Heterotrimeric G proteins, also known as guanine nucleotide-binding proteins, are a class of proteins involved in cellular signaling and the transmission of extracellular signals to intracellular signaling pathways. They are called heterotrimeric proteins because they consist of three subunits, designated α, β, and γ, which are tightly associated with one another.
Heterotrimeric G proteins are integral membrane proteins that reside on the inner surface of the cell membrane. When an extracellular signaling molecule, known as a ligand, binds to a specific receptor on the cell membrane's surface, it triggers a conformational change in the receptor. This conformational change leads to the activation of the heterotrimeric G protein, which results in the release of GDP (guanosine diphosphate) from the α subunit and its subsequent binding of GTP (guanosine triphosphate), leading to a dissociation of the α subunit from the βγ complex.
The activated α subunit, along with the βγ subunits, then interact with various effector proteins within the cell, such as enzymes or ion channels, initiating a cascade of intracellular signaling events. These events ultimately determine the cellular response to the original extracellular signal.
Heterotrimeric G proteins play a crucial role in a wide range of physiological processes, including neurotransmission, hormone signaling, sensory perception, and immune response. Dysregulation of heterotrimeric G protein signaling has been implicated in numerous human diseases, making them an important target for therapeutic intervention.
