BETA-GLUCOSIDASE, BETA-GALACTOSIDASE, FAMILY-A CELLULASES, FAMILY-F XYLANASES AND 2 BARLEY GLYCANASES FORM A SUPERFAMILY OF ENZYMES WITH 8-FOLD BETA ALPHA-ARCHITECTURE AND WITH 2 CONSERVED GLUTAMATES NEAR THE CARBOXY-TERMINAL ENDS OF BETA-STRAND-4 AND BETA-STRAND-7/
J. Jenkins et al., BETA-GLUCOSIDASE, BETA-GALACTOSIDASE, FAMILY-A CELLULASES, FAMILY-F XYLANASES AND 2 BARLEY GLYCANASES FORM A SUPERFAMILY OF ENZYMES WITH 8-FOLD BETA ALPHA-ARCHITECTURE AND WITH 2 CONSERVED GLUTAMATES NEAR THE CARBOXY-TERMINAL ENDS OF BETA-STRAND-4 AND BETA-STRAND-7/, FEBS letters, 362(3), 1995, pp. 281-285
Comparison of the recently determined crystal structures Pseudomonas f
luorescens subsp. cellulosa family F xylanase, (1-3)-beta-glucanase an
d (1-3,1-4)-beta-glucanase and the catalytic domain of E. coli beta-ga
lactosidase reveals that they belong to a superfamily of 8-fold beta/a
lpha-barrels with similar amino acid residues at their active sites, I
n the three families that these enzymes represent, the nucleophile is
a glutamate, which is located close to the carboxy-terminus of beta-st
rand seven, In addition all three enzymes have the sequence asparagine
-glutamate close to the carboxy-terminus of beta-strand four. This glu
tamate has been identified as the acid/base in the family F xylanases
and is essential for catalysis in beta-galactosidase. We suggest that
the equivalent residue in the barley glucanases is the acid/base. Anal
ysis of the sequences of family 1 beta-glucosidases and family 5 cellu
lases shows that these enzymes also belong to this superfamily which w
e call the 4/7 superfamily.