Kodera Chie, Yorimitsu Tomohiro, Sato Ken
From the Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 and.
the Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan.
J Biol Chem. 2014 Aug 1;289(31):21423-32. doi: 10.1074/jbc.M114.553917. Epub 2014 Jun 19.
The coat protein complex II (COPII) generates transport carriers from the endoplasmic reticulum (ER) under the control of the small GTPase Sar1. Sec23 is well known as a structural component of the COPII coat and as a GTPase-activating protein (GAP) for Sar1. Here, we showed that Saccharomyces cerevisiae contains a novel Sec23 paralog, Nel1, which appears not to function as a subunit of the COPII coat. Nel1 does not associate with any of the COPII components, but it exhibits strong Sar1 GAP activity. We also demonstrated that the chromosomal deletion of NEL1 leads to a significant growth defect in the temperature-sensitive sar1D32G background, suggesting a possible functional link between these proteins. In contrast to Sec23, which is predominantly localized at ER exit sites on the ER membrane, a major proportion of Nel1 is localized throughout the cytosol. Our findings highlight a possible role of Nel1 as a novel GAP for Sar1.
在小GTP酶Sar1的控制下，II型被膜小泡蛋白复合物（COPII）从内质网（ER）产生运输载体。Sec23作为COPII衣被的结构成分以及Sar1的GTP酶激活蛋白（GAP）而广为人知。在此，我们发现酿酒酵母含有一种新的Sec23旁系同源物Nel1，它似乎并不作为COPII衣被的亚基发挥作用。Nel1不与任何COPII成分结合，但它表现出很强的Sar1 GAP活性。我们还证明，NEL1的染色体缺失会导致温度敏感型sar1D32G背景下显著的生长缺陷，这表明这些蛋白质之间可能存在功能联系。与主要定位于内质网膜上内质网出口位点的Sec23不同，大部分Nel1定位于整个细胞质中。我们的发现突出了Nel1作为Sar1新GAP的可能作用。
