User:Ilya/Yeast/Mating pheromone response pathway/Ras

Ras - GTPase switch protein


 * transduces signals from different RTKs (Receptor Tyrosine Kinases)


 * Activation:
 * dissociation of GDP by GEF (guanine nucleotide-exchange factor), activator
 * binding of GTP spontaneously due to higher concentration of GTP in cell
 * Deactivation:
 * binding of GAP (GTPase-activating protein), inhibitor
 * hydrolysis of GTP w/release of Pi and GAP
 * When "on", binds to and activates effector proteins that control growth and differentiation.

Ras and G protein are GTPase switch proteins (members of GTPase (Switch) superfamily)


 * Ras ~170AA, Gα ~330AA
 * 3D structure of Ras is similar to GTP-binding domain of Gα (Ras-like domain)
 * Both are present in all eukaryotic cells whic indicates that a single type of GTPase originated very early. Then gene duplicated and evolved into a superfamily (100s of proteins).
 * G protein coupled directly to receptors.
 * Ras is linked indirectly via other proteins.