Sequence-structural features and evolution of the α-amylase family GH119 revealed by the in silico analysis of its relatedness to the family GH57

In the sequence-based classification of glycoside hydrolases (GHs) of the CAZy database, the family GH119 represents one of the four α-amylase GH families. The family GH119 was established based on a study describing the α-amylase from Bacillus circulans (currently re-classified as Niallia circulans), a product of the igtZ gene. This family with ~ 40 members belongs to the smallest GH families. In addition to a partial biochemical characterization of the α-amylase from N. circulans, nothing has been found in GH119 until now. There was only a single in silico study predicting the catalytic domain structure, catalytic machinery and conserved sequence regions (CSRs) as shared with those well-established in the second α-amylase family GH57. The present bioinformatics study was undertaken in an effort to deliver a detailed analysis of all family GH119 members with regard to their domain arrangement, exact location of all five CSRs and potentially unique sequence features. In order to perform a relevant comparison, the studied set of actual GH119 members was completed by all characterized family GH57 members, i.e. 80 sequences were compared in total. Taking into account the experimentally determined tertiary structure of the GH57 Thermococcus litoralis 4-α-glucanotransferase and the AlphaFold database model of the GH119 N. circulans α-amylase, the position of the CSR-5 in the family GH119 has been precisely re-defined. Phylogenetic trees constructed separately for the N-terminal and C-terminal parts of sequences demonstrated that taxonomy was most probably the main driving factor governing the evolution of the family GH119.