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Bacterial stigmasterol degradation involving radical flavin delta-24 desaturase and molybdenum-dependent C26 hydroxylase.
- Source :
-
Journal of Biological Chemistry . May2024, Vol. 300 Issue 5, p1-13. 13p. - Publication Year :
- 2024
-
Abstract
- Sterols are ubiquitous membrane constituents that persist to a large extent in the environment due to their water insolubility and chemical inertness. Recently, an oxygenase-independent sterol degradation pathway was discovered in a cholesterolgrown denitrifying bacterium Sterolibacterium (S.) denitrificans. It achieves hydroxylation of the unactivated primary C26 of the isoprenoid side chain to an allylic alcohol via a phosphorylated intermediate in a four-step ATP-dependent enzyme cascade. However, this pathway is incompatible with the degradation of widely distributed steroids containing a double bond at C22 in the isoprenoid side chain such as the plant sterol stigmasterol. Here, we have enriched a prototypical delta-24 desaturase from S. denitrificans, which catalyzes the electron acceptor-dependent oxidation of the intermediate stigmast-1,4-diene-3-one to a conjugated (22,24)-diene. We suggest an α4β4 architecture of the 440 kDa enzyme, with each subunit covalently binding an flavin mononucleotide cofactor to a histidyl residue. As isolated, both flavins are present as red semiquinone radicals, which can be reduced by stigmast-1,4- diene-3-one but cannot be oxidized even with strong oxidizing agents. We propose a mechanism involving an allylic radical intermediate in which two flavin semiquinones each abstract one hydrogen atom from the substrate. The conjugated delta-22,24 moiety formed allows for the subsequent hydroxylation of the terminal C26 with water by a heterologously produced molybdenum-dependent steroid C26 dehydrogenase 2. In conclusion, the pathway elucidated for delta-22 steroids achieves oxygen-independent hydroxylation of the isoprenoid side chain by bypassing the ATP-dependent formation of a phosphorylated intermediate. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00219258
- Volume :
- 300
- Issue :
- 5
- Database :
- Academic Search Index
- Journal :
- Journal of Biological Chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 177637002
- Full Text :
- https://doi.org/10.1016/j.jbc.2024.107243