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My book lists two important differences between GCPRs and receptor protein kinases:

  • GCPRs do not directly activate a signal transduction pathway. It only does so indirectly, via a G protein. On the other hand, RTKs directly activate a signal transduction pathway, bypassing the mediation of a G protein. (Any G proteins involved with RTKs act as relay molecules in themselves and are part of the signal transduction pathway.)
  • GCPRs only activate one signal transduction pathway, while RTKs can activate many pathways.

From what I can tell, receptor protein kinases are faster and more versatile than GPCRs. They do not require as many intermediate steps and can activate many pathways at once. However, GPCRs make up the most largest class of ligand receptors in human cells. This leads me to think there is a great advantage GPCRs have over RTKs that I’m not seeing.

If RTKs are more advantageous than GPCRs, why are there more GPCRs than RTKs?

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I think GPCRs are evolutionary more older since tyrosine kinase signalling is relative recent evolved system. This could be one explanation for why their is more diversity in GPCRs

By the way GPCRs can actually signal g-protein independent, for example via B-arrestin. Also their are many types of g-proteins witch can all induce signaling via different signaling pathways. So GPCRS are actually quite versitile.

And then their is also a lot of crosstalk between GPCRs and RTKs

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  • $\begingroup$ Since both systems are widely distributed, they are both evolutionary pretty old. I would rather say "RTKs are evolutionary newer than GPCR" and not that they appeared relatively recently. $\endgroup$ – Chris Jan 30 '16 at 13:30
  • $\begingroup$ Thats is indeed what I ment $\endgroup$ – Robin Jan 30 '16 at 13:34

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