Abstract
The small GTPase Arf1 of the RAS superfamily plays an important role in vesicular trafficing. On the Golgi membrane, the formation and fission of coat protein I (COPI) transport vesicles proceeds via local deformation of the lipid bilayer by a curvature generating COPI protein coat. The assembly of this complex is initiated by the GTPase Arf1 in a nucleotide-dependent manner. After GDP/GTP exchange, soluble Arf1 becomes membrane bound by insertion of its myristoylated N-terminal amphipathic helix (myrAH) into the proximal leaflet of the Golgi membrane. The subsequent liberation of transport vesicles requires the full COPI complex and has been observed in vivo and in vitro.As the role of Arf1 in the process of curvature induction has not been fully elucidated, we have studied binding and incorporation of recombinant S. cerevisiae Arf1p into lipid mono- and bilayers using binding assays with a Langmuir film balance setup and artificial, unilamellar liposomes. We observe myristoylation-dependent binding to membranes and an increase in membrane surface area upon addition of Arf1p. Confocal laser scanning microscopy and cryo electron microscopy reveal highly curved membrane structures upon incorporation of myristoylated Arf1p. Our results support a mechanism of curvature induction based on the bilayer couple theory.
Published Version
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