The hepatitis C virus (HCV) has developed a small
membrane protein, p7, which remarkably can self-assemble into a large channel complex that selectively conducts
cations. We wanted to examine the structural
solution that the
viroporin adopts in order to achieve selective
cation conduction, because p7 has no homology with any of the known prokaryotic or eukaryotic channel
proteins. The activity of p7 can be inhibited by
amantadine and
rimantadine, which are potent blockers of the
influenza M2 channel and licensed drugs against
influenza infections. The
adamantane derivatives have been used in HCV clinical trials, but large variation in
drug efficacy among the various HCV genotypes has been difficult to explain without detailed molecular structures. Here we determine the structures of this HCV
viroporin as well as its
drug-binding site using the latest nuclear magnetic resonance (NMR) technologies. The structure exhibits an unusual mode of hexameric assembly, where the individual p7 monomers, i, not only interact with their immediate neighbours, but also reach farther to associate with the i+2 and i+3 monomers, forming a sophisticated, funnel-like architecture. The structure also points to a mechanism of
cation selection: an
asparagine/
histidine ring that constricts the narrow end of the funnel serves as a broad
cation selectivity filter, whereas an
arginine/lysine ring that defines the wide end of the funnel may selectively allow
cation diffusion into the channel. Our functional investigation using whole-cell channel recording shows that these residues are critical for channel activity. NMR measurements of the channel-
drug complex revealed six equivalent hydrophobic pockets between the peripheral and pore-forming helices to which
amantadine or
rimantadine binds, and compound binding specifically to this position may allosterically inhibit
cation conduction by preventing the channel from opening. Our data provide a molecular explanation for p7-mediated
cation conductance and its inhibition by
adamantane derivatives.