New insight into the catalytic properties of bile salt hydrolase

Bile salt hydrolase (BSH), the enzyme deconjugating bile potentially plays an important role in reduction of blood cholesterol level. BSH enzymes from various sources differ in characteristics, substrates preference and specific catalytic activity. In this study, two BSH enzymes (BSH1 and BSH2) from Lactobacillus salivarius were heterologously expressed and purified. Both of them were characterized as homotetramer according to their molecular weight from size exclusion chromatograph. BSH1 showed a broad pH optimum over the range from 5.5 to 7.0, while a narrower range of pH optimum from 5.5 to 6.0 for BSH2 was detected. The enzymatic kinetics of the purified BSH1 and BSH2 have demonstrated BSH enzymes from bacteria were allosteric enzymes, and have also revealed their striking differences in positive cooperativity, catalytic efficiency and substrate preference for the first time. In contrast to the enzymatic reactions of BSH in the absence of dithiothreitol, the kinetics curves of BSH1 and BSH2 were similar to hyperbolic forms of Michaelis–Menten kinetics in the presence of dithiothreitol.