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Substrate Inhibition of 5β-Δ(4)-3-Ketosteroid Dehydrogenase in Sphingobium sp. Strain Chol11 Acts as Circuit Breaker During Growth With Toxic Bile Salts
In contrast to many steroid hormones and cholesterol, mammalian bile salts are 5β-steroids, which leads to a bent structure of the steroid core. Bile salts are surface-active steroids excreted into the environment in large amounts, where they are subject to bacterial degradation. Bacterial steroid d...
Autores principales: | , , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
Frontiers Media S.A.
2021
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8044976/ https://www.ncbi.nlm.nih.gov/pubmed/33868213 http://dx.doi.org/10.3389/fmicb.2021.655312 |
Sumario: | In contrast to many steroid hormones and cholesterol, mammalian bile salts are 5β-steroids, which leads to a bent structure of the steroid core. Bile salts are surface-active steroids excreted into the environment in large amounts, where they are subject to bacterial degradation. Bacterial steroid degradation is initiated by the oxidation of the A-ring leading to canonical Δ(4)-3-keto steroids with a double bond in the A-ring. For 5β-bile salts, this Δ(4)-double bond is introduced into 3-keto-bile salts by a 5β-Δ(4)-ketosteroid dehydrogenase (5β-Δ(4)-KSTD). With the Nov2c019 protein from bile-salt degrading Sphingobium sp. strain Chol11, a novel 5β-Δ(4)-KSTD for bile-salt degradation belonging to the Old Yellow Enzyme family was identified and named 5β-Δ(4)-KSTD1. By heterologous production in Escherichia coli, 5β-Δ(4)-KSTD function could be shown for 5β-Δ(4)-KSTD1 as well as the homolog CasH from bile-salt degrading Rhodococcus jostii RHA1. The deletion mutant of 5β-Δ(4)-kstd1 had a prolonged lag-phase with cholate as sole carbon source and, in accordance with the function of 5β-Δ(4)-KSTD1, showed delayed 3-ketocholate transformation. Purified 5β-Δ(4)-KSTD1 was specific for 5β-steroids in contrast to 5α-steroids and converted steroids with a variety of hydroxy groups regardless of the presence of a side chain. 5β-Δ(4)-KSTD1 showed a relatively low K(m) for 3-ketocholate, a very high specific activity and pronounced substrate inhibition. With respect to the toxicity of bile salts, these kinetic properties indicate that 5β-Δ(4)-KSTD1 can achieve fast detoxification of the detergent character as well as prevention of an overflow of the catabolic pathway in presence of increased bile-salt concentrations. |
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