Nanodomain Formation in Planar Supported Lipid Bilayers Composed of Fluid and Polymerized Dienoyl Lipids

Abstract

Polymerization of synthetic phospholipid monomers has been widely used to enhance the stability of lipid membranes in applications such as membrane-based biosensing, where the inherent instability of fluid-phase lipid bilayers can be problematic. However, lipid polymerization typically decreases membrane fluidity, which may be required to maintain the activity of reconstituted integral proteins and peptides. Prior work has shown that a bilayer composed of binary mixtures of poly(lipid) and fluid lipid exhibits enhanced stability and supports the function of incorporated biomolecules. This work examines the structural basis of these findings using planar supported lipid bilayers (PSLBs) composed of binary mixtures of a polymerizable lipid, 1,2-bis[10-(2′,4′-hexadienoloxy)decanoyl]-sn-glycero-3-phosphocholine (bis-SorbPC), and a nonpolymerizable lipid, 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC). Fluorescence recovery after photobleaching (FRAP) measurements showed that long-range lateral diffusion was minimally affected when the poly(lipid) mole ratio was ≤0.7. Atomic force microscopy, used to examine phase segregation in these PSLBs, showed that DPhPC forms a continuous lipid matrix that is 0.2−0.4 nm thicker than the island-like poly(bis-SorbPC) domains, with lateral dimensions of ≤200 nm. The nanoscale phase segregation allows for long-range lateral diffusion of lipid probes in the DPhPC matrix. The combination of fluidity and stability in these materials should make them useful in membrane-based biosensing applications.

Nanomechanical Properties of Artificial Lipid Bilayers Composed of Fluid and Polymerizable Lipids

“…The poly­(bis-SorbPC) domains are irregularly shaped islands, with areas of 3000–6000 nm 2 , and the DPhPC domains are somewhat larger. The height difference between the domains, 0.3–0.4 nm, indicates that the lipids in the upper and lower leaflets of the bilayer are mostly in registry . The present study extends the previous publication.…”

“…Binary planar supported lipid bilayers (PSLBs) composed of 1,2-diphytanoyl- sn -glycero-3-phosphocholine (DPhPC), a fluid-phase lipid, and 1,2-bis­[10-(2′,4′-hexadienoloxy)­decanoyl]- sn -glycero-3-phosphocholine (bis-SorbPC), a polymerizable lipid are the subject of the present study (the molecular structures are shown in Figure S1). In a previous publication, we showed that polymerization of DPhPC/bis-SorbPC PSLBs induces phase segregation, resulting in the formation of subμm domains composed predominately of poly­(bis-SorbPC) surrounded by a semicontinuous phase composed predominately of DPhPC; a typical AFM image is shown in Figure . The poly­(bis-SorbPC) domains are irregularly shaped islands, with areas of 3000–6000 nm 2 , and the DPhPC domains are somewhat larger.…”

“…Continued development of these technologies also will be advanced by enhancing membrane stability. The weak, noncovalent intermolecular interactions among the lipids in a fluid-phase bilayer may be disrupted by chemical and mechanical stresses such as exposure to solvents/surfactants, extended storage time, drying/rehydration, and vibration, leading to partial or complete loss of the bilayer structure. ,, Consequently, considerable research has been devoted to the development of techniques to stabilize planar lipid bilayers. ,− Polymerization of reactive lipid monomers is one approach that greatly increases bilayer stability; ,,,, however, it can alter important properties such as lateral lipid diffusion and membrane material and mechanical properties. ,,,− …”

“…Properties intermediate between those of a fully polymerized bilayer and a fluid bilayer can be obtained by mixing nonpolymerizable and polymerizable lipids. For example, we have shown that polymerization of binary mixtures of the fluid phase, nonpolymerizable lipids, and polymerizable dienoyl lipids generates planar lipid bilayers in which long-range lateral diffusion is retained as well as the activity of peptides that require fluidity to reversibly associate to form transmembrane ion channels. , In addition, the stability of these binary membranes is intermediate relative to the single-component bilayers …”

Cell-Free Synthesis of a Transmembrane Mechanosensitive Channel Protein into a Hybrid-Supported Lipid Bilayer

“…SLBs can be readily assembled on solid surfaces by a number of convenient methods from liposome fusion, Langmuir–Blodgett–Schaeffer transfer, or solvent-assisted lipid bilayer formation . Due to their planar geometry, SLBs are compatible with various surface-sensitive characterization and analytical tools, including quartz crystal microbalance with dissipation (QCM-D), , surface plasmon resonance, atomic force microscopy, ,, electrochemical impedance spectroscopy, , and fluorescence microscopy . The stability of SLBs (owing to the solid support) and their compatibility with various analytical techniques make them popular and convenient model biomembrane surfaces. , …”