| 1. |
- Comfort, Donald A., et al.
(författare)
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Biochemical analysis of Thermotoga maritima GH36 alpha-galactosidase (TmGalA) confirms the mechanistic commonality of clan GH-D glycoside hydrolases
- 2007
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 46:11, s. 3319-3330
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Tidskriftsartikel (refereegranskat)abstract
- Organization of glycoside hydrolase (GH) families into clans expands the utility of information on catalytic mechanisms of member enzymes. This issue was examined for GH27 and GH36 through biochemical analysis of GH36 alpha-galactosidase from Thermotoga maritima (TmGalA). Catalytic residues in TmGalA were inferred through structural homology with GH27 members to facilitate design of site-directed mutants. Product analysis confirmed that the wild type (WT) acted with retention of anomeric stereochemistry, analogous to GH27 enzymes. Conserved acidic residues were confirmed through kinetic analysis of D327G and D387G mutant enzymes, azide rescue, and determination of azide rescue products. Mutation of Asp327 to Gly resulted in a mutant that had a 200-800-fold lower catalytic rate on aryl galactosides relative to the WT enzyme. Azide rescue experiments using the D327G enzyme showed a 30-fold higher catalytic rate compared to without azide. Addition of azide to the reaction resulted in formation of azide beta-D-galactopyranoside, confirming Asp327 as the nucleophilic residue. The Asp387Gly mutation was 1500-fold catalytically slower than the WT enzyme on p-nitrophenyl alpha-D-galactopyranoside. Analysis at different pH values produced a bell-shaped curve of the WT enzyme, but D387G exhibited higher activity with increasing pH. Catalyzed reactions with the D387G mutant in the presence of azide resulted in formation of azide alpha-D-galactopryanoside as the product of a retaining mechanism. These results confirm that Asp387 is the acid/base residue of TmGalA. Furthermore, they show that the biochemical characteristics of GH36 TmGalA are closely related to GH27 enzymes, confirming the mechanistic commonality of clan GH-D members.
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| 2. |
- Eneyskaya, E. V., et al.
(författare)
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Chemo-enzymatic synthesis of 4-methylumbelliferyl beta-(1 -> 4)-D-xylooligosides : new substrates for beta-D-xylanase assays
- 2005
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Ingår i: Organic and biomolecular chemistry. - : Royal Society of Chemistry (RSC). - 1477-0520 .- 1477-0539. ; 3:1, s. 146-151
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Tidskriftsartikel (refereegranskat)abstract
- Transglycosylation catalyzed by a beta-D-xylosidase from Aspergillus sp. was used to synthesize a set of 4-methylumbelliferyl (MU) beta-1-->4-D-xylooligosides having the common structure [beta-D-Xyl-(1-->4)](2-5)-beta- D-Xyl-MU. MU xylobioside synthesized chemically by the condensation of protected MU beta-D-xylopyranoside with ethyl 2,3,4-tri-O-acetyl-1-thio-beta-D-xylopyranoside was used as a substrate for transglycosylation with the beta-D- xylosidase from Aspergillus sp. to produce higher MU xylooligosides. The structures of oligosaccharides obtained were established by H-1 and C-13 NMR spectroscopy and electrospray tandem mass spectrometry. MU beta-D-xylooligosides synthesized were tested as fluorogenic substrates for the GH-10 family beta-D-xylanase from Aspergillus orizae and the GH-11 family beta-D- xylanase I from Trichoderma reesei. Both xylanases released the aglycone from MU xylobioside and the corresponding trioside. With substrates having d.p. 4 and 5, the enzymes manifested endolytic activities, splitting off MU, MUX, and MUX2 primarily.
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| 3. |
- Eneyskaya, Elena V., et al.
(författare)
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Transglycosylating and hydrolytic activities of the beta-mannosidase from Trichoderma reesei
- 2009
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Ingår i: Biochimie. - : Elsevier BV. - 0300-9084 .- 1638-6183. ; 91:5, s. 632-638
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Tidskriftsartikel (refereegranskat)abstract
- A purified beta-mannosidase (EC 3.2.1.25) from the fungus Trichoderma reesei has been identified as a member of glycoside hydrolase family 2 through mass spectrometry analysis of tryptic peptides. In addition to hydrolysis, the enzyme catalyzes substrate transglycosylation with p-nitrophenyl beta-mannopyranoside. Structures of the major and minor products of this reaction were identified by NMR analysis as p-nitrophenyl mannobiosides and p-nitrophenyl mannotriosides containing beta-(1 -> 4) and beta-(1 -> 3) linkages. The rate of donor substrate hydrolysis increased in presence of acetonitrile and dimethylformamide, while transglycosylation was weakly suppressed by these organic solvents. Differential ultraviolet spectra of the protein indicate that a rearrangement of the hydrophobic environment of the active site following the addition of the organic solvents may be responsible for this hydrolytic activation.
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| 4. |
- Neustroev, Kirill N., et al.
(författare)
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Transferase and hydrolytic activities of the laminarinase from rhodothermus marinus and its M133A, M133C, and M133W mutants
- 2006
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Ingår i: Glycoconjugate Journal. - : Springer Science and Business Media LLC. - 0282-0080 .- 1573-4986. ; 23:08-jul, s. 501-511
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Tidskriftsartikel (refereegranskat)abstract
- Comparative studies of the transglycosylation and hydrolytic activities have been performed on the Rhodothermus marinus beta-1,3-glucanase (laminarinase) and its M133A, M133C, and M133W mutants. The M133C mutant demonstrated near 20% greater rate of transglycosylation activity in comparison with the M133A and M133W mutants that was measured by NMR quantitation of nascent beta(1-4) and beta(1-6) linkages. To obtain kinetic probes for the wild-type enzyme and Met-133 mutants, p-nitrophenyl beta-laminarin oligosaccharides of degree of polymerisation 2-8 were synthesized enzymatically. Catalytic efficiency values, k (cat)/K (m), of the laminarinase catalysed hydrolysis of these oligosaccharides suggested possibility of four negative and at least three positive binding subsites in the active site. Comparison of action patterns of the wild-type and M133C mutant in the hydrolysis of the p-nitrophenyl-beta-D-oligosac- charides indicated that the increased transglycosylation activity of the M133C mutant did not result from altered subsite affinities. The stereospecificity of the transglycosylation reaction also was unchanged in all mutants; the major transglycosylation products in hydrolysis of p-nitrophenyl laminaribioside were beta-glucopyranosyl-beta-1,3-D-glucopy- ranosyl-beta-1,3-D-glucopyranose and beta-glucopyranosyl-beta-1, 3-D-glucopyranosyl-beta-1,3-D-glucpyranosyl-beta-1,3-D- glucopyranoxside.
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