Structure of an inactive conformation of GTP-bound RhoA GTPase

By using 31P NMR, we present evidence that the Rho family GTPase RhoA, similar to Ras GTPases, exists in an equilibrium of conformations when bound to GTP. High-resolution crystal structures of RhoA bound to the GTP analog GMPPNP and to GDP show that they display a similar overall inactive conformation. In contrast to the previously reported crystal structures of GTP analog-bound forms of two RhoA dominantly active mutants (G14V and Q63L), GMPPNP-bound RhoA assumes an open conformation in the Switch I loop with a previously unseen interaction between the γ-phosphate and Pro36, instead of the canonical Thr37. Molecular dynamics simulations found that the oncogenic RhoAG14V mutant displays a reduced flexibility in the Switch regions, consistent with a crystal structure of GDP-bound RhoAG14V. Thus, GDP- and GTP-bound RhoA can present similar inactive conformations, and the molecular dynamics in the Switch regions are likely to have a role in RhoA activation.