Compare and contrast GPCR and RTK receptors with respect to (a) structure–especially the transmembrane region, (b) activation mechanism, (c) initial signal transduction across the membrane
What will be an ideal response?
Answer:
a) GPCRs have seven transmembrane helices with only connecting loops and the N- and C-terminal regions projecting from the membrane. RTKs have only a single transmembrane domain with large globular regions projecting outside and inside the membrane.
b) Ligand binding to a GPCR causes a conformation change in the transmembrane helices, which changes the conformation of the cytoplasmic regions to form a binding site for a G-protein. Ligand binding causes a conformational change in the RTK extracellular domain, but with only a single transmembrane region that conformational change cannot be transmitted to the cytoplasmic domain. Instead, the extracellular domain conformation change cause two RTKs to dimerize, which brings the cytoplasmic domains close enough to autophosphorylate tyrosines to provide binding sites to recruit SH2-domain proteins.
c) Binding of G-proteins to activated GPCRs and SH2-domain proteins to activated RTKs transmits the signal into the cell.
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