Allosteric modulation of ghrelin receptor signaling by lipids

Abstract

The membrane is an integral component of the G protein-coupled receptor signaling machinery. Here we demonstrate that lipids regulate the signaling efficacy and selectivity of the ghrelin receptor GHSR through specific interactions and bulk effects. We find that PIP2 shifts the conformational equilibrium of GHSR away from its inactive state, favoring basal and agonist-induced G protein activation. This occurs because of a preferential binding of PIP2 to specific intracellular sites in the receptor active state. Another lipid, GM3, also binds GHSR and favors G protein activation, but mostly in a ghrelin-dependent manner. Finally, we find that not only selective interactions but also the thickness of the bilayer reshapes the conformational repertoire of GHSR, with direct consequences on G protein selectivity. Taken together, this data illuminates the multifaceted role of the membrane components as allosteric modulators of how ghrelin signal could be propagated.

Insights into the Role of Membrane Lipids in the Structure, Function and Regulation of Integral Membrane Proteins

“…The important role of PIP lipids is underlined by a study that utilised a combination of mass spectrometry analyses and MD simulations revealing that PtdIns(4,5)P 2 binds to positively charged residues on the intracellular side of class A GPCRs, stabilising the active states of the receptors [25]. Similar results have been obtained for the GSHR, ghrelin receptor, with FRET analysis using labelled PtdIns(4,5)P 2 and labelled ghrelin receptor revealing that PtdIns(4,5)P 2 binds preferentially to the active form of the receptor [45].…”

Concerted conformational dynamics and water movements in the ghrelin G protein-coupled receptor

“…To provide an illustration of the impact of the environment of the ghrelin receptor on its local hydration, we finally analyzed the effect of the lipid composition of the nanodiscs on 7H4MC fluorescence for the two positions that were affected by receptor activation. Specifically, we measured the hydration parameter for the probe at positions 5.58 and 6.44 with GHSR assembled into POPC:POPG nanodiscs in the absence or presence of phosphatidylinositol-4,5-bisphosphate (PIP2), a lipid that has been shown to impact on the activity of many different membrane proteins ( Hammond and Burke, 2020 ) including GPCRs ( Yen et al, 2018 ) and, more recently, the ghrelin receptor ( Damian et al, 2021 ). As shown in Figure 5 , the H parameter for the two positions that were sensitive to receptor activation was further affected by PIP2.…”

“…This suggests that PIP2 further shifts the conformational equilibrium toward hydration pattern associated with the active-like conformation of GHSR, indicative of an allosteric coupling between the full agonist and PIP2 for stabilizing this state. This effect could explain the impact of PIP2 on GHSR-catalyzed G protein activation ( Damian et al, 2021 ).…”

“…Among the lipids reported to affect GPCR signaling such as cholesterol ( Casiraghi et al, 2016 ; Zocher et al, 2012 ) or charged phospholipids ( Strohman et al, 2019 ; Dawaliby et al, 2016 ), PIP2 has been shown to stabilize the receptor:G protein complex for the adenosine A2a-, β 1 -adrenergic, and neurotensin receptor 1 ( Yen et al, 2018 ). More recently, we showed that PIP2 could be an allosteric regulator of ghrelin signaling ( Damian et al, 2021 ). Accordingly, we observed here that including PIP2 in the nanodiscs was associated with a further amplification of the changes in 7H4MC fluorescence triggered by ghrelin, reflecting the allosteric coupling between the full agonist and this lipid for stabilizing an active-like hydration pattern of GHSR.…”

Biased Ghrelin Receptor Signaling and the Dopaminergic System as Potential Targets for Metabolic and Psychological Symptoms of Anorexia Nervosa

“…As the metabolic state changes quite drastically throughout the course of AN it is possible that an altered activation of the GhrR affects the signaling in the DAergic system and therefore the motivational drive of the patients. That microenvironmental changes can affect GhrR signaling patterns, is supported by a recent study observing that lipid membrane composition and thickness have the potential to alter the GhrR activation and conformational state ( 116 ). Altered lipid composition and integrity of cell membranes have been observed in AN patients ( 117 , 118 ).…”