TheB class cell-attachedephrinsmediate contact-dependent cell–cell communications and transduce the contact signals to the host cells through the binding interactions of their cytoplasmic domains. Two classes of intracellular effectors of B ephrins have been identified: one contains the PSD-95/ Dlg/ZO-1 (PDZ)domain(for examplePDZ-RGS3), and the second the Src homology 2 (SH2) domain (. the Grb4 adaptor protein). The interaction with Grb4 requires phos-phorylation of tyrosine residues on the conserved cytoplas-mic C-terminal region of B ephrins, while binding to the PDZ domain is independent of tyrosine phosphorylation
