Small-Angle Neutron Scattering for Studying Lipid Bilayer Membranes

Abstract

Small-angle neutron scattering (SANS) is a powerful tool for studying biological membranes and model lipid bilayer membranes. The length scales probed by SANS, being from 1 nm to over 100 nm, are well-matched to the relevant length scales of the bilayer, particularly when it is in the form of a vesicle. However, it is the ability of SANS to differentiate between isotopes of hydrogen as well as the availability of deuterium labeled lipids that truly enable SANS to reveal details of membranes that are not accessible with the use of other techniques, such as small-angle X-ray scattering. In this work, an overview of the use of SANS for studying unilamellar lipid bilayer vesicles is presented. The technique is briefly presented, and the power of selective deuteration and contrast variation methods is discussed. Approaches to modeling SANS data from unilamellar lipid bilayer vesicles are presented. Finally, recent examples are discussed. While the emphasis is on studies of unilamellar vesicles, examples of the use of SANS to study intact cells are also presented.

Interplay of Hydropathy and Heterogeneous Diffusion in the Molecular Transport within Lamellar Lipid Mesophases

“…It is expected that quantitative results depend on the choice of these parameters, but the qualitative impact of hydrophobicity and spatial dependence of diffusion on molecular transport does not change once the values of and h have been fixed. We note that, for any system of interest, these parameters can be obtained directly from experiments such as small-angle X-ray or neutron scattering; particularly, a can be obtained by analyzing the peak positions of the scattering profiles [ 17 ], while l and correspond to half the thickness of the bilayer and of its hydrophobic part, respectively, which can be computed by suitably fitting the scattering profiles [ 67 ] or by employing geometric arguments based on the known composition of the system [ 1 ].…”

Small-Angle Neutron Scattering Study of a Phosphatidylcholine–Phosphatidylethanolamine Mixture

“…The total thickness of the bilayer is 3.6 Å thinner at 55 °C than it is at 30 °C. The total number of water molecules found to be associated with the lipid headgroups, per the self-consistent slab model, − described in Section , is also presented in the table.…”

“…The right image shows a zoomed-in view of the top of the vesicle that better presents the differences in A L and leaflet thicknesses of the inner and outer leaflets. The image was rendered using Persistence of Vision Raytracer software from an input file produced by software written for the generation of this kind of vesicle schematic that has been used previously. , The software was modified to show the differences in the structures of the inner and outer leaflets.…”

“…The present results provide new information about the structure of the lipid bilayer vesicles made of a 7:3 molar mixture of DMPC and DMPE and how it depends on the temperature. The use of deuterium-labeled DMPC made it possible to observe differences in the structures of the two leaflets of the bialyer. , The A L of the lipids in the inner leaflet of the bilayer displays a stronger temperature dependence than that of the outer one. The SANS results also revealed considerable asymmetry in the composition of the inner and outer leaflets of the bilayer, which Figure highlights clearly.…”

“…SANS data were fit using the 4-shell core–shell model that has been employed previously by this group for modeling lipid bilayer mixtures containing one species of deuterium-labeled lipid. , However, the model was modified to be a self-consistent slab model − that employed the sample composition and known physical parameters for the lipids. The model is described in detail below.…”