Complex Structural Examination of Protein-Lipid Interactions with Neutron Scattering Techniques

Neutron scattering has significant benefits for examining the structure of protein-lipid complexes. Cold neutrons are non-damaging and predominantly interact with the atomic nucleus, meaning that neutron beams can penetrate deeply into samples, which allows for flexibility in the design of samples studied. Components within a complex can be individually resolved by leveraging the strong difference in neutron scattering length between protium ( ${}^{1}H$ , 99.984% natural abundance) and deuterium ( ${}^{2}H$ or D, 0.016%) namely through the mixing of H₂O and D₂O in the samples or by the deuterium labelling of the biomolecules. Thus, the relative distribution of components within a membrane can be elucidated. Using neutron scattering techniques lipid-protein complexes are most commonly studied using neutron reflectometry (NR) and small-angle neutron scattering (SANS). In this review, the methodologies to produce and examine a variety of model biological membrane systems using SANS and NR are detailed. These systems include supported lipid bilayers derived from vesicle dispersions or Langmuir-Blodgett deposition, tethered and floating bilayer systems, membrane protein-lipid complexes, and polymer wrapped lipid nanodiscs. The three key stages of any SANS/NR study on model membrane systems-sample preparation, data collection, and analysis-are described together with some background on the techniques themselves.