Understanding the Structure and Dynamics of Complex Biomembrane Interactions by Neutron Scattering Techniques

Abstract

The membrane is one of the key structural materials of biology at the cellular level. Composed predominantly of a bilayer of lipids with embedded and bound proteins, it defines the boundaries of the cell and many organelles essential to life and therefore is involved in almost all biological processes. Membrane-specific interactions, such as drug binding to a membrane receptor or the interactions of an antimicrobial compound with the lipid matrix of a pathogen membrane, are of interest across the scientific disciplines. Herein we present a review, aimed at nonexperts, of the major neutron scattering techniques used in membrane studies: small-angle neutron scattering, neutron membrane diffraction, neutron reflectometry, quasielastic neutron scattering, and neutron spin echo. Neutron scattering techniques are well suited to studying biological membranes. The nondestructive nature of cold neutrons means that samples can be measured for long periods without fear of beam damage from ultraviolet, electron, or X-ray radiation, and neutron beams are highly penetrating, thus offering flexibility in samples and sample environments. Most important is the strong difference in neutron scattering lengths between the two most abundant forms of hydrogen, protium and deuterium. Changing the relative amounts of protium/deuterium in a sample allows the production of a series of neutron scattering data sets, enabling the observation of differing components within complex membrane architectures. This approach can be as simple as using the naturally occurring neutron contrast between different biomolecules to study components in a complex by changing the solution H2O/D2O ratio or as complex as selectively labeling individual components with hydrogen isotopes. This review presents an overview of each experimental technique with the neutron instrument configuration, related sample preparation and sample environment, and data analysis, highlighted by a special emphasis on using prominent neutron contrast to understand structure and dynamics. This review gives researchers a practical introduction to the often enigmatic suite of neutron beamlines, thereby lowering the barrier to taking advantage of these large-facility techniques to achieve new understandings of membranes and their interactions with other molecules.

Pore Forming Protein Induced Biomembrane Reorganization and Dynamics: A Focused Review

“…Another classical method for elucidating the structural and dynamic changes that happens during lipid protein interaction include neutron scattering techniques such as inelastic and quasielastic neutron scattering ( Swenson et al, 2008 ; Wood and Zaccai, 2008 ; Armstrong et al, 2012 ) as well as neutron spin echo ( Kumarage et al, 2021 ). The quasielastic neutron scattering data can be converted to the dynamic nature of lipid membranes based on scattering laws ( Qian et al, 2020 ). Based on the broadening or narrowing of the quasielastic peaks, the order of the lipid bilayer can be extracted.…”

Structure of Diisobutylene Maleic Acid Copolymer (DIBMA) and Its Lipid Particle as a “Stealth” Membrane-Mimetic for Membrane Protein Research

“…It is worth mentioning that the compositional difference between a typical lipid headgroup and the hydrocarbon chain deviated from the average 12% D 2 O, with each having its own CMP. 38 Sometimes, this difference created a scattering feature of near 0.10 Å −1 , corresponding to a typical lipid chain thickness when a high concentration of lipid was used. If the lipid particle size was significantly different, this could be decoupled or ignored.…”

“…While the amount of hydrogen in a 12% D 2 O (88% H 2 O) buffer gave rise to a relatively high incoherent background, the contrast between the protein and the lipid particles was still significant and provided a reasonable signal-to-noise ratio for the SANS study. It is worth mentioning that the compositional difference between a typical lipid headgroup and the hydrocarbon chain deviated from the average 12% D 2 O, with each having its own CMP . Sometimes, this difference created a scattering feature of near 0.10 Å –1 , corresponding to a typical lipid chain thickness when a high concentration of lipid was used.…”

“…SANS/SAXS techniques provide straightforward structural information, such as overall dimensions, shape, and molecular organization in solution, over length scales ranging from a few nanometers to hundreds of nanometers. They have been widely used for understanding the hierarchical structures of many polymers and biomacromolecules, including lipids and membrane proteins in aqueous solutions. − Understanding DIBMA and DIBMALP morphologies and assembly processes under different conditions will aid in developing better strategies for solubilizing membranes. SANS/SAXS techniques also benefit from the application of DIBMALPs to the solubilization of membrane proteins.…”

Methods for the solubilisation of membrane proteins: the micelle-aneous world of membrane protein solubilisation

“…Furthermore, micelles present a relatively poor lipid-bilayer mimetic, generally attributed to the lack of lateral pressure usually implemented by the membrane [ 30 ]. Furthermore, neutron reflectometry has revealed the membrane bilayer to be a complex structure with physiochemically distinct layers [ 31 ], which detergent micelles cannot replicate comprehensively due to their micellar morphology differing fundamentally from the membrane leaflet architecture. Consequently, MP stability, structure and activity within these mimetic systems may be altered compared with those within the native membrane environment.…”