1bvv: Difference between revisions
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==Overview== | ==Overview== | ||
The 1.8 A resolution structure of the glycosyl-enzyme intermediate formed, on the retaining beta-1,4-xylanase from Bacillus circulans has been, determined using X-ray crystallographic techniques. The 2-fluoro-xylose, residue bound in the -1 subsite adopts a 2,5B (boat) conformation, allowing atoms C5, O5, C1, and C2 of the sugar to achieve coplanarity as, required at the oxocarbenium ion-like transition states of the, double-displacement catalytic mechanism. Comparison of this structure to, that of a mutant of this same enzyme noncovalently complexed with, xylotetraose [Wakarchuk et al. (1994) Protein Sci. 3, 467-475] reveals a, number of differences beyond the distortion of the sugar moiety. Most, notably, a bifurcated hydrogen bond interaction is formed in the, glycosyl-enzyme ... | The 1.8 A resolution structure of the glycosyl-enzyme intermediate formed, on the retaining beta-1,4-xylanase from Bacillus circulans has been, determined using X-ray crystallographic techniques. The 2-fluoro-xylose, residue bound in the -1 subsite adopts a 2,5B (boat) conformation, allowing atoms C5, O5, C1, and C2 of the sugar to achieve coplanarity as, required at the oxocarbenium ion-like transition states of the, double-displacement catalytic mechanism. Comparison of this structure to, that of a mutant of this same enzyme noncovalently complexed with, xylotetraose [Wakarchuk et al. (1994) Protein Sci. 3, 467-475] reveals a, number of differences beyond the distortion of the sugar moiety. Most, notably, a bifurcated hydrogen bond interaction is formed in the, glycosyl-enzyme intermediate involving Heta of Tyr69, the endocyclic, oxygen (O5) of the xylose residue in the -1 subsite, and Oepsilon2 of the, catalytic nucleophile, Glu78. To gain additional understanding of the role, of Tyr69 at the active site of this enzyme, we also determined the 1.5 A, resolution structure of the catalytically inactive Tyr69Phe mutant., Interestingly, no significant structural perturbation due to the loss of, the phenolic group is observed. These results suggest that the, interactions involving the phenolic group of Tyr69, O5 of the proximal, saccharide, and Glu78 Oepsilon2 are important for the catalytic mechanism, of this enzyme, and it is proposed that, through charge redistribution, these interactions serve to stabilize the oxocarbenium-like ion of the, transition state. Studies of the covalent glycosyl-enzyme intermediate of, this xylanase also provide insight into specificity, as contacts with C5, of the xylose moiety exclude sugars with hydroxymethyl substituents, and, the mechanism of catalysis, including aspects of stereoelectronic theory, as applied to glycoside hydrolysis. | ||
==About this Structure== | ==About this Structure== | ||
1BVV is a | 1BVV is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Bacillus_circulans Bacillus circulans] with XYP and DFX as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Endo-1,4-beta-xylanase Endo-1,4-beta-xylanase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.2.1.8 3.2.1.8] Structure known Active Sites: ABC and NUC. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1BVV OCA]. | ||
==Reference== | ==Reference== | ||
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[[Category: xylanase]] | [[Category: xylanase]] | ||
''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on | ''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on Mon Nov 5 14:25:13 2007'' | ||
Revision as of 15:19, 5 November 2007
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SUGAR RING DISTORTION IN THE GLYCOSYL-ENZYME INTERMEDIATE OF A FAMILY G/11 XYLANASE
OverviewOverview
The 1.8 A resolution structure of the glycosyl-enzyme intermediate formed, on the retaining beta-1,4-xylanase from Bacillus circulans has been, determined using X-ray crystallographic techniques. The 2-fluoro-xylose, residue bound in the -1 subsite adopts a 2,5B (boat) conformation, allowing atoms C5, O5, C1, and C2 of the sugar to achieve coplanarity as, required at the oxocarbenium ion-like transition states of the, double-displacement catalytic mechanism. Comparison of this structure to, that of a mutant of this same enzyme noncovalently complexed with, xylotetraose [Wakarchuk et al. (1994) Protein Sci. 3, 467-475] reveals a, number of differences beyond the distortion of the sugar moiety. Most, notably, a bifurcated hydrogen bond interaction is formed in the, glycosyl-enzyme intermediate involving Heta of Tyr69, the endocyclic, oxygen (O5) of the xylose residue in the -1 subsite, and Oepsilon2 of the, catalytic nucleophile, Glu78. To gain additional understanding of the role, of Tyr69 at the active site of this enzyme, we also determined the 1.5 A, resolution structure of the catalytically inactive Tyr69Phe mutant., Interestingly, no significant structural perturbation due to the loss of, the phenolic group is observed. These results suggest that the, interactions involving the phenolic group of Tyr69, O5 of the proximal, saccharide, and Glu78 Oepsilon2 are important for the catalytic mechanism, of this enzyme, and it is proposed that, through charge redistribution, these interactions serve to stabilize the oxocarbenium-like ion of the, transition state. Studies of the covalent glycosyl-enzyme intermediate of, this xylanase also provide insight into specificity, as contacts with C5, of the xylose moiety exclude sugars with hydroxymethyl substituents, and, the mechanism of catalysis, including aspects of stereoelectronic theory, as applied to glycoside hydrolysis.
About this StructureAbout this Structure
1BVV is a Single protein structure of sequence from Bacillus circulans with XYP and DFX as ligands. Active as Endo-1,4-beta-xylanase, with EC number 3.2.1.8 Structure known Active Sites: ABC and NUC. Full crystallographic information is available from OCA.
ReferenceReference
Sugar ring distortion in the glycosyl-enzyme intermediate of a family G/11 xylanase., Sidhu G, Withers SG, Nguyen NT, McIntosh LP, Ziser L, Brayer GD, Biochemistry. 1999 Apr 27;38(17):5346-54. PMID:10220321
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