COMPUTED 3-DIMENSIONAL STRUCTURES FOR THE RAS-BINDING DOMAIN OF THE RAF-P74 PROTEIN COMPLEXED WITH RAS-P21 AND WITH ITS SUPPRESSOR PROTEIN,RAP-1A

The three-dimensional structures of the ras-p21 protein and its protei n inhibitor, rap-1A, have been computed bound to the ras-binding domai n, RBD (residues 55-131), of the raf-p74 protein, a critical target pr otein of ras-p21 in the ms-induced mitogenic signal transduction pathw ay. The coordinates of RBD have been reconstructed from the stereoview of an X-ray crystal structure of this domain bound to rap-1A and have been subjected to energy minimization. The energy-minimized structure s of both ras-p21 and rap-1A, obtained in previous studies, have been docked against RBD, using the stereo figure of the RBD-rap-1A complex, based on a six-step procedure. The final energy-minimized structure o f rap-1A-RBD is identical to the X-ray crystal structure. Comparison o f the ras-p21- and rap-1A-RBD complexes reveals differences in the str uctures of effector domains of ras-p21 and rap-1a, including residues 32-47, a domain that directly interacts with RBD, 60-66, 96-110, invol ved in the interaction of ras-p21 with jun kinase (JNK) and jun protei n, and 115-126, involved in the interaction of p21 with JNK. The struc ture of the RBD remained the same in both complexes with the exception of small deviations in its beta-2 binding loop (residues 63-71) and r esidues 89-91, also involved in binding to rap-1A. The results suggest that the binding of these two proteins to RBD may allow them to inter act with other cellular target proteins such as JNK and jun.