Modulation of the Interaction between Neurotensin Receptor NTS1 and Gq Protein by Lipid

Membrane lipids have been implicated to influence the activity of G protein-coupled receptors (GPCRs). Almost all of our knowledge on the role of lipids on GPCR and G protein function comes from work on the visual pigment rhodopsin and its G protein transducin, which reside in a highly specialized membrane environment. Thus insight gained from rhodopsin signaling may not be simply translated to other non-visual GPCRs. Here, we investigated the effect of lipid head group charges on the signal transduction properties of the class A GPCR neurotensin receptor 1 (NTS1) under defined experimental conditions, using self-assembled phospholipid nanodiscs prepared with the zwitter-ionic lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), the negatively charged 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (POPG), or a POPC/POPG mixture. A combination of dynamic light scattering and sedimentation velocity showed that NTS1 was monomeric in POPC-, POPC/POPG- and POPG-nanodiscs. Binding of the agonist neurotensin to NTS1 occurred with similar affinities and was essentially unaffected by the phospholipid composition. In contrast, Gq protein coupling to NTS1 in various lipid nanodiscs was significantly different and the apparent affinity of Gαq and Gβ1γ1 to activated NTS1 increased with increasing POPG content. NTS1-catalyzed GDP/GTPγS nucleotide exchange at Gαq in the presence of Gβ1γ1 and neurotensin was crucially affected by the lipid type, with exchange rates higher by one or two orders of magnitude in POPC/POPG- and POPG-nanodiscs, respectively, compared to POPC-nanodiscs. Our data demonstrate that negatively charged lipids in the immediate vicinity of a non-visual GPCR modulate the G protein-coupling step.