Structure of the human ADP-ribosylation factor 1 complexed with GDP

ADP-ribosylation factors (ARFs) are essential and ubiquitous in eukaryotes, being involved in vesicular transport and functioning as an activator of phospholipase D (refs 1,2) and cholera toxin^3,4. The functions of ARF proteins in membrane traffic and organelle integrity^5,6 are intimately tied to its reversible association with membranes and specific interactions with membrane phospholipids. One common feature of these functions is their regulation by the binding and hydrolysis of GTP. Here we report the three-dimensional structure of full-length human ARF1 (M_r 21,000) in its GDP-bound non-myristoylated form. The presence of a unique amino-terminal α-helix and loop, together with differences in Mg²⁺ ligation and the existence of a non-crystallographic dimer, set this structure apart from other GTP-binding proteins. These features provide a structural basis for the GTP-dependent modulation of membrane affinity, the lack of intrinsic GTPase activity, and the nature of effector binding surfaces.