title: Interfacial properties of an amphipathic alpha-helix consensus peptide of exchangeable apolipoproteins at air/water and oil/water interfaces.
abstract: Amphipathic alpha-helices are the main structure and the major lipid binding motif of exchangeable apolipoproteins. To understand how these apolipoproteins behave at an hydrophobic lipoprotein interface, the interfacial properties of a consensus sequence peptide (CSP) derived from three exchangeable apolipoproteins (A-I, A-IV, and E) were studied using an oil drop tensiometer at air/water (A/W) and dodecane/water (DD/W) interfaces. CSP ((PLAEELRARLRAQLEELRERLG)2-NH2) contains two 22-amino acid tandem repeat sequences that form amphipathic alpha-helices. CSP, when added into the aqueous phase, lowered the interfacial tension (gamma) of A/W and DD/W in a concentration-dependent fashion. The gammaA/W was lowered approximately 24 mn/m, and gammaDD/W approximately 31 mn/m, indicating a greater affinity of CSP for DD/W. Using the Gibbs equation for surface, the surface area per CSP molecule was estimated at approximately 702 A2 ( approximately 16 A2/amino acid) on A/W and approximately 622 A2 on DD/W ( approximately 14 A2/amino acid) suggesting that adsorbed CSP lies flat with alpha-helices in the plane of both interfaces. At equilibrium gamma, CSP desorbed from the interface when compressed and re-adsorbed when expanded. The adsorption rate was concentration-dependent, but the desorption rate was not. Less CSP desorbed from DD/W than A/W indicating that CSP has higher affinity for DD/W. Dynamic analysis of elasticity shows that the faster the oscillation period (4, 8 s) and the lower the oscillation amplitude the more elastic the surfaces. CSP can be compressed 6-12% while remaining on the surface, but large increases in pressure eject it from the surface. We suggest that surface pressure-mediated desorption and readsorption of amphipathic alpha-helices provide lipoprotein stability during remodeling reactions in plasma.
authors.affiliation: Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
authors.forename: Libo
authors.initials: L
authors.lastname: Wang
authors.forename: David
authors.initials: D
authors.lastname: Atkinson
authors.forename: Donald M
authors.initials: DM
authors.lastname: Small
mesh_terms: D000595:Amino Acid Sequence; D016632:Apolipoprotein A-I / Q000737:chemistry*; D001054:Apolipoproteins A / Q000737:chemistry*; D001057:Apolipoproteins E / Q000737:chemistry*; D016384:Consensus Sequence; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D013500:Surface Tension
chemical_list: D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; D001057:Apolipoproteins E; C022205:apolipoprotein A-IV