title: The interfacial properties of ApoA-I and an amphipathic alpha-helix consensus peptide of exchangeable apolipoproteins at the triolein/water interface.
abstract: Apolipoprotein A-I (apoA-I) is the major protein in high density lipoprotein (HDL). During lipid metabolism, apoA-I moves among HDL and triacylglycerol-rich lipoproteins. The main structure and the major lipid binding motif of apoA-I is the amphipathic alpha-helix. To understand how apoA-I behaves at hydrophobic lipoprotein interfaces, the interfacial properties of apoA-I and an amphipathic alpha-helical consensus sequence peptide (CSP) were studied at the triolein/water (TO/W) interface. CSP ((PLAEELRARLRAQLEELRERLG)2-NH2) contains two 22-residue tandem repeat sequences that form amphipathic alpha-helices modeling the central part of apoA-I. ApoA-I or CSP added into the aqueous phase surrounding a triolein drop lowered the interfacial tension (gamma) of TO/W in a concentration- and time-dependent fashion. The gamma(TO/W) was lowered approximately 16 millinewtons (mN)/m by apoA-I at 1.4 x 10(-6) m and approximately 15 mN/m by CSP at 2.6 x 10(-6) m. At equilibrium gamma, both apoA-I and CSP desorbed from the interface when compressed and readsorbed when expanded. The maximum surface pressure CSP could withstand without being ejected (PiMAX) was 16 mN/m. The PiMAX) of apoA-I was only 14.8 mN/m, but re-adsorption kinetics suggested that only part of the apoA-I desorbed at Pi between 14.8 and 19 mN/m. However, above approximately 19 mN/m (PiOFF) the entire apoA-I molecule desorbed into the water. ApoA-I was more flexible at the TO/W interface than CSP and showed more elasticity at oscillation periods 4-128 s even at high compression, whereas CSP was elastic only at faster periods (4 and 8 s) and moderate compression. Flexibility and surface pressure-mediated desorption and re-adsorption of apoA-I probably provides lipoprotein stability during metabolic-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: D016632:Apolipoprotein A-I / Q000737:chemistry* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007700:Kinetics; D008055:Lipids / Q000737:chemistry; D008074:Lipoproteins / Q000737:chemistry; D008075:Lipoproteins, HDL / Q000737:chemistry; D008954:Models, Biological; D009991:Oscillometry; D010455:Peptides / Q000737:chemistry; D011312:Pressure; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013997:Time Factors; D014280:Triglycerides / Q000737:chemistry; D014304:Triolein / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D016632:Apolipoprotein A-I; D008055:Lipids; D008074:Lipoproteins; D008075:Lipoproteins, HDL; D010455:Peptides; D014280:Triglycerides; D014867:Water; D014304:Triolein