SEQUENCE OF ARCHAEAL METHANOCOCCUS-JANNASCHII ALPHA-AMYLASE CONTAINS FEATURES OF FAMILY-13 AND FAMILY-57 OF GLYCOSYL HYDROLASES - A TRACE OF THEIR COMMON ANCESTOR

Two sequentially different, seemingly unrelated alpha-amylase families exist, known as family-13 and family-57 glycosyl hydrolases. Despite the common enzyme activity, it has as yet been impossible to detect an y sequence similarity between the two families. The detailed analysis of the recently determined sequence of the alpha-amylase from methanog enic archaeon Methanococcus jannaschii using the sensitive Hydrophobic Cluster Analysis method revealed that this alpha-amylase contains fea tures of both families of alpha-amylases. Thus the M. jannaschii alpha -amylase is similar to the Pyrococcus furiosus alpha-amylase from fami ly 57 while it obviously contains most of the sequence fingerprints ch aracteristic for alpha-amylase family 13. Importantly, a glutamic acid residue equivalent with the family-13 catalytic glutamate positioned in the beta 5-strand segment was identified in members of family 57. T he results presented in this report indicate that the two families, 13 and 57, are either the products of a very distant common ancestor or have evolved from each other, although at present they can represent t wo different alpha-amylase families with evolved different catalytic m echanisms, catalytic machinery and folds.