Structural and biochemical analysis of Ras-effector signaling via RalGDS

The structure of the complex of Ras with the Ras-binding domain of its effe ctor RalGDS (RGS-RBD), the first genuine Ras-effector complex, has been sol ved by X-ray crystallography. As with the Rap-RafRBD complex (Nasser et al. , 1995), the interaction is via an inter-protein beta-sheet between the swi tch I region of Ras and the second strand of the RGS-RBD sheet, but the det ails of the interactions in the interface are remarkably different. Mutatio nal studies were performed to investigate the contribution of selected inte rface residues to the binding affinity. Gel filtration experiments show tha t the Ras RGS-RBD complex is a monomer, The results are compared to a recen tly determined structure of a similar complex using a Ras mutant (Huang et al., 1998) and are discussed in relation to partial loss-of-function mutati ons and the specificity of Ras versus Rap binding. (C) 1999 Federation of E uropean Biochemical Societies.