Effects of cholesterol on the size distribution and bending modulus of lipid vesicles.

Mohammad Abu Sayem Karal,Marina Belaya,Victor Levadny,Shareef Ahammed,Md Kabir Ahamed,Marzuk Ahmed,Nadia Akter Mokta,Sheereen Majd

doi:10.1371/journal.pone.0263119

Abstract

The influence of cholesterol fraction in the membranes of giant unilamellar vesicles (GUVs) on their size distributions and bending moduli has been investigated. The membranes of GUVs were synthesized by a mixture of two elements: electrically neutral lipid 1, 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and cholesterol and also a mixture of three elements: electrically charged lipid 1,2-dioleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (DOPG), DOPC and cholesterol. The size distributions of GUVs have been presented by a set of histograms. The classical lognormal distribution is well fitted to the histograms, from where the average size of vesicle is obtained. The increase of cholesterol content in the membranes of GUVs increases the average size of vesicles in the population. Using the framework of Helmholtz free energy of the system, the theory developed by us is extended to explain the experimental results. The theory determines the influence of cholesterol on the bending modulus of membranes from the fitting of the proper histograms. The increase of cholesterol in GUVs increases both the average size of vesicles in population and the bending modulus of membranes.

Highlights

Lipid molecules dispersed in buffer solution exhibit a self-assembled system that transforms into the aggregates of various sizes and shapes [1,2,3]
To investigate the effects of cholesterol on the size distribution of giant unilamellar vesicles (GUVs) in vesicle population, primarily we considered the GUVs with neutral membranes using various molar ratios of Ch
D, of N = 350 GUVs (i.e., N is the number of measured GUVs) from the several phase contrast images of DOPC/chol (100/0)-GUVs, a histogram of the size distribution of GUVs was obtained (Fig 2B)

Summary

Introduction

Lipid molecules dispersed in buffer solution exhibit a self-assembled system that transforms into the aggregates of various sizes and shapes [1,2,3]. Spherical structures formed by a double lipid layer ranging from nano- to micrometer in diameter. There are several methods of forming the unilamellar vesicles which produce different sizes of vesicles. Among the different unilamellar vesicles, giant unilamellar vesicles (GUVs) of diameters 10 μm or more have attracted special interest due to the visualization of their size and shape using optical microscopes [6, 7]. Such vesicles can be obtained through the natural swelling method [7,8,9,10]. The GUVs have been used to investigate the elasticity of lipid membranes [8, 11], rupture/pore formation of vesicles using mechanical/

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Conclusion