TOWARDS A CLASSIFICATION OF GLYCOSYLTRANSFERASES BASED ON AMINO-ACID-SEQUENCE SIMILARITIES - PROKARYOTIC ALPHA-MANNOSYLTRANSFERASES

A number of genes encoding bacterial glycosyltransferases have been se quenced during the last few years, but their low sequence similarity h as prevented a straightforward grouping of these enzymes into families . The sequences of several bacterial alpha-mannosyltransferases have b een compared using current alignment algorithms as well as hydrophobic cluster analysis (HCA). These sequences show a similarity which is si gnificant but too low to be reliably aligned using automatic alignment methods. However, a region spanning approx. 270 residues in these pro teins could be aligned by HCA, and several invariant amino acid residu es were identified. These features were also found in several other gl ycosyltransferases, as well as in proteins of unknown function present in sequence databases. This similarity most probably reflects the exi stence of a family of proteins with conserved structural and mechanist ic features, It is argued that the present IUBMB classification of gly cosyltransferases could be complemented by a classification of these e nzymes based on sequence similarities analogous to that which we propo sed for glycosyl hydrolases [Henrissat, B. (1991) Biochem. J. 280, 309 -316].