Model Bio‐Membranes Investigated by AFM and AFS: A Suitable Tool to Unravel Lipid Organization and their Interaction with Proteins

Abstract

Th e study of the biological membrane has largely benefi tted from the exploitation of model bilayer systems. Th ese simplifi ed models of the complex biological membrane composed of thousands of diff erent types of molecules allow both to understand basic physical principles underlying the membrane functioning and to test new techniques that will be subsequently applied to biological membranes. Here we concentrate on one of the most used model systems for this kind of investigations: the Supported Lipid Bilayer (SLB). In particular, we analyze the possibilities of investigation off ered by Atomic Force Microscopy and Spectroscopy (AFM/ AFS) on this model system. We discuss the information that these techniques are able to provide on the phase behavior of the lipid bilayers and on the partitioning of membrane proteins relative to the bilayer lateral heterogeneity. We discuss also the possibility to characterize the mechanical properties of lipid bilayers on the nanometer scale lateral resolution.

Behavior of Bilayer Leaflets in Asymmetric Model Membranes: Atomistic Simulation Studies

“…Nevertheless, the present studies of nonphase-separated asymmetric systems show that dynamic chain interdigitation is weak, consistent with observations in supported lipid bilayer studies. 78 Our simulation results highlight that of the leaflet properties studied, deuterium order parameters and bending moduli are affected by intraleaflet lipid packing. This interplay between the local lipid density and bending modulus may play a role in governing interleaflet domain coupling in lipid bilayers.…”

“…Interleaflet domain coupling (raft registration/antiregistration) is likely the result of the balance between several competing mechanisms. , To account for line tension, it would require transversally asymmetric and laterally nonhomogeneous bilayer models (with mixed Lo and Ld phases in the same leaflet) to be studied; all-atom simulations of such bilayer systems are currently ongoing. Nevertheless, the present studies of nonphase-separated asymmetric systems show that dynamic chain interdigitation is weak, consistent with observations in supported lipid bilayer studies . Our simulation results highlight that of the leaflet properties studied, deuterium order parameters and bending moduli are affected by intraleaflet lipid packing.…”

Behavior of Citrate-Capped Ultrasmall Gold Nanoparticles on a Supported Lipid Bilayer Interface at Atomic Resolution

“…High-resolution amplitude-modulated (AM)-AFM imaging was conducted in liquid using small-amplitude imaging protocols previously developed for interfacial imaging of ionic solutes, ,− viscous fluids, ,,− and soft matter interfaces. , For all experiments, surface-adsorbed flat lipid bilayers were formed via the previously reported vesicle fusion method (see Figure S1). ,, Figure A shows representative low-resolution (5 μm × 5 μm) and high-resolution (500 nm × 500 nm, insert) AFM height images of a DOPC SLB.…”

“…We comparatively examine fluid- and gel-phase bilayers since the mobility of the molecules in the membranes is a key physical parameter in controlling the evolution and fate of a given system. We use SLBs where the membrane is loosely adhered to a solid substrate, but maintaining a ∼1 nm thick water layer which preserves molecular mobility within the bilayer. − Synthetic SLBs , are often used as model systems for studying the fundamental biophysical processes of cell membranes, , because they offer full control of the model membranes both chemically and structurally. − The fact that SLBs are supported is also arguably a better representation of the crowded cell-wall environment where biomembranes are heavily constrained by the supporting cytoskeleton as well as often the glycocalyx. , …”