Discrete determinants in ArfGAP2/3 conferring Golgi localization and regulation by the COPI coat.

From yeast to mammals, two types of GTPase-activating proteins, ArfGAP1 and ArfGAP2/3, control guanosine triphosphate (GTP) hydrolysis on the small G protein ADP-ribosylation factor (Arf) 1 at the Golgi apparatus. Although functionally interchangeable, they display little similarity outside the catalytic GTPase-activating protein (GAP) domain, suggesting differential regulation. ArfGAP1 is controlled by membrane curvature through its amphipathic lipid packing sensor motifs, whereas Golgi targeting of ArfGAP2 depends on coatomer, the building block of the COPI coat.

Topology of amphipathic motifs mediating Golgi localization in ArfGAP1 and its splice isoforms.

The interaction of the Arf1-directed GTPase-activating protein ArfGAP1 with the Golgi apparatus depends on motifs in its noncatalytic part that are unstructured in solution but are capable of folding into amphipathic helices in vitro upon interaction with poorly packed lipids. In previous studies a few hydrophobic residues that are critical for lipid binding and Golgi localization were identified, but the precise topology of the amphipathic motifs has not been determined. Here we present a detailed analysis of the Golgi targeting and in vitro folding features of the region encompassing the amphipathic motifs (residues 199-294).