Publications

• Single A326G mutation converts human CYP24A1 from 25-OH-D3-24-hydroxylase into -23-hydroxylase, generating 1alpha,25-(OH)2D3-26,23-lactone.

  Prosser D.E., Kaufmann M., O'Leary B., Byford V., Jones G.

  Studies of 25-hydroxyvitamin D(3)-24-hydroxylase (CYP24A1) have demonstrated that it is a bifunctional enzyme capable of the 24-hydroxylation of 1alpha,25-(OH)(2)D(3), leading to the excretory form, calcitroic acid, and 23-hydroxylation, culminating in 1alpha,25-(OH)(2)D(3)-26,23-lactone. The degr ... >> More

  Studies of 25-hydroxyvitamin D(3)-24-hydroxylase (CYP24A1) have demonstrated that it is a bifunctional enzyme capable of the 24-hydroxylation of 1alpha,25-(OH)(2)D(3), leading to the excretory form, calcitroic acid, and 23-hydroxylation, culminating in 1alpha,25-(OH)(2)D(3)-26,23-lactone. The degree to which CYP24A1 performs either 23- or 24-hydroxylation is species-dependent. In this paper, we show that the human enzyme that predominantly 24-hydroxylates its substrate differs from the opossum enzyme that 23-hydroxylates it at only a limited number of amino acid residues. Mutagenesis of the human form at a single substrate-binding residue (A326G) dramatically changes the regioselectivity of the enzyme from a 24-hydroxylase to a 23-hydroxylase, whereas other modifications have no effect. Ala-326 is located in the I-helix, close to the terminus of the docked 25-hydroxylated side chain in a CYP24A1 homology model, a result that we interpret indicates that substitution of a glycine at 326 provides extra space for the side chain of the substrate to move deeper into the pocket and place it in a optimal stereochemical position for 23-hydroxylation. We discuss the physiological ramifications of these results for species possessing the A326G substitution, as well as implications for optimal vitamin D analog design. << Less

  Proc Natl Acad Sci U S A 104:12673-12678(2007) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Structure-function analysis of vitamin D 24-hydroxylase (CYP24A1) by site-directed mutagenesis: amino acid residues responsible for species-based difference of CYP24A1 between humans and rats.

  Hamamoto H., Kusudo T., Urushino N., Masuno H., Yamamoto K., Yamada S., Kamakura M., Ohta M., Inouye K., Sakaki T.

  Our previous studies revealed the species-based difference of CYP24A1-dependent vitamin D metabolism. Although human CYP24A1 catalyzes both C-23 and C-24 oxidation pathways, rat CYP24A1 shows almost no C-23 oxidation pathway. We tried to identify amino acid residues that cause the species-based di ... >> More

  Our previous studies revealed the species-based difference of CYP24A1-dependent vitamin D metabolism. Although human CYP24A1 catalyzes both C-23 and C-24 oxidation pathways, rat CYP24A1 shows almost no C-23 oxidation pathway. We tried to identify amino acid residues that cause the species-based difference by site-directed mutagenesis. In the putative substrate-binding regions, amino acid residue of rat CYP24A1 was converted to the corresponding residue of human CYP24A1. Among eight mutants examined, T416M and I500T showed C-23 oxidation pathway. In addition, the mutant I500F showed quite a different metabolism of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] from both human and rat CYP24A1. These results strongly suggest that the amino acid residues at positions 416 and 500 play a crucial role in substrate binding and greatly affect substrate orientation. A three-dimensional model of CYP24A1 indicated that the A-ring and triene part of 1alpha,25(OH)2D3 could be located close to amino acid residues at positions 416 and 500, respectively. Our findings provide useful information for the development of new vitamin D analogs for clinical use. << Less

  Mol. Pharmacol. 70:120-128(2006) [PubMed] [EuropePMC]

  This publication is cited by 5 other entries.

• Kinetic analysis of human CYP24A1 metabolism of vitamin D via the C24-oxidation pathway.

  Tieu E.W., Tang E.K., Tuckey R.C.

  CYP24A1 is the multicatalytic cytochrome P450 responsible for the catabolism of vitamin D via the C23- and C24-oxidation pathways. We successfully expressed the labile human enzyme in Escherichia coli and partially purified it in an active state that permitted detailed characterization of its meta ... >> More

  CYP24A1 is the multicatalytic cytochrome P450 responsible for the catabolism of vitamin D via the C23- and C24-oxidation pathways. We successfully expressed the labile human enzyme in Escherichia coli and partially purified it in an active state that permitted detailed characterization of its metabolism of 1,25-dihydroxyvitamin D3 [1,25(OH)2 D3] and the intermediates of the C24-oxidation pathway in a phospholipid-vesicle reconstituted system. The C24-oxidation pathway intermediates, 1,24,25-trihydroxyvitamin D3, 24-oxo-1,25-dihydroxyvitamin D3, 24-oxo-1,23,25-trihydroxyvitamin D3 and tetranor-1,23-dihydroxyvitamin D3, were enzymatically produced from 1,25(OH)2 D3 using rat CYP24A1. Both 1,25(OH)2 D3 and 1,23-dihydroxy-24,25,26,27-tetranorvitamin D3 were found to partition strongly into the phospholipid bilayer when in aqueous medium. Changes to the phospholipid concentration did not affect the kinetic parameters for the metabolism of 1,25(OH)2 D3 by CYP24A1, indicating that it is the concentration of substrates in the membrane phase (mol substrate·mol phospholipid(-1) ) that determines their rate of metabolism. CYP24A1 exhibited Km values for the different C24-intermediates ranging from 0.34 to 15 mmol·mol phospholipid(-1) , with 24-oxo-1,23,25-trihydroxyvitamin D3 [24-oxo-1,23,25(OH)3 D3] displaying the lowest and 1,24,25-trihydroxyvitamin D3 [1,24,25(OH)3 D3] displaying the highest. The kcat values varied by up to 3.8-fold, with 1,24,25(OH)3 D3 displaying the highest kcat (34 min(-1) ) and 24-oxo-1,23,25(OH)3 D3 the lowest. The data show that the cleavage of the side chain of 24-oxo-1,23,25(OH)3 D3 occurs with the highest catalytic efficiency (kcat /Km ) and produces 1-hydroxy-23-oxo-24,25,26,27-tetranorvitamin D3 and not 1,23-dihydroxy-24,25,26,27-tetranorvitamin D3, as the primary product. These kinetic analyses also show that intermediates of the C24-oxidation pathway effectively compete with precursor substrates for binding to the active site of the enzyme, which manifests as an accumulation of intermediates, indicating that they dissociate after each catalytic step. << Less

  FEBS J. 281:3280-3296(2014) [PubMed] [EuropePMC]

  This publication is cited by 9 other entries.