Zuber C, Fan J Y, Guhl B, Parodi A, Fessler J H, Parker C, Roth J
Division of Cell and Molecular Pathology, Department of Pathology, University of Zurich, CH-8091 Zurich, Switzerland.
Proc Natl Acad Sci U S A. 2001 Sep 11;98(19):10710-5. doi: 10.1073/pnas.191359198. Epub 2001 Sep 4.
The UDP-glucose:glycoprotein glucosyltransferase (GT) is a protein folding sensor and glycosyltransferase that constitutes an important component of the protein quality control machinery. With the use of quantitative immunogold electron microscopy, we established the subcellular distribution of GT in rat liver and pancreas and Drosophila melanogaster salivary gland as well as cell lines and correlated it with that of glucosidase II, calreticulin, and pre-Golgi intermediate markers. Labeling for GT, as well as for glucosidase II and calreticulin, was found in the endoplasmic reticulum (ER), including nuclear envelope and pre-Golgi intermediates located between ER and Golgi apparatus, and in the cell periphery. In the rough ER, labeling for GT was inhomogeneous, with variously sized labeled and unlabeled cisternal regions alternating, indicative of a meshwork of quality control checkpoints. Notably, labeling intensity for GT was highest in pre-Golgi intermediates, corresponding to twice that of rough ER, whereas the Golgi apparatus exhibited no specific labeling. These results suggest that protein quality control is not restricted to the ER and that the pre-Golgi intermediates, by virtue of the presence of GT, glucosidase II, and calreticulin, are involved in this fundamental cellular process.
UDP-葡萄糖：糖蛋白葡糖基转移酶（GT）是一种蛋白质折叠传感器和糖基转移酶，是蛋白质质量控制机制的重要组成部分。通过定量免疫金电子显微镜技术，我们确定了GT在大鼠肝脏、胰腺、果蝇唾液腺以及细胞系中的亚细胞分布，并将其与葡糖苷酶II、钙网蛋白和高尔基体前体中间标志物的分布进行了关联。在内质网（ER）中发现了GT以及葡糖苷酶II和钙网蛋白的标记，包括核膜和位于ER与高尔基体之间的高尔基体前体中间物，以及细胞周边。在粗面内质网中，GT的标记是不均匀的，大小不同的标记和未标记的潴泡区域交替出现，这表明存在质量控制检查点网络。值得注意的是，GT在高尔基体前体中间物中的标记强度最高，是粗面内质网的两倍，而高尔基体则没有特异性标记。这些结果表明，蛋白质质量控制并不局限于内质网，并且由于GT、葡糖苷酶II和钙网蛋白的存在，高尔基体前体中间物参与了这一基本细胞过程。
