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Proteins. 2016 Mar;84(3):316-31. doi: 10.1002/prot.24971. Epub 2016 Jan 18.

Structure and functional characterization of a bile acid 7α dehydratase BaiE in secondary bile acid synthesis.

Author information

1
Joint Center for Structural Genomics, (http://www.jcsg.org).
2
Department of Integrative Structural and Computational Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California, 92037.
3
Genomics Institute of Novartis Research Foundation, 10675 John Jay Hopkins Drive, San Diego, California, 92121.
4
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, MS 9, Menlo Park, California, 94025.
5
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond, Virginia, 23298.
6
McGuire VA Medical Center, Richmond, Virginia, 23298.
7
USDA ARS, US Meat Animal Research Center, Clay Center, Nebraska, 68933.

Abstract

Conversion of the primary bile acids cholic acid (CA) and chenodeoxycholic acid (CDCA) to the secondary bile acids deoxycholic acid (DCA) and lithocholic acid (LCA) is performed by a few species of intestinal bacteria in the genus Clostridium through a multistep biochemical pathway that removes a 7α-hydroxyl group. The rate-determining enzyme in this pathway is bile acid 7α-dehydratase (baiE). In this study, crystal structures of apo-BaiE and its putative product-bound [3-oxo-Δ(4,6) -lithocholyl-Coenzyme A (CoA)] complex are reported. BaiE is a trimer with a twisted α + β barrel fold with similarity to the Nuclear Transport Factor 2 (NTF2) superfamily. Tyr30, Asp35, and His83 form a catalytic triad that is conserved across this family. Site-directed mutagenesis of BaiE from Clostridium scindens VPI 12708 confirm that these residues are essential for catalysis and also the importance of other conserved residues, Tyr54 and Arg146, which are involved in substrate binding and affect catalytic turnover. Steady-state kinetic studies reveal that the BaiE homologs are able to turn over 3-oxo-Δ(4) -bile acid and CoA-conjugated 3-oxo-Δ(4) -bile acid substrates with comparable efficiency questioning the role of CoA-conjugation in the bile acid metabolism pathway.

KEYWORDS:

7α-dehyroxylation; bile acid 7α-dehydratase; gut microbe mediated human metabolite; gut microbes; nuclear transport factor-2 superfamily; primary bile acid; secondary bile acid; secondary bile acid synthesis; structural genomics

PMID:
26650892
PMCID:
PMC4755848
[Available on 2017-03-01]
DOI:
10.1002/prot.24971
[Indexed for MEDLINE]
Free PMC Article

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