Miller Elizabeth, Antonny Bruno, Hamamoto Susan, Schekman Randy
Department of Molecular and Cell Biology and Howard Hughes Medical Institute, University of California, Berkeley, CA 94720-3202, USA.
EMBO J. 2002 Nov 15;21(22):6105-13. doi: 10.1093/emboj/cdf605.
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.
分泌蛋白从内质网（ER）的输出由COPII包被复合体产生的囊泡介导。为了了解货物分子是如何被这种细胞质包被选择的，我们研究了Sec24p同源物Lst1p的功能作用。我们发现，Lst1p可以在天然内质网膜和合成脂质体上独立于Sec24p作为COPII亚基发挥作用。然而，在没有Sec24p的情况下由Lst1p产生的囊泡在一个独特的货物分子亚群中存在缺陷，包括SNARE蛋白Bet1p、Bos1p和Sec22p。与缺乏任何SNARE蛋白一致，这些囊泡无法与高尔基体膜融合。此外，与Sec24p不同，Lst1p在体外不能与Bet1p结合，表明货物结合与招募到囊泡之间存在直接关联。我们的数据表明，Sec24p的主要作用是区分货物分子以便纳入COPII囊泡。
