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A novel member of glycoside hydrolase family 30 subfamily 8 with altered substrate specificity
Author(s) -
St John Franz J.,
Dietrich Diane,
Crooks Casey,
Pozharski Edwin,
González Javier M.,
Bales Elizabeth,
Smith Ken,
Hurlbert Jason C.
Publication year - 2014
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
ISSN - 1399-0047
DOI - 10.1107/s1399004714019531
Subject(s) - subfamily , glycoside hydrolase , xylanase , arabinoxylan , biochemistry , chemistry , hydrolase , enzyme , bacillus subtilis , hydrolysis , stereochemistry , xylan , biology , bacteria , genetics , gene
Endoxylanases classified into glycoside hydrolase family 30 subfamily 8 (GH30‐8) are known to hydrolyze the hemicellulosic polysaccharide glucuronoxylan (GX) but not arabinoxylan or neutral xylooligosaccharides. This is owing to the specificity of these enzymes for the α‐1,2‐linked glucuronate (GA) appendage of GX. Limit hydrolysis of this substrate produces a series of aldouronates each containing a single GA substituted on the xylose penultimate to the reducing terminus. In this work, the structural and biochemical characterization of xylanase 30A from Clostridium papyrosolvens ( Cp Xyn30A) is presented. This xylanase possesses a high degree of amino‐acid identity to the canonical GH30‐8 enzymes, but lacks the hallmark β8–α8 loop region which in part defines the function of this GH30 subfamily and its role in GA recognition. Cp Xyn30A is shown to have a similarly low activity on all xylan substrates, while hydrolysis of xylohexaose revealed a competing transglycosylation reaction. These findings are directly compared with the model GH30‐8 enzyme from Bacillus subtilis , XynC. Despite its high sequence identity to the GH30‐8 enzymes, Cp Xyn30A does not have any apparent specificity for the GA appendage. These findings confirm that the typically conserved β8–α8 loop region of these enzymes influences xylan substrate specificity but not necessarily β‐1,4‐xylanase function.

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