Alpha subunits

Reconstitution experiments carried out in the early 1980s showed that purified G_α subunits can directly activate effector enzymes. The GTP form of the α subunit of transducin (G_t) activates the cyclic GMP phosphodiesterase from retinal rod outer segments, and the GTP form of the α subunit of the stimulatory G protein (G_s) activates hormone-sensitive adenylate cyclase.

G_α subunits consist of two domains, the GTPase domain, and the alpha-helical domain. There exist at least 20 different G_α subunits, which are separated into four main families. This nomenclature is based on their sequence homologies:

G-protein-family	α-subunit	Gene	Signal transduction	Use/Receptors (examples)	Effects (examples)
Gi-family
Gi/o	αi, αo	GNAO1, GNAI1, GNAI2, GNAI3	Inhibition of adenylate cyclase, opens K^+-channels (via β/γ subunits), closes Ca^2+-channels	Muscarinic M2 and M4, chemokine receptors, α2-Adrenoreceptors, Serotonin 5-HT1 receptors, Histamine H3 and H4, Dopamine D2-like receptors	Smooth muscle contraction, depress neuronal activity
Gt	αt (Transducin)	GNAT1, GNAT	Activation of phosphodiesterase 6	Rhodopsin	Vision
Ggust	αgust (Gustducin)	GNAT3	Activation of phosphodiesterase 6	Taste receptors	Taste
Gz	αz	GNAZ	Inhibition of adenylate cyclase	?	Maintaining the ionic balance of perilymphatic and endolymphatic cochlear fluids.
Gs-family
Gs	αs	GNAS	Activation of adenylate cyclase	Beta-adrenoreceptors; Serotonin 5-HT4, 5-HT6 and 5-HT7; Dopamine D1-like receptors, Histamine H2	Increase heart rate, Smooth muscle relaxation, stimulate neuronal activity
Golf	αolf	GNAL	Activation of adenylate cyclase	olfactory receptors	Smell
Gq-family
Gq	αq, α11, α14, α15, α16	GNAQ, GNA11, GNA14, GNA15	Activation of phospholipase C	α1-Adrenoreceptors, Histamine H1, Serotonin 5-HT2 receptors, Muscarinic M1 M3, and M5	Smooth muscle contraction, Ca^2+ flux
G12/13-family
G12/13	α12, α13	GNA12, GNA13	Activation of the Rho family of GTPases		Cytoskelatal functions, Smooth muscle contraction

Дата добавления: 2014-01-14