title: Alignment of the apolipophorin-III alpha-helices in complex with dimyristoylphosphatidylcholine. A unique spatial orientation.
abstract: Apolipophorin-III (apoLp-III) from Manduca sexta can exist in two alternate states: as a globular, lipid-free helix bundle or a lipid surface-associated apolipoprotein. Previous papers (Ryan R.O., Oikawa K., and Kay C. M. (1993) J. Biol. Chem. 268, 1525-1530; Wientzek M., Kay C.M., Oikawa K., and Ryan R.O. (1994) J. Biol. Chem. 269, 4605-4612) have investigated the structures and properties of apolipophorin-III from M. sexta in the lipid-free state and associated to lipids. Association of apoLp-III with dimyristoylphosphatidylcholine vesicles leads to the formation of uniform lipid discs with an average diameter and thickness of 18.5 +/- 2.0 and 4.8 +/- 0.8 nm, respectively. These discs contain six molecules of apoLp-III. Geometrical calculations based on these data, together with x-ray crystallographic data from the homologous L. migratoria apoLp-III (Breiter D. R., Kanost M.R., Benning M.M., Wesenberg G., Law J.H., Wells M.A., Rayment I., and Holden H.M. (1991) Biochemistry 30, 603-608), have allowed the presentation of a model of lipid-protein interaction, in which the alpha-helices of the apoLp-III orient perpendicular to the phospholipid chains and surround the lipid disc. Here, using polarized Fourier transform-attenuated total reflection infrared spectroscopy, we provide the first experimental evidence of a unique perpendicular orientation of the alpha-helices with respect to the fatty acyl chains of the phospholipids in the disc.
authors.affiliation: Laboratoire de Chimie Physique des Macromolécules aux Interfaces, Université Libre de Bruxelles, Belgium.
authors.forename: V
authors.initials: V
authors.lastname: Raussens
authors.forename: V
authors.initials: V
authors.lastname: Narayanaswami
authors.forename: E
authors.initials: E
authors.lastname: Goormaghtigh
authors.forename: R O
authors.initials: RO
authors.lastname: Ryan
authors.forename: J M
authors.initials: JM
authors.lastname: Ruysschaert
mesh_terms: D000818:Animals; D001053:Apolipoproteins / Q000737:chemistry* / Q000378:metabolism; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry* / Q000378:metabolism; D018402:Manduca; D008956:Models, Chemical; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D001053:Apolipoproteins; C042470:apolipophorin III; D004134:Dimyristoylphosphatidylcholine