Signaling at zero G: G-protein-independent functions for 7-TM receptors

Eukaryotic cells, whether free-living, single-celled microbes or components of complex metazoa. can sense environmental cues through specialized seven-transmembrane (7-TM) receptors (also called heptahelical or G-protein-coupled receptors). 7-TM receptors detect 'inputs' such as light. peptide hormones, neurotransmitters, pheromones, odorants, morphogens and chemoattractants, linking extracellular stimuli to intracellular signaling networks via heterotrimeric G proteins. Recently, this obligatory paradigm has been challenged. A growing body of evidence indicates that 7-TM receptors can also transmit extracellular signals through mechanisms that function independently of G-protein coupling. This review discusses pathways and protein interactions for 7-TM receptors signaling 'at zero G' in Dictyostelium acid mammalian cells.