STRUCTURAL DETERMINANTS OF THE INTERACTION BETWEEN THE ERBB2 RECEPTORAND THE SRC HOMOLOGY-2 DOMAIN OF GRB7

The Src homology 2 (SH2) domain-containing protein Grb7 and the erbB2 receptor tyrosine kinase are over expressed in a subset of human breas t cancers. They also co-immunoprecipitate from cell lysates and associ ate directly in vitro. Whereas the Grb7 SH2 domain binds strongly to e rbB2, the SH2 domain of Grb14, a protein closely related to Grb7, does not. We have investigated the preferred binding site of Grb7 within t he erbB2 intracellular domain and the SH2 domain residues that determi ne the high affinity of Grb7 compared with Grb14 for this site, Phosph opeptide competition and site-directed mutagenesis revealed that Tyr-1 139 of erbB2 is the major binding site for the Grb7 SH2 domain, indica ting an overlap in binding specificity between the Grb7 and Grb2 SH2 d omains. Substituting individual amino acids in the Grb14 SH2 domain wi th the corresponding residues from Grb7 demonstrated that a Gin to Leu change at the beta D6 position imparted high affinity erbB2 interacti on, paralleled by a marked increase in affinity for the Tyr-1139 phosp hopeptide. The reverse switch at the beta D6 position abrogated Grb7 b inding to erbB2. This residue therefore represents an important determ inant of SH2 domain specificity within the Grb7 family.