Gsubenheter

Gsubenheter, or G-subunits, are components of heterotrimeric G proteins that translate signals from G protein-coupled receptors (GPCRs) into intracellular responses. A functional G protein is a heterotrimer composed of a Gα subunit bound to a Gβγ dimer. In resting cells, Gα binds GDP and associates with Gβγ. When a GPCR is activated by a ligand, it acts as a guanine nucleotide exchange factor, promoting exchange of GDP for GTP on Gα. The GTP-bound Gα dissociates from the Gβγ dimer and both components regulate downstream effectors. After GTP hydrolysis, Gα returns to the GDP-bound state and reassociates with Gβγ to terminate the signal.

Gα subunits are divided into four major families: Gs, Gi/o, Gq/11, and G12/13. Gs stimulates adenylyl cyclase, increasing cAMP; Gi/o inhibits adenylyl cyclase, decreasing cAMP; Gq/11 activates phospholipase Cβ, generating IP3 and DAG; G12/13 activates Rho family GEFs, influencing the cytoskeleton and cell movement. Gβγ dimers, formed by one Gβ and one Gγ subunit, can also regulate signaling by directly modulating ion channels (such as GIRK), certain isoforms of adenylyl cyclase and phospholipase Cβ, and by influencing kinases and MAP kinase pathways.

G-subunits are encoded by multiple gene families: GNA genes encode Gα subunits, GNB genes encode Gβ, and GNG genes encode Gγ subunits, with numerous isoforms that vary in tissue distribution and signaling bias. The coordinated action of Gα and Gβγ subunits enables GPCRs to regulate a wide range of physiological processes, including sensory perception, cardiovascular function, neurotransmission, and development. Dysregulation or mutation of G-subunits is associated with various diseases and pharmacological responses.

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