Fig. 1: AArfs form a clade in the Arf GTPase family.

a The role of inward budding in the establishment of eukaryotic endomembrane system. Inward membrane budding refers to the bending of membrane towards the cytosol, either from the surface of organelles or from the plasma membrane. Inward budding supports endomembrane organelle biogenesis either by forming organelle precursors, such as in peroxisome biogenesis, or by forming transport vesicles that supply organelle building blocks. Outward budding refers to the projecting of membrane away from the cytosol, either into the extracellular space or into the lumen of organelles. Outward budding is often employed for disposal of materials to the outside or into the lumen of endocytic/lytic organelles. b Phylogeny of AArfs in relation to other small GTPases. Maximum likelihood phylogenetic tree of small GTPases based on aligned amino acid sequences (179 positions) using IQ-TREE with the LG + R10 model. Branch support values were assessed with the Ultrafast bootstrap algorithm and the SH-aLRT test (both 1000 replicates). c Structural similarity between AArfs and Arf. Structures of AArfs were generated using AlphaFold2. An alignment of yeast Arf1 (PDB: 2K5U) and two AArfs is shown on top. d The G-box motifs are conserved in AArfs. Shown are sequence logos of G-boxes in eukaryotic Arfs, AArfs, and eukaryotic Rabs. e Switch regions are conserved in AArfs. Shown are sequence logos of switch I, II and inter-switch regions in eukaryotic Arfs, AArfs, and eukaryotic Rabs. f Key surface regions, including the guanine nucleotide binding pocket and the effector interacting surface (denoted by yellow circle), are conserved in AArfs. Surface fill models of AArf and eukaryotic Arf are colored by the level of sequence conservation.