Functional insight for beta-glucuronidase in Escherichia coli and Staphylococcus sp. RLH1.

Glycosyl hydrolases hydrolyze the glycosidic bond either in carbohydrates or between carbohydrate and non-carbohydrate moiety. The beta-glucuronidase (beta D-glucuronoside glucuronosohydrolase; EC 3.2.1.31) enzyme belongs to the family-2 glycosyl hydrolase. The E. coli borne beta-glucuronidase gene (uidA) was devised as a gene fusion marker in plant genetic transformation experiments. Recent plant transformation vectors contain a novel beta-glucuronidase (gusA) derived from Staphylococcus sp. RLH1 for E. coli uidA. It is known to have a ten fold higher sensitivity compared to E. coli beta-glucuronidase. The functional superiority of Staphylococcus (gusA) over E. coli (uidA) activity is not fully known. The comparison of secondary structural elements among them revealed an increased percentage of random coils in Staphylococcus beta-glucuronidase. The 3D model of gusA shows catalytic site residues 396Glu, 508Glu and 471Tyr of gusA in loop regions. Accessible surface area (ASA) calculations on the 3D model showed increased ASA for active site residues in Staphylococcus beta-glucuronidase. Increased random coil, the presence of catalytic residues in loops, greater solvent accessibility of active residues and increased charged residues in gusA of Staphylococcus might facilitate interaction with the solvent. This hypothesizes the enhanced catalytic activity of beta-glucuronidase in Staphylococcus sp. RLH1 compared to that in E. coli.