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J. Biol. Chem., Vol. 280, Issue 6, 4154-4165, February 11, 2005
The Interfacial Properties of ApoA-I and an Amphipathic 
-Helix Consensus Peptide of Exchangeable Apolipoproteins at the Triolein/Water Interface*
From the Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118
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 
-helix. To understand how apoA-I behaves at hydrophobic lipoprotein interfaces, the interfacial properties of apoA-I and an amphipathic -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 -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 (
) of TO/W in a concentration- and time-dependent fashion. The TO/W was lowered 
16 millinewtons (mN)/m by apoA-I at 1.4 x 10–6 M and 15 mN/m by CSP at 2.6 x 10–6 M. At equilibrium , 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 (
MAX) was 16 mN/m. The MAX of apoA-I was only 14.8 mN/m, but re-adsorption kinetics suggested that only part of the apoA-I desorbed at between 14.8 and 19 mN/m. However, above 19 mN/m (OFF) 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.
Received for publication, October 12, 2004 , and in revised form, November 12, 2004.
* This work was supported by NHLBI, National Institutes of Health Grant 2P01-HL26335-21. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
To whom correspondence should be addressed: Dept. of Physiology and Biophysics, Boston University School of Medicine, 715 Albany St., W-302, Boston, MA 02118. Tel.: 617-638-4001; Fax: 617-638-4041; E-mail: dmsmall{at}bu.edu
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