IDENTIFICATION OF THE CATALYTIC NUCLEOPHILE IN THE CELLULASE FROM SCHIZOPHYLLUM-COMMUNE AND ASSIGNMENT OF THE ENZYME TO FAMILY-5, SUBTYPE-5OF THE GLYCOSIDASES

Differential chemical modification of the cellulase from Schizophyllum commune with -ethyl-3(4-azonia-4,4-dimethylpentyl)-carbodiimide in th e presence and absence of substrate identified an active site glutamat e residue within the peptide: Leu-Gln-Ala-Ala-Thr-Glu-Trp-Leu-(Lys). T his Glu residue is proposed to participate in binding of substrate as amino acid sequence homology studies combined with mechanism-based inh ibition of the cellulase with 4',5'-epoxypentyl-beta-D-cellobioside id entified a neighboring Glu residue, which conforms to the Glu-X-Gly mo tif of Family 5 glycosidases, as the catalytic nucleophile, These data allow the assignment of the S. commune cellulase to Family 5, subtype 5 of the glycosidases. (C) 1997 Federation of European Biochemical So cieties.