Toward Nanodisc Tailoring for SANS Study of Membrane Proteins

Although membrane proteins are of major importance in both physiology and disease, they remain less studied than soluble proteins due to the complex amphiphilic environments required to preserve their structure and function. As a consequence, membrane proteins are under-represented in structural databases. In this work, we present a robust structural characterization of lipid nanodiscs designed to facilitate membrane protein studies by small-angle neutron scattering. By combining small-angle X-ray and neutron scattering, we investigate nanodiscs of three different sizes and three lipid compositions to accommodate a broad range of systems. Specifically, nanodiscs with diameters of approximately 9 nm, 12 nm, and 15 nm were examined. Beyond the commonly used di-myristoyl-phosphatidylcholine lipid, we produced and characterized polar lipid extracts from a Gram-negative bacterium (Escherichia coli) and a Gram-positive bacterium (Bacillus subtilis) under both protonated and deuterated conditions. In conclusion, solubility-enhanced variants of the scaffold protein yield more stable nanodiscs and are therefore preferable for extended structural investigations. The co-fitting of small-angle scattering data provides robust geometrical models of these nanodiscs, which can be treated as well-defined reference systems for future studies of membrane proteins in native-like lipid environments.