garman
- Departments of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003; From the Departments of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003.
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21
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Gloster TM, Davies GJ. Glycosidase inhibition: assessing mimicry of the transition state. Org Biomol Chem 2010; 8:305-20. [PMID: 20066263 PMCID: PMC2822703 DOI: 10.1039/b915870g] [Citation(s) in RCA: 191] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2009] [Accepted: 09/30/2009] [Indexed: 12/15/2022]
Abstract
Glycoside hydrolases, the enzymes responsible for hydrolysis of the glycosidic bond in di-, oligo- and polysaccharides, and glycoconjugates, are ubiquitous in Nature and fundamental to existence. The extreme stability of the glycosidic bond has meant these enzymes have evolved into highly proficient catalysts, with an estimated 10(17) fold rate enhancement over the uncatalysed reaction. Such rate enhancements mean that enzymes bind the substrate at the transition state with extraordinary affinity; the dissociation constant for the transition state is predicted to be 10(-22) M. Inhibition of glycoside hydrolases has widespread application in the treatment of viral infections, such as influenza and HIV, lysosomal storage disorders, cancer and diabetes. If inhibitors are designed to mimic the transition state, it should be possible to harness some of the transition state affinity, resulting in highly potent and specific drugs. Here we examine a number of glycosidase inhibitors which have been developed over the past half century, either by Nature or synthetically by man. A number of criteria have been proposed to ascertain which of these inhibitors are true transition state mimics, but these features have only be critically investigated in a very few cases.
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Affiliation(s)
- Tracey M. Gloster
- York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5YW, UK. ; ; Fax: +44 1904 328266; Tel: +44 1904 328260
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Gideon J. Davies
- York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5YW, UK. ; ; Fax: +44 1904 328266; Tel: +44 1904 328260
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22
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Ganesan M, Madhukarrao RV, Ramesh NG. Design and synthesis of new amino-modified iminocyclitols: selective inhibitors of α-galactosidase. Org Biomol Chem 2010; 8:1527-30. [DOI: 10.1039/b926123k] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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23
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Chang YC, Chir JL, Tsai SY, Juang WF, Wu AT. Microwave-assisted synthesis of pyrrolidine derivatives. Tetrahedron Lett 2009. [DOI: 10.1016/j.tetlet.2009.06.062] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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24
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Li RJ, Bols M, Rousseau C, Zhang XG, Wang RW, Qing FL. Synthesis and biological evaluation of potent glycosidase inhibitors: 4-deoxy-4,4-difluoroisofagomine and analogues. Tetrahedron 2009. [DOI: 10.1016/j.tet.2009.02.079] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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25
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Vocadlo DJ, Davies GJ. Mechanistic insights into glycosidase chemistry. Curr Opin Chem Biol 2009; 12:539-55. [PMID: 18558099 DOI: 10.1016/j.cbpa.2008.05.010] [Citation(s) in RCA: 300] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2008] [Accepted: 05/19/2008] [Indexed: 11/16/2022]
Abstract
The enzymatic hydrolysis of the glycosidic bond continues to gain importance, reflecting the critically important roles complex glycans play in health and disease as well as the rekindled interest in enzymatic biomass conversion. Recent advances include the broadening of our understanding of enzyme reaction coordinates, through both computational and structural studies, improved understanding of enzyme inhibition through transition state mimicry and fascinating insights into mechanism yielded by physical organic chemistry approaches.
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Affiliation(s)
- David J Vocadlo
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, V5A 1S6, Canada.
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26
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Yang MT, Woerpel KA. The effect of electrostatic interactions on conformational equilibria of multiply substituted tetrahydropyran oxocarbenium ions. J Org Chem 2009; 74:545-53. [PMID: 19072093 DOI: 10.1021/jo8017846] [Citation(s) in RCA: 110] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The three-dimensional structures of dioxocarbenium ions related to glycosyl cations were determined by an analysis of spectroscopic, computational, and reactivity data. Hypothetical low-energy structures of the dioxocarbenium ions were correlated with both experimentally determined (1)H NMR coupling constants and diastereoselectivity results from nucleophilic substitution reactions. This method confirmed the pseudoaxial preference of C-3 alkoxy-substituted systems and revealed the conformational preference of the C-5 alkoxymethyl group. Although the monosubstituted C-5 alkoxymethyl substituent preferred a pseudoequatorial orientation, the C-5-C-6 bond rotation was controlled by an electrostatic effect. The preferred diaxial conformer of the trans-4,5-disubstituted tetrahydropyranyl system underscored the importance of electrostatic effects in dictating conformational equilibria. In the 2-deoxymannose system, although steric effects influenced the orientation of the C-5 alkoxymethyl substituent, the all-axial conformer was favored because of electrostatic stabilization.
