Signaling by G Protein-Coupled Receptors

G protein-coupled receptors represent one of the largest families of cell surface receptors in nature. These receptors play fundamental roles in diverse physiological processes such as neurotransmission, cellular metabolism, cell differentiation and growth as well as immune response. In response to extracellular ligands, G protein-coupled receptors specifically interact with heterotrimeric G proteins that can then activate or inhibit effector enzymes, ultimately leading to the physiological response. Biochemical and mutational studies have revealed the molecular mechanisms of ligand-receptor interaction, receptor activation and receptor-G protein coupling selectivity. In the last few years, increasing evidence suggested that G protein-coupled receptor are also involved in other novel signaling pathways in addition to classical G protein-mediated pathways. This review will briefly summarize recent studies on structural and functional aspects of G protein-coupled receptors with emphasis on molecular mechanisms of receptor activation.