A Novel Endoplasmic Reticulum Export Signal PROLINE AT THE + 2-POSITION FROM THE SIGNAL PEPTIDE CLEAVAGE SITE
A Novel Endoplasmic Reticulum Export Signal PROLINE AT THE + 2-POSITION FROM THE SIGNAL PEPTIDE CLEAVAGE SITE
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DOI：
10.1074/jbc.m109.021592
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发表时间：
2009-10-02
影响因子：
4.8
通讯作者：
Tomida, Akihiro
中科院分区：
文献类型：
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作者：
Tsukumo, Yoshinori;Tsukahara, Satomi;Tomida, Akihiro
NUCB 1（nucleobindin 1）是一种定位于高尔基体的可溶性蛋白，具有信号肽和多个功能结构域。我们最近报道NUCB 1是未折叠蛋白反应的负调节因子，激活各种内质网（ER）起源的信号通路。在该报告中，我们还表明，高尔基体定位NUCB 1是必不可少的调节未折叠的蛋白质反应。然而，NUCB 1的定位机制仍然是未知的。在这里，我们报告的脯氨酸残基在+2-位置（Pro（+2））的信号肽切割位点是决定NUCB 1蛋白出口从ER和随后的运输到高尔基体。N-末端氨基酸1-35肽区，包括信号肽（氨基酸1-26）和Pro（+2）的融合，足以使增强的绿色荧光蛋白定位于高尔基体，而Pro（+2）的单个氨基酸突变导致从ER的缺陷输出而不影响蛋白质成熟过程。此外，我们证明了Pro（+2）对于增强型绿色荧光蛋白融合蛋白在ER内的运输囊泡形成位点（通常称为ER出口位点）浓缩是重要的。有趣的是，这种Pro（+2）在其他高尔基体定位的可溶性蛋白中也是功能保守的，Cab 45（45 kDa的Ca 2+结合蛋白），网织红蛋白1和钙调蛋白。我们的研究结果表明，Pro（+2）可以作为一种新的内质网输出信号的一些高尔基体蛋白。
NUCB1 (nucleobindin 1) is a Golgi-localized soluble protein with a signal peptide and multiple functional domains. We reported recently that NUCB1 is a negative regulator of the unfolded protein response that activates various endoplasmic reticulum (ER)-originating signaling pathways. In that report, we also showed that Golgi localization of NUCB1 was essential to regulate the unfolded protein response. However, the localization mechanism of NUCB1 is still unknown. Here, we report that the proline residue at the +2-position (Pro(+2)) from the signal peptide cleavage site is the determinant of NUCB1 protein export from the ER and subsequent transport to the Golgi. Fusion of the N-terminal amino acids 1-35 peptide region, including both signal peptide (amino acids 1-26) and Pro(+2), was sufficient for enhanced green fluorescent protein to localize in the Golgi, whereas single amino acid mutation of Pro(+2) resulted in defective export from the ER without affecting the protein maturation process. Furthermore, we demonstrated that Pro(+2) was important for the enhanced green fluorescent protein fusion protein to concentrate at a transport vesicle formation site within the ER, often termed the ER exit site. Interestingly, such a Pro(+2) has also been functionally conserved in other Golgi-localized soluble proteins, Cab45 (Ca2+-binding protein of 45 kDa), reticulocalbin 1, and calumenin. Our findings indicate that Pro(+2) can function as a novel ER export signal of some Golgi proteins.