title: Sec24C/D-isoform-specific sorting of the preassembled ER-Golgi Q-SNARE complex.
abstract: Secretory proteins are exported from the endoplasmic reticulum in COPII vesicles. SNARE proteins-core machinery for membrane fusion-are incorporated into COPII vesicles by direct interaction with Sec24. Here we report a novel mechanism for sorting of the ER-Golgi Q-SNAREs into COPII vesicles. Different mammalian Sec24 isoforms recruit either the R-SNARE Sec22b or the Q-SNAREs Syntaxin5, GS27, and Bet1. Syntaxin5 is the only Q-SNARE that directly interacts with Sec24C, requiring its "open" conformation. Mutation within the IxM cargo-binding site of Sec24C led to a drastic reduction in sorting of all three Q-SNAREs into COPII vesicles, implying their ER export as a preassembled complex. Analysis of immunoisolated COPII vesicles and intracellular localization of Sec24 isoforms indicate that all ER-Golgi SNAREs are present on the same vesicle. Combined with existing data, our findings yield a general concept of how Sec24 isoforms can recruit fusogenic SNARE subunits to keep them functionally apart and thus prime mammalian COPII vesicles for homotypic fusion.
authors.affiliation: Heidelberg University Biochemistry Center, Heidelberg University, 69120 Heidelberg, Germany Frank.adolf@bzh.uni-heidelberg.de felix.wieland@bzh.uni-heidelberg.de.
authors.forename: Frank
authors.initials: F
authors.lastname: Adolf
authors.affiliation: Heidelberg University Biochemistry Center, Heidelberg University, 69120 Heidelberg, Germany.
authors.forename: Manuel
authors.initials: M
authors.lastname: Rhiel
authors.affiliation: Heidelberg University Biochemistry Center, Heidelberg University, 69120 Heidelberg, Germany.
authors.forename: Ingeborg
authors.initials: I
authors.lastname: Reckmann
authors.affiliation: Heidelberg University Biochemistry Center, Heidelberg University, 69120 Heidelberg, Germany Frank.adolf@bzh.uni-heidelberg.de felix.wieland@bzh.uni-heidelberg.de.
authors.forename: Felix T
authors.initials: FT
authors.lastname: Wieland
mesh_terms: D001665:Binding Sites; D022181:COP-Coated Vesicles / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D008561:Membrane Fusion / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms / Q000378:metabolism; D021381:Protein Transport; D050682:Q-SNARE Proteins / Q000378:metabolism; D050683:R-SNARE Proteins / Q000378:metabolism; D050600:SNARE Proteins / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D020033:Protein Isoforms; D050682:Q-SNARE Proteins; D050683:R-SNARE Proteins; C530638:SEC24A protein, human; C530639:SEC24B protein, human; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins