Vitamin D Research Today is a free monthly online journal that collates and summarizes the latest research about Vitamin D, including details on sources, melanin, benefits, deficiency, supplements, calcium absorption.

Generation of a homology model for the human cytochrome P450, CYP24A1, and the testing of putative substrate binding residues by site-directed mutagenesis and enzyme activity studies.

Masuda S, Prosser DE, Guo YD, Kaufmann M, Jones G

Department of Biochemistry, Queen's University, Kingston, ON, Canada K7L 3N6.

A systematic analysis of conserved H-bonding patterns and tertiary structural motifs from 13 crystal structures was used to create a homology model for the human multicatalytic cytochrome P450, CYP24A1, involved in catabolism of 1alpha,25-dihydroxyvitamin D3. The substrate was docked in the active site and used to identify potential substrate contact residues in the B' helix, B'/C loop, F-helix and the beta-5 hairpin. Seven CYP24A1 mutants were created and studied by mammalian cell transfection and CYP24A1 activity assay. Mutants showed reduced metabolic rates and altered metabolite patterns compared to wild-type. We conclude that: Ile-131 positions substrate via A-ring and cis-triene contacts; Trp-134 and Gly-499 are determinants of substrate access; Leu-148 contacts the substrate side-chain; Met-246 is important in mediating regioselectivity. Our findings validate the new model of CYP24A1, which can now be used to predict structural modifications for rational vitamin D drug design.

Published 23 April 2007 in Arch Biochem Biophys, 460(2): 177-91.
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