A MOLECULAR REDOX SWITCH ON P21(RAS) - STRUCTURAL BASIS FOR THE NITRIC OXIDE-P21(RAS) INTERACTION

We have identified the site of molecular interaction between nitric ox ide (NO) and p21(ras) responsible for initiation of signal transductio n, We found that p21(ras) was singly S-nitrosylated and localized this modification to a fragment of p21(ras) containing Cys(118). A mutant form of p21(ras), in which Cys(118) was changed to a serine residue an d termed p21(ras)C118S, was not S-nitrosylated, NO-related species sti mulated guanine nucleotide exchange on wild-type p21(ras), resulting i n an active form, but not on p21(ras)C118S. Furthermore, in contrast t o parental Jurkat T cells, NO-related species did not stimulate mitoge n-activated protein kinase activity in cells transfected with p21(ras) C118S. These data indicate that Cys(118) is a critical site of redox r egulation of p21(ras), and S-nitrosylation of this residue triggers gu anine nucleotide exchange and downstream signaling.