1om0 | pdb_00001om0
crystal structure of xylanase inhibitor protein (XIP-I) from wheat
Structural highlights
FunctionXIP1_WHEAT Fungal xylanase inhibitor. Possesses competitive inhibiting activity against fungal endo-1,4-beta-D-xylanases belonging to glycoside hydrolase family 10 (GH10) and family 11 (GH11). Possesses also inhibitory activity towards barley alpha-amylases. Binding to xylanases or amylases is necessary for inhibition activity. May function in plant defense against secreted fungal pathogen xylanases. Is similar to class III chitinases, but does not exhibit chitinase activity.[1] [2] [3] [4] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedA 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 A (1 A=0.1 nm) resolution. The inhibitor possesses a (beta/alpha)(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, Ser(36)-Phe and Trp(256)-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 [Glu(127) in hevamine, a chitinase/lysozyme from the rubber tree (Hevea brasiliensis)] is conserved in the structure of the inhibitor (Glu(128)), but its side chain is fully engaged in salt bridges with two neighbouring arginine residues. Gly(81), located in subsite -1 of hevamine, where the reaction intermediate is formed, is replaced by Tyr(80) in XIP-I. The tyrosine side chain fills the subsite area and makes a strong hydrogen bond with the side chain of Glu(190) 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. Structural analysis of xylanase inhibitor protein I (XIP-I), a proteinaceous xylanase inhibitor from wheat (Triticum aestivum, var. Soisson).,Payan F, Flatman R, Porciero S, Williamson G, Juge N, Roussel A Biochem J. 2003 Jun 1;372(Pt 2):399-405. PMID:12617724[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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