Restoring structural parameters of lipid mixtures from small-angle X-ray scattering data.

Petr V Konarev,Andrey Yu Gruzinov,Dmitri I Svergun,Haydyn D T Mertens

doi:10.1107/s1600576720015368

Abstract

Small-angle X-ray scattering (SAXS) is widely utilized to study soluble macromolecules, including those embedded into lipid carriers and delivery systems such as surfactant micelles, phospho-lipid vesicles and bilayered nanodiscs. To adequately describe the scattering from such systems, one needs to account for both the form factor (overall structure) and long-range-order Bragg reflections emerging from the organization of bilayers, which is a non-trivial task. Presently existing methods separate the analysis of lipid mixtures into distinct procedures using form-factor fitting and the fitting of the Bragg peak regions. This article describes a general approach for the computation and analysis of SAXS data from lipid mixtures over the entire angular range of an experiment. The approach allows one to restore the electron density of a lipid bilayer and simultaneously recover the corresponding size distribution and multilamellar organization of the vesicles. The method is implemented in a computer program, LIPMIX, and its performance is demonstrated on an aqueous solution of layered lipid vesicles undergoing an extrusion process. The approach is expected to be useful for the analysis of various types of lipid-based systems, e.g. for the characterization of interactions between target drug molecules and potential carrier/delivery systems.

Highlights

Phospholipids play an important role in the formation of intracellular and extracellular compartments
We present a program, LIPMIX, that builds upon the methodology first described by Pabst et al (2000) to derive structural parameters of polydisperse multilamellar lipid mixtures utilizing the scattering data collected over the entire angular range of a Small-angle X-ray scattering (SAXS) experiment
We demonstrate the use of the method to analyze the SAXS data from lipid vesicles undergoing an extrusion process in aqueous solution

Summary

Introduction

Phospholipids play an important role in the formation of intracellular and extracellular compartments. They are amphiphilic molecules and self-assemble in aqueous solutions into layered aggregate structures. Phospholipids form bilayered components of biological membranes, serving as a scaffold for both hydrophilic and hydrophobic regions of macromolecules and the separation of cellular components. Phospholipids form ordered aggregates such as vesicles and liposomes that adopt single- or multi-lamellar microstructures. Studied bilayered lipid particles formed in aqueous solution include single unilamellar vesicles (SUVs) and multi-lamellar vesicles (MLVs) (Fig. 1). Vesicular and lipid systems are important targets in studies of phase transitions and drug delivery mechanisms, and they are often used to facilitate protein crystallization (Yamashita et al, 2002; Landau & Rosenbusch, 1996; Cherezov, 2011)

Methods

Results

Conclusion