COMPARTMENTALIZATION OF B-CELL ANTIGEN RECEPTOR FUNCTIONS

Receptor tyrosine kinases (RTK), like the PDGF-receptor, translate inf ormation from the extracellular environment into cytoplasmic signals t hat regulate a spectrum of cellular functions. RTK molecules consist o f ligand binding extracellular domains, cytoplasmic kinase domains and tyrosine phosphorylation sites [Ullrich and Schlessinger, 1990 (Cell 61, 203-212); Heldin, 1992 (EMBO J. 11, 4251-259)]. Upon ligand-induce d RTK oligomerization, the kinase domains will become activated and in duce auto(trans)phosphorylation of a number of cytoplasmic tyrosine re sidues. These phosphorylated tyrosine residues are incorporated in dis tinct sequence motifs and act as specific docking sites for SH2 domain -containing proteins [Songyang et al., 1993 (Cell 72, 767-778)]. In co ntrast to single- or oligo-chain RTK, immunological receptors such as antigen receptors, FcR and cytokine receptors are multi-chain complexe s in which distinct receptor functions appear to be compartimentalized in distinct polypeptides. Here, we summarize current knowledge on the structural and functional characteristics of the B-cell antigen recep tor complex (BCR) and address the specific ability of accessory molecu les to recruit intracellular signaling intermediates towards the activ ated receptor complex. Copyright (C) 1996 Elsevier Science Ltd.