Exomer: A coat complex for transport of select membrane proteins from the trans-Golgi network to the plasma membrane in yeast.
A yeast plasma membrane protein, Chs3p, transits to the mother-bud neck from a reservoir comprising the trans-Golgi network (TGN) and endosomal system. Two TGN/endosomal peripheral proteins, Chs5p and Chs6p, and three Chs6p paralogues form a complex that is required for the TGN to cell surface transport of Chs3p. The role of these peripheral proteins has not been clear, and we now provide evidence that they create a coat complex required for the capture of membrane proteins en route to the cell surface. Sec7p, a Golgi protein required for general membrane traffic and functioning as a nucleotide exchange factor for the guanosine triphosphate (GTP)-binding protein Arf1p, is required to recruit Chs5p to the TGN surface in vivo. Recombinant forms of Chs5p, Chs6p, and the Chs6p paralogues expressed in baculovirus form a complex of approximately 1 MD that binds synthetic liposomes in a reaction requiring acidic phospholipids, Arf1p, and the nonhydrolyzable GTPgammaS. The complex remains bound to liposomes centrifuged on a sucrose density gradient. Thin section electron microscopy reveals a spiky coat structure on liposomes incubated with the full complex, Arf1p, and GTPgammaS. We termed the novel coat exomer for its role in exocytosis from the TGN to the cell surface. Unlike other coats (e.g., coat protein complex I, II, and clathrin/adaptor protein complex), the exomer does not form buds or vesicles on liposomes.
Wang
Chao-Wen
CW
Department of Molecular Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
Hamamoto
Susan
S
Orci
Lelio
L
Schekman
Randy
R
D020823:ADP-Ribosylation Factor 1 / Q000378:metabolism; D033942:Adaptor Proteins, Vesicular Transport; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D002687:Chitin Synthase / Q000378:metabolism; D018699:Coated Vesicles / Q000502:physiology; D005656:Fungal Proteins / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D009227:Myristic Acids / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D021601:trans-Golgi Network / Q000378:metabolism*
D033942:Adaptor Proteins, Vesicular Transport; C509470:CHS6 protein, S cerevisiae; D002352:Carrier Proteins; D005656:Fungal Proteins; D020662:Guanine Nucleotide Exchange Factors; D008081:Liposomes; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D009227:Myristic Acids; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; C066755:Sec7 guanine nucleotide exchange factors; D002687:Chitin Synthase; D020823:ADP-Ribosylation Factor 1