SEQUENCE-FUNCTION RELATIONSHIPS OF PROKARYOTIC AND EUKARYOTIC GALACTOSYLTRANSFERASES

Galactosyltransferases are enzymes which transfer galactose from UDP-G al to various accepters with either retention of the anomeric configur ation to form alpha 1,2-, alpha 1,3-, alpha 1,4-, and alpha 1,6-linkag es, or inversion of the anomeric configuration to form beta 1,3-, beta 1,4-, and beta 1-ceramide linkages. During the last few years, severa l (c)DNA sequences coding for galactosyltransferases became available. We have retrieved these sequences and conducted sequence similarity s tudies. On the basis of both the nature of the reaction catalyzed and the protein sequence identity, these enzymes can be classified into tw elve groups. Using a sensitive graphics method for protein comparison, conserved structural features were found in some of the galactosyltra nsferase groups, and other classes of glycosyltransferases, resulting in the definition of five families. The lengths and locations of the c onserved regions as well as the invariant residues are described for e ach family, In addition, the DxD motif that may be important for subst rate recognition and/or catalysis is demonstrated to occur in all fami lies but one.