文章基本信息

标题：Efficient glycosylation site utilization by intracellular apolipoprotein B: implications for proteasomal degradation
本地全文：下载
作者：Xue F. Huang ; Gregory S. Shelness
期刊名称：JLR Papers In Press
印刷版ISSN：0022-2275
电子版ISSN：1539-7262
出版年度：1999
卷号：40
期号：12
页码：2212-2222
语种：English
出版社：American Society for Biochemistry and Molecular Biology
摘要：The balance between the hepatic assembly of apolipoprotein B (apoB) and its presecretory degradation at the level of the endoplasmic reticulum (ER) may control the secretion of apoB-containing lipoproteins. In one model, apoB that fails to assemble with lipid undergoes translocation arrest, exposing the protein to the cytosolic proteasome. To examine apoB's translocation behavior under various metabolic conditions, glycosylation site utilization studies were performed. A 70-amino acid peptide containing three sites for N-linked glycosylation was appended to the C-terminus of apoB-50 (amino-terminal 50% of apoB) and expressed in both hepatic and nonhepatic cell lines. When the C-terminal reporter peptide was released by cyanogen bromide cleavage, all of the sites were glycosylated irrespective of cell type, labeling time, or assembly status. Similar peptide mapping of endogenous apoB-100 expressed in HepG2 cells was performed to monitor glycosylation at Asn residues 2752 (apoB-61), 2955 (apoB-65), and 3074 (apoB-68). N-linked glycosylation occurred at a minimum of two of the three sites, a frequency identical to that observed in apoB-100 recovered from cell media. Treatment of cells with proteasome inhibitors produced a 2.5-fold increase in intracellular apoB but failed to cause accumulation of an unglycosylated form. These results indicate that 1 ) the efficient translocation of apoB into the ER occurs independently of microsomal triglyceride transfer protein and its assembly with lipid and 2 ) despite its large size and affinity for lipid, delivery of misassembled apoB to the proteasome requires retrograde translocation from the ER lumen to cytosol.— Huang, X. F., and G. S. Shelness. Efficient glycosylation site utilization by intracellular apolipoprotein B: implications for proteasomal degradation. J. Lipid Res. 1999. 40: 2212–2222.
关键词：endoplasmic reticulum ; protein turnover ; proteolysis ; quality control ; translocation ; retrograde translocation ; dislocation ; lipoprotein assembly ; very low density lipoprotein ; HepG2 cells