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.
