1. RAS activation
RAS activation (A) RAS is bound to GDP in the inactive state. Signal transduction can lead to the activation of RAS, via a GEF (GDP/GTP exchange factor), which displaces GDP from RAS, allowing the binding of GTP. This causes a change in conformation of RAS that enables interaction with effector proteins, thereby passing the activation signal onwards. Deactivation of RAS occurs by hydrolysis of GTP to GDP, assisted by GTPase-activating proteins (GAP). (B) Proteins of the RAF family are among several effectors of RAS. RAF proteins are serine/threonine kinases. Activated RAS binds to RAF, leading to a change in conformation of the latter and activating its kinase activity. RAF then phosphorylates its substrate MEK (which is also a kinase) thus activating it, and so the signal proceeds. This describes part of well-known signal transduction pathway, the mitogen activated protein kinase (MAPK) pathway.
Maria Jackson et al. Essays Biochem. 2018;62:
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