WFU Physics and CSB^* Colloquium

TITLE: Redox Regulation of Ras Superfamily GTPases

SPEAKER: Professor Sharon Campbell,

TIME: Tuesday Sept. 25, 2007 at 4:00 PM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

We previously demonstrated that free radical redox agents (i.e. peroxynitrite, superoxide) can react with Ras and Rho GTPases, and alter guanine nucleotide binding via a radical-based mechanism. Here, reactive nitrogen and oxygen species promote formation of thiol radical intermediates that facilitate guanine nucleotide oxidation and release of guanine nucleotide substrates. While our studies of Ras indicate that oxidation of the redox active thiol by non-radical mechanisms does not alter guanine nucleotide binding, we postulate that Rho GTPases may be regulated by additional non-radical oxidative mechanisms due to the location of the redox active cysteine in the Rho GTPase phosphoryl binding loop. In support of this premise, we have shown that thiol crosslinking agents can promote RhoA guanine nucleotide dissociation through an ionic pathway. We also provide evidence that thiol oxidation of the redox active cysteine in the P-loop of Rac1 modulates Rac1 guanine nucleotide exchange. Thus, redox active Rho GTPases may be regulated by a variety of redox agents through both ionic and radical-mediated pathways. Finally, we provide evidence that reactive oxygen species directly affect the activity of RhoA via cysteine modification in a cellular context. These results, taken together, suggest that Rho GTPases can be directly modified by both radical and non-radical thiol oxidants to regulate cellular function.