Nesting Lipid Bilayers in Nanopores: Effect of Pore Diameter on Macroscopic Order and the Layer Count

Abstract

Nanotubular lipid bilayer membranes formed by self-assembly and confined by macroscopically aligned nanopores exhibit several attractive features for biophysics and bio-nanotechnology. When fully hydrated such bilayers systems are stable for at least a month and allow for a quick exchange of buffers and other water-soluble molecules. Even more importantly the bilayers have well-defined curvature and are macroscopically aligned over an exceptionally broad range of temperature, pH, and ionic strength. The latter feature facilitates studies of membrane and membrane proteins under close to native cellular membrane conditions by solid-state NMR and other spectroscopic methods. Here we report on the effect of nanoscale pore diameter on packing of lipid bilayers and macroscopic alignment of POPC (2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine) lipids inside the pores. We show that the pores from 36 to 44, 50 and 72 nm in diameter accommodate progressively larger number of nesting lipid bilayers – from up to two nanotubes for the smallest 36 nm pore to about four for 50 nm wide pore at 40 oC. This is consistent with 26-27 nm being the smallest diameter for the POPC nanotubes. Static 31P linewidth at 300 MHz 1H frequency indicated the best macroscopic alignment corresponding to just 1-3% of mosaic spread for either one or two nesting lipid nanotubes for all pore sizes. 31P linewidth and bilayer macroscopic alignment degraded notably for three nesting bilayers formed in the nanopores and even more for four. The latter is consistent with a formation of wavy lipid tubules previously reported for much larger 140-180 nm nanopores. Supported by DE-FG02-02ER15354 to AIS.