Dissection of Catalytic Site in Crucial Gut Microbiome Enzyme: Bile Salt Hydrolase

Bile Salt Hydrolases (BSHs) are enzymes from enteric bacteria that catalyze the hydrolysis of Bile Acids and consequently promote the reduction of cholesterol level in the mammalian body. Out of several reported BSHs, the Enterococcus faecalis BSH ( Ef BSH) has been reported to have the highest enzymatic activity. Herein, we have investigated the mechanistic details of the Ef BSH activity. The study was carried out employing two mutants of Ef BSH: E269A and R207A, which shows differential catalytic activity. The mutant E269A exhibits significant loss in the BSH activity with an increased affinity towards the substrate as compared to R207A mutant. Further, R207A was found to be involved in allostery with an increased Ef BSH activity towards tauro-conjugated bile acids. The structural and electrostatic force analyses of the active sites of the E269A mutant and the wild type Ef BSH (wt Ef BSH) revealed that the interaction between Glu21 and Arg207 is the determining factor in maintaining the dynamic allostery and high activity of Ef BSH.