Disruption of the C-terminal helix by single amino acid deletion is directly responsible for impaired cholesterol efflux ability of apolipoprotein A-I Nichinan.
Apolipoprotein A-I (apoA-I) Nichinan, a naturally occurring variant with DeltaE235 in the C terminus, is associated with low plasma HDL levels. Here, we investigated the tertiary structure, lipid-binding properties, and ability to induce cellular cholesterol efflux of apoA-I Nichinan and its C-terminal peptide. Thermal and chemical denaturation experiments demonstrated that the DeltaE235 mutation decreased the protein stability compared with wild type (WT). ApoA-I Nichinan exhibited capabilities to bind to or solubilize lipid vesicles that are intermediate to that of WT and a L230P/L233P/Y236P variant in which the C-terminal alpha-helix folding is completely disrupted and forms relatively larger and unstable discoidal complexes, indicating that perturbation of the C-terminal alpha-helical structure by the DeltaE235 mutation leads to reduced lipid binding. Supporting this, apoA-I 209-241/DeltaE235 peptide showed significantly decreased ability to form alpha-helix both in the lipid-free and lipid-bound states, and reduced efficiency to solubilize vesicles. In addition, both apoA-I Nichinan and its C-terminal peptide exhibited reduced activity in ABCA1-mediated cellular cholesterol efflux. Thus, the disruption of the ability of the C-terminal region to form alpha-helix caused by the E235 deletion appears to be the important determinant of impaired lipid binding and cholesterol efflux ability and, consequently, the low plasma HDL levels of apoA-I Nichinan probands.
Kono
Momoe
M
Department of Biophysical Chemistry, Kobe Pharmaceutical University, Kobe, Japan.
Tanaka
Toshitaka
T
Tanaka
Masafumi
M
Vedhachalam
Charulatha
C
Chetty
Palaniappan S
PS
Nguyen
David
D
Dhanasekaran
Padmaja
P
Lund-Katz
Sissel
S
Phillips
Michael C
MC
Saito
Hiroyuki
H
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D016632:Apolipoprotein A-I / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D002942:Circular Dichroism; D006224:Cricetinae; D006358:Hot Temperature; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D051379:Mice; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011489:Protein Denaturation; D055550:Protein Stability; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary; D013997:Time Factors; D053835:Unilamellar Liposomes / Q000737:chemistry
C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D050505:Mutant Proteins; D010446:Peptide Fragments; D053835:Unilamellar Liposomes; D002784:Cholesterol