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Lipoprotein assembly. Apolipoprotein B size determines lipoprotein core circumference
D J Spring1, L W Chen-Liu, J E Chatterton
1Department of Chemistry and Biochemistry, University of California, Los Angeles 90024.
The Journal of Biological Chemistry
|July 25, 1992
Summary
Apolipoprotein B (apoB) fragment length directly correlates with lipoprotein core circumference, revealing a key mechanism in lipoprotein assembly. This finding impacts understanding of lipid metabolism and related diseases.
Area of Science:
- Biochemistry
- Molecular Biology
- Lipid Metabolism
Background:
- Apolipoprotein B (apoB) is crucial for synthesizing triglyceride-rich lipoproteins like chylomicrons and very low-density lipoproteins.
- While apoB's role in lipoprotein clearance is known, its function in nascent lipoprotein assembly is less understood.
Purpose of the Study:
- To investigate the relationship between N-terminal apoB fragment length and the characteristics of associated lipoproteins.
- To elucidate the mechanism of lipoprotein assembly in HepG2 cells.
Main Methods:
- HepG2 cells were treated with puromycin to secrete C-terminally truncated apoB fragments.
- Plasmids encoding specific apoB fragments were used for transient transfection in HepG2 cells.
- Metabolically labeled lipoproteins were isolated and characterized by size, density, flotation, and composition.
Main Results:
- A series of C-terminally truncated apoB fragments (e.g., apoB25 to apoB80) were secreted on lipoprotein particles.
- Lipoprotein radii, derived from flotation coefficients and densities, correlated with apoB fragment size.
- A linear relationship was observed between apoB size and lipoprotein core circumference (approx. 1 Å/kDa).
Conclusions:
- Apolipoprotein B fragment size is a primary determinant of lipoprotein core circumference.
- A model for lipoprotein assembly is proposed, emphasizing the role of apoB size in determining lipoprotein particle dimensions.