51
|
Transient oxidation as a mechanistic strategy in enzymatic catalysis. Curr Opin Chem Biol 2008; 12:532-8. [DOI: 10.1016/j.cbpa.2008.06.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2008] [Accepted: 06/17/2008] [Indexed: 11/18/2022]
|
52
|
Characterization of Bacillus halodurans alpha-galactosidase Mel4A encoded by the mel4A gene (BH2228). Biosci Biotechnol Biochem 2008; 72:2459-62. [PMID: 18776668 DOI: 10.1271/bbb.80242] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A family-4 alpha-galactosidase Mel4A of Bacillus halodurans was expressed in Escherichia coli and characterized. Recombinant enzyme rMel4A depended on NAD+, some divalent cations such as Mn2+, and reducing reagents such as dithiothreitol. rMel4A was active on small saccharides such as raffinose but not on highly polymerized galactomannan. Immunological analysis indicated that raffinose induced the production of Mel4A in B. halodurans.
Collapse
|
53
|
Namboori SC, Graham DE. Enzymatic analysis of uridine diphosphate N-acetyl-D-glucosamine. Anal Biochem 2008; 381:94-100. [PMID: 18634748 DOI: 10.1016/j.ab.2008.06.034] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2008] [Revised: 06/22/2008] [Accepted: 06/25/2008] [Indexed: 11/30/2022]
Abstract
The Methanococcus maripaludis MMP0352 protein belongs to an oxidoreductase family that has been proposed to catalyze the NAD(+)-dependent oxidation of the 3'' position of uridine diphosphate N-acetyl-D-glucosamine (UDP-GlcNAc), forming a 3-hexulose sugar nucleotide. The heterologously expressed MMP0352 protein was purified and shown to efficiently catalyze UDP-GlcNAc oxidation, forming one NADH equivalent. This enzyme was used to develop a fixed endpoint fluorometric method to analyze UDP-GlcNAc. The enzyme is highly specific for this acetamido sugar nucleotide, and the procedure had a detection limit of 0.2 microM UDP-GlcNAc in a 1-ml sample. Using the method of standard addition, UDP-GlcNAc concentrations were measured in deproteinized extracts of Escherichia coli, Saccharomyces cerevisiae, and HeLa carcinoma cells. Equivalent concentrations were determined by both enzymatic and chromatographic analyses, validating this method. This procedure can be adapted for the high-throughput analysis of changes in cellular UDP-GlcNAc concentrations in time series experiments or inhibitor screens.
Collapse
Affiliation(s)
- Seema C Namboori
- Institute for Cellular and Molecular Biology and Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, TX 78712, USA
| | | |
Collapse
|
54
|
Park H, Hwang KY, Kim YH, Oh KH, Lee JY, Kim K. Discovery and biological evaluation of novel alpha-glucosidase inhibitors with in vivo antidiabetic effect. Bioorg Med Chem Lett 2008; 18:3711-5. [PMID: 18524587 DOI: 10.1016/j.bmcl.2008.05.056] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2008] [Revised: 05/14/2008] [Accepted: 05/15/2008] [Indexed: 11/15/2022]
Abstract
Discovery of alpha-glucosidase inhibitors has been actively pursued with the aim to develop therapeutics for the treatment of diabetes and the other carbohydrate-mediated diseases. We have identified four novel alpha-glucosidase inhibitors by means of a drug design protocol involving the structure-based virtual screening under consideration of the effects of ligand solvation in the scoring function and in vitro enzyme assay. Because the newly identified inhibitors reveal in vivo antidiabetic activity as well as a significant potency with more than 70% inhibition of the catalytic activity of alpha-glucosidase at 50 microM, all of them seem to deserve further development to discover new drugs for diabetes. Structural features relevant to the interactions of the newly identified inhibitors with the active site residues of alpha-glucosidase are discussed in detail.
Collapse
Affiliation(s)
- Hwangseo Park
- Department of Bioscience and Biotechnology, Sejong University, 98 Kunja-Dong, Kwangjin-Ku, Seoul 143-747, Republic of Korea.
