ARF1GTP

Arf1GTP is the GTP-bound, active state of ADP-ribosylation factor 1 (ARF1), a small GTPase of the ARF family that regulates membrane trafficking within the early secretory pathway. In cells, ARF1 cycles between a GDP-bound, cytosolic form bound to the GDP-dissociation inhibitor (GDI) and a GTP-bound, membrane-associated form. Guanine nucleotide exchange factors (GEFs), such as GBF1, promote the exchange of GDP for GTP, enabling ARF1 to insert its N-terminal myristoylated amphipathic helix into membranes and become Arf1GTP. This activation triggers conformational changes that allow ARF1GTP to recruit effector proteins to membranes.

The primary role of Arf1GTP is to drive vesicle formation at the Golgi apparatus. It recruits the COPI coatomer complex to Golgi membranes, facilitating retrograde transport from the Golgi back to the endoplasmic reticulum and supporting overall Golgi architecture. Arf1GTP also participates in lipid signaling and membrane remodeling by stimulating enzymes such as phospholipase D and by influencing phosphoinositide dynamics, which help generate membrane curvature and organize trafficking sites.

Cycle and regulation are tightly controlled: GTP hydrolysis to GDP, accelerated by GTPase-activating proteins (GAPs) including ARFGAPs, returns ARF1 to its inactive cytosolic state, leading to coat disassembly and recycling of ARF1. Proper cycling of Arf1 between its GTP- and GDP-bound forms is essential for Golgi function, cargo sorting, and vesicle trafficking in eukaryotic cells.