Structural and biochemical characterization of 20?-hydroxysteroid dehydrogenase from Bifidobacterium adolescentis strain L2-32.

ABSTRACT: Anaerobic bacteria inhabiting the human gastrointestinal tract have evolved various enzymes that modify host-derived steroids. The bacterial steroid-17,20-desmolase pathway cleaves the cortisol side chain, forming pro-androgens predicted to impact host physiology. Bacterial 20?-hydroxysteroid dehydrogenase (20?-HSDH) regulates cortisol side-chain cleavage by reducing the C-20 carboxyl group on cortisol, yielding 20?-dihydrocortisol. Recently, the gene encoding 20?-HSDH in Butyricicoccus desmolans ATCC 43058 was reported, and a nonredundant protein search yielded a candidate 20?-HSDH gene in Bifidobacterium adolescentis strain L2-32. B. adolescentis 20?-HSDH could regulate cortisol side-chain cleavage by limiting pro-androgen formation in bacteria such as Clostridium scindens and 21-dehydroxylation by Eggerthella lenta Here, the putative B. adolescentis 20?-HSDH was cloned, overexpressed, and purified. 20?-HSDH activity was confirmed through whole-cell and pure enzymatic assays, and it is specific for cortisol. Next, we solved the structures of recombinant 20?-HSDH in both the apo- and holo-forms at 2.0-2.2 Å resolutions, revealing close overlap except for rearrangements near the active site. Interestingly, the structures contain a large, flexible N-terminal region that was investigated by gel-filtration chromatography and CD spectroscopy. This extended N terminus is important for protein stability because deletions of varying lengths caused structural changes and reduced enzymatic activity. A nonconserved extended N terminus was also observed in several short-chain dehydrogenase/reductase family members. B. adolescentis strains capable of 20?-HSDH activity could alter glucocorticoid metabolism in the gut and thereby serve as potential probiotics for the management of androgen-dependent diseases.

SUBMITTER: Doden HL 

PROVIDER: S-EPMC6690682 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature