Exploring Membrane Cholesterol Binding to the CB1 Receptor: A Computational Perspective

Cholesterol (CHOL) is a potential allosteric modulator of the CB1 receptor. In this work, we use atomistic molecular dynamics simulations to study how CHOL interacts with CB1 and to identify its binding sites (BS) and residence times on specific receptor zones. Our results evince minimal changes in CB1 conformational dynamics and secondary structure due to CHOL. We report five BSs, three of which coincide with previously described interaction regions (BS1, BS2, and BS3), while BS4 and BS5 are proposed as new BSs. Quantum descriptors of bonding such as Natural Bond Orbitals (NBO), Quantum Theory of Atoms in Molecules (QTAIM), and Noncovalent Interactions (NCI) analyses are employed to characterize the CHOL-BS interactions. The results show an exponential correlation between the strength of the interactions (mainly hydrogen bonds and hydrophobic contacts) and the residence time at the BSs. Although other approaches exist to identify high-affinity protein sites, our methodology integrates classical and quantum descriptions to better characterize BSs and predict ligand residence times in CB1, distinguishing persistent from transitory contacts. Since CHOL has been suggested as a potential endogenous allosteric ligand, our flexible strategy allows studying interactions that stabilize CHOL in CB1, could be extended to cannabinoid binding, and contribute to designing improved receptor ligands.