| | | | | | | | | | | |
Collapse
|
55
|
Toward the Virtual Screening of α-Glucosidase Inhibitors with the Homology-Modeled Protein Structure. B KOREAN CHEM SOC 2008. [DOI: 10.5012/bkcs.2008.29.5.921] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
|
56
|
The sim operon facilitates the transport and metabolism of sucrose isomers in Lactobacillus casei ATCC 334. J Bacteriol 2008; 190:3362-73. [PMID: 18310337 DOI: 10.1128/jb.02008-07] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Inspection of the genome sequence of Lactobacillus casei ATCC 334 revealed two operons that might dissimilate the five isomers of sucrose. To test this hypothesis, cells of L. casei ATCC 334 were grown in a defined medium supplemented with various sugars, including each of the five isomeric disaccharides. Extracts prepared from cells grown on the sucrose isomers contained high levels of two polypeptides with M(r)s of approximately 50,000 and approximately 17,500. Neither protein was present in cells grown on glucose, maltose or sucrose. Proteomic, enzymatic, and Western blot analyses identified the approximately 50-kDa protein as an NAD(+)- and metal ion-dependent phospho-alpha-glucosidase. The oligomeric enzyme was purified, and a catalytic mechanism is proposed. The smaller polypeptide represented an EIIA component of the phosphoenolpyruvate-dependent sugar phosphotransferase system. Phospho-alpha-glucosidase and EIIA are encoded by genes at the LSEI_0369 (simA) and LSEI_0374 (simF) loci, respectively, in a block of seven genes comprising the sucrose isomer metabolism (sim) operon. Northern blot analyses provided evidence that three mRNA transcripts were up-regulated during logarithmic growth of L. casei ATCC 334 on sucrose isomers. Internal simA and simF gene probes hybridized to approximately 1.5- and approximately 1.3-kb transcripts, respectively. A 6.8-kb mRNA transcript was detected by both probes, which was indicative of cotranscription of the entire sim operon.
Collapse
|
57
|
Liu QP, Yuan H, Bennett EP, Levery SB, Nudelman E, Spence J, Pietz G, Saunders K, White T, Olsson ML, Henrissat B, Sulzenbacher G, Clausen H. Identification of a GH110 subfamily of alpha 1,3-galactosidases: novel enzymes for removal of the alpha 3Gal xenotransplantation antigen. J Biol Chem 2008; 283:8545-54. [PMID: 18227066 DOI: 10.1074/jbc.m709020200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In search of alpha-galactosidases with improved kinetic properties for removal of the immunodominant alpha1,3-linked galactose residues of blood group B antigens, we recently identified a novel prokaryotic family of alpha-galactosidases (CAZy GH110) with highly restricted substrate specificity and neutral pH optimum (Liu, Q. P., Sulzenbacher, G., Yuan, H., Bennett, E. P., Pietz, G., Saunders, K., Spence, J., Nudelman, E., Levery, S. B., White, T., Neveu, J. M., Lane, W. S., Bourne, Y., Olsson, M. L., Henrissat, B., and Clausen, H. (2007) Nat. Biotechnol. 25, 454-464). One member of this family from Bacteroides fragilis had exquisite substrate specificity for the branched blood group B structure Galalpha1-3(Fucalpha1-2)Gal, whereas linear oligosaccharides terminated by alpha1,3-linked galactose such as the immunodominant xenotransplantation epitope Galalpha1-3Galbeta1-4GlcNAc did not serve as substrates. Here we demonstrate the existence of two distinct subfamilies of GH110 in B. fragilis and thetaiotaomicron strains. Members of one subfamily have exclusive specificity for the branched blood group B structures, whereas members of a newly identified subfamily represent linkage specific alpha1,3-galactosidases that act equally well on both branched blood group B and linear alpha1,3Gal structures. We determined by one-dimensional (1)H NMR spectroscopy that GH110 enzymes function with an inverting mechanism, which is in striking contrast to all other known alpha-galactosidases that use a retaining mechanism. The novel GH110 subfamily offers enzymes with highly improved performance in enzymatic removal of the immunodominant alpha3Gal xenotransplantation epitope.
Collapse
|
58
|
Park H, Hwang KY, Oh KH, Kim YH, Lee JY, Kim K. Discovery of novel alpha-glucosidase inhibitors based on the virtual screening with the homology-modeled protein structure. Bioorg Med Chem 2007; 16:284-92. [PMID: 17920282 DOI: 10.1016/j.bmc.2007.09.036] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2007] [Revised: 09/17/2007] [Accepted: 09/19/2007] [Indexed: 10/22/2022]
Abstract
Discovery of alpha-glucosidase inhibitors has been actively pursued with the aim to develop therapeutics for the treatment of diabetes and the other carbohydrate mediated diseases. We have been able to identify 13 novel alpha-glucosidase inhibitors by means of a computer-aided drug design protocol involving homology modeling of the target protein and the virtual screening with docking simulations under consideration of the effects of ligand solvation in the binding free energy function. Because the newly discovered inhibitors are structurally diverse and reveal a significant potency with IC(50) values lower than 50 microM, all of them can be considered for further development by structure-activity relationship studies or de novo design methods. Structural features relevant to the interactions of the newly identified inhibitors with the active site residues of alpha-glucosidase are discussed in detail.
