Structural evidence for feedback activation by Ras·GTP of the Ras-specific nucleotide exchange factor SOS

S. Mariana Margarit, Holger Sondermann, Brian E. Hall, Bhushan Nagar, Andre Hoelz, Michelle Pirruccello, Dafna Bar-Sagi, and John Kuriyan

Cell, Vol 112, 685-695, 7 March 2003 (local copy)

Abstract / Figures from the paper / Crystal Table


Growth factor receptors activate Ras by recruiting the nucleotide exchange factor son of sevenless (SOS) to the cell membrane, thereby triggering the production of GTP-loaded Ras. Crystallographic analyses of Ras bound to the catalytic module of SOS have led to the unexpected discovery of a highly conserved Ras binding site on SOS that is located distal to the active site and is specific for Ras·GTP. The crystal structures suggest that Ras·GTP stabilizes the active site of SOS allosterically, and we show that Ras·GTP forms ternary complexes with SOScat in solution and increases significantly the rate of SOScat-stimulated nucleotide release from Ras. These results demonstrate the existence of a positive feedback mechanism for the spatial and temporal regulation of Ras.

Illustrations from the paper. Click on the small image to get a bigger one.

Crystal Table

Table 1. Data Collection and Refinement Statistics