Grb2

 Growth Factor receptor-bound protein 2 (Grb2) is a signal transducing adaptor protein involved in cell signalling cascades, particularly the Ras pathway. The protein has three domains: one SH2 and two SH3 domains. The protein acts as a link between growth factor receptors and the Ras pathway in order to activate it. Grb2 is vital for most cellular functions, and a deficiency or impairment of the protein's function can lead to developmental problems in many organisms.