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Affiliation(s)
- Michael T Yang
- Department of Chemistry, University of California, Irvine, California 92697-2025, USA
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27
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Golicnik M, Olguin LF, Feng G, Baxter NJ, Waltho JP, Williams NH, Hollfelder F. Kinetic analysis of beta-phosphoglucomutase and its inhibition by magnesium fluoride. J Am Chem Soc 2009; 131:1575-88. [PMID: 19132841 DOI: 10.1021/ja806421f] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The isomerization of beta-glucose-1-phosphate (betaG1P) to beta-glucose-6-phosphate (G6P) catalyzed by beta-phosphoglucomutase (betaPGM) has been examined using steady- and presteady-state kinetic analysis. In the presence of low concentrations of beta-glucose-1,6-bisphosphate (betaG16BP), the reaction proceeds through a Ping Pong Bi Bi mechanism with substrate inhibition (kcat = 65 s(-1), K(betaG1P) = 15 microM, K(betaG16BP) = 0.7 microM, Ki = 122 microM). If alphaG16BP is used as a cofactor, more complex kinetic behavior is observed, but the nonlinear progress curves can be fit to reveal further catalytic parameters (kcat = 74 s(-1), K(betaG1P) = 15 microM, K(betaG16BP) = 0.8 microM, Ki = 122 microM, K(alphaG16BP) = 91 microM for productive binding, K(alphaG16BP) = 21 microM for unproductive binding). These data reveal that variations in the substrate structure affect transition-state affinity (approximately 140,000-fold in terms of rate acceleration) substantially more than ground-state binding (110-fold in terms of binding affinity). When fluoride and magnesium ions are present, time-dependent inhibition of the betaPGM is observed. The concentration dependence of the parameters obtained from fitting these progress curves shows that a betaG1P x MgF3(-) x betaPGM inhibitory complex is formed under the reaction conditions. The overall stability constant for this complex is approximately 2 x 10(-16) M(5) and suggests an affinity of the MgF3(-) moiety to this transition-state analogue (TSA) of < or = 70 nM. The detailed kinetic analysis shows how a special type of TSA that does not exist in solution is assembled in the active site of an enzyme. Further experiments show that under the conditions of previous structural studies, phosphorylated glucose only persists when bound to the enzyme as the TSA. The preference for TSA formation when fluoride is present, and the hydrolysis of substrates when it is not, rules out the formation of a stable pentavalent phosphorane intermediate in the active site of betaPGM.
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Affiliation(s)
- Marko Golicnik
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, United Kingdom
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28
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Kumari N, Reddy BG, Vankar YD. Efficient and Stereodivergent Syntheses of D- and L-Fagomines and Their Analogues. European J Org Chem 2008. [DOI: 10.1002/ejoc.200800796] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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29
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Kuntz DA, Tarling CA, Withers SG, Rose DR. Structural Analysis of Golgi α-Mannosidase II Inhibitors Identified from a Focused Glycosidase Inhibitor Screen. Biochemistry 2008; 47:10058-68. [DOI: 10.1021/bi8010785] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Douglas A. Kuntz
- Ontario Cancer Institute and Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, and Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada
| | - Chris A. Tarling
- Ontario Cancer Institute and Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, and Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada
| | - Stephen G. Withers
- Ontario Cancer Institute and Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, and Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada
| | - David R. Rose
- Ontario Cancer Institute and Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, and Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada
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30
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N-Acetylhexosaminidase inhibitory properties of C-1 homologated GlcNAc- and GalNAc-thiazolines. Bioorg Med Chem Lett 2008; 18:2944-7. [DOI: 10.1016/j.bmcl.2008.03.067] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2008] [Accepted: 03/24/2008] [Indexed: 11/17/2022]
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31
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Tailford LE, Offen WA, Smith NL, Dumon C, Morland C, Gratien J, Heck MP, Stick RV, Blériot Y, Vasella A, Gilbert HJ, Davies GJ. Structural and biochemical evidence for a boat-like transition state in β-mannosidases. Nat Chem Biol 2008; 4:306-12. [PMID: 18408714 DOI: 10.1038/nchembio.81] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Accepted: 02/15/2008] [Indexed: 11/09/2022]
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32
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Kelly RM, Leemhuis H, Gätjen L, Dijkhuizen L. Evolution toward Small Molecule Inhibitor Resistance Affects Native Enzyme Function and Stability, Generating Acarbose-insensitive Cyclodextrin Glucanotransferase Variants. J Biol Chem 2008; 283:10727-34. [DOI: 10.1074/jbc.m709287200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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33
