Solution structure of grb2 reveals extensive flexibility necessary for target recognition

Grb2 is an adaptor protein composed of a single SH2 domain flanked by two S H3 domains. Grb2 functions as an important evolutionary conserved link betw een a variety of cell membrane receptors and the Ras/MAP kinase-signaling c ascade. Here, we describe the solution structure of Grb2 as revealed by NMR and small angle X-ray scattering measurements. We demonstrate that Grb2 is a flexible protein in which the C-terminal SH3 domain is connected to the SH2 domain via a flexible linker. This is in contrast to the previously des cribed Grb2 crystal structure, which showed a compact structure with intram olecular contact between two SH3 domains. Binding experiments on Grb2 and p eptides containing two different proline-rich sequences indicate that Grb2 adapts the relative position and orientation of the two SH3 domains to bind bivalently to the target peptide sequences. (C) 2001 Academic Press.