# Gs alpha subunit

The G$_s$ alpha subunit (G$_{αs}$, G$_s$α) is a subunit of the heterotrimeric G protein G$_s$ that stimulates the cAMP-dependent pathway by activating adenylyl cyclase. G$_s$α is a GTPase that functions as a cellular signaling protein. G$_s$α is the founding member of one of the four families of heterotrimeric G proteins, defined by the alpha subunits they contain: the G$_{αs}$ family, G$_{αi}$/G$_{αo}$ family, G$_{αq}$ family, and G$_{α12}$/G$_{α13}$ family. The Gs-family has only two members: the other member is G$_{olf}$, named for its predominant expression in the olfactory system. In humans, G$_s$α is encoded by the GNAS complex locus, while G$_{olf}$α is encoded by the GNAL gene.

## Function

The general function of G$_s$ is to activate intracellular signaling pathways in response to activation of cell surface G protein-coupled receptors (GPCRs). GPCRs function as part of a three-component system of receptor-transducer-effector. The transducer in this system is a heterotrimeric G protein, composed of three subunits: a Gα protein such as G$_s$α, and a complex of two tightly linked proteins called Gβ and Gγ in a Gβγ complex. When not stimulated by a receptor, Gα is bound to GDP and to Gβγ to form the inactive G protein trimer. When the receptor binds an activating ligand outside the cell (such as a hormone or neurotransmitter), the activated receptor acts as a guanine nucleotide exchange factor to promote GDP release from and GTP binding to Gα, which drives dissociation of GTP-bound Gα from Gβγ. In particular, GTP-bound, activated G$_s$α binds to adenylyl cyclase to produce the second messenger cAMP, which in turn activates the cAMP-dependent protein kinase (also called Protein Kinase A or PKA). Cellular effects of G$_s$α acting through PKA are described here.
Although each GTP-bound G$_s$α can activate only one adenylyl cyclase enzyme, amplification of the signal occurs because one receptor can activate multiple copies of G$_s$ while that receptor remains bound to its activating agonist, and each G$_s$α-bound adenylyl cyclase enzyme can generate substantial cAMP to activate many copies of PKA.

## Receptors

The G protein-coupled receptors that couple to the G$_s$ family proteins include:
* 5-HT$_4$, 5-HT$_6$ and 5-HT$_7$ serotonergic receptors
* Adenosine receptor types A$_{2a}$ and A$_{2b}$
* Adrenocorticotropic hormone receptor (a.k.a. MC2R)
* Arginine vasopressin receptor 2
* β-adrenergic receptors types β$_1$, β$_2$ and β$_3$
* Calcitonin receptor
* Calcitonin gene-related peptide receptor
* Corticotropin-releasing hormone receptor
* Dopamine D$_1$ and D$_5$ receptors
* Follicle-stimulating hormone receptor
* Gastric inhibitory polypeptide receptor
* Glucagon receptor
* Growth-hormone-releasing hormone receptor
* Histamine H$_2$ receptor
* Luteinizing hormone/choriogonadotropin receptor
* Melanocortin receptor: MC1R, MC2R (a.k.a. ACTH receptor), MC3R, MC4R, MC5R
* Olfactory receptors, through G$_{olf}$ in the olfactory neurons
* Parathyroid hormone receptors PTH1R and PTH2R
* Prostaglandin receptor types D$_2$ and I$_2$
* Secretin receptor
* Thyrotropin receptor
* Trace amine-associated receptor 1
* Vasopressin receptor 2