Estimation of the surface area of a detergent molecule at the interphase boundary of mixed lipid-detergent aggregates

Abstract

A new approach was proposed for estimating the surface area of a detergent molecule, ad, at the interphase boundary of mixed lipid-detergent aggregates. The approach is based on consideration of the relationship between geometrical packing parameters of lipid and detergent molecules and the composition of mixed aggregates. The structural transitions between various aggregates are described in terms of the molecular packing parameter, δ, generalized for the case of a two-component lipid-detergent system (Goltsov, A.N. and Barsukov, L.I., J. Biol. Phys., 2000, vol. 26, pp. 27–41). The effective packing parameter, δcr, was shown to be a function of the detergent/lipid ratio required for complete solubilization of mixed aggregates, Resol, the interfacial surface area of a detergent molecule, ad, and some other molecular packing parameters dependent on the chemical structure of detergent and lipid. The ad values calculated using the proposed approach are in a fairly good agreement with the experimental data available in literature. The approach ensures effective evaluation of the dependence of ad on the medium composition, temperature, and the chemical structure of detergent in a broad range of temperatures and detergent/lipid ratios. The conditions of saturation of the lipid bilayer with detergent at the beginning of solubilization were analyzed. The relationship between Resol and the lipid/detergent ratio required for the saturation of lipid bilayer with detergent, Resat, was found. A method was developed for Resat estimation using the Resol values available in the literature. The results of the present study can be used in the theoretical analysis of mixed lipid-detergent and protein-detergent aggregates.