Re-evaluating the p7 viroporin structure

Unexpected features of the p7 oligomeric structure2 include: (i) the His17 side chain, known to be involved in ion conduction3,4, points outward towards the membrane bilayer; (ii) the orientation of the best fit of the oligomeric structure to the electron microscopy envelope contradicts antibody binding data5; and (iii) a short outer transmembrane helix exposes polar residues to the hydrophobic region of the membrane so that the structure cannot be accommodated in lipid bilayers without large structural rearrangements or membrane thinning6,7 (Extended Data Fig. 1a, b). A third sample prepared using a different protocol8 (50 mM DPC), indicated a protein mass of 7.8 ± 1.1 kDa associated with a detergent micelle of 24.7 ± 0.6 kDa (Extended Data Fig. 3a). [...]NMR spectra matching exactly the protein and detergent concentrations at the monomeric SEC-MALS peak summit (5 pM protein and 50 mM DPC) show good overlap with the spectrum published in ref. 2 (Extended Data Fig. 2d). [...]we find that p7 is monomeric over a range of protein and DPC concentrations, including the NMR conditions used to determine an oligomeric structure2, and that NOEs identified as unambiguously intermolecular are consistent with artefacts from residual protonation. [...]it cannot be excluded that the p7 oligomeric complexes observed by electron microscopy represent a small proportion of the total protein sample that is not detectable by NMR or sEc-MALS.