G protein

G protein or guanine nucleotide-binding proteins are a family of proteins involved in transmitting chemical signals outside the cell, and causing changes inside the cell. They communicate signals from a variety of stimuli outside a cell to its interior.

Function

G proteins are involved in a variety of cellular functions including cell division, cell differentiation, and cell growth. They are also involved in transmitting signals from various stimuli outside a cell to its interior.

Structure

G proteins are made up of three subunits: alpha (α), beta (β), and gamma (γ). The alpha subunit binds to guanine nucleotides, and has a part in determining the specificity of the G protein for particular receptors.

Types

There are four main types of G proteins:

• G_s proteins stimulate the production of cyclic AMP (cAMP) from ATP.
• G_i proteins inhibit the production of cAMP from ATP.
• G_q proteins stimulate the formation of inositol trisphosphate (IP3) and diacylglycerol (DAG) from phosphatidylinositol 4,5-bisphosphate (PIP2).
• G_12/13 proteins are involved in the regulation of the cytoskeleton.

Role in disease

Mutations in G proteins can lead to a variety of diseases, including cancer, diabetes, and Albright's hereditary osteodystrophy.

See also

• Signal transduction
• Second messenger system
• G protein-coupled receptor

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