A novel class of proteinaceous inhibitors exhibiting specificity towards microbial xylanases has recently been discovered in cereals. The three-dimensional structure of xylanase inhibitor protein I (XIP-I) from wheat (Triticum aestivum, var. Soisson) was determined by X-ray crystallography at 1.8 Å (1 Å=0.1 nm) resolution. The inhibitor possesses a (β/α)8 barrel fold and has structural features typical of glycoside hydrolase family 18, namely two consensus regions, approximately corresponding to the third and fourth barrel strands, and two non-proline cis-peptide bonds, Ser36–Phe and Trp256–Asp (in XIP-I numbering). However, detailed structural analysis of XIP-I revealed several differences in the region homologous with the active site of chitinases. The catalytic glutamic acid residue of family 18 chitinases [Glu127 in hevamine, a chitinase/lysozyme from the rubber tree (Hevea brasiliensis)] is conserved in the structure of the inhibitor (Glu128), but its side chain is fully engaged in salt bridges with two neighbouring arginine residues. Gly81, located in subsite −1 of hevamine, where the reaction intermediate is formed, is replaced by Tyr80 in XIP-I. The tyrosine side chain fills the subsite area and makes a strong hydrogen bond with the side chain of Glu190 located at the opposite side of the cleft, preventing access of the substrate to the catalytic glutamic acid. The structural differences in the inhibitor cleft structure probably account for the lack of activity of XIP-I towards chitin.
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June 2003
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Research Article|
June 01 2003
Structural analysis of xylanase inhibitor protein I (XIP-I), a proteinaceous xylanase inhibitor from wheat (Triticum aestivum, var. Soisson)
Françoise PAYAN;
Françoise PAYAN
1
∗Architecture et Fonction des Macromolécules Biologiques, UMR6098, CNRS and Universities Aix-Marseille I and II, 31 chemin Joseph Aiguier, F-13402 Marseille, France
1To whom correspondence should be addressed (fran@afmb.cnrs-mrs.fr).
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Ruth FLATMAN;
Ruth FLATMAN
†Institute of Food Research (IFR), Colney Lane, Norwich NR4 7UA, U.K.
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Sophie PORCIERO;
Sophie PORCIERO
∗Architecture et Fonction des Macromolécules Biologiques, UMR6098, CNRS and Universities Aix-Marseille I and II, 31 chemin Joseph Aiguier, F-13402 Marseille, France
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Gary WILLIAMSON;
Gary WILLIAMSON
2
†Institute of Food Research (IFR), Colney Lane, Norwich NR4 7UA, U.K.
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Nathalie JUGE;
Nathalie JUGE
†Institute of Food Research (IFR), Colney Lane, Norwich NR4 7UA, U.K.
‡Institut Méditerranéen de Recherche en Nutrition, UMR INRA 1111, Faculté des Sciences et Techniques de St Jérôme, avenue Escadrille Normandie Niemen, F-13397 Marseille, France
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Alain ROUSSEL
Alain ROUSSEL
∗Architecture et Fonction des Macromolécules Biologiques, UMR6098, CNRS and Universities Aix-Marseille I and II, 31 chemin Joseph Aiguier, F-13402 Marseille, France
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Publisher: Portland Press Ltd
Received:
November 19 2002
Revision Received:
February 27 2003
Accepted:
March 05 2003
Accepted Manuscript online:
March 05 2003
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London ©2003
2003
Biochem J (2003) 372 (2): 399–405.
Article history
Received:
November 19 2002
Revision Received:
February 27 2003
Accepted:
March 05 2003
Accepted Manuscript online:
March 05 2003
Citation
Françoise PAYAN, Ruth FLATMAN, Sophie PORCIERO, Gary WILLIAMSON, Nathalie JUGE, Alain ROUSSEL; Structural analysis of xylanase inhibitor protein I (XIP-I), a proteinaceous xylanase inhibitor from wheat (Triticum aestivum, var. Soisson). Biochem J 1 June 2003; 372 (2): 399–405. doi: https://doi.org/10.1042/bj20021802
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