title: A new insight into the role of rat cytochrome P450 24A1 in metabolism of selective analogs of 1α,25-dihydroxyvitamin D₃.
abstract: We examined the metabolism of two synthetic analogs of 1α,25-dihydroxyvitamin D₃ (1), namely 1α,25-dihydroxy-16-ene-23-yne-vitamin D₃ (2) and 1α,25-dihydroxy-16-ene-23-yne-26,27-dimethyl-vitamin D₃ (4) using rat cytochrome P450 24A1 (CYP24A1) in a reconstituted system. We noted that 2 is metabolized into a single metabolite identified as C26-hydroxy-2 while 4 is metabolized into two metabolites, identified as C26-hydroxy-4 and C26a-hydroxy-4. The structural modification of adding methyl groups to the side chain of 1 as in 4 is also featured in another analog, 1α,25-dihydroxy-22,24-diene-24,26,27-trihomo-vitamin D₃ (6). In a previous study, 6 was shown to be metabolized exactly like 4, however, the enzyme responsible for its metabolism was found to be not CYP24A1. To gain a better insight into the structural determinants for substrate recognition of different analogs, we performed an in silico docking analysis using the crystal structure of rat CYP24A1 that had been solved for the substrate-free open form. Whereas analogs 2 and 4 docked similar to 1, 6 showed altered interactions for both the A-ring and side chain, despite prototypical recognition of the CD-ring. These findings hint that CYP24A1 metabolizes selectively different analogs of 1, based on their ability to generate discrete recognition cues required to close the enzyme and trigger the catalytic mechanism.
authors.affiliation: Epimer LLC, North Smithfield, RI 02896, USA.
authors.forename: Steve Y
authors.initials: SY
authors.lastname: Rhieu
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Annalora
authors.forename: Rose M
authors.initials: RM
authors.lastname: Gathungu
authors.forename: Paul
authors.initials: P
authors.lastname: Vouros
authors.forename: Milan R
authors.initials: MR
authors.lastname: Uskokovic
authors.forename: Inge
authors.initials: I
authors.lastname: Schuster
authors.forename: G Tayhas R
authors.initials: GT
authors.lastname: Palmore
authors.forename: G Satyanarayana
authors.initials: GS
authors.lastname: Reddy
mesh_terms: D000818:Animals; D008401:Gas Chromatography-Mass Spectrometry; D008958:Models, Molecular; D011485:Protein Binding; D051381:Rats; D013250:Steroid Hydroxylases / Q000737:chemistry / Q000378:metabolism*; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D065668:Vitamin D3 24-Hydroxylase
chemical_list: C118756:dihydroxy-vitamin D3; D014807:Vitamin D; D013250:Steroid Hydroxylases; C585551:Cyp24a1 protein, rat; D065668:Vitamin D3 24-Hydroxylase