Heterotrimeric G protein

Heterotrimeric G proteins are a type of protein that are involved in transmitting signals from a variety of stimuli outside a cell to its interior. They are called "heterotrimeric" because they consist of three different subunits: alpha (α), beta (β), and gamma (γ).

Structure

The three subunits of a heterotrimeric G protein are bound together in a complex. The α subunit contains a binding site for guanosine diphosphate (GDP) and guanosine triphosphate (GTP), which are important for the protein's function. The β and γ subunits are tightly bound to each other and form a functional dimer.

Function

Heterotrimeric G proteins are crucial in the process of signal transduction, the transmission of a signal from the outside of a cell to its inside. When a ligand (a molecule that binds to a receptor) binds to a G protein-coupled receptor (GPCR) on the cell surface, it causes a conformational change in the GPCR. This change allows the GPCR to act as a guanine nucleotide exchange factor (GEF), which prompts the α subunit to release its bound GDP and replace it with GTP. This exchange triggers the dissociation of the α subunit from the βγ dimer, allowing both to interact with other proteins within the cell and propagate the signal.

Types

There are four main types of α subunits in mammals: Gαs, Gαi/o, Gαq/11, and Gα12/13, each of which interacts with different downstream effectors and mediates different cellular responses. The β and γ subunits also exist in several different forms, which can influence the specificity of G protein signaling.

Role in disease

Mutations in the genes encoding heterotrimeric G proteins can lead to a variety of diseases. For example, mutations in GNAS, the gene encoding the Gαs subunit, can cause Albright's hereditary osteodystrophy, a disorder characterized by short stature, obesity, and resistance to certain hormones.

See also

• G protein-coupled receptor
• Signal transduction
• Albright's hereditary osteodystrophy