Grb2 is an adaptor protein that plays a key role in cell signaling. It contains one SH2 domain flanked by two SH3 domains, which allow it to bind to tyrosine phosphorylated proteins and form complexes with other proline-rich proteins. This enables Grb2 to transmit signals from growth factor receptors to downstream proteins like Ras and the ERK kinases. The SH2 domain specifically recognizes phosphotyrosine motifs to determine what other molecules Grb2 interacts with.