Abstract

Mitochondrial cytochromes P450 (P450s) are responsible for important metabolic reactions, including steps involved in steroid and vitamin D metabolism. The mitochondrial P450 24A1 (CYP24A1) is responsible for deactivation of the bioactive form of vitamin D, 1,25(OH)2D3. Its function relies on formation of a P450-redox partner complex with the ferredoxin and electron donor adrenodoxin (Adx). However, very little is known about how the Adx-CYP24A1 complex forms. In this study, we report the results of solution NMR in which we monitor isotopically labeled full-length Adx as it binds CYP24A1 in complex with the P450 inhibitor clotrimazole. The NMR titration data suggested a mode for P450-Adx interactions in which formation of the complex relies on contributions from multiple recognition sites on the Adx core domain, some of which have not previously been reported. To evaluate differences among CYP24A1-Adx complexes from different mammalian species and displaying distinct regioselectivity for 1,25(OH)2D3, all bound spectra were acquired in parallel for human (carbon-23 and -24 hydroxylase), rat (carbon-24 hydroxylase), and opossum (carbon-23 hydroxylase) CYP24A1 isoforms. Binding data from a series of single and double charge-neutralizing substitutions of Adx confirmed that species-specific CYP24A1 isoforms differ in binding to Adx, providing evidence that variations in redox partner interactions correlate with P450 regioselectivity. In summary, these findings reveal that CYP24A1-Adx interactions rely on several recognition sites and that variations in CYP24A1 isoforms modulate formation of the complex, thus providing insight into the variable and complex nature of mitochondrial P450-Adx interactions.

Highlights

  • Mitochondrial cytochromes P450 (P450s) are responsible for important metabolic reactions, including steps involved in steroid and vitamin D metabolism

  • Mitochondrial cytochromes P450 (P450s)2 are responsible for a host of biological reactions, including steps necessary in steroid and vitamin D metabolism

  • A similar approach was utilized here, in which incorporation of the P450 inhibitor clotrimazole resulted in enhanced bacterial expression of recombinant CYP24A1 isoforms when supplemented in growth media as well as conferring enhanced stability and solubility in NMR samples

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Summary

The abbreviations used are

P450; cytochrome P450; Adx, adrenodoxin; HSQC, heteronuclear single quantum coherence; BME, ␤-mercaptoethanol. More recent analysis of cross-linking data for CYP11B1 and the closely related CYP11B2 reinforces the role of electrostatic interactions with the acidic helix 3, in addition to a previously unreported contact with Adx Asp113 near the C terminus, modeled as an interaction with a second molecule of an Adx dimer [10] Taken together, these studies suggest a redox complex with Adx that may be variable between particular P450 systems. To evaluate differences between the Adx redox complex with CYP24A1 isoforms displaying distinct C23 or C24 regioselective preferences, we carried out NMR binding studies in parallel with human, rat, and opossum CYP24A1 isoforms These results provide evidence for a CYP24A1–Adx redox interaction that is complex and variable between species

Results
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