RAS

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Ras is a member of a class of proteins called the small G proteins. It is a very prominent signal-transduction component.

The mechanism by which this intracellular monomeric GTPase is activated is well established. The signalling molecule tends to be an epidermal growth factor's (EGF) that are involved in cell proliferation and differentiation. These EGF's bind to the receptor (usually RTK's) causing dimerization which induces cross-phosophorylation of the two adjacent kinase domains. These activated kinase regions act as a docking site for other intracellular signalling proteins, the first one being Grb2. A protein known as Sos, which is a Ras gunanine-nucleotide exchange factor (GEF), then binds to Grb2 which causes inactivated Ras (bound to GDP) to release the GDP and uptake GTP, thus becoming activated[1]. Ras is then involved in causing transcription of some genes by a protein kinases cascade known as the MAP-kinase pathway. Firstly, Ras activates protein kinase kinase kinase (Raf) by conformational change . Raf then activates protein kinase kinase (Mek) by phosphorylation which then actives protein kinase (Erk) by phosphorylation. Each of these activation stages is closely regulated by cytosolic enzymes. Erk is then able to pass through into the nucleus, in turn activating transcription factors causing the expression of some genes[2].

Ras (Ras Protein) is a monomeric GTPase of the Ras superfamily that helps to relay signals from cell-surface RTK receptors to the nucleus, frequently in response to signals that stimulate cell division[3].

Named for the ras gene, first identified in viruses that cause rat sarcomas[4][5].

References

  1. Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto, Jr and Lubert Stryer. Biochemistry, Eighth Edition, New York: Kate Ahr Parker 2015.
  2. Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto, Jr and Lubert Stryer. Biochemistry, Eighth Edition, New York: Kate Ahr Parker 2015.
  3. Alberts, B. et al. (2008) pG:32. Molecular Biology of The Cell. 5th Ed. New York: Garland Science
  4. Berg, J. M. et al. (2012) p.431. Biochemistry. 7th Ed. New York: W. H. Freeman and Company
  5. Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto, Jr and Lubert Stryer. Biochemistry, Eighth Edition, New York: Kate Ahr Parker 2015.
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