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Mane RS, Kumar KSA, Dhavale DD. Synthesis of γ-Hydroxyalkyl Substituted Piperidine Iminosugars from d-Glucose. J Org Chem 2008; 73:3284-7. [DOI: 10.1021/jo800044r] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Rajendra S. Mane
- Department of Chemistry, Garware Research Centre, University of Pune, Pune- 411 007, India %
| | - K. S. Ajish Kumar
- Department of Chemistry, Garware Research Centre, University of Pune, Pune- 411 007, India %
| | - Dilip D. Dhavale
- Department of Chemistry, Garware Research Centre, University of Pune, Pune- 411 007, India %
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34
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Kumar A, Rawal GK, Vankar YD. Synthesis of hybrids of d-glucose and d-galactose with 1-deoxynojirimycin analogues using ring-closing metathesis. Tetrahedron 2008. [DOI: 10.1016/j.tet.2008.01.005] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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35
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Ludwiczek ML, Heller M, Kantner T, McIntosh LP. A secondary xylan-binding site enhances the catalytic activity of a single-domain family 11 glycoside hydrolase. J Mol Biol 2007; 373:337-54. [PMID: 17822716 DOI: 10.1016/j.jmb.2007.07.057] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2007] [Accepted: 07/24/2007] [Indexed: 11/20/2022]
Abstract
Bacillus circulans xylanase (BcX) is a single-domain family 11 glycoside hydrolase. Using NMR-monitored titrations, we discovered that an inactive variant of this enzyme, E78Q-BcX, bound xylooligosaccharides not only within its pronounced active site (AS) cleft, but also at a distal surface region. Chemical shift perturbation mapping and affinity electrophoresis, combined with mutational studies, identified the xylan-specific secondary binding site (SBS) as a shallow groove lined by Asn, Ser, and Thr residues and with a Trp at one end. The AS and SBS bound short xylooligosaccharides with similar dissociation constants in the millimolar range. However, the on and off-rates to the SBS were at least tenfold faster than those of kon approximately 3x10(5) M(-1) s(-1) and koff approximately 1000 s(-1) measured for xylotetraose to the AS of E78Q-BcX. Consistent with their structural differences, this suggests that a conformational change in the enzyme and/or the substrate is required for association to and dissociation from the deep AS, but not the shallow SBS. In contrast to the independent binding of small xylooligosaccharides, high-affinity binding of soluble and insoluble xylan, as well as xylododecaose, occurred cooperatively to the two sites. This was evidenced by an approximately 100-fold increase in relative Kd values for these ligands upon mutation of the SBS. The SBS also enhances the activity of BcX towards soluble and insoluble xylan through a significant reduction in the Michaelis KM values for these polymeric substrates. This study provides an unexpected example of how a single domain family 11 xylanase overcomes the lack of a carbohydrate-binding module through the use of a secondary binding site to enhance substrate specificity and affinity.
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Affiliation(s)
- Martin L Ludwiczek
- Department of Biochemistry and Molecular Biology, Department of Chemistry, The Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
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36
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Whitfield DM. DFT studies of the ionization of alpha and beta glycopyranosyl donors. Carbohydr Res 2007; 342:1726-40. [PMID: 17555731 DOI: 10.1016/j.carres.2007.05.012] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2007] [Revised: 04/26/2007] [Accepted: 05/06/2007] [Indexed: 11/28/2022]
Abstract
Current attempts at mimicking the transition states (TSs) of glycosyl processing enzymes (GPEs) that proceed through TSs with a high degree of oxacarbenium ion formation suffer from a paucity of data about the conformations of such oxacarbenium ions. Because TSs are maxima, the current models based on minimized structures may need some refinement. As part of studies directed at optimizing chemical glycosylation the ionization of 3,4,6-tri-O-acetyl-alpha/beta-D-glucopyranosyl chlorides and triflates, 2,3,4,6-tetra-O-methyl-alpha/beta-D-glucopyranosyl fluorides, chlorides and triflates, 2,3,4,6-tetra-O-methyl-alpha/beta-D-mannopyranosyl fluorides, 2,3-di-O-methyl 4,6-O-benzylidene alpha/beta-D-mannopyranosyl triflates and 2,3-di-O-methyl 4,6-O-benzylidene alpha/beta-D-glucopyranosyl triflates was studied by a prototypic density functional theory (DFT) procedure. In all cases, the alpha-anomers ionized smoothly to 4H3 half chair conformations or adjacent envelopes. By contrast, all beta-anomers exhibited an abrupt conformational change before ionization was complete. The nature of the conformations sampled depends on both the leaving group and the protecting group. The methods presented can be readily adapted to the study of any GPE or chemical glycosylation and provide a method for initial evaluation of plausible TSs, which in turn can be used in mimetic design.
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Affiliation(s)
- Dennis M Whitfield
- Institute for Biological Sciences, NRC Canada, 100 Sussex Drive, Ottawa, ON, Canada K1A 0R6.
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