The use of isomeric testosterone dimers to explore allosteric effects in substrate binding to cytochrome P450 CYP3A4

• Binding of synthetic cis and trans-testosterone dimers to CYP3A4 monomer in Nanodiscs
• Monomeric testosterone improves spectral response and affinity for testosterone dimer.
• Resonance Raman spectra show difference in packing of cis and trans-testosterone dimers.
• Affinity and spin shift are different for cis and trans-testosterone dimers.

Cytochrome P450 CYP3A4 is the main drug-metabolizing enzyme in the human liver, being responsible for oxidation of 50% of all pharmaceuticals metabolized by human P450 enzymes. Possessing a large substrate binding pocket, it can simultaneously bind several substrate molecules and often exhibits a complex pattern of drug–drug interactions. In order to better understand structural and functional aspects of binding of multiple substrate molecules to CYP3A4 we used resonance Raman and UV–VIS spectroscopy to document the effects of binding of synthetic testosterone dimers of different configurations, cis-TST2 and trans-TST2. We directly demonstrate that the binding of two steroid molecules, which can assume multiple possible configurations inside the substrate binding pocket of monomeric CYP3A4, can lead to active site structural changes that affect functional properties. Using resonance Raman spectroscopy, we have documented perturbations in the ferric and Fe-CO states by these substrates, and compared these results with effects caused by binding of monomeric TST. While the binding of trans-TST2 yields results similar to those obtained with monomeric TST, the binding of cis-TST2 is much tighter and results in significantly more pronounced conformational changes of the porphyrin side chains and Fe-CO unit. In addition, binding of an additional monomeric TST molecule in the remote allosteric site significantly improves binding affinity and the overall spin shift for CYP3A4 with trans-TST2 dimer bound inside the substrate binding pocket. This result provides the first direct evidence for an allosteric effect of the peripheral binding site at the protein-membrane interface on the functional properties of CYP3A4.

Synthetic dimers of the steroid testosterone are used to address directly the mechanisms of multiple substrate binding at the active site of cytochrome P450 3A4 and the role of substrate binding at a distal site in the control of allostery in this central enzyme of human drug metabolism.Figure optionsDownload as PowerPoint slide