Lysolecithin and Cholesterol Interact Stoichiometrically Forming Bimolecular Lamellar Structures in the Presence of Excess Water, or Lysolecithin or Cholesterol

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Abstract
The structural interaction of egg lysolecithin, derived from egg lecithin, and cholesterol in aqueous solution has been investigated using X-ray diffraction. When mixed in any proportions, either suspended in excess buffer or up to 85% lipid by dry weight, a separate lamellar phase containing equimolar proportions of lysolecithin and cholesterol forms, separate from excess water, or lysolecithin or cholesterol. The cholesterol disorders the crystalline chains of the lysolecithin. The equimolar phase is stable up to 50 °C unlike lysolecithin alone, which forms micelles. These results show that lysolecithin and cholesterol combine stoichiometrically in a stable complex. We propose as a structural model, that cholesterol fills the space of the missing fatty acyl chain making the lysolecithin more cylindrical rather than wedge shaped. This interaction could reduce both the lytic action of lysolecithin on membranes and its induction of cell fusion. It suggests another role of cholesterol in cell membranes: namely, to act as a stabilizer of bilayer structure by being a mobile component that can fill free volume in the hydrocarbon interior. Lysolecithin–cholesterol interaction may also be important in the early events of atherosclerosis where lysolecithin levels in vessel walls increase fivefold.

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