The TCR and BCR Are Each Composed of Two Modules

Essay

The TCR and BCR are each composed of two modules, an antigen-binding module and a signaling module; furthermore, in each case, the two functional modules are encoded by distinct polypeptides. In addition, the tyrosine kinases that initiate antigen receptor signaling are also separate proteins from those of each receptor. This is a different strategy for receptor signaling than the case of receptor tyrosine kinases, where the enzyme is an intrinsic component of the ligand-binding receptor protein. Name one advantage of this organization of the TCR and BCR that accounts for the expression of ZAP-70 and Syk, as well as ITAM-containing immunoreceptors, in many different subsets of immune cells.