[8] While the majority of primary bile acids are recirculated back to the liver via enterohepatic circulation, a small portion remain in the gastrointestinal tract, where they are modified by bacteria carrying BSH enzymes.
[7] BSH specificity is thought to be determined by enzymatic structural differences and slight variations in amino acid composition.
[9] Deconjugation begins with the recognition of the substrate, which consists of a steroid core and a glyco- or tauro- amino acid.
[2] Upon recognition by the BSH, deconjugation begins with a nucleophilic attack by Cys2 on the amide bond of the target bile acid.
[2] The negative charge on Cys2 is resolved by deacylation with water to finally produce a deconjugated primary bile acid.
[18] BSHs shape the microbiota by altering the bile acid pool and creating substrates for further modification by other gut bacteria.
Due to this imbalance, a diseased state of the gut is associated with changes to the bile acid pool and different BSH phylotypes.
[17] BSHs are critical for secondary bile acid transformations, which are performed by different members of the gut microbiota.
The composition of the gut microbiome is shaped in part by the deconjugated primary bile acids made available by BSHs.
BSHs are often found in candidate probiotic organisms due to their myriad effects on both human health and the gut microbiota.
[17] BSHs play roles in reducing cholesterol levels and detoxifying bile acids that may damage the gut in high concentrations.