Degradation of the acyl side chain of the steroid compound cholate in Pseudomonas sp. strain Chol1 proceeds via an aldehyde intermediate

Bacterial degradation of steroids is widespread, but the metabolic pathways have rarely been explored. Previous studies with Pseudomonas sp. strain Chol1 and the C₂₄ steroid cholate have shown that cholate degradation proceeds via oxidation of the A ring, followed by cleavage of the C₅ acyl side chain attached to C-17, with 7α,12β-dihydroxy-androsta-1,4-diene-3,17-dione (12β-DHADD) as the product. In this study, the pathway for degradation of the acyl side chain of cholate was investigated in vitro with cell extracts of strain Chol1. For this, intermediates of cholate degradation were produced with mutants of strain Chol1 and submitted to enzymatic assays containing coenzyme A (CoA), ATP, and NAD⁺ as cosubstrates. When the C₂₄ steroid (22E)-7α,12α-dihydroxy-3-oxochola-1,4,22-triene-24-oate (DHOCTO) was used as the substrate, it was completely transformed to 12α-DHADD and 7α-hydroxy-androsta-1,4-diene-3,12,17-trione (HADT) as end products, indicating complete removal of the acyl side chain. The same products were formed with the C₂₂ steroid 7α,12α-dihydroxy-3-oxopregna-1,4-diene-20-carboxylate (DHOPDC) as the substrate. The 12-keto compound HADT was transformed into 12β-DHADD in an NADPH-dependent reaction. When NAD⁺ was omitted from assays with DHOCTO, a new product, identified as 7α,12α-dihydroxy-3-oxopregna-1,4-diene-20S-carbaldehyde (DHOPDCA), was formed. This aldehyde was transformed to DHOPDC and DHOPDC-CoA in the presence of NAD⁺, CoA, and ATP. These results revealed that degradation of the C₅ acyl side chain of cholate does not proceed via classical β-oxidation but via a free aldehyde that is oxidized to the corresponding acid. The reaction leading to the aldehyde is presumably catalyzed by an aldolase encoded by the gene skt, which was previously predicted to be a β-ketothiolase.

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HOLERT, Johannes, Zarko KULIC, Onur YÜCEL, Vemparthan SUVEKBALA, Marc J.-F. SUTER, Heiko M. MÖLLER, Bodo PHILIPP, 2013. Degradation of the acyl side chain of the steroid compound cholate in Pseudomonas sp. strain Chol1 proceeds via an aldehyde intermediate. In: Journal of Bacteriology. 2013, 195(3), pp. 585-595. ISSN 0021-9193. eISSN 1098-5530. Available under: doi: 10.1128/JB.01961-12

BibTex

@article{Holert2013-02Degra-28252,
  year={2013},
  doi={10.1128/JB.01961-12},
  title={Degradation of the acyl side chain of the steroid compound cholate in Pseudomonas sp. strain Chol1 proceeds via an aldehyde intermediate},
  number={3},
  volume={195},
  issn={0021-9193},
  journal={Journal of Bacteriology},
  pages={585--595},
  author={Holert, Johannes and Kulic, Zarko and Yücel, Onur and Suvekbala, Vemparthan and Suter, Marc J.-F. and Möller, Heiko M. and Philipp, Bodo}
}

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    <dcterms:abstract xml:lang="eng">Bacterial degradation of steroids is widespread, but the metabolic pathways have rarely been explored. Previous studies with Pseudomonas sp. strain Chol1 and the C&lt;sub&gt;24&lt;/sub&gt; steroid cholate have shown that cholate degradation proceeds via oxidation of the A ring, followed by cleavage of the C&lt;sub&gt;5&lt;/sub&gt; acyl side chain attached to C-17, with 7α,12β-dihydroxy-androsta-1,4-diene-3,17-dione (12β-DHADD) as the product. In this study, the pathway for degradation of the acyl side chain of cholate was investigated in vitro with cell extracts of strain Chol1. For this, intermediates of cholate degradation were produced with mutants of strain Chol1 and submitted to enzymatic assays containing coenzyme A (CoA), ATP, and NAD&lt;sup&gt;+&lt;/sup&gt; as cosubstrates. When the C&lt;sub&gt;24&lt;/sub&gt; steroid (22E)-7α,12α-dihydroxy-3-oxochola-1,4,22-triene-24-oate (DHOCTO) was used as the substrate, it was completely transformed to 12α-DHADD and 7α-hydroxy-androsta-1,4-diene-3,12,17-trione (HADT) as end products, indicating complete removal of the acyl side chain. The same products were formed with the C&lt;sub&gt;22&lt;/sub&gt; steroid 7α,12α-dihydroxy-3-oxopregna-1,4-diene-20-carboxylate (DHOPDC) as the substrate. The 12-keto compound HADT was transformed into 12β-DHADD in an NADPH-dependent reaction. When NAD&lt;sup&gt;+&lt;/sup&gt; was omitted from assays with DHOCTO, a new product, identified as 7α,12α-dihydroxy-3-oxopregna-1,4-diene-20S-carbaldehyde (DHOPDCA), was formed. This aldehyde was transformed to DHOPDC and DHOPDC-CoA in the presence of NAD&lt;sup&gt;+&lt;/sup&gt;, CoA, and ATP. These results revealed that degradation of the C&lt;sub&gt;5&lt;/sub&gt; acyl side chain of cholate does not proceed via classical β-oxidation but via a free aldehyde that is oxidized to the corresponding acid. The reaction leading to the aldehyde is presumably catalyzed by an aldolase encoded by the gene skt, which was previously predicted to be a β-ketothiolase.</dcterms:abstract>
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