A new group of glycoside hydrolase family 13 α-amylases with an aberrant catalytic triad

alpha-Amylases are glycoside hydrolase enzymes that act on the alpha(1 -> 4) glycosidic linkages in glycogen, starch, and related a-glucans, and are ubiquitously present in Nature. Most a-amylases have been classified in glycoside hydrolase family 13 with a typical (beta/alpha)(8)-barrel containing two aspartic acid and one glutamic acid residue that play an essential role in catalysis. An atypical a-amylase (BmaN1) with only two of the three invariant catalytic residues present was isolated from Bacillus megaterium strain NL3, a bacterial isolate from a sea anemone of Kakaban landlocked marine lake, Derawan Island, Indonesia. In BmaN1 the third residue, the aspartic acid that acts as the transition state stabilizer, was replaced by a histidine. Three-dimensional structure modeling of the BmaN1 amino acid sequence confirmed the aberrant catalytic triad. Glucose and maltose were found as products of the action of the novel alpha-amylase on soluble starch, demonstrating that it is active in spite of the peculiar catalytic triad. This novel BmaN1 alpha-amylase is part of a group of alpha-amylases that all have this atypical catalytic triad, consisting of aspartic acid, glutamic acid and histidine. Phylogenetic analysis showed that this group of a-amylases comprises a new subfamily of the glycoside hydrolase family 13.