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?