Collapse
Affiliation(s)
- Hwangseo Park
- Department of Bioscience and Biotechnology, Sejong University, 98 Kunja-Dong, Kwangjin-Ku, Seoul 143-747, Republic of Korea.
| | | | | | | | | | | |
Collapse
|
59
|
Yeang CH, Haussler D. Detecting coevolution in and among protein domains. PLoS Comput Biol 2007; 3:e211. [PMID: 17983264 PMCID: PMC2098842 DOI: 10.1371/journal.pcbi.0030211] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2007] [Accepted: 09/17/2007] [Indexed: 01/17/2023] Open
Abstract
Correlated changes of nucleic or amino acids have provided strong information about the structures and interactions of molecules. Despite the rich literature in coevolutionary sequence analysis, previous methods often have to trade off between generality, simplicity, phylogenetic information, and specific knowledge about interactions. Furthermore, despite the evidence of coevolution in selected protein families, a comprehensive screening of coevolution among all protein domains is still lacking. We propose an augmented continuous-time Markov process model for sequence coevolution. The model can handle different types of interactions, incorporate phylogenetic information and sequence substitution, has only one extra free parameter, and requires no knowledge about interaction rules. We employ this model to large-scale screenings on the entire protein domain database (Pfam). Strikingly, with 0.1 trillion tests executed, the majority of the inferred coevolving protein domains are functionally related, and the coevolving amino acid residues are spatially coupled. Moreover, many of the coevolving positions are located at functionally important sites of proteins/protein complexes, such as the subunit linkers of superoxide dismutase, the tRNA binding sites of ribosomes, the DNA binding region of RNA polymerase, and the active and ligand binding sites of various enzymes. The results suggest sequence coevolution manifests structural and functional constraints of proteins. The intricate relations between sequence coevolution and various selective constraints are worth pursuing at a deeper level. The sequences of different components within and across genes often undergo coordinated changes in order to maintain the structures or functions of the genes. Identifying the coordinated changes—the “coevolution”—of those components in the context of evolution is important in predicting the structures, interactions, and functions of genes. The authors incur a large-scale screening on all the known protein sequences and build a compendium about the coevolving relations of all protein domains—subunits of proteins. The majority of the coevolving protein domains either belongs to the same proteins, appears in the same protein complexes, or shares the same functional annotations. Furthermore, coevolving positions in the same proteins or protein complexes are spatially coupled, as they tend to be closer than random positions in the 3-D structures of the proteins/protein complexes. More strikingly, many coevolving positions are located at functionally important sites of the molecules. The results provide useful insights about the relations between sequence evolution and protein structures and functions.
Collapse
Affiliation(s)
- Chen-Hsiang Yeang
- Simons Center for Systems Biology, Institute for Advanced Study, Princeton, New Jersey, United States of America.
| | | |
Collapse
|
60
|
|
61
|
Liu QP, Sulzenbacher G, Yuan H, Bennett EP, Pietz G, Saunders K, Spence J, Nudelman E, Levery SB, White T, Neveu JM, Lane WS, Bourne Y, Olsson ML, Henrissat B, Clausen H. Bacterial glycosidases for the production of universal red blood cells. Nat Biotechnol 2007; 25:454-64. [PMID: 17401360 DOI: 10.1038/nbt1298] [Citation(s) in RCA: 191] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2006] [Accepted: 02/04/2007] [Indexed: 11/08/2022]
Abstract
Enzymatic removal of blood group ABO antigens to develop universal red blood cells (RBCs) was a pioneering vision originally proposed more than 25 years ago. Although the feasibility of this approach was demonstrated in clinical trials for group B RBCs, a major obstacle in translating this technology to clinical practice has been the lack of efficient glycosidase enzymes. Here we report two bacterial glycosidase gene families that provide enzymes capable of efficient removal of A and B antigens at neutral pH with low consumption of recombinant enzymes. The crystal structure of a member of the alpha-N-acetylgalactosaminidase family reveals an unusual catalytic mechanism involving NAD+. The enzymatic conversion processes we describe hold promise for achieving the goal of producing universal RBCs, which would improve the blood supply while enhancing the safety of clinical transfusions.
