Heterotrimeric G proteins GTPase

these g proteins made 3 subunits, g domain located on largest 1 (the α unit); 2 smaller subunits (β , γ units), form tightly associated protein complex. α , γ unit associated membrane lipid anchors. heterotrimeric g proteins act specific reaction partners of g protein-coupled receptors. gtpase inactive. upon receptor activation, intracellular receptor domain activates gtpase, in turn activates other molecules of signal transduction chain, either via α unit or βγ complex. among target molecules of active gtpase adenylate cyclase , ion channels. heterotrimeric g proteins can classified sequence homology of α unit 4 families:

by combination of different α, β , γ subunits, great variety (>1000) g proteins can produced. gdp not needed gtp.

activation cycle of heterotrimeric g proteins

in basic state, gα-gdp-gβγ complex , receptor can activate separately associated membrane. on receptor activation, receptor becomes highly affine g protein - gdp complex. on binding complex, gdp dissociates complex; receptor works gef - gdp-gtp exchange factor; free complex has high affinity gtp. upon gtp binding, both gα-gtp , gβγ separate both receptor , each other. depending on lifetime of active state of receptor, can activate more g proteins way.

both gα-gtp , gβγ can activate separate and/or same effector molecules, sending signal further down signal reaction chain. once intrinsic gtpase activity of α unit has hydrolyzed gtp gdp, , 2 parts associate original, inactive state. speed of hydrolysis reaction works internal clock length of signal.