Functional diversity of GPCR-Gustducin complexes controls signaling output and suppresses alternative pathways

Gustducin (Ggust), the G protein mediating taste receptor signaling, is expressed not only in sensory taste cells but throughout the human body alongside numerous non-taste G protein-coupled receptors (GPCRs). Whether and how these receptors engage Ggust, and the functional consequences of such interactions, remain poorly understood. Here, we developed two complementary biosensors that enable direct monitoring of GPCR-Ggust interaction and downstream signaling in living cells, allowing pharmacological characterization of Ggust activity by non-taste GPCRs. Unexpectedly, we find that several non-taste GPCRs do not activate Ggust but instead stabilize the G protein heterotrimer and suppress basal signaling by forming unproductive GPCR-G protein complexes, whereas others induce conventional Ggust activation and signal transduction. We further show that these unproductive GPCR-Ggust complexes suppress the activation of alternative signaling pathways by sequestering receptors from other G proteins. This previously unrecognized mode of interaction functionally partitions GPCRs into activators and inactivators of Ggust and represents a mechanism for balancing concurrent signaling pathways within a cell. HighlightsO_LIDevelopment of biosensors for gustducin activation and signal transduction C_LIO_LIAnalysis of single-cell co-expression data of non-tastant GPCRs and gustducin C_LIO_LIProfiling of non-tastant GPCR-induced gustducin activation and signal transduction C_LIO_LIProductive and unproductive GPCR-gustducin complexes revealed C_LIO_LIUnproductive GPCR-gustducin complexes suppress alternative signaling pathways C_LI