Metabolism of Oxo-Bile Acids and Characterization of Recombinant 12α-Hydroxysteroid Dehydrogenases from Bile Acid 7α-Dehydroxylating Human Gut Bacteria

• Published in: Applied and environmental microbiology Vol. 84; no. 10
• Main Authors: Doden, Heidi, Sallam, Lina A, Devendran, Saravanan, Ly, Lindsey, Doden, Greta, Daniel, Steven L, Alves, João M P, Ridlon, Jason M
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 15-05-2018
• Subjects: Enzymology and Protein Engineering; cholic acid; 12α-hydroxysteroid dehydrogenase; Clostridium hiranonis; deoxycholic acid; human gut bacteria; Clostridium hylemonae; bile acid 7α-dehydroxylation; oxo-bile acids; Clostridium scindens
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.00235-18

Bile acids are important cholesterol-derived nutrient signaling hormones, synthesized in the liver, that act as detergents to solubilize dietary lipids. Bile acid 7α-dehydroxylating gut bacteria generate the toxic bile acids deoxycholic acid and lithocholic acid from host bile acids. The ability of these bacteria to remove the 7-hydroxyl group is partially dependent on 7α-hydroxysteroid dehydrogenase (HSDH) activity, which reduces 7-oxo-bile acids generated by other gut bacteria. 3α-HSDH has an important enzymatic activity in the bile acid 7α-dehydroxylation pathway. 12α-HSDH activity has been reported for the low-activity bile acid 7α-dehydroxylating bacterium
; however, this activity has not been reported for high-activity bile acid 7α-dehydroxylating bacteria, such as
,
, and
Here, we demonstrate that these strains express bile acid 12α-HSDH. The recombinant enzymes were characterized from each species and shown to preferentially reduce 12-oxolithocholic acid to deoxycholic acid, with low activity against 12-oxochenodeoxycholic acid and reduced activity when bile acids were conjugated to taurine or glycine. Phylogenetic analysis suggests that 12α-HSDH is widespread among
,
in the
family, and human gut
12α-HSDH activity has been established in the medically important bile acid 7α-dehydroxylating bacteria
,
, and
Experiments with recombinant 12α-HSDHs from these strains are consistent with culture-based experiments that show a robust preference for 12-oxolithocholic acid over 12-oxochenodeoxycholic acid. Phylogenetic analysis identified novel members of the gut microbiome encoding 12α-HSDH. Future reengineering of 12α-HSDH enzymes to preferentially oxidize cholic acid may provide a means to industrially produce the therapeutic bile acid ursodeoxycholic acid. In addition, a cholic acid-specific 12α-HSDH expressed in the gut may be useful for the reduction in deoxycholic acid concentration, a bile acid implicated in cancers of the gastrointestinal (GI) tract.