COMPARATIVE AMINO-ACID-SEQUENCE ANALYSIS OF THERMOTOGA-MARITIMA BETA-GLUCOSIDASE (BGLA) DEDUCED FROM THE NUCLEOTIDE-SEQUENCE OF THE GENE INDICATES DISTANT RELATIONSHIP BETWEEN BETA-GLUCOSIDASES OF THE BGA FAMILY AND OTHER FAMILIES OF BETA-1,4-GLYCOSYL HYDROLASES

The primary structure of the bglA gene region encoding a beta-glucosid ase of Thermotoga maritima strain MSB8 was determined. The bglA gene h as the potential to code for a polypeptide of 446 amino acids with a p redicted molecular mass of 51545 Da. The T. maritima beta-glucosidase (BglA) was overexpressed in E. coli at a level comprising approximatel y 15-20% of soluble cellular protein. Based on its amino acid sequence , as deduced from the nucleotide sequence of the gene, BglA can be cla ssified as a broad-specificity beta-glucosidase and as a member of the beta-glucosidase family BGA, in agreement with the results of enzymat ic characterization of the recombinant protein. Comparative sequence a nalysis revealed distant amino acid sequence similarities between BGA family beta-glucosidases, a beta-xylosidase, beta-1,4-glycanases of th e enzyme family F (mostly xylanases), and other families of beta-1,4-g lycosyl hydrolases. This result indicates that BGA beta-glucosidases m ay comprise one enzyme family within a large 'enzyme order' of retaini ng beta-glycosyl hydrolases, and that the members of these enzyme grou ps may be inter-related at the level of active site architecture and p erhaps even on the level of overall three-dimensional fold.