Gs protein

Gs is the G protein that turns the volume up. When a receptor coupled to Gs is activated, Gs goes and switches on the cyclic-AMP-making machinery, so the cell's internal cyclic-AMP signal rises and downstream activity speeds up.

Concretely, the activated Gs alpha subunit binds GTP, dissociates from beta-gamma, and stimulates adenylyl cyclase. Adenylyl cyclase then converts ATP into cyclic AMP, which activates protein kinase A and a cascade of phosphorylation events. The "s" stands for stimulatory.

Receptors that couple to Gs include beta-adrenoceptors (adrenaline, salbutamol), the glucagon receptor, many dopamine D1 and histamine H2 receptors, and the receptors for several peptide hormones. Drugs acting at these receptors — a beta-2 agonist relaxing airway muscle, for instance — exert their effect by raising cyclic AMP through Gs. Persistent overactivation of this pathway underlies diseases such as cholera, where the toxin freezes Gs in the on state and floods the gut with fluid.