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Identification of Asp-130 as the catalytic nucleophile in the main alpha-galactosidase from Phanerochaete chrysosporium, a family 27 glycosyl hydrolase
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2000 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 39, no 32, 9826-9836 p.Article in journal (Refereed) Published
Abstract [en]

Characterization of the complete gene sequence encoding the alpha-galactosidase from Phanerochaete chrysosporium confirms that this enzyme is a member of glycosyl hydrolase family 27 [Henrissat, B., and Bairoch, A. (1996) Biochem. J. 316, 695-696]. This family, together with the family 36 alpha-galactosidases, forms glycosyl hydrolase dan GH-D, a superfamily of alpha-galactosidases, alpha-N-acetylgalactosaminidases, and isomaltodextranases which are likely to share a common catalytic mechanism and structural topology. Identification of the active site catalytic nucleophile was achieved by labeling with the mechanism-based inactivator 2',4',6'-trinitrophenyl 2-deoxy-2,2-difluoro-alpha-D- lyxo-hexopyranoside; this inactivator was synthesized by anomeric deprotection of the known 1,3,4,6-tetra-O-acetyl-2-deoxy-2,2-difluoro-D-lyxo-hexopyranoside [McCarter, J. D., Adam, M. J., Braun, C., Namchuk, M., Tull, D., and Withers, S. G. (1993) Carbohydr. Res. 249, 77-90], picrylation with picryl fluoride and 2,6-di-tert-butylpyridine, and O-deacetylation with methanolic HCl. Enzyme inactivation is a result of the formation of a stable 2-deoxy-2,2-difluoro-beta-D-lyxo-hexopyranosyl-enzyme intermediate. Following peptic digestion, comparative liquid chromatographic/mass spectrometric analysis of inactivated and control enzyme samples served to identify the covalently modified peptide. After purification of the labeled peptide, benzylamine was shown to successfully replace the 2-deoxy-2,2-difluoro-D-lyxo-hexopyranosyl peptidyl ester by aminolysis. The labeled amino acid was identified as Asp-130 of the mature protein by further tandem mass spectrometric analysis of the native and derivatized peptides in combination with Edman degradation analysis. Asp-130 is found within the sequence YLKYDNC, which is highly conserved in all known family 27 glycosyl hydrolases.

Place, publisher, year, edition, pages
2000. Vol. 39, no 32, 9826-9836 p.
Keyword [en]
active-site nucleophile, substrate-assisted catalysis, hydrophobic cluster-analysis, beta-glucosidase, glycosidase inhibitors, enzyme intermediate, mass-spectrometry, mechanism, phosphates, hydrolysis
URN: urn:nbn:se:kth:diva-19980ISI: 000088835700023OAI: diva2:338673
QC 20100525Available from: 2010-08-10 Created: 2010-08-10Bibliographically approved

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