The N-linked oligosaccharides at the amino terminus of human apoB are important for the assembly and secretion of VLDL

J Lipid Res. 2002 Sep;43(9):1496-507. doi: 10.1194/jlr.m200077-jlr200.

Abstract

We determined the role of N-linked glycosylation of apolipoprotein B (apoB) in the assembly and secretion of lipoproteins using transfected rat hepatoma McA-RH7777 cells expressing human apoB-17, apoB-37, and apoB-50, three apoB variants with different ability to recruit neutral lipids. Substituting Asn residue with Gln at the single glycosylation site within apoB-17 (N(158)) decreased its secretion efficiency to a level equivalent to that of wild-type apoB-17 treated with tunicamycin, but had little effect on its synthesis or intracellular distribution. When selective N-to-Q substitution was introduced at one or more of the five N-linked glycosylation sites within apoB-37 (N(158), N(956), N(1341), N(1350), and N(1496)), secretion efficiency of apoB-37 from transiently transfected cells was variably affected. When all five N-linked glycosylation sites were mutated within apoB-37, the secretion efficiency and association with lipoproteins were decreased by >50% as compared with wild-type apoB-37. Similarly, mutant apoB-50 with all of its N-linked glycosylation sites mutagenized showed decreased secretion efficiency and decreased lipoprotein association in both d < 1.02 and d > 1.02 g/ml fractions. The inability of mutant apoB-37 and apoB-50 to associate with very low-density lipoproteins was attributable to impaired assembly and was not due to the limitation of lipid availability. The decreased secretion of mutant apoB-17 and apoB-37 was not accompanied by accumulation within the cells, suggesting that the proportion of mutant apoB not secreted was rapidly degraded. However unlike apoB-17 or apoB-37, accumulation of mutant apoB-50 was observed within the endoplasmic reticulum and Golgi compartments. These data imply that the N-glycans at the amino terminus of apoB play an important role in the assembly and secretion of lipoproteins containing the carboxyl terminally truncated apoB.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Substitution / genetics
  • Apolipoproteins B / chemistry*
  • Apolipoproteins B / genetics
  • Apolipoproteins B / metabolism*
  • Asparagine / metabolism
  • Glutamine / metabolism
  • Humans
  • Lipoproteins, VLDL / biosynthesis*
  • Lipoproteins, VLDL / metabolism*
  • Oligosaccharides / metabolism*
  • Structure-Activity Relationship
  • Tunicamycin / pharmacology

Substances

  • Apolipoproteins B
  • Lipoproteins, VLDL
  • Oligosaccharides
  • apolipoprotein B-37
  • apolipoprotein b-17
  • Glutamine
  • Tunicamycin
  • Asparagine