Functional characterisation of natural variants of the hepatitis C virus p7 ion channel protein

The HCV p7 protein is a viroporin that acts to increase endosomal pH to preserve the infectivity of nascent virions. Previous work has identified several key residues in p7 that are critical for its function. A number of compounds have been found to inhibit p7 activity in vitro and genotype variation in the p7 sequence is known to have significant effects on p7 inhibitor sensitivity. This study aimed to further our understanding of the role of p7 during HCV infection. The effects of six naturally-occurring p7 variants, within a single genotype, isolated from 5 patients of varying disease severity were investigated.
It was found in in vitro liposome assays that the patient polymorphisms caused a wide variation in p7 channel activity. The previously-observed low-pH activation in J4 p7 was also observed in JFH1 p7, but not in H77 p7; this showed a ‘V’ shaped activation profile, with its lowest activity at pH 6.7 and peak activity at pH 6.2 and 7.4. Four of the patient isolates shared the same activation pattern as H77; two with non-synonymous mutations of S21P and Y31H displaying low-pH activation. In virus, the Y31H mutant was the only Seattle variant to show a significant reduction in the production of infectious virus.
JFH1 intracellular virions have previously been shown to be sensitive to transient exposure to reduced pH, while secreted virions were insensitive to such changes. In this study, it is shown that H77 secreted virions are sensitive to transient reductions in pH, while the Seattle isolate viruses showed reduced pH sensitivity. The Y31H isolate also showed increased sensitivity to the p7 inhibitor rimantadine.
In conclusion, this study found that natural polymorphisms in p7 within a single genotype can cause significant changes in p7 activity. These changes did not show any correlation with the severity of disease in the original patients.