Characterization of the lipid-binding properties and lipoprotein lipase inhibition of a novel apolipoprotein C-III variant Ala23Thr

• Published in: Journal of lipid research 2000-11, Vol.41 (11), p.1760-1771
• Main Authors: Liu, H, Labeur, C, Xu, C F, Ferrell, R, Lins, L, Brasseur, R, Rosseneu, M, Weiss, K M, Humphries, S E, Talmud, P J
• Format: Article
• Language: English
• Subjects: 1,2-Dipalmitoylphosphatidylcholine - metabolism; Amino Acid Sequence; apoE displacement; Apolipoprotein C-III; Apolipoproteins C - deficiency; Apolipoproteins C - genetics; Apolipoproteins C - metabolism; Apolipoproteins E - metabolism; Biochemistry, biophysics & molecular biology; Biochimie, biophysique & biologie moléculaire; Central America; Chemical Phenomena; Chemistry, Physical; Dimyristoylphosphatidylcholine - metabolism; DMPC; DNA Mutational Analysis; Enzyme Inhibitors - pharmacology; genetic variation; Humans; Indians, Central American; Life sciences; lipid binding; Lipid Metabolism; Lipoprotein Lipase - antagonists & inhibitors; LPL inhibition; Male; Middle Aged; Models, Molecular; Molecular Sequence Data; Mutation; Polymerase Chain Reaction; Recombinant Proteins - pharmacology; Sciences du vivant
• ISSN: 0022-2275; 1539-7262
• DOI: 10.1016/s0022-2275(20)31969-6

We have identified a G-to-A transition in exon 3 of the APOC3 gene resulting in a novel Ala23Thr apolipoprotein (apo) C-III variant, associated with apoC-III deficiency in three unrelated Yucatan Indians. The Ala23Thr substitution modifies the hydrophobic/hydrophilic repartition of the helical N-terminal peptide and hence could disturb the lipid association. In vitro expression in Escherichia coli of wild-type and mutant apoC-III enabled the characterization of the variant. Compared with wild-type apoC-III-Ala23, the mutant apoC-III-Thr23 showed reduced affinity for dimyristoylphosphatidylcholine (DMPC) multilamellar vesicles with higher amounts of free apoC-III. Displacement of apoE from discoidal apoE:dipalmitoylphosphatidycholine (DPPC) complex by apoC-III-Thr23 was comparable to wild type but the less efficient binding of the apoC-III-Thr23 to the discoidal complex resulted in a higher apoE/apoC-III (mol/mol) ratio (34%) than with wild-type/apoE:DPPC mixtures. The inhibition of lipoprotein lipase (LPL) by apoC-III-Thr23 was comparable to that of wild type, and therefore effects on LPL activity could not explain the lower triglyceride (Tg) levels in Thr-23 carriers. Thus, these in vitro results suggest that in vivo the less efficient lipid binding of apoC-III-Thr23 might lead to a faster catabolism of free apoC-III, reflected in the reduced plasma apoC-III levels identified in Thr-23 carriers, and poorer competition with apoE, which might enhance clearance of Tg-rich lipoproteins and lower plasma Tg levels seen in Thr-23 carriers.