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Authors: Yoko Shiba, Ruibai Luo, Jenny E. Hinshaw, Tomasz Szul, Ryo Hayashi, Elizabeth Sztul, Kunio Nagashima, Ulrich Baxa and Paul A. Randazzo

Yoko Shiba

Laboratory of Cellular and Molecular BIology; National Cancer Institute, Bethesda, MD USA

Ruibai Luo

Laboratory of Cellular and Molecular BIology; National Cancer Institute, Bethesda, MD USA

Jenny E. Hinshaw

National Institute of Diabetes and Digestive and Kidney Disease; National Institutes of Health; Bethesda, MD USA

Tomasz Szul

Department of Cell Biology; The University of Alabama at Birmingham; Birmingham, AL USA

Ryo Hayashi

Laboratory of Cell Biology; National Cancer Institute; Bethesda, MD USA

Elizabeth Sztul

Department of Cell Biology; The University of Alabama at Birmingham; Birmingham, AL USA

Kunio Nagashima

Electron Microscopy Laboratory, ATP, SAIC-Frederick, Center for Cancer Research, National Cancer Institute; Frederick, MD USA

Ulrich Baxa

Electron Microscopy Laboratory, ATP, SAIC-Frederick, Center for Cancer Research, National Cancer Institute; Frederick, MD USA

Paul A. Randazzo

Corresponding author: randazzp@mail.nih.gov
Laboratory of Cellular and Molecular BIology; National Cancer Institute, Bethesda, MD USA

Abstract:
The role of ArfGAP1 in COPI vesicle biogenesis has been controversial. In work using isolated Golgi membranes, ArfGAP1 was found to promote COPI vesicle formation. In contrast, in studies using large unilamellar vesicles (LUVs) as model membranes, ArfGAP1 functioned as an uncoating factor inhibiting COPI vesicle formation. We set out to discriminate between these models. First, we reexamined the effect of ArfGAP1 on LUVs. We found that ArfGAP1 increased the efficiency of coatomer-induced deformation of LUVs. Second, ArfGAP1 and peptides from cargo facilitated self-assembly of coatomer into spherical structures in the absence of membranes, reminiscent of clathrin self-assembly. Third, in vivo, ArfGAP1 overexpression induced the accumulation of vesicles and allowed normal trafficking of a COPI cargo. Taken together, these data support the model in which ArfGAP1 promotes COPI vesicle formation and membrane traffic and identify a function for ArfGAP1 in the assembly of coatomer into COPI.

Received: June 1, 2011; Accepted: November 29, 2011

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