The Arf GTPases are regulators of intracellular traffic and signaling. In cells, Arfs undergo a catalytic cycle between an inactive, GDP-bound form, and an active, GTP-bound form, where they act at membranes to direct signaling cascades. This transition from a GDP-bound to a GTP-bound form, and vice versa, involves a large rearrangement of several secondary structural elements, which in vivo is aided by guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs). Despite the high similarity of the endpoint (GDP- and GTP-bound) structures of members of the Arf family, Arf homologs exhibit high specificity for their protein partners and their location within cells. Using a combination of biochemical and biophysical techniques (e.g., NMR, SAXS, and fluorescence) coupled with pressure perturbation, we have shown that small changes within the protein sequence result in significant thermodynamic differences propagated to the switch regions the protein, modulating the GDP to GTP switch. Here, we use the same approaches to examine the conformational landscape of the GTP-bound form of Arf6. Combining these results with those of the GDP-bound, inactive form will help to define a potential pathway for the switching transitions.
Hantman et al. (Sun,) studied this question.