Laboratory of Molecular and Cell Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
J Cell Biol. 2012 Apr 16;197(2):209-17. doi: 10.1083/jcb.201111115.
The endoplasmic reticulum (ER) forms a network of tubules and sheets that requires homotypic membrane fusion to be maintained. In metazoans, this process is mediated by dynamin-like guanosine triphosphatases (GTPases) called atlastins (ATLs), which are also required to maintain ER morphology. Previous work suggested that the dynamin-like GTPase Sey1p was needed to maintain ER morphology in Saccharomyces cerevisiae. In this paper, we demonstrate that Sey1p, like ATLs, mediates homotypic ER fusion. The absence of Sey1p resulted in the ER undergoing delayed fusion in vivo and proteoliposomes containing purified Sey1p fused in a GTP-dependent manner in vitro. Sey1p could be partially replaced by ATL1 in vivo. Like ATL1, Sey1p underwent GTP-dependent dimerization. We found that the residual ER-ER fusion that occurred in cells lacking Sey1p required the ER SNARE Ufe1p. Collectively, our results show that Sey1p and its homologues function analogously to ATLs in mediating ER fusion. They also indicate that S. cerevisiae has an alternative fusion mechanism that requires ER SNAREs.
内质网（ER）形成了一个管状和片状的网络，需要同源膜融合来维持。在后生动物中，这个过程是由称为 atlastins（ATLs）的类似于 dynamin 的鸟苷三磷酸酶（GTPases）介导的，ATLs 也需要维持 ER 形态。以前的工作表明，类似于 dynamin 的 GTPase Sey1p 对于维持酿酒酵母中的 ER 形态是必需的。在本文中，我们证明 Sey1p 与 ATLs 一样，介导同源 ER 融合。Sey1p 的缺失导致 ER 在体内融合延迟，并且含有纯化的 Sey1p 的脂蛋白体在体外以 GTP 依赖性方式融合。Sey1p 可以在体内部分被 ATL1 取代。与 ATL1 一样，Sey1p 经历 GTP 依赖性二聚化。我们发现，在缺乏 Sey1p 的细胞中发生的残留 ER-ER 融合需要 ER SNARE Ufe1p。总之，我们的结果表明，Sey1p 和其同源物在介导 ER 融合方面与 ATLs 具有类似的功能。它们还表明，酿酒酵母具有需要 ER SNARE 的替代融合机制。
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