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J. Biol. Chem., Vol. 278, Issue 39, 37480-37491, September 26, 2003

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Interfacial Properties of an Amphipathic -Helix Consensus Peptide of Exchangeable Apolipoproteins at Air/Water and Oil/Water Interfaces^*

Libo Wang, David Atkinson and Donald M. Small 

From the Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118

Amphipathic -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 -helices. CSP, when added into the aqueous phase, lowered the interfacial tension () of A/W and DD/W in a concentration-dependant fashion. The _A/W was lowered 24 mN/m, and _DD/W 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 702 Ų (16 Ų/amino acid) on A/W and 622 Ų on DD/W (14 Ų/amino acid) suggesting that adsorbed CSP lies flat with -helices in the plane of both interfaces. At equilibrium , CSP desorbed from the interface when compressed and re-adsorbed when expanded. The adsorption rate was concentration-dependant, 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 -helices provide lipoprotein stability during remodeling reactions in plasma.

Received for publication, March 26, 2003 , and in revised form, June 24, 2003.

^* This work was supported in part 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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