Capturing the nanoscale complexity of cellular membranes in supported lipid bilayers

Abstract

The lateral mobility of cell membranes plays an important role in cell signaling, governing the rate at which embedded proteins can interact with other biomolecules. The past two decades have seen a dramatic transformation in understanding of this environment, as the mechanisms and potential implications of nanoscale structure of these systems has become accessible to theoretical and experimental investigation. In particular, emerging micro- and nano-scale fabrication techniques have made possible the direct manipulation of model membranes at the scales relevant to these biological processes. This review focuses on recent advances in nanopatterning of supported lipid bilayers, capturing the impact of membrane nanostructure on molecular diffusion and providing a powerful platform for further investigation of the role of this spatial complexity on cell signaling.

Figure 1

Nanoscale organization of cell membranes. (A) Two mechanisms for this organization in living cells are the presence of microdomains (red forms) and cytoskeletal structures (orange grid and blue transmembrane proteins) both of which limit long-range diffusion. The random-walk trajectory of a cell signaling molecule (green) that is excluded from these domains and restricted by the cytoskeletal elements is illustrated in this panel. (B) Strategies for capturing nanoscale membrane complexity in supported lipid bilayers include the patterning of non- compatible materials (orange) onto the substrate, or the use of lipid mixtures that demix to form stable analogs of the native microdomains.

Figure 2

(A) Live cell imaging allows measurement of molecular diffusion. (B,C) Illustration of the basic FRAP experiment. (D,E) Single particle tracking provides a different, complementary insight into diffusive motion.

Figure 3

(A) Patterning of barrier materials using lithographic approaches. (B-D) Anisotropic diffusion of lipids on a nanopatterned surface containing chromium barriers. Panel B details the nanoscale layout of barriers used to induce anisotropic, long-range diffusion. Panel C shows a surface patterned with chromium barriers of this geometry. Panel D shows an anisotropic FRAP experiment on these surfaces. The barriers run vertically in this image. (E) Schematic of an alternative bilayer configuration, based on the use of materials that support formation of a continuous supported membrane.