The Glycosphingolipid GM3 Modulates Conformational Dynamics of the Glucagon Receptor

Abstract

The extracellular domain (ECD) of Class B1 G-protein coupled receptors (GPCRs) plays a central role in signal transduction and is uniquely positioned to sense both the extracellular and membrane environments. Whilst recent studies suggest a role for membrane lipids in the modulation of Class A and Class F GPCR signalling properties, little is known about the effect of lipids on Class B1 receptors. In this study, we employed multiscale molecular dynamics (MD) simulations to access the dynamics of the glucagon receptor (GCGR) ECD in the presence of native-like membrane bilayers. Simulations showed that the ECD could move about a hinge region formed by residues Q122-E126 to adopt both closed and open conformations relative to the TMD. ECD movements were modulated by binding of the glycosphingolipid GM3. These large-scale fluctuations in ECD conformation that may affect the ligand binding and receptor activation properties. We also identify a unique PIP2 interaction profile near ICL2/TM3 at the G-protein coupling interface, suggesting a mechanism of engaging G-proteins which may have a distinct dependence on PIP2 compared to Class A GPCRs. Given the structural conservation of Class B1 GPCRs, the modulatory effects of GM3 and PIP2 on GCGR may be conserved across these receptors, offering new insights into potential therapeutic targeting. Statement of SignificanceThe role of lipids in regulation of Class B GPCRs remains elusive, despite recent structural advances. In this study, multi-scale molecular dynamics simulations are used to evaluate lipid interactions with the glucagon receptor, a Class B1 GPCR. We find that the glycosphingolipid GM3 binds to the glucagon receptor extracellular domain (ECD), modulating the dynamics of the ECD and promoting movement away from the transmembrane domain. We also identify a unique PIP2 interaction fingerprint in a region known to be important for bridging G-protein coupling in Class A GPCRs. Thus, this study provides molecular insight into the behaviour of the glucagon receptor in a complex lipid bilayer environment which may aid understanding of glucagon receptor signalling properties.