The p7 Protein of Hepatitis C Virus Forms Structurally Plastic, Minimalist Ion Channels

Abstract

Hepatitis C virus (HCV) p7 is a membrane-associated oligomeric protein harboring ion channel activity. It is essential for effective assembly and release of infectious HCV particles and an attractive target for antiviral intervention. Yet, the self-assembly and molecular mechanism of p7 ion channelling are currently only partially understood. Using molecular dynamics simulations (aggregate time 1.2 µs), we show that p7 can form stable oligomers of four to seven subunits, with a bias towards six or seven subunits, and suggest that p7 self-assembles in a sequential manner, with tetrameric and pentameric complexes forming as intermediate states leading to the final hexameric or heptameric assembly. We describe a model of a hexameric p7 complex, which forms a transiently-open channel capable of conducting ions in simulation. We investigate the ability of the hexameric model to flexibly rearrange to adapt to the local lipid environment, and demonstrate how this model can be reconciled with low-resolution electron microscopy data. In the light of these results, a view of p7 oligomerization is proposed, wherein hexameric and heptameric complexes may coexist, forming minimalist, yet robust functional ion channels. In the absence of a high-resolution p7 structure, the models presented in this paper can prove valuable as a substitute structure in future studies of p7 function, or in the search for p7-inhibiting drugs.

Viroporins: structure, function and potential as antiviral targets

“…The stoichiometry of p7 channel complexes has been reported as both hexameric and heptameric in membrane-mimetic detergents and lipid bilayers, with some studies reporting mixtures of both forms (Clarke et al, 2006;Griffin et al, 2003;Luik et al, 2009;OuYang et al, 2013;StGelais et al, 2009;Whitfield et al, 2011). Molecular dynamics confirms that both species are theoretically viable, although both display a degree of metastability (Chandler et al, 2012). The membrane environment appears to exert significant influence over p7 structure and channel activity, with potential fluctuations in both the monomeric and oligomeric form proposed to regulate its behaviour (Whitfield et al, 2011 Elegant transmission electron microscopy reconstruction studies of hexameric genotype 2a p7 channel complexes in detergent micelles revealed a flower-shaped channel complex with both N/C termini membrane-exposed and oriented to the broad 'petals' of the channels by immuno-gold labelling, consistent with a hairpin monomeric conformation (Luik et al, 2009).…”

“…Further along the spectrum towards a pore, HCV p7 has been shown to adopt both single-channel and 'burst-activity' behaviour in bilayers, with single-channel activity also comprising more than one conductance state (Chew et al, 2009;Clarke et al, 2006;Griffin et al, 2003;Pavlović et al, 2003;Premkumar et al, 2004;Whitfield et al, 2011). This may reflect p7 behaviour whilst conducting a non-preferred ionic substrate, although p7 activity is also differentially modulated by several factors, including virus genotype (Atkins et al, 2014), the formation of different oligomers (Clarke et al, 2006;Luik et al, 2009) and membrane composition (Whitfield et al, 2011), all of which may influence the meta-stable nature of channel complexes (Chandler et al, 2012).…”

Subcellular Localization and Function of an Epitope-Tagged p7 Viroporin in Hepatitis C Virus-Producing Cells

“…Notably, the precise oligomeric state of p7 is still debated, with both hexameric (2,13,15) and heptameric (12,15) species having been reported. Each p7 monomer consists of two transmembrane segments separated by a hydrophilic loop orientated toward the cytosol.…”

“…Regarding the ion-channeling activity of p7, the ion specificity has not been fully established (15), although a preference for the channeling of cations has been reported (5). Recently, p7-mediated transfer of protons across intracellular membranes was observed (17).…”

Infecciones de Transmisión Sexual en Semen: El Hombre como Vector de Transmisión

“…Posee un genoma RNA lineal de aproximadamente 10.000 nucleótidos (Chandler et al, 2012). Generalmente es transmitida por el uso de drogas y transfusiones de sangre, aunque también se puede dar por contacto sexual y transmisión vertical.…”