Aromatic residues in the C terminus of apolipoprotein C-III mediate lipid binding and LPL inhibition.
Plasma apoC-III levels correlate with triglyceride (TG) levels and are a strong predictor of CVD outcomes. ApoC-III elevates TG in part by inhibiting LPL. ApoC-III likely inhibits LPL by competing for lipid binding. To probe this, we used oil-drop tensiometry to characterize binding of six apoC-III variants to lipid/water interfaces. This technique monitors the dependence of lipid binding on surface pressure, which increases during TG hydrolysis by LPL. ApoC-III adsorption increased surface pressure by upward of 18 mN/m at phospholipid/TG/water interfaces. ApoC-III was retained to high pressures at these interfaces, desorbing at 21-25 mN/m. Point mutants, which substituted alanine for aromatic residues, impaired the lipid binding of apoC-III. Adsorption and retention pressures decreased by 1-6 mN/m in point mutants, with the magnitude determined by the location of alanine substitutions. Trp42 was most critical to mediating lipid binding. These results strongly correlate with our previous results, linking apoC-III point mutants to increased LPL binding and activity at lipid surfaces. We propose that aromatic residues in the C-terminal half of apoC-III mediate binding to TG-rich lipoproteins. Increased apoC-III expression in the hypertriglyceridemic state allows apoC-III to accumulate on lipoproteins and inhibit LPL by preventing binding and/or access to substrate.
Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA.|Department of Virology and Immunology, Gladstone Institutes, San Francisco, CA.
Nathan L
NL
Meyers
Department of Medicine, University of California, Los Angeles, Los Angeles, CA.
Mikael
M
Larsson
Department of Medical Biosciences/Physiological Chemistry, Umeå University, Umeå, Sweden.
Evelina
E
Vorrsjö
Department of Medical Biosciences/Physiological Chemistry, Umeå University, Umeå, Sweden.
Gunilla
G
Olivecrona
Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA dmsmall@bu.edu.
Donald M
DM
Small
D000327:Adsorption; D000595:Amino Acid Sequence; D053304:Apolipoprotein C-II / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D050356:Lipid Metabolism; D008071:Lipoprotein Lipase / Q000037:antagonists & inhibitors*; D009154:Mutation; D013329:Structure-Activity Relationship; D014280:Triglycerides / Q000378:metabolism
D053304:Apolipoprotein C-II; D014280:Triglycerides; D008071:Lipoprotein Lipase
LDL/metabolism; drop tensiometry; lipid and lipoprotein metabolism; lipid/emulsions; lipoprotein lipase; protein-lipid interaction; surface pressure