The absence of an identifiable single catalytic base residue in Thermobifida fusca exocellulase Cel6B.

Thermobifida fusca exocellulase Cel6B acts by an inverting hydrolysis mechanism; however, the catalytic acid and base residues for this enzyme have not been confirmed. Site-directed mutagenesis and kinetic studies were used to show that Asp274 is the catalytic acid, which is consistent with what is found for other members of family-6 glycoside hydrolases; however, a single catalytic base was not identified. Mutation of all putative catalytic base residues, within 6 A of the -1/+1 glucose subsites, including the highly conserved Asp226, Asp497 and Glu495, as well as Ser232 and Tyr220, did not reveal a catalytic base, although these residues are all important for activity. We propose a novel hydrolysis mechanism for T. fusca Cel6B involving a proton-transferring network to carry out the catalytic base function.

Citation

Thu V Vuong, David B Wilson. The absence of an identifiable single catalytic base residue in Thermobifida fusca exocellulase Cel6B. The FEBS journal. 2009 Jul;276(14):3837-45

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PMID: 19523117

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