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Title: Beta-D-xylosidase from Selenomonas ruminantium: role of glutamate 186 in catalysis revealed by site-directed mutagenesis, alternate substrates, and inhibitors

Author
item Jordan, Douglas
item Braker, Jay

Submitted to: Biotechnology for Fuels and Chemicals Symposium Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 5/6/2009
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Beta-D-xylosidase from Selenomonas ruminantium is the best catalyst known for promoting hydrolysis of 1,4-beta-D-xylooligosaccharides, and it has potential utility in industrial saccharification processes. Kinetic parameters, kcat and kcat/Km, are more than 10-fold larger than those reported for the enzyme isolated from other organisms. In cleaving 1,4 glycosidic bonds, the family 43 glycoside hydrolase acts through an inversion mechanism and cleaves a single xylose residue from the nonreducing end of xylooligosaccharides per catalytic cycle without processivity. The three-dimensional structure indicates that the enzyme active site has only two subsites for recognition of substrate; larger substrates extend from the active site to the solvent. In addition to its beta-xylosidase activity, the enzyme efficiently catalyzes hydrolysis of 4-nitrophenyl-alpha-L-arabinofuranoside using the same active site as for its beta-xylosidase activity. Glutamate 186 is thought to serve as a general acid in catalyzing the hydrolysis reaction. Here, we probe the role of E186 by comparing kinetic parameters of the native enzyme to the E186A variant using alternate substrates, inhibitors, and pH profiles.