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

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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.