Evidence of Allosteric Coupling between Substrate Binding and Adx Recognition in the Vitamin D Carbon-24 Hydroxylase CYP24A1.

Metabolic inactivation of 1,25(OH)2D3 requires molecular recognition between the mitochondrial enzyme cytochrome P450 24A1 (CYP24A1) and its cognate redox partner adrenodoxin (Adx). Recent evidence supports a model of CYP24A1 function in which substrate binding and Adx recognition are structurally linked. However, the details of this allosteric connection are not clear. In this study, we utilize chemical cross-linking coupled to mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy, and CYP24A1 functional assays to inform a working model of a CYP24A1-Adx complex. We report that differential cross-linking internal to CYP24A1 points toward an Adx-induced conformational change that perturbs the F and G helices, which are required for substrate binding. Moreover, the modeled complex suggests that a semiconserved nonpolar interaction at the interface may influence CYP24A1 regioselectivity. Taken together, these findings contribute to our understanding of Adx recognition in a critical vitamin D-inactivating enzyme and provide broader insight regarding the variability inherent in CYP-Adx interactions.