Interaction of POPC, DPPC, and POPE with the μ opioid receptor: A coarse-grained molecular dynamics study

The mu opioid receptor (mu OR), which is part of the G protein-coupled receptors family, is a membrane protein that is modulated by its lipid environment. In the present work, we model mu OR in three different membrane systems: POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine), POPE (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine), and DPPC (1, 2-dipalmitoyl-sn-glycero-3-phosphocholine) through 45 mu s molecular dynamics (MD) simulations at the coarse-grained level. Our theoretical studies provide new insights to the lipid-induced modulation of the receptor. Particularly, to characterize how mu OR interacts with each lipid, we analyze the tilt of the protein, the number of contacts occurring between the lipids and each amino acid of the receptor, and the mu OR-lipid interface described as a network graph. We also analyze the variations in the number and the nature of the protein contacts that are induced by the lipid structure. We show that POPC interacts preferentially with helix 1 (H1) and helices H5-H6, POPE, with H5-H6 and H6-H7, and DPPC, with H4 and H6. We demonstrate how each of the three lipids shape the structure of the mu OR.