Nanoscale mechanical properties of lipid bilayers and their relevance in biomembrane organization and function

Abstract

The mechanical properties of biological systems are emerging as fundamental in determining their functional activity. For example, cells continuously probe their environment by applying forces and, at the same time, are exposed to forces produced by the same environment. Also in biological membranes, the activity of membrane related proteins are affected by the overall mechanical properties of the hosting environment. Traditionally, the mesoscopic mechanical properties of lipid bilayers have been studied by micropipette aspiration techniques. In recent years, the possibility of probing mechanical properties of lipid bilayers at the nanoscale has been promoted by the force spectroscopy potentiality of Atomic Force Microscopes (AFM). By acquiring force-curves on supported lipid bilayers (SLBs) it is possible to probe the mechanical properties on a scale relevant to the interaction between membrane proteins and lipid bilayers and to monitor changes of these properties as a result of a changing environment. Here, we review a series of force spectroscopy experiments performed on SLBs with an emphasis on the functional consequences the measured mechanical properties can have on membrane proteins. We also discuss the force spectroscopy experiments on SLBs in the context of theories developed for dynamic force spectroscopy experiments with the aim to extract the kinetic and energetic description of the process of membrane rupture.

The temperature-dependent physical state of polar lipids and their miscibility impact the topography and mechanical properties of bilayer models of the milk fat globule membrane

“…protection of the neonate from bacteria and viruses [3] and anti-inflammatory properties [64]. The partitioning of proteins in the MFGM, proteinlipid interactions and bioactivity of MFGM proteins are likely to depend on the physical state and packing of the polar lipids as well as on the mechanical properties which in turn highly depend on temperature as shown in this study [17,52]. …”

“…The increase in F B values of both the continuous and dispersed phases with decreasing temperature is consistent with other reports. Garcia-Manyes et al [22], Picas et al [49], Redondo-Morata et al [42] or Alessandrini and Facci [52] have investigated the mechanical properties of pure or binary phospholipid bilayers using AFM. As a general trend, F B decreases with increasing temperature, due to the increase in molecular area and agitation, which reduces lateral interactions and facilitates penetration of the bilayer by the AFM tip [22].…”

“…As a general trend, F B decreases with increasing temperature, due to the increase in molecular area and agitation, which reduces lateral interactions and facilitates penetration of the bilayer by the AFM tip [22]. The phase transition is sometimes marked by a sharper decrease or a local minimum of F B around Tm [22,52]. Furthermore, due to the higher order and molecular compactness, the F B values obtained on single-phospholipid bilayers in the s o phase are notably higher that those recorded in the l d phase [22,53].…”

“…In recent years, the measurement of F B has gained increasing interest as the nanoscale signature of the relative mechanical stability of phospholipid membranes [17,28,52,54].…”

Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids

“…Therefore, during recent decades AFM-FS has been a suitable technique to perform nanomechanical studies on a wide range of systems, such as indenting hard materials while the AFM tip is approaching the surface [44] or pulling individual macromolecules—polysaccharides [43,45], proteins [46,47,48], and DNA [49]—during the retraction of the AFM tip from the surface. In the case of lipid bilayers, AFM-FS has become a very valuable approach to probe the mechanical properties at the nanoscale with high spatial and force resolution [9,34,35,50]. …”