第7章-细胞质基质与内膜系统(翟中和第四版).pptVIP

1.含有(Glc)3 (Man)9 (GlcNAc)2 的寡聚糖首先在内质网磷酸多萜醇载体上组装，然后在糖基转移酶的催化下，寡聚糖基从磷酸多萜醇载体转 移到新生肽链的天冬酰胺残基上 2~3. 在分子伴侣Bip 和蛋白二硫键异构酶的帮助下，蛋白质折叠时，3 个葡萄糖残基分别被葡糖苷酶所切 除（3 a 在内质网蛋白质正确折叠时起作用） 4. 一个 Man 残基被移除，形成(Man)8 (GlcNAc)2 高甘露糖型寡聚糖. * 内质网中有一种蛋白二硫键异构酶（protein disulfide isomerase，PDI），它附着在内质网膜腔面上， 可以切断二硫键，形成自由能最低的蛋白质构象，从 而帮助新合成的蛋白质重新形成二硫键并产生正确折 叠的构象。 * 赖氨酸 天冬氨酸 谷氨酸 亮氨酸 Schematic representation of the ubiquitin-proteasome pathway and the secretory pathway with the quality control machinery that dislocate misfolded proteins from the ER. The acronyms of the transcripts contained in IMP1 granules are indicated in red. For full names refer to Table I (1). Proteins to be glycosylated enter the ER in an unfolded state upon co-translational translocation through the heterotrimeric Sec61 channel. Nascent polypeptides are covalently modified by attachment of high mannose core oligosaccharides. N-Linked glycosylation is carried out by the oligosaccharyltransferase complex. Both DAD1 and DC2 have been identified as members of the large oligosaccharyltransferase complex (54). In the ER, the core glycan Glc3Man9GlcNAc2 is trimmed by ER glucosidases I and II and ER mannosidase I (MANBAL and MANEAL) before glycoproteins become competent to leave this compartment. Biosynthesis of a glycosylphosphatidylinositol anchor depends on the presence of phosphatidylinositol glycan (PIG) of which PIGF, -H, and -S are members (2). If proteins are correctly folded they can leave the ER through COPII-coated vesicles, which coordinate the budding of transport vesicles from the endoplasmic reticulum in the initial step of the secretory pathway. Among others the Sec13/31 subcomplex takes part in organizing this process (55). Another component necessary for this transport is Yif1 (56). In the Golgi apparatus, proteins can be packed into secretory vesicles at the trans-Golgi network where members of the secretory carrier membrane protein (SCAMP) gene family and Arf1 are located (57). Proteins destined for the lysosome are