Non-Brownian Diffusion of Membrane Molecules in Nanopatterned Supported Lipid Bilayers

Abstract

Molecules associated with the outer surface of living cells exhibit complex, non-Brownian patterns of diffusion. In this report, supported lipid bilayers were patterned with nanoscale barriers to capture key aspects of this anomalous diffusion in a controllable format. First, long-range diffusion coefficients of membrane-associated molecules were significantly reduced by the presence of the barriers, while short-range diffusion was unaffected. Second, this modulation was more pronounced for large molecular complexes than for individual lipids. Surprisingly, the quantitative effect of these barriers on long-range lipid diffusion could be accurately simulated using a simple, continuum-based model of diffusion on a nanostructured surface; we thus describe a metamaterial that captures the properties of the outer membrane of living cells.The outer surface of cells presents a complex, nanostructured, yet fluid environment that controls the movement of signaling proteins. The lateral movement of many membrane biomolecules, including transmembrane or tethered proteins as well as lipids themselves, can be interpreted as being free and isotropic within compartments of the cell membrane measuring tens to hundreds of nanometers in scale [1][2][3][4][5][6] . These compartments are delineated by semipermeable barriers that arise from interactions between the plasma membrane, underlying cytoskeleton, and associated proteins [6][7][8] . Fluctuations in these structures allow biomolecules to occasionally cross between compartments, allowing long-range, but comparatively slow, transport over the cell surface. More formally, transport along the membrane is an anomalous, non-Brownian process that can be characterized by two diffusion coefficients, one that describes short-range motion within an individual compartment and a second, smaller, effective diffusion coefficient that is associated with long-range motion over many barriers. The extent to which these values differ is dependent on the spacing and properties of the barriers as well as the diffusing molecule. Emerging models suggest significant impacts of this behavior on cell signaling 2, 9, 10 , but experimental systems for testing these hypotheses are not widely available. In this report, we capture this anomalous diffusion by nanopatterning supported lipid bilayers with barriers to lipid diffusion using a geometry that captures the semipermeable nature of those posed to be present in living cells. As is posed by models of these interactions, we aim to gain control over long-range diffusion, while maintaining local, isotropic diffusion associated with a membrane in the absence of such barriers. We demonstrate that these nanopatterned barriers give rise to different short-and long-range diffusion coefficients of lipids and membrane-associated proteins, and provide a quantitative model of this diffusion that suggests specific aspects of membrane structure at the sub-micrometer level. The basic substrate supported lipid bilayer system consists of a phospholipid membrane...

Lipid-nanostructure hybrids and their applications in nanobiotechnology

“…In that study, glass substrates were patterned with 50-nm wide Cr lines with 125-nm or 250-nm spacing and sub-50-nm gaps interspersed throughout the Cr barriers (Figure 7a). 77 In fluorescence recovery after photobleaching experiments, it was demonstrated that the longrange diffusion of the lipids on these substrates was significantly reduced, whereas the short-range diffusion was preserved. Furthermore, the cholera toxin subunit B/GM 1 complexes were less likely to cross the nanoscale barriers than the individual lipid molecules.…”

Simulation for diffusion behaviour of molecules in nanopattern-supported lipid bilayers based on random walk theory

“…Tsai et al [22] proposed that anomalous diffusion can be characterised by two diffusion coefficients, one describes short-range motion within an individual compartment and the other, smaller, effective diffusion coefficient is associated with long-range motion over many barriers. Specifically, molecular motion parallel to the barriers is unhindered, in the absence of any impact of the barriers on local membrane mobility, long-range diffusion coefficients measured in this direc- …”

“…[15] This concept of the molecular filtering effect was recently confirmed by the use of a single nanogate. [19,21] In 2008, Tsai et al [22] designed arrays of nanoscale linear barriers patterned on glass substrates to capture key aspects of anomalous diffusion. They found that diffusion coefficients of the molecule depended on barrier spacing, gap size and barrier material.…”

“…In recent decades, the behaviour of RW in molecules or ions manipulation has been a focus of intense research, primarily owing to their potential application in purification, catalysis in mesoporous materials and separation of molecules. [35 -37] In this work, a model of which the geometrical structure is the same as Tsai's [22] experiment ( Figure 1) was constructed to investigate the single molecular diffusion behaviour. The barrier's length, width, spacing, gap and the interaction with molecules were investigated to find their impact on the molecular diffusion behaviour.…”

Nanofabrication for the Analysis and Manipulation of Membranes

“…For example, studying lipid diffusion around nanofabricated channels 90,95 and nanogates 66 has provided insights of membrane diffusion on complex surfaces. Carefully designed surface patterns may be applied for selective sorting of membrane components based on molecular mobility, size, or charge.…”