Substrate-Induced Structure and Molecular Dynamics in a Lipid Bilayer Membrane

Abstract

The solid-substrate-dependent structure and dynamics of molecules in a supported lipid bilayer (SLB) were directly investigated via atomic force microscopy (AFM) and single particle tracking (SPT) measurements. The appearance of either vertical or horizontal heterogeneities in the SLB was found to be strongly dependent on the underlying substrates. SLB has been widely used as a biointerface with incorporated proteins and other biological materials. Both silica and mica are popular substrates for SLB. Using single-molecule dynamics, the fluidity of the upper and lower membrane leaflets was found to depend on the substrate, undergoing coupling and decoupling on the SiO/Si and mica substrates, respectively. The anisotropic diffusion caused by the locally destabilized structure of the SLB at atomic steps appeared on the AlO(0001) substrate because of the strong van der Waals interaction between the SLB and the substrate. Our finding that the well-defined surfaces of mica and sapphire result in asymmetry and anisotropy in the plasma membrane is useful for the design of new plasma-membrane-mimetic systems. The application of well-defined supporting substrates for SLBs should have similar effects as cell membrane scaffolds, which regulate the dynamic structure of the membrane.

Nanoscale Substrate Roughness Hinders Domain Formation in Supported Lipid Bilayers

“…The Ra roughness of glass (0.15 nm) after piranha cleaning and UV ozone cleaning is over 4 times rougher than mica (0.03 nm) after cleavage ( Figure 5A+B). These values match closely to previous AFM roughness measurements of mica, 15,37 and piranha cleaned glass. 14 We also studied other substrates used to support lipid bilayers, including glass with a differing composition (Glass 2), quartz, silicon and thermally oxidised silicon ( Figure 2).…”

“…Whilst FCS experiments have found that there is no significant difference between DOPC diffusion on glass and mica, 12 for SLBs formed using the same vesicle fusion bilayer deposition method as in this paper, there are many varied results in the literature. 22,31,37 To verify the finding of an identical Figure S6) and in literature. 44,45 It should be noted that this is a DSC cooling scan value to match the FRAP data also collected during cooling, and that cooling rates cause an offset in Tm values away from the true value (details in SI).…”

“…In addition, our diffusion values agree with literature values from different techniques, which vary between 0.5-5.0 µm 2 /s for fluid lipid systems. 12,22,31,37 Atomic Force Microscopy (AFM) AFM Images were acquired using a Bruker Dimension ICON. Bruker ScanAsyst-Fluid (0.7 N/m, 150 kHz) were used for imaging bilayers using Peak Force Tapping in liquid.…”

Coarse-Grain Simulations of Solid Supported Lipid Bilayers with Varying Hydration Levels

“…The SLBs' stability and their constrained orientation make it possible to study them using 2 surface-sensitive measurement techniques such as atomic force microscopy, particle tracking via fluorescence measurements, surface plasmon resonance, surface second harmonic generation spectrometry, neutron or X-ray specular reflectometry [5][6][7][8][9][10] . Molecular dynamics (MD) simulations can also be advantageously used to investigate SLBs, to cross-validate the results of the experimental approaches, or to provide structural and dynamical descriptions at the molecular level 5,11?…”

“…Despite the molecular insight that can be gained by numerical simulations 13,[16][17][18][19][20] , relatively few computational studies have been reported yet (see the review by Hirtz et al 21 ). Indeed, both experiments and simulations 8,[22][23][24] have highlighted how strongly the SLB properties change, depending on the interplay between the membrane/solid, membrane/solvent and solid/solvent interactions.…”