Mechanisms of Lipid Scrambling by the G Protein-Coupled Receptor Opsin

• Published in: Structure (London) 2018-02, Vol.26 (2), p.356-367.e3
• Main Authors: Morra, Giulia, Razavi, Asghar M., Pandey, Kalpana, Weinstein, Harel, Menon, Anant K., Khelashvili, George
• Format: Article
• Language: English
• Subjects: adaptive sampling; Biological Transport; Computer Simulation; GPCR; Humans; Lipid Bilayers - metabolism; lipid flip-flop; Markov state models; Molecular Dynamics Simulation; molecular dynamics simulations; Opsins - metabolism; phospholipid; Phospholipid Transfer Proteins - metabolism; rhodopsin; scramblase
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2017.11.020

Several class-A G protein-coupled receptor (GPCR) proteins act as constitutive phospholipid scramblases catalyzing the transbilayer translocation of >10,000 phospholipids per second when reconstituted into synthetic vesicles. To address the molecular mechanism by which these proteins facilitate rapid lipid scrambling, we carried out large-scale ensemble atomistic molecular dynamics simulations of the opsin GPCR. We report that, in the process of scrambling, lipid head groups traverse a dynamically revealed hydrophilic pathway in the region between transmembrane helices 6 and 7 of the protein while their hydrophobic tails remain in the bilayer environment. We present quantitative kinetic models of the translocation process based on Markov State Model analysis. As key residues on the lipid translocation pathway are conserved within the class-A GPCR family, our results illuminate unique aspects of GPCR structure and dynamics while providing a rigorous basis for the design of variants of these proteins with defined scramblase activity. [Display omitted] •Extensive all-atom molecular dynamics simulations of the opsin GPCR•A hydrophilic pathway is revealed between transmembrane helices 6 and 7 of opsin•Lipids traverse the pathway according to the credit card reader mechanism•Kinetics of the lipid translocation process is quantified using Markov State Models Morra et al. analyze molecular dynamics simulations of the G protein-coupled receptor (GPCR) opsin to provide insight into the molecular mechanism of lipid scrambling by a GPCR. The study uncovers unique aspects of the structure and dynamics of this important superfamily of receptors.