Receptor/ligand binding membrane-associated molecules

PTKs are monomeric in the active form, and consist of an extracellular binding domain, single membrane-associated a-helix and cytosolic domain with the kinase activity. Ligand binding induces dimerization and autophosphorylation that enables binding to adaptor molecules. These molecules connect the receptor to the signal transmitting biopolymers. 

Extrinsic (death receptor) pathway of caspase activation during apoptosis involves the binding of death ligands to cell surface receptors (e.g., Fas/ CD95/Apo-l or TNF receptor), recruitment of adaptor molecules Fas-associated death domain (FADD) or TNF receptor-associated death domain (TRADD) to the cytosolic end of the receptor, and formation of the death-inducing signaling complex (DISC) at the plasma membrane. DISC recruits and activates the initiator caspases, caspase-8 or -10. 

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