A Search for a new chaperone proteins on the endoplasmic retical

在细胞中，大多数分泌蛋白和膜蛋白在内质网（ER）中合成，只有正确折叠的蛋白被运送到高尔基体进行进一步加工。内质网中存在伴侣蛋白，如GRP78、GRP94、calnexin和calreticulin，它们协助新合成或错误折叠的蛋白折叠。尽管如此，预计重要的伴侣蛋白仍有待于在内质网中恢复。在这项研究中，我在内质网中寻找新的伴侣蛋白，并分析其功能，以阐明内质网中蛋白质折叠的机制和质量控制。为了克隆新的伴侣蛋白，我从内质网应激的细胞中采用了抑制减法杂交（SSH）方法，因为伴侣蛋白在内质网应激下可能会上调。我专注于一个类似于α-甘露糖苷酶的EST克隆。在克隆了该EST克隆的全基因后，我分析了该基因产物在细胞中的功能，并将其命名为EDEM （ER降解增强α-甘露糖酶样蛋白）。EDEM加速了内质网中错误折叠糖蛋白的降解，这取决于n -链寡糖的甘露糖修饰程度，有望成为内质网相关降解或内质网质量控制的关键分子。

In cells, most of the secretory and membrane proteins are synthesized in the endoplasmic reticulum (ER), and only correctly folded proteins are transported to the Golgi apparatus for further processing. There are chaperone proteins such as GRP78, GRP94, calnexin, and calreticulin in the ER, and they assist the folding of newly synthesized or misfolded proteins. Still, it is expected that important chaperone proteins remains to be recovered in the ER.In this study, I searched for new chaperone proteins in the ER, and analyzed its function to clarify the mechanisms of protein folding and the quality control in the ER.To clone new chaperone proteins, I employed supression subtractive hybridization (SSH) method from cells treated with ER stress, because chapereone proteins are expected to be upregulated by ER stress. I focused on an EST clone which was similar to α-mannosidase. After cloning the whole gene of this EST clone, I analyzed the fundction of this gene product in the cells, and named it as EDEM (ER degradation enhancing α-mannosidase-like protein). EDEM accelerated the degradation of misfolded glycoprotein in the ER, depending on the extent of mannose trimming of N-linked oligosaccharides, and expected to be the key molecule of the ER associated degradation or ER quality control.