Membrane-associated small GTPases are key regulators of intracellular trafficking. The small GTPase Arf1, which is involved in the Coat Protein Complex I (COPI) retrograde vesicular machinery, has been reported to form tubular membrane carriers. Arf1 cycles between an inactive GDP-bound state and an active GTP-bound state, whereby exchange to GTP exposes a myristoylated N-terminal amphipathic helix that results in membrane anchoring. Here, we present cryo-EM structures of Arf1-GTPgS-coated membrane tubules at 3.1 Å resolution, revealing polar tubular arrangements of the Arf1-GTPgS globular domains with a consistent back-to-face orientation. Implications of the structure will be discussed.
