CLOSE EVOLUTIONARY RELATEDNESS AMONG FUNCTIONALLY DISTANTLY RELATED MEMBERS OF THE (ALPHA BETA)(8)-BARREL GLYCOSYL HYDROLASES SUGGESTED BY THE SIMILARITY OF THEIR 5TH CONSERVED SEQUENCE REGION/

A short conserved sequence equivalent to the fifth conserved sequence region of alpha-amylases (173_LPDLD, Aspergillus oryzae alpha-amylase) comprising the calcium-ligand aspartate, Asp-175, was identified in t he amino acid sequences of several members of the family of (alpha/bet a)(8)-barrel glycosyl hydrolases, Despite the fact that the aspartate is not invariantly conserved, the stretch can be easily recognised in all sequences to be positioned 26-28 amino acid residues in front of t he well-known catalytic aspartate (Asp-206, A, oryzae alpha-amylase) l ocated in the beta 4-strand of the barrel, The identification of this region revealed remarkable similarities between some alpha-amylases (t hose from Bacillus megaterium, Bacillus subtilis and Dictyoglomus ther mophilum) on the one hand and several different enzyme specificities ( such as oligo-1,6-glucosidase, amylomaltase and neopullulanase, respec tively) on the other hand, The most interesting example was offered by B, subtilis alpha-amylase and potato amylomaltase with the regions LY DWN and LYDWK, respectively, These observations support the idea that all members of the family of glycosyl hydrolases adopting the structur e of the alpha-amylase-type (alpha/beta)(8)-barrel are mutually closel y related and the strict evolutionary borders separating the individua l enzyme specificities can be hardly defined.