Heterotrimeric G proteins

Gbetagamma subunits

post translationally modified at C terminus that tethers the Gbetagamma heterodimer to the membrane

G protein activity

GTPase activity of Galpha subunit is increased on contact with effector enzymes, activated on contact with adnylyl cyclase to ensure that subunit is active for long enough to make a productive encounter

Galpha subunit interaction

Galpha N and C terminal helices determine specificity of interaction with receptor

G protein switch mechanism

Receptor binding of Galpha causes change to Walker A motif, GDP is released and allows GTP to bind and a conformational change in the switch I and II regions of G protein, allowing release from Gbetagamma and activation of effector proteins

G protein alpha subunits

alpha0 found in all cells derived from embryonic neural crest, a2 found in neurons and a16 in hematopoietic cells

GTPase super family

intracellular switch proteins that hydrolyse GTP to GDP, active form is GTP bound and inactive form is GDP bound

Heterotrimeric G protein activation cycle

ligand binds and releases GDP from subunit, GTP is able to bind and dissociates Galpha subunit, Galpha binds to effector and activates it. hydrolysis of GTP to GDP causes Galpha to dissociate from effector