Cholesterol Distribution in Small Unilamellar Vesicles

Abstract

The plasma membrane has heterogeneity, where the constituents are not only asymmetrically distributed between the inner leaflet and the outer leaflet but also laterally organized within each leaflet. There is still an ongoing controversy over the cholesterol distribution between the two leaflets, and it is also significant to explore the lateral flow and localization of cholesterol. The unilamellar vesicle is extensively employed as a simplified model of the plasma membrane in research studies. In this work, we study the spontaneous spatial distribution of cholesterol in the small unilamellar vesicles with a single type of phospholipid as the bilayer backbone through coarse-grained molecular dynamics simulations. The results show that in a spherical vesicle under ambient pressure, cholesterol is more abundant in the inner leaflet than in the outer leaflet. As the vesicle is deformed under pressurization, the net lateral flow of cholesterol in the two leaflets is in the exactly opposite directions, finally leading to a distribution strongly associated with the monolayer curvature. One of the possible explanations for our results is from the point of view of curvature elastic energy. Another possibility is from the point of view of stress: according to the correlation between the cholesterol distribution and the tail angles of lipids, it is suggested that the possible governing mechanism for the distribution of cholesterol in a membrane is to alleviate the mismatch of stress between the two leaflets. Additionally, we obtain the effect of cholesterol infiltration on the bending modulus and the spontaneous curvature of the vesicles.

Progress and Outlook of Supercritical CO2–Heavy Oil Viscosity Reduction Technology: A Minireview

“…The speed of diffusion can be determined from the diffusion coefficient (D), which is the mass or number of moles of a substance that diffuses vertically through a unit area per unit time and a unit concentration gradient along the diffusion direction. Additionally, Wei et al 48 used the pressure drop method to determine the diffusion coefficient of supercritical CO 2 in heavy oil with a viscosity of 591 mPa•s at 25 °C and established a method for calculating the diffusion concentration field. Their results showed that the diffusion coefficient of supercritical CO 2 in crude oil was on the order of 1 × 10 −8 m 2 /s.…”

Effects of lipid saturation on bicelle to vesicle transition of a binary phospholipid mixture: a molecular dynamics simulation study

“…To our knowledge, only limited lipid compositions have been used in MD simulation studies of vesicles. [19][20][21][22][23][24] Previously, we investigated a binary unsaturated/saturated lipids system, 22 although the focus was limited to an unsaturated lipid component. The degree of unsaturation is essential in determining various dynamic and static properties of lipids systems 14,[25][26][27][28][29][30][31] Moreover, vesicles composed of various unsaturated/saturated lipid mixtures are more practical for tailor-made purposes.…”