Abstract
SummaryLipoproteins in plasma present the property to exchange lipids between themselves and also with different types of cells. Associated proteins known as apolipoproteins give these particles their lipid exchange characteristics, and also provide a way to control their directionality and ability to interact with receptors located at the surface of cells. In order to provide information on the three dimensional structure of apolipoprotein AII (apoAII), an important constituent of high density lipoprotein particles (HDL), we have studied monolayers of this apolipoproteins combining Langmuir techniques with Brewster Angle Microscopy and Atomic Force Microscopy. We describe the gas/liquid-phase transition in this protein and a phase transition between two condensed phases at high lateral pressures. This transition corresponds to a conformational change of the protein due to the desorption of one of its α-helix segments from the subphase. This result suggests that changes in lateral pressure along changes in shape, size, and composition of HDL particles, might affect the conformation of apolipoproteins including apoAII interacting with the surface of the lipoprotein. This type of conformational change in apoAII might be involved with the exchangeability process as observed with this class of apolipoproteins, as well as with protein recognition by specific receptors at the cell surface.
Published Version
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