Module 1: Figure stimuli for enzyme-linked receptors
Growth and survival factors engage enzyme-linked receptors.
These single-membrane-spanning receptors have an extracellular ligand-binding domain and an intracellular domain that contains either a tyrosine kinase (TK) or a serine/threonine kinase. The protein tyrosine kinase-linked receptors (PTKRs), which usually function as dimers, assemble a complex of scaffolding proteins (green) and transducers (red) that relay information out to amplifiers that function in different signalling pathways. The serine/threonine kinase-linked receptors (S/TKRs) function as tetramers and have a much simpler signalling pathway in that the serine/threonine kinase functions as both the transducer and amplifier to generate the Smad messengers.