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Identification of structural determinants for inhibition strength and specificity of wheat xylanase inhibitors TAXI‐IA and TAXI‐IIA
Author(s) -
Pollet Annick,
Sansen Stefaan,
Raedschelders Gert,
Gebruers Kurt,
Rabijns Anja,
Delcour Jan A.,
Courtin Christophe M.
Publication year - 2009
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2009.07105.x
Subject(s) - xylanase , biochemistry , glycoside hydrolase , bacillus subtilis , chemistry , hydrolase , active site , asparagine , enzyme , residue (chemistry) , stereochemistry , biology , bacteria , genetics
Triticum aestivum xylanase inhibitor (TAXI)‐type inhibitors are active against microbial xylanases from glycoside hydrolase family 11, but the inhibition strength and the specificity towards different xylanases differ between TAXI isoforms. Mutational and biochemical analyses of TAXI‐I, TAXI‐IIA and Bacillus subtilis xylanase A showed that inhibition strength and specificity depend on the identity of only a few key residues of inhibitor and xylanase [Fierens K et al. (2005) FEBS J 272 , 5872–5882; Raedschelders G et al. (2005) Biochem Biophys Res Commun 335 , 512–522; Sørensen JF & Sibbesen O (2006) Protein Eng Des Sel 19 , 205–210; Bourgois TM et al. (2007) J Biotechnol 130 , 95–105]. Crystallographic analysis of the structures of TAXI‐IA and TAXI‐IIA in complex with glycoside hydrolase family 11 B. subtilis xylanase A now provides a substantial explanation for these observations and a detailed insight into the structural determinants for inhibition strength and specificity. Structures of the xylanase–inhibitor complexes show that inhibition is established by loop interactions with active‐site residues and substrate‐mimicking contacts in the binding subsites. The interaction of residues Leu292 of TAXI‐IA and Pro294 of TAXI‐IIA with the −2 glycon subsite of the xylanase is shown to be critical for both inhibition strength and specificity. Also, detailed analysis of the interaction interfaces of the complexes illustrates that the inhibition strength of TAXI is related to the presence of an aspartate or asparagine residue adjacent to the acid/base catalyst of the xylanase, and therefore to the pH optimum of the xylanase. The lower the pH optimum of the xylanase, the stronger will be the interaction between enzyme and inhibitor, and the stronger the resulting inhibition. Structured digital abstract• MINT‐7101869 : BSX (uniprotkb: P18429 ) and TAXI‐IA (uniprotkb: Q8H0K8 ) bind ( MI:0407 ) by x‐ray crystallography ( MI:0114 ) • MINT‐7101880 : BSX (uniprotkb: P18429 ) and TAXI‐IIA (uniprotkb: Q53IQ4 ) bind ( MI:0407 ) by x‐ray crystallography ( MI:0114 )