COVALENT BINDING OF 3 EPOXYALKYL XYLOSIDES TO THE ACTIVE-SITE OF ENDO-1,4-XYLANASE-II FROM TRICHODERMA-REESEI

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