Vps45p stabilizes the syntaxin homologue Tlg2p and positively regulates SNARE complex formation
Vps45p stabilizes the syntaxin homologue Tlg2p and positively regulates SNARE complex formation
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DOI：
10.1093/emboj/20.13.3380
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发表时间：
2001-07-02
期刊：
影响因子：
11.4
通讯作者：
James, DE
中科院分区：
文献类型：
--
作者：
Bryant, NJ;James, DE
Sec1p-like/Munc-18 （SM）蛋白结合t-SNAREs并抑制三元复合物的形成。矛盾的是，SM蛋白的缺失并不会导致本构膜融合。在这里，我们发现在缺乏SM蛋白Vps45p的酵母细胞中，t-SNARE Tlg2p通过快速蛋白酶体降解被下调至不可检测的水平。在Vps45p缺失的情况下，Tlg2p可以通过取消蛋白酶体活性来稳定。令人惊讶的是，稳定的Tlg2p被靶向到正确的细胞内位置。然而，在缺乏Vps45p的情况下，稳定的Tlg2p是无功能的，不能结合其同源的SNARE结合伙伴Tlg1p和Vti1p。缺乏Tlg2p前230个残基的截断突变体不再结合Vps45p，但能够与Tlg1p和Vti1p形成复合物。这些数据为我们了解SM蛋白的功能提供了两个有价值的见解。首先，SM蛋白作为其同源t-SNARE的伴侣样分子，其次，SM蛋白在激活过程中发挥重要作用，使其同源t-SNARE参与三元复合物的形成。
Sec1p-like/Munc-18 (SM) proteins bind to t-SNAREs and inhibit ternary complex formation. Paradoxically, the absence of SM proteins does not result in constitutive membrane fusion, Here, we show that in yeast cells lacking the SM protein Vps45p, the t-SNARE Tlg2p is down-regulated, to undetectable levels, by rapid proteasomal degradation. In the absence of Vps45p, Tlg2p can be stabilized through abolition of proteasome activity. Surprisingly, the stabilized Tlg2p was targeted to the correct intracellular location. However, the stabilized Tlg2p is non-functional and unable to bind its cognate SNARE binding partners, Tlg1p and Vti1p, in the absence of Vps45p, A truncation mutant lacking the first 230 residues of Tlg2p no longer bound Vps45p but was able to form complexes with Tlg1p and Vti1p in the absence of the SM protein. These data provide us with two valuable insights into the function of SM proteins. First, SM proteins act as chaperone-like molecules for their cognate t-SNAREs, Secondly, SM proteins play an essential role in the activation process allowing their cognate t-SNARE to participate in ternary complex formation.