Sequence-Structural Features and Evolutionary Relationships of Family GH57 α-Amylases and Their Putative α-Amylase-Like Homologues

The glycoside hydrolase family 57 (GH57) contains alpha-amylase and a few other amylolytic specificities. It counts similar to 400 members from Archaea (1/4) and Bacteria (3/4), mostly of extremophilic prokaryotes. Only 17 GH57 enzymes have been biochemically characterized. The main goal of the present bioinformatics study was to analyze sequences having the clear GH57 alpha-amylase features. Of the 107 GH57 sequences, 59 were evaluated as alpha-amylases (containing both GH57 catalytic residues), whereas 48 were assigned as GH57 alpha-amylase-like proteins (having a substitution in one or both catalytic residues). Forty-eight of 59 alpha-amylases were from Archaea, but 42 of 48 alpha-amylase-like proteins were of bacterial origin. The catalytic residues were substituted in most cases in Bacteroides and Prevotella by serine (instead of catalytic nucleophile glutamate) and glutamate (instead of proton donor aspartate). The GH57 alpha-amylase specificity has thus been evolved and kept enzymatically active mainly in Archaea.