AbstractCytochrome P450 3A4 (CYP3A4) is the most important drug-metabolizing enzyme in humans and has been associated with harmful drug interactions. The activity of CYP3A4 is known to be modulated by several compounds, as well as by the electron transfer partner, cytochrome P450 reductase (CPR). The underlying mechanism of these effects however is poorly understood. We have used hydrogen-deuterium exchange mass spectroscopy (HDX-MS) to investigate the impact of CPR and three different substrates (7-benzyloxy-4-trifluoromethyl-coumarin, testosterone and progesterone) on the conformational dynamics of CYP3A4. Here, we report that interaction of CYP3A4 with substrates or with the oxidized or reduced form of CPR leads to a global rigidification of the CYP3A4 structure. This was evident from a suppression of deuterium exchange in several regions of CYP3A4, including those known to be involved in protein-protein interactions (C-helix) as well as substrate binding and specificity (B’-, E-helices and K/β1-loop). Furthermore, the bimodal isotopic distributions observed for some CYP3A4-derived peptides were drastically impacted by CPR and/or substrates, suggesting the existence of stable CYP3A4 conformational populations that are perturbed by ligand/CPR binding. The results have implications for understanding the mechanisms of allostery, ligand binding, and catalysis in CYP enzymes.
Structural Dynamics of Cytochrome P450 3A4 in the Presence of Substrates and Cytochrome P450 Reductase
