Chemical proteomic analysis of bile acid-protein targets in Enterococcus faecium .

Bile acids are important gut microbiota metabolites that regulate both host and microbial functions. To identify the direct protein targets of bile acids in Enterococcus , we synthesized and validated the activity of a lithocholic acid (LCA) photoaffinity reporter, x-alk-LCA-3. Chemical proteomics of x-alk-LCA-3 in E. faecium Com15 reveals many candidate LCA-interacting proteins, which are involved in cell well synthesis, transcriptional regulation and metabolism. To validate the utility of bile acid photoaffinity labeling, we characterized a putative bile salt hydrolase (BSH) crosslinked by x-alk-LCA-3, and demonstrated that this BSH was effective in converting taurolithocholic acid (TLCA) to LCA in E. faecium and in vitro . Chemical proteomics should afford new opportunities to characterize bile acid-protein targets and mechanisms of action in the future.