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.