Figure 1.

A schematic of a hypothetical model of a classical signalling pathway (A). ‘a’ is an extracellular ligand that binds to a multimeric receptor. ‘b’ is a member of a complex that triggers a pathway of protein kinases, of which ‘c’ is a member. ‘d’ is a possible regulator of that pathway but is not included in the canonical pathway definition (interactome resources would show ‘d’ interacting with members of the signalling pathway). ‘e’ is a transcription factor that regulates downstream expression. (B) i–iv show additional possible drug targets defined across functional categories, as detailed in the main text.