Apolipoprotein A-V N-terminal domain lipid interaction properties in vitro explain the hypertriglyceridemic phenotype associated with natural truncation mutants.
The N-terminal 146 residues of apolipoprotein (apo) A-V adopt a helix bundle conformation in the absence of lipid. Because similarly sized truncation mutants in human subjects correlate with severe hypertriglyceridemia, the lipid binding properties of apoA-V(1-146) were studied. Upon incubation with phospholipid in vitro, apoA-V(1-146) forms reconstituted high density lipoproteins 15-17 nm in diameter. Far UV circular dichroism spectroscopy analyses of lipid-bound apoA-V(1-146) yielded an alpha-helix secondary structure content of 60%. Fourier transformed infrared spectroscopy analysis revealed that apoA-V(1-146) alpha-helix segments align perpendicular with respect to particle phospholipid fatty acyl chains. Fluorescence spectroscopy of single Trp variant apoA-V(1-146) indicates that lipid interaction is accompanied by a conformational change. The data are consistent with a model wherein apoA-V(1-146) alpha-helices circumscribe the perimeter of a disk-shaped bilayer. The ability of apoA-V(1-146) to solubilize dimyristoylphosphatidylcholine vesicles at a rate faster than full-length apoA-V suggests that N- and C-terminal interactions in the full-length protein modulate its lipid binding properties. Preferential association of apoA-V(1-146) with murine plasma HDL, but not with VLDL, suggests that particle size is a determinant of its lipoprotein binding specificity. It may be concluded that defective lipoprotein binding of truncated apoA-V contributes to the hypertriglyceridemia phenotype associated with truncation mutations in human subjects.
Wong-Mauldin
Kasuen
K
Center for Prevention of Obesity, Diabetes and Cardiovascular Disease, Children's Hospital Oakland Research Institute, Oakland, California 94609, USA.
Raussens
Vincent
V
Forte
Trudy M
TM
Ryan
Robert O
RO
D000818:Animals; D000072040:Apolipoprotein A-V; D001053:Apolipoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001054:Apolipoproteins A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002942:Circular Dichroism; D006801:Humans; D015228:Hypertriglyceridemia / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D015151:Immunoblotting; D007700:Kinetics; D008075:Lipoproteins, HDL / Q000097:blood / Q000378:metabolism; D008079:Lipoproteins, VLDL / Q000097:blood / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D010743:Phospholipids / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D017550:Spectroscopy, Fourier Transform Infrared
C437704:APOA5 protein, human; C499058:Apoa5 protein, mouse; D000072040:Apolipoprotein A-V; D001053:Apolipoproteins; D001054:Apolipoproteins A; D008075:Lipoproteins, HDL; D008079:Lipoproteins, VLDL; D010743:Phospholipids