Arl1p regulates spatial membrane organization at the trans -Golgi network through interaction with Arf-GEF Gea2p and flippase Drs2p

Abstract

Significance Membrane asymmetry, curvature, and dynamics have major roles in cellular processes, including vesicle transport. The GTPase ADP ribosylation factor (Arf) and a lipid translocase (flippase) are critical for membrane reorganization during vesicle formation. Direct evidence that Arf and flippase work in concert on membrane transformation/architecture is, however, lacking. We demonstrate that activated Arf-like protein Arl1 interacts with the Arf-activating guanine nucleotide-exchange factor Gea2 and flippase Drs2, forming a ternary complex that is required for lipid asymmetry and Arl1 function at the Golgi. These findings represent a previously missing piece of the puzzle that is our understanding of Arf-mediated membrane remodeling.

Arl1 gets into the membrane remodeling business with a flippase and ArfGEF

“…An N-terminal fragment of the ArfGEF Gea2 was identified as a potential Arl1 binding protein. This binding is shown to be direct, GTP-dependent, and confined to a site within the first 250 aa of Gea2 containing its dimerization and cyclophilin binding domain (2).…”

“…TGN. Therefore, Tsai et al predict that there must be other effectors of Arl1, and they perform a yeast two-hybrid screen using a "GTP-locked" mutant form of Arl1 (Q72L mutation) as bait (2). An N-terminal fragment of the ArfGEF Gea2 was identified as a potential Arl1 binding protein.…”

“…Tsai et al then ask if Arl1 is part of this Drs2-Gea2 complex and helps to stimulate flippase activity (2). The answer to these questions was yes.…”

“…However, a few links between Arfs and lipid modifying events have been reported (1). In PNAS, Tsai et al report a unique function for Arl1, arguably the least understood member of the Arf family, in stimulating the activity of a phospholipid flippase in the trans-Golgi network (TGN) of budding yeast (2). Remarkably, this function of Arl1 also requires interaction with an ArfGEF (not an ArlGEF), infusing a bit of intrigue into the Arf family tree.…”

“…Remarkably, this function of Arl1 also requires interaction with an ArfGEF (not an ArlGEF), infusing a bit of intrigue into the Arf family tree. These interactions are shown to be important for protein transport from the Golgi and the establishment of membrane asymmetry (2) (Fig. 1).…”