Structural insights into positive and negative allosteric regulation of a G protein-coupled receptor through protein-lipid interactions

Abstract

Lipids are becoming known as essential allosteric modulators of G protein-coupled receptor (GPCRs). However, how they exert their effects on GPCR conformation at the atomic level is still unclear. In light of recent experimental data, we have performed several long-timescale molecular dynamics (MD) simulations, totalling 24 μs, to rigorously map allosteric modulation and conformational changes in the β2 adrenergic receptor (β2AR) that occur as a result of interactions with three different phospholipids. In particular, we identify different sequential mechanisms behind receptor activation and deactivation, respectively, mediated by specific lipid interactions with key receptor regions. We show that net negatively charged lipids stabilize an active-like state of β2AR that is able to dock Gsα protein. Clustering of anionic lipids around the receptor with local distortion of membrane thickness is also apparent. On the other hand, net-neutral zwitterionic lipids inactivate the receptor, generating either fully inactive or intermediate states, with kinetics depending on lipid headgroup charge distribution and hydrophobicity. These chemical differences alter membrane thickness and density, which differentially destabilize the β2AR active state through lateral compression effects.

G-Protein-Coupled Receptor-Membrane Interactions Depend on the Receptor Activation state

“…This was consistent with another study favored partial deactivation of the b2AR was found in the 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipids (27). In coarse-grained MD simulations, Song et.…”

“…The only positive correlation between the transmembrane helices and the lipids was observed between the intracellular region of TM6 and lipids in the lower leaflet of active A1AR. Four lysine residues (K263 6.25 , K267 6.29 , K270 6.32 and K273 6.35 ) present in the intracellular end in the b2AR of TM6 were also known to interact with negatively-charged headgroups of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) lipid molecules in and thus stabilize the GPCR active state (27).…”

“…The R 3.50 and E 6.30 are highly conserved residues in GPCRs and often form an ionic lock in inactive receptors. In contrast, lipids with negatively-charged PE headgroup formed favorable interactions with the positively-charged residues in the TM6 and stabilized active state of the b2AR (27). Salas-Estrada et.…”

“…Both atomistic and coarse-grained MD simulations have been applied to study the effects of lipids in protein dynamics and cellular signaling. (27). The negative charge in PG molecules favored interaction with positively-charged residues in the intracellular loop 3 (ICL3) and intracellular end of transmembrane helix 6 (TM6).…”

The Glycosphingolipid GM3 Modulates Conformational Dynamics of the Glucagon Receptor

“…However, the role of lipids in activation of Class B1 GPCRs is less well understood. Whilst the activation of Class A GPCRs is modulated by membrane lipids (14)(15)(16) which may act as allosteric regulators of GPCR activity (15,17,18), the interactions of lipids with Class B GPCRs have not been extensively characterised.…”