Structural highlights
Publication Abstract from PubMedEndoxylanases 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 alpha-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 (CpXyn30A) is presented. This xylanase possesses a high degree of amino-acid identity to the canonical GH30-8 enzymes, but lacks the hallmark beta8-alpha8 loop region which in part defines the function of this GH30 subfamily and its role in GA recognition. CpXyn30A 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, CpXyn30A does not have any apparent specificity for the GA appendage. These findings confirm that the typically conserved beta8-alpha8 loop region of these enzymes influences xylan substrate specificity but not necessarily beta-1,4-xylanase function. A novel member of glycoside hydrolase family 30 subfamily 8 with altered substrate specificity.,St John FJ, Dietrich D, Crooks C, Pozharski E, Gonzalez JM, Bales E, Smith K, Hurlbert JC Acta Crystallogr D Biol Crystallogr. 2014 Nov;70(Pt 11):2950-8. doi:, 10.1107/S1399004714019531. Epub 2014 Oct 23. PMID:25372685[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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