Cargo selection into COPII vesicles is driven by the Sec24p subunit.
Transport of secretory proteins out of the endoplasmic reticulum (ER) is mediated by vesicles generated by the COPII coat complex. In order to understand how cargo molecules are selected by this cytoplasmic coat, we investigated the functional role of the Sec24p homolog, Lst1p. We show that Lst1p can function as a COPII subunit independently of Sec24p on native ER membranes and on synthetic liposomes. However, vesicles generated with Lst1p in the absence of Sec24p are deficient in a distinct subset of cargo molecules, including the SNAREs, Bet1p, Bos1p and Sec22p. Consistent with the absence of any SNAREs, these vesicles are unable to fuse with Golgi membranes. Furthermore, unlike Sec24p, Lst1p fails to bind to Bet1p in vitro, indicating a direct correlation between cargo binding and recruitment into vesicles. Our data suggest that the principle role of Sec24p is to discriminate cargo molecules for incorporation into COPII vesicles.
Miller
Elizabeth
E
Department of Molecular and Cell Biology and Howard Hughes Medical Institute, University of California, Berkeley, CA 94720-3202, USA.
Antonny
Bruno
B
Hamamoto
Susan
S
Schekman
Randy
R
D022181:COP-Coated Vesicles / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008561:Membrane Fusion; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000378:metabolism; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D021122:Protein Subunits; D021381:Protein Transport / Q000502:physiology*; D050767:Qc-SNARE Proteins; D050600:SNARE Proteins; D012441:Saccharomyces cerevisiae / Q000378:metabolism* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D013329:Structure-Activity Relationship; D033921:Vesicular Transport Proteins
C107845:BET1 protein, S cerevisiae; D008081:Liposomes; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D021122:Protein Subunits; D050767:Qc-SNARE Proteins; C118289:SEC24 protein, S cerevisiae; C120079:SFB3 protein, S cerevisiae; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D020559:Monomeric GTP-Binding Proteins; C077395:SAR1 protein, S cerevisiae