ADP ribosylation factor

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ADP-ribosylation factors (ARFs) are small GTP-binding proteins in the Ras superfamily found in all eukaryotic cells. In mammals, six ARFs are highly conserved (ARF1–ARF6) and they mostly work at membranes thanks to a lipid modification added to their N-terminus. ARFs regulate vesicle formation and can also influence actin remodeling.

ARFs switch between an inactive GDP-bound form and an active GTP-bound form. This GDP/GTP cycle is controlled by GTPase-activating proteins (GAPs), which promote GTP hydrolysis, and guanine nucleotide exchange factors (GEFs), which promote exchange of GDP for GTP. The switch involves two regions that change shape when GDP or GTP is bound; in some ARFs, an additional interswitch region and the N-terminus help coordinate these changes.

When bound to GTP, ARFs bind to vesicle coat proteins and lipids to promote coat assembly, guiding vesicle formation. In the GDP-bound form, they tend to interact with other membrane proteins and do not promote coat assembly.

ARFs are part of a larger family that includes ARLs, ARPs, and Sar proteins. The six mammalian ARFs are ARF1, ARF2, ARF3, ARF4, ARF5, and ARF6.