Sequences and homology analysis of two genes encoding beta-glucosidases from Bacillus polymyxa

The nucleotide sequences of the bglA and bglB genes encoding beta-glucosidases from Bacillus polymyxa have been determined. Both genes contain coding regions of 1344 bp, corresponding to polypeptides with Mrs of 51,643 and 51,547, respectively. Patterns of codon usage indicate that both genes are expressed at a low frequency. Previous data suggested that the proteins encoded by bglA and bglB were intra- and extracellular enzymes, respectively; however, neither of the two deduced amino acid sequences has N termini with the typical features of a leader peptide. The proteins encoded by bglA and bglB show remarkable homology to each other and to other beta-glucosidases (Bgl) and beta-galactosidases (beta Gal). On the basis of the observed homologies, we can define two groups of microbial Bgl: one of them, type I, including most bacterial Bgl, and type II, including enzymes from different yeast species and one from Clostridium thermocellum. Likewise, at least two groups of beta Gal can be distinguished: type I, including enzymes homologous to type-I Bgl, and type II, showing no homology to any of the previous groups.