CONSERVED CATALYTIC MACHINERY AND THE PREDICTION OF A COMMON FOLD FORSEVERAL FAMILIES OF GLYCOSYL HYDROLASES

The regions surrounding the catalytic amino acids previously identifie d in a few ''retaining'' O-glycosyl hydrolases (EC 3.2.1) have been an alyzed by hydrophobic cluster analysis and have been used to define se quence motifs. These motifs have been found in more than 150 glycosyl hydrolase sequences representing at least eight established protein fa milies that act on a large variety of substrates. This allows the loca lization and the precise role of the catalytic residues (nucleophile a nd acid catalyst) to be predicted for each of these enzymes, including several lysosomal glycosidases. An identical arrangement of the catal ytic nucleophile was also found for S-glycosyl hydrolases (myrosinases ; EC 3.2.3.1) for which the acid catalyst is lacking. A (beta/alpha)(8 ) barrel structure has been reported for two of the eight families of proteins that have been grouped. It is suggested that the six other fa milies also share this fold at their catalytic domain. These enzymes i llustrate how evolutionary events led to a wide diversification of sub strate specificity with a similar disposition of identical catalytic r esidues onto the same ancestral (beta/alpha)(8) barrel structure.