Covalent Binding of Three Epoxyalkyl Xylosides to the Active Site of endo-1,4-Xylanase II from Trichoderma reesei,

Abstract
The three-dimensional structures of endo-1,4-xylanase II (XYNII) from Trichoderma reesei complexed with 4,5-epoxypentyl β-d-xyloside (X-O-C5), 3,4-epoxybutyl β-d-xyloside (X-O-C4), and 2,3-epoxypropyl β-d-xyloside (X-O-C3) were determined by X-ray crystallography. High-resolution measurement revealed clear electron densities for each ligand. Both X-O-C5 and X-O-C3 were found to form a covalent bond with the putative nucleophile Glu86. Unexpectedly, X-O-C4 was found to bind to the putative acid/base catalyst Glu177. In all three complexes, clear conformational changes were found in XYNII compared to the native structure. These changes were largest in the X-O-C3 complex structure.