The activation mechanism of class-III G-protein coupled receptors

Class-III G-protein coupled receptors (GPCRs) represent a distant group among the large family of GPCRs. This class includes the receptors for the main neurotransmitters, glutamate and GABA, and the receptors for Ca 2 + , some taste and pheromone molecules, as well as some orphan receptors. Like any other GPCRs, class-III receptors possess a heptahelical domain (HD) involved in heterotrimeric G-protein activation, but most of them also have a large extracellular domain (ECD) responsible for agonist recognition and binding. The aim of this article is to highlight our actual understanding of the way agonists by interacting in the large ECD lead to the necessary change in conformation of the HD for G-protein activation.