Collapse
Affiliation(s)
- Qiyong P Liu
- ZymeQuest Inc., 100 Cummings Center, Suite 436H, Beverly, Massachusetts 01915, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
62
|
Pikis A, Hess S, Arnold I, Erni B, Thompson J. Genetic requirements for growth of Escherichia coli K12 on methyl-alpha-D-glucopyranoside and the five alpha-D-glucosyl-D-fructose isomers of sucrose. J Biol Chem 2006; 281:17900-8. [PMID: 16636060 DOI: 10.1074/jbc.m601183200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Strains of Escherichia coli K12, including MG-1655, accumulate methyl-alpha-D-glucopyranoside via the phosphoenolpyruvate-dependent glucose:phosphotransferase system (IICB(Glc)/IIA(Glc)). High concentrations of intracellular methyl-alpha-D-glucopyranoside 6-phosphate are toxic, and cell growth is prevented. However, transformation of E. coli MG-1655 with a plasmid (pAP1) encoding the gene aglB from Klebsiella pneumoniae resulted in excellent growth of the transformant MG-1655 (pAP1) on the glucose analog. AglB is an unusual NAD+/Mn2+-dependent phospho-alpha-glucosidase that promotes growth of MG-1655 (pAP1) by catalyzing the in vivo hydrolysis of methyl-alpha-D-glucopyranoside 6-phosphate to yield glucose 6-phosphate and methanol. When transformed with plasmid pAP2 encoding the K. pneumoniae genes aglB and aglA (an alpha-glucoside-specific transporter AglA (IICB(Agl))), strain MG-1655 (pAP2) metabolized a variety of other alpha-linked glucosides, including maltitol, isomaltose, and the following five isomers of sucrose: trehalulose alpha(1-->1), turanose alpha(1-->3), maltulose alpha(1-->4), leucrose alpha(1-->5), and palatinose alpha(1-->6). Remarkably, MG-1655 (pAP2) failed to metabolize sucrose alpha(1-->2). The E. coli K12 strain ZSC112L (ptsG::cat manXYZ nagE glk lac) can neither grow on glucose nor transport methyl-alpha-D-glucopyranoside. However, when transformed with pTSGH11 (encoding ptsG) or pAP2, this organism provided membranes that contained either the PtsG or AglA transporters, respectively. In vitro complementation of transporter-specific membranes with purified general phosphotransferase components showed that although PtsG and AglA recognized glucose and methyl-alpha-D-glucopyranoside, only AglA accepted other alpha-D-glucosides as substrates. Complementation experiments also revealed that IIA(Glc) was required for functional activity of both PtsG and AglA transporters. We conclude that AglA, AglB, and IIA(Glc) are necessary and sufficient for growth of E. coli K12 on methyl-alpha-D-glucoside and related alpha-D-glucopyranosides.
Collapse
Affiliation(s)
- Andreas Pikis
- Microbial Biochemistry and Genetics Unit, Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research/NIH, Bldg. 30, Convent Drive, Bethesda, MD 20892, USA
| | | | | | | | | |
Collapse
|
63
|
Yip VLY, Withers SG. Breakdown of oligosaccharides by the process of elimination. Curr Opin Chem Biol 2006; 10:147-55. [PMID: 16495121 DOI: 10.1016/j.cbpa.2006.02.005] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2005] [Accepted: 02/09/2006] [Indexed: 12/22/2022]
Abstract
Several new mechanisms for enzyme-catalyzed breakdown of oligosaccharides have been uncovered in recent years. A common feature is the recruitment of elimination steps rather than direct displacements. Bond cleavage can proceed via E1 mechanisms with cationic transition states or E1(cb) mechanisms with anionic transition states, and can even involve NAD(+)-mediated redox steps. A common feature emerging from studies on disparate syn-eliminating enzymes is the use of a single catalytic residue, often tyrosine, as both general acid and base.
Collapse
Affiliation(s)
- Vivian L Y Yip
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada
| | | |
Collapse
|
64
|
Davies GJ, Gloster TM, Henrissat B. Recent structural insights into the expanding world of carbohydrate-active enzymes. Curr Opin Struct Biol 2005; 15:637-45. [PMID: 16263268 DOI: 10.1016/j.sbi.2005.10.008] [Citation(s) in RCA: 199] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2005] [Revised: 09/21/2005] [Accepted: 10/20/2005] [Indexed: 11/16/2022]
Abstract
Enzymes that catalyse the synthesis and breakdown of glycosidic bonds account for 1-3% of the proteins encoded by the genomes of most organisms. At the current rate, over 12 000 glycosyltransferase and glycoside hydrolase open reading frames will appear during 2006. Recent advances in the study of the structure and mechanism of these carbohydrate-active enzymes reveal that glycoside hydrolases continue to display a wide variety of scaffolds, whereas nucleotide-sugar-dependent glycosyltransferases tend to be grafted onto just two protein folds. The past two years have seen significant advances, including the discovery of a novel NAD+-dependent glycosidase mechanism, the dissection of the reaction coordinate of sialidases and a better understanding of the expanding roles of auxiliary carbohydrate-binding domains.
