Image courtesy of Atul Parikh, UC Davis
With increasing hydration within the interlayer space of the initially disordered lipid membranes, lateral layer-by-layer phase separation begins. Stacking of cholesterol-enriched saturated lipid domains (orange) emerges in fluid lipid zones (purple) facilitated by organization of interlayer water (aqua). Ultimately, a stacked columnar phase is produced within the membrane. The picture is deduced from quantitative analyses of fluorescence and atomic force microscopies as well as X-ray scattering measurements.
For the first time, researchers demonstrated that distinct regions within individual biological lipid membranes will align and stack in multi-layered structures driven by their composition and the water molecules between the layers. Lipids are fatty substances like oils, waxes, and related compounds.
The results are a major step forward towards developing novel self-assembly-based strategies for the alignment and long-range serial coupling of functional domains in membrane assemblies, and suggest that control of interfacial water structure is an important design criterion for building biologically-inspired synthetic materials.
Research on multilayer lipid membranes has largely focused on uniform, single lipid systems. This study tackled more complex multiple lipid biological membranes similar to those found in the thylakoid membrane, the region where photosynthesis takes place in plants, or electrocyte cells in electric eels. Within a single bilayer membrane composed of multiple lipids, discrete zones of more highly-ordered regions (liquid-crystalline domains) form via a process called lateral phase separation. Using X-ray diffraction and atomic force and fluorescence microscopies, researchers at University of California-Davis, University of California-San Diego, and Oklahoma State University demonstrated that these domains help seed formation of columnar structures across hundreds of lipid bilayers spanning several micrometers. Analysis of the dynamics suggests the structural order in the top layer is influenced by that of the layer directly below, assisted by hydrogen-bonded networks of water molecules within the narrow spaces between layers, a process referred to as cooperative, multilamellar epitaxy. These results represent a major step forward towards understanding self-assembly of complex membrane stacks found in nature and could inform self-assembly-based strategies for long-range serial coupling of functional domains in membrane-based materials. This research may lead to practical applications for optics, photonics, and sensing as well as other biomimetic energy applications including bio-inspired synthetic membranes for solar energy capture/conversion.
University of California at Davis
Department of Energy, Office of Science, Basic Energy Sciences program.
L. Tayebi, Y. Ma, D. Vashaee, G. Chen, S. K. Sinha, A. N. Parikh, “Long-range interlayer alignment of intralayer domains in stacked lipid bilayers”, Nature Materials, 11, 1074 (2012). [DOI: 10.1038/NMAT3451]