Point mutations in apolipoprotein A-I mimic the phenotype observed in patients with classical lecithin:cholesterol acyltransferase deficiency.

Abstract

We have analyzed the effect of charged to neutral amino acid substitutions around the kinks flanking helices 4 and 6 of apoA-I and of the deletion of helix 6 on the in vivo activity of LCAT and the biogenesis of HDL. The LCAT activation capacity of apoA-I in vitro was nearly abolished by the helix 6 point (helix 6P-apoA-I[R160V/H162A]) and deletion {helix 6Delta-apoA-I[Delta(144-165)]} mutants, but was reduced to 50% in the helix 4 point mutant (helix 4P-apoA-I[D102A/D103A]). Following adenovirus-mediated gene transfer in apoA-I deficient mice, the level of plasma HDL cholesterol was greatly reduced in helix 6P and helix 6Delta mutants. Electron microscopy and two-dimensional gel electrophoresis showed that the helix 6P mutant formed predominantly high levels of apoA-I containing discoidal particles and had an increased prebeta1-HDL/alpha-HDL ratio. The helix 6Delta mutant formed few spherical particles and had an increased prebeta1-HDL/alpha-HDL ratio. Mice infected with adenovirus expressing the helix 4P mutant or wild-type apoA-I had normal HDL cholesterol and formed spherical alpha-HDL particles. Coinfection of mice with adenoviruses expressing human LCAT and the helix 6P mutant dramatically increased plasma HDL and apoA-I levels and converted the discoidal into spherical HDL, indicating that the LCAT activity was rate-limiting for the biogenesis of HDL. The LCAT treatment caused only a small increase in HDL cholesterol and apoA-I levels and in alpha-HDL particle numbers in the helix 6Delta mutant. The findings indicate a critical contribution of residue 160 of apoA-I to the in vivo activity of LCAT and the subsequent maturation of HDL and explain the low HDL levels in heterozygous subjects carrying this mutation.

• Authors: Angeliki Chroni, Adelina Duka, Horng-Yuan Kan, Tong Liu, Vassilis I Zannis
• Journal: Biochemistry (Biochemistry) Vol. 44 Issue 43 Pg. 14353-66 (Nov 01 2005) ISSN: 0006-2960 [Print] United States
• PMID: 16245952 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Apolipoprotein A-I
• High-Density Lipoproteins, Pre-beta
• Lipoproteins, HDL
• Phosphatidylcholines
• Sterol O-Acyltransferase

Topics

• Animals
• Apolipoprotein A-I (genetics, metabolism)
• Base Sequence
• High-Density Lipoproteins, Pre-beta
• Humans
• Lipoproteins, HDL (metabolism)
• Mice
• Molecular Mimicry
• Phenotype
• Phosphatidylcholines (deficiency, genetics, metabolism)
• Point Mutation
• Sterol O-Acyltransferase (deficiency, genetics, metabolism)