Collapse
Affiliation(s)
- Gideon J Davies
- Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5YW, UK.
| | | | | |
Collapse
|
65
|
Jaeger T, Arsic M, Mayer C. Scission of the lactyl ether bond of N-acetylmuramic acid by Escherichia coli "etherase". J Biol Chem 2005; 280:30100-6. [PMID: 15983044 DOI: 10.1074/jbc.m502208200] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ubiquitous bacterial cell wall sugar N-acetylmuramic acid (MurNAc) carries a unique D-lactyl ether substituent at the C3 position. Recently, we proposed an etherase capable of cleaving this lactyl ether to be part of the novel bacterial MurNAc dissimilation pathway (Dahl, U., Jaeger, T., Nguyen, B. T., Sattler, J. M., Mayer, C. (2004) J. Bacteriol. 186, 2385-2392). Here, we report the identification of the first known MurNAc etherase. The encoding gene murQ is located at 55 min on the Escherichia coli chromosome adjacent to murP, the MurNAc-specific phosphotransferase system. A murQ deletion mutant could not grow on MurNAc as the sole source of carbon and energy but could be complemented by expressing murQ from a plasmid. The mutant had no obvious phenotype when grown on different carbon sources but accumulated MurNAc 6-phosphate at millimolar concentrations from externally supplied MurNAc. Purified MurQ-His6 fusion protein and extracts of cells expressing murQ both catalyze the cleavage of MurNAc 6-phosphate, with GlcNAc 6-phosphate and D-lactate being the primary products. The 18O label from enriched water is incorporated into the sugar molecule, showing that the C3-O bond is cleaved and reformed by the enzyme. Moreover, an intermediate was detected and identified as an unsaturated sugar molecule. Based on this observation, we suggested a lyase-type mechanism (beta-elimination/hydration) for the cleavage of the lactyl ether bond of MurNAc 6-phosphate. Close homologs of murQ were found on the chromosome of several bacteria, and amino acid sequence similarity with the N-terminal domain of human glucokinase-regulatory protein (GckR or GKRP) was recognized.
Collapse
Affiliation(s)
- Tina Jaeger
- Fachbereich Biologie, Microbiology, University of Konstanz, 78457 Konstanz, Germany
| | | | | |
Collapse
|
66
|
Varrot A, Yip VLY, Li Y, Rajan SS, Yang X, Anderson WF, Thompson J, Withers SG, Davies GJ. NAD+ and metal-ion dependent hydrolysis by family 4 glycosidases: structural insight into specificity for phospho-beta-D-glucosides. J Mol Biol 2005; 346:423-35. [PMID: 15670594 DOI: 10.1016/j.jmb.2004.11.058] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2004] [Revised: 11/14/2004] [Accepted: 11/23/2004] [Indexed: 11/17/2022]
Abstract
The import of disaccharides by many bacteria is achieved through their simultaneous translocation and phosphorylation by the phosphoenolpyruvate-dependent phosphotransferase system (PEP-PTS). The imported phospho-disaccharides are, in some cases, subsequently hydrolyzed by members of the unusual glycoside hydrolase family GH4. The GH4 enzymes, occasionally found also in bacteria such as Thermotoga maritima that do not utilise a PEP-PTS system, require both NAD(+) and Mn(2+) for catalysis. A further curiosity of this family is that closely related enzymes may show specificity for either alpha-d- or beta-d-glycosides. Here, we present, for the first time, the three-dimensional structure (using single-wavelength anomalous dispersion methods, harnessing extensive non-crystallographic symmetry) of the 6-phospho-beta-glycosidase, BglT, from T.maritima in native and complexed (NAD(+) and Glc6P) forms. Comparison of the active-center structure with that of the 6-phospho-alpha-glucosidase GlvA from Bacillus subtilis reveals a striking degree of structural similarity that, in light of previous kinetic isotope effect data, allows the postulation of a common reaction mechanism for both alpha and beta-glycosidases. Given that the "chemistry" occurs primarily on the glycone sugar and features no nucleophilic attack on the intact disaccharide substrate, modulation of anomeric specificity for alpha and beta-linkages is accommodated through comparatively minor structural changes.
Collapse
Affiliation(s)
- Annabelle Varrot
- York Structural Biology Laboratory, Department of Chemistry, University of York, York, YO10 5YW, UK
| | | | | | | | | | | | | | | | | |
Collapse
|