Abstract
Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information.
Highlights
Biological membranes are self-sealing boundaries, confining the permeability barriers of cells and organelles and yielding the means to compartmentalize functions
As reported form Atomic force microscope (AFM) and FSC studies, DOPC:SM:Chol bilayers display three different topographical levels when a part of the SM content is replaced by Cer: a thinner ld phase enriched in DOPC, an intermediate lo phase enriched in SM and Chol, and a thicker one corresponding to domains rich in Cer together with SM [89,90]
Chol plays an important role in adjusting the physical properties of biological membranes, managing the membrane fluidity and mechanical resistance, by controlling the organization and phase behavior of the lipid bilayer
Summary
Biological membranes are self-sealing boundaries, confining the permeability barriers of cells and organelles and yielding the means to compartmentalize functions. Chol plays an essential role in modulating membrane physical properties, being highly important in the function and evolution of the biological membrane [2,7]. It regulates membrane fluidity, controls the lipid organization and phase behavior, and increases the mechanical stability of the membrane [8,9,10]. Several articles review the use of AFM to study model membranes mechanics, in this contribution we review the AFM-based approach to evaluate the structure and nanomechanics of model membranes, focusing on recent studies on the effect of Chol on model SLBs under temperature variations.
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