Proton-gated coincidence detection is a common feature of GPCR signaling

Abstract

The evolutionary expansion of G protein-coupled receptors (GPCRs) has produced a rich diversity of transmembrane sensors for many physical and chemical signals. In humans alone, over 800 GPCRs detect stimuli such as light, hormones, and metabolites to guide cellular decision-making primarily using intracellular G protein signaling networks. This diversity is further enriched by GPCRs that function as molecular sensors capable of discerning multiple inputs to transduce cues encoded in complex, context-dependent signals. Here, we show that many GPCRs are coincidence detectors that couple proton (H+) binding to GPCR signaling. Using a panel of 28 receptors covering 280 individual GPCR-Gα coupling combinations, we show that H+ gating both positively and negatively modulates GPCR signaling. Notably, these observations extend to all modes of GPCR pharmacology including ligand efficacy, potency, and cooperativity. Additionally, we show that GPCR antagonism and constitutive activity are regulated by H+ gating and report the discovery of an acid sensor, the adenosine A2a receptor, which can be activated solely by acidic pH. Together, these findings establish a paradigm for GPCR signaling, biology, and pharmacology applicable to acidified microenvironments such as endosomes, synapses, tumors, and ischemic vasculature.

Physiological relevance of proton-activated GPCRs

“…In summary, all three GPCRs can signal via different Gα subunits and coupling may occur in a cell-specific manner. Moreover, the sensitivity to pH may also dependent on the Gα subunit associated to the respective GPCR [52] (Fig. 1).…”

“…It should be also noted that multiple other GPCRs may be modulated positively or negatively by protons and GPCRs other than those covered in this review may also function as protons sensors. For example, Kopolka et al demonstrated that the adenosine A2a receptor can be activated solely by H + [52]. Also, the affinity of the calcium-sensing receptor (CaSR) to calcium is modulated by extracellular protons [17].…”

Serotonin G Protein-Coupled Receptor-Based Biosensing Modalities in Yeast

“…However, it deserves to be mentioned that the general acidification spent medium from cultivated yeast is an important parameter to consider when establishing and optimizing biosensing workflows, especially when using GPCRs with proton-gated coincidence detection such as 5-HT4. 51 Indeed, we observed a general lowering of the pH with increasing ratio of the spent medium added to the medium with the sensor ( Supporting Information Figure S5).…”

Screening microbially produced Δ9-tetrahydrocannabinol using a yeast biosensor workflow

“…As pH has recently been shown to drastically modulate the signalling of human G protein-coupled receptors in yeast, we first assessed the dose-response of the CB2 biosensor to THC over a range of physiologically relevant conditions 37 (Supplementary Fig. 5a ).…”

“…As shown in this work, not all mammalian GPCRs functionally express in yeast, and those that have been previously reported may not work in other settings without the original knowhow. Work is needed to uncover more universal principles for improving the expression, localisation, and coupling of GPCRs in yeast, but progress towards this is underway 37 , 39 .…”