As an adaptor protein, Growth Factor Receptor-Bound Protein 2 (GRB2) is involved in siganl transduction and consists of a central SH2 domain flanked by two SH3 domains. GRB2 associates with activated Tyr-phosphorylated EGF receptor/EGFR and PDGF receptors via its SH2 domain, stimulating GTP binding to Ras, which in turn activates MAPK and other signaling pathway.It also associates to other cellular Tyr-phosphorylated proteins such as SIT1, IRS1, IRS4, SHC and LNK. probably via the concerted action of both its SH2 and SH3 domains.