BIOL 2021 Lecture Notes - Lecture 13: G Protein–Coupled Receptor, Conformational Change, Enzyme
13 May 2018
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• Classification of receptors:
• Enzyme coupled cell surface receptors.
• Fig 15-43 some RTKs
o Similar to GPCRs:
o Transmembrane proteins.
o Bind ligand on outer surface of PM. the binding of the signal protein to the
ligand-binding domain on the extracellular side of the receptor activates
the tyrosine kinase domain on the cytosolic side.
o Can activate the same signaling pathways.
o No need to know the types.
o A tyrosine domain in the cytosolic side.
o Different from GPCRs:
▪ Cytosolic domain has enzyme activity or associated with enzyme.
▪ Only one transmembrane domain, not seven.
• Question: G protein coupled receptors and enzyme coupled receptors often
activate some of the same signaling pathways. Why do some extracellular
signals use one kind of receptor rather than another kind?
o Answer: we don’t know.
• Receptor tyrosine kinases
o Receptor tyrosine kinases = RTKs.
o Phosphorylate tyrosine, not ser/thr (the 2 kinase domains phosphorylate
each other).
• Table 15-4 signal proteins that act through RTKs.
o Many extracellular signal proteins act through receptor tyrosine kinases
(RTKs). Ligands are extracellular signal proteins.
o Examples: EGF, insulin, NGF, ephrin, etc.
o Cell survival, growth, division of membrane bound ligand on another cell
(cell-cell recognition).
o Examples: ephrins, important in development and migration. Don’t have
soluble protein.
o Example of contact dependent signaling.
• Fig 15-44 activation of RTKs by dimerization:
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