Towards structural studies of self-assembled subviral particles: combining cell-free expression with 100 kHz MAS NMR.

Viral membrane proteins are prime targets in combatting infection. Still, the determination of their structure remains a challenge, both with respect to sample preparation and the need for structural methods allowing for analysis in a native-like lipid environment. Cell-free protein synthesis and solid-state NMR spectroscopy are promising approaches in this context, the former with respect to its great potential in the native expression of complex proteins, and the latter for the analysis of membrane proteins in lipids. Herein, we show that milligram amounts of the small envelope protein of the duck hepatitis B virus (DHBV) can be produced by cell-free expression, and that the protein self-assembles into subviral particles. Proton-detected 2D NMR spectra recorded at a magic-angle-spinning frequency of 110 kHz on < 500 mu g protein show a number of isolated peaks with line widths comparable to those of model membrane proteins, paving the way for structural studies of this protein that is homologous to a potential drug target in HBV infection.