Biochemical exploration of family GH119 reveals a single α-amylase specificity and confirms shared catalytic machinery with GH57 enzymes

While hundreds of starch- and glycogen-degrading enzymes have been characterized experimentally in historical families such as GH13, GH14, GH15, GH57 and GH126 of the CAZy database (www.cazy.org), the alpha-amylase from Bacillus circulans is the only enzyme that has been characterized in family GH119. Since glycosidase families have been shown to often group enzymes with different substrates or products, a single characterized enzyme in a family is insufficient to extrapolate enzyme function based solely on sequence similarity. Here we report the rational exploration of family GH119 through the biochemical characterization of five GH119 members. All enzymes shared single alpha-amylase specificity but display distinct product profile. We also report the first kinetic constants in family GH119 and the first experimental validation of previously predicted catalytic residues in family GH119, confirming that families GH119 and GH57 can be grouped in the novel clan GH-T of the CAZy database.