The inhibitory G protein Gi, also known as Gαi, is a type of heterotrimeric G protein found in cells and plays a crucial role in intracellular signaling pathways. It is classified as α subunit of the Gi family, which consists of three closely related isoforms: Giα1, Giα2, and Giα3.
Inhibitory G proteins are an essential component of signal transduction cascades triggered by various receptors, including G protein-coupled receptors (GPCRs). When a ligand binds to its specific receptor, it promotes the exchange of GDP (guanosine diphosphate) bound to Gαi with GTP (guanosine triphosphate), leading to Gαi activation.
Activated Gαi dissociates from the βγ subunits and interacts with effector proteins, such as ion channels and enzymes. Unlike other G protein subtypes, the primary function of Gαi is to inhibit the activity of intracellular signaling pathways. It accomplishes this by decreasing intracellular levels of cyclic adenosine monophosphate (cAMP) or other second messengers, ultimately suppressing downstream cellular responses.
The inhibitory actions of Gαi are widespread in various tissues and organs, such as neuronal tissues, heart, and smooth muscle cells. They are involved in regulating processes like neurotransmission, hormonal secretion, cell growth, and immune responses. Dysregulation of the inhibitory G protein Gi has been associated with several diseases, including cardiovascular disorders, cancer, and neurological conditions.
Overall, the inhibitory G protein Gi acts as a mediator of inhibitory signaling pathways, providing fine-tuning and regulation of cellular responses in a wide range of physiological and pathophysiological contexts.
