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Crystal structure of beta-D-xylosidase from Thermoanaerobacterium saccharolyticum, a family 39 glycoside hydrolase

TitleCrystal structure of beta-D-xylosidase from Thermoanaerobacterium saccharolyticum, a family 39 glycoside hydrolase
Publication TypeJournal Article
Year of Publication2004
AuthorsYang, JK, Yoon, HJ, Ahn, HJ, Lee, BI, Pedelacq, JD, Liong, EC, Berendzen, J, Laivenieks, M, Vieille, C, Zeikus, GJ, Vocadlo, DJ, Withers, SG, Suh, SW
JournalJOURNAL OF MOLECULAR BIOLOGY
Volume335
Pagination155-165
Date PublishedJAN 2
ISSN0022-2836
Abstract

1,4-beta-D-Xylan is the major component of plant cell-wall hemicelluloses. beta-D-Xylosidases are involved in the breakdown of xylans into xylose and belong to families 3, 39, 43, 52, and 54 of glycoside hydrolases. Here, we report the first crystal structure of a member of family 39 glycoside hydrolase, i.e. beta-D-xylosidase from Thermoanaerobacterium saccharolyticum strain B6A-RI. This study also represents the first structure of any P-xylosidase of the above five glycoside hydrolase families. Each monomer of T saccharolyticum P-xylosidase comprises three distinct domains; a catalytic domain of the canonical (P/alpha)(8)-barrel fold, a P-sandwich domain, and a small alpha-helical domain. We have determined the structure in two forms: D-xylose-bound enzyme and a covalent 2-deoxy2-fluoro-alpha-D-xylosyl-enzyme intermediate complex, thus providing two snapshots in the reaction pathway. This study provides structural evidence for the proposed double displacement mechanism that involves a covalent intermediate. Furthermore, it reveals possible functional roles for His228 as the auxiliary acid/base and Glu323 as a key residue in substrate recognition.

DOI10.1016/j.jmb.2003.10.026