Human very low density lipoprotein structure: Interaction of the C apolipoproteins with apolipoprotein B-100

C. Y. Yang, Z. W. Gu, N. Valentinova, H. J. Pownall, B. Lee, M. Yang, Y. H. Xie -, J. R. Guyton, T. N. Vlasik, J. C. Fruchart, A. M. Gotto

Research output: Contribution to journalArticle

20 Scopus citations

Abstract

Very low density lipoproteins (VLDL) are a heterogenous population of particles differing in size and composition. Heparin-Sepharose chromatography yields three VLDL subfractions. Two subfractions, VLDL(NR-1) and VLDL(NR-2), which are not retained by heparin, contain little or no detectable apolipoprotein (apo)E. According to negative stain electron microscopy, VLDL(NR-1) is slightly larger than VLDL(NR-2). The third fraction, VLDL(R), is composed of smaller particles that are retained by the heparin-Sepharose and contain apoE. The C apolipoproteins of the respective VLDL subfractions transfer to 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC) single bilayer vesicles giving three subfractions designated VLDL(NR-1)-C, VLDL(NR-2)-C, and VLDL(R)-C. The protein, phospholipid, and cholesterol (free + esterified) contents decrease in the order VLDL(R)>VLDL(NR-2)>VLDL(NR-1). Triglyceride content decreases in the opposite order. POPC treatment of each VLDL subfraction increases the phospholipid and decreases the protein, triglyceride, and cholesteryl ester contents, while free cholesterol remains unchanged. According to immunological analysis of each subfraction with well- characterized monoclonal antibodies, the accessibility of some epitopes of apoB-100 on VLDL is changed by POPC treatment. Electron-microscopic analysis of POPC-treated VLDL subfraction reveals vacancies on the surfaces of each particle. VLDL(NR-1), VLDL(NR-2), and VLDL(R) are resistant to thrombin cleavage, whereas the lipoproteins lacking C apolipoproteins are not. Thrombin cleavage (8 h) of apoB-100 of VLDL(NR-2)-C and VLDL(R)-C gives two fragments, T1 and T2, that are converted to smaller fragments only after prolonged treatment. In contrast, apoB-100 of VLDL(NR-1)-C is converted into small fragments after 8 h thrombin treatment. These results suggest that removal of apoCs affects the accessibility and conformation of apoB-100 in the individual VLDL subfractions in the region near residue 3249, which is the primary thrombin cleavage site and the epitope of monoclonal antibody 4C11.

Original languageEnglish (US)
Pages (from-to)1311-1321
Number of pages11
JournalJournal of lipid research
Volume34
Issue number8
StatePublished - 1993

Keywords

  • 1-palmitoyl- 2-olcoyl-phosphatidylcholine
  • conformation of apoB-100
  • thrombic cleavage
  • VLDL subfraction

ASJC Scopus subject areas

  • Endocrinology

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