title: Biosynthesis of a cholesterol-derived brassinosteroid, 28-norcastasterone, in Arabidopsis thaliana.
abstract: A metabolic study revealed that 28-norcastasterone in Arabidopsis is synthesized from cholesterol via the late C-6 oxidation pathway. On the other hand, the early C-6 oxidation pathway was found to be interrupted because cholestanol is converted to 6-oxocholestanol, but further metabolism to 28-norcathasterone was not observed. The 6-oxoBRs were found to have been produced from the respective 6-deoxoBRs administered to the enzyme solution, thus indicating that these 6-oxoBRs are supplied from the late C-6 oxidation pathway. Heterologously expressed CYP85A1 and CYP85A2 in yeast catalysed this C-6 oxidation, with CYP85A2 being much more efficient than CYP85A1. Abnormal growth of det2 and dwf4 was restored via the application of 28-norcastasterone and closer precursors. Furthermore, det2 and dwf4 could not convert cholesterol to cholestanol and cholestanol to 6-deoxo-28-norcathasterone, respectively. It is, therefore, most likely that the same enzyme system is operant in the synthesis of both 28-norcastasterone and castasterone. In the presence of S-adenosyl-L-methionine, the cell-free enzyme extract catalysed the C-24 methylation of 28-norcastasterone to castasterone, although the conversion rates of 28-norteasterone to teasterone and 28-nortyphasterol to typhasterol were much lower; this suggests that 28-norcastasterone is the primary precursor for the generation of C(28)-BRs from C(27)-BRs.
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul, Korea.
authors.forename: Se-Hwan
authors.initials: SH
authors.lastname: Joo
authors.forename: Tae-Wuk
authors.initials: TW
authors.lastname: Kim
authors.forename: Seung-Hyun
authors.initials: SH
authors.lastname: Son
authors.forename: Woo Sung
authors.initials: WS
authors.lastname: Lee
authors.forename: Takao
authors.initials: T
authors.lastname: Yokota
authors.forename: Seong-Ki
authors.initials: SK
authors.lastname: Kim
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D060406:Brassinosteroids / Q000378:metabolism*; D002777:Cholestanols / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D009154:Mutation; D010084:Oxidation-Reduction; D010937:Plant Growth Regulators / Q000378:metabolism*; D012440:Saccharomyces / Q000235:genetics / Q000378:metabolism; D019076:Transgenes
chemical_list: C419985:28-norcastasterone; D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D002777:Cholestanols; D010937:Plant Growth Regulators; C083545:castasterone; D003577:Cytochrome P-450 Enzyme System; D002784:Cholesterol; C474078:brassinosteroid-6 oxidase 1, Arabidopsis; C474079:brassinosteroid-6 oxidase 2, Arabidopsis