The helicase from hepatitis C virus is active as an oligomer

The helicase from hepatitis C virus (HCV NS3h) residing on the C-terminal domain of nonstructural protein 3 was considered to be monomeric by several researchers. Here we demonstrate, based on biochemical kinetic data, that the HCV helicase acts as an oligomer. The increase in the ATPase k(cat) of the NS3h protein with increasing protein concentration provided evidence for oligomerization. A sharp decrease in the unwinding rate was observed when the wild type NS3h was mixed with the ATPase deficient mutants of NS3h protein. This provided strong support for both mixed oligomer formation and subunit interactions for the HCV helicase. Chemical cross-linking of NS3h protein was an inefficient process, but yielded cross-linked protein oligomers of various sizes. The information currently available for HCV helicase is consistent with the hypothesis that oligomers of NS3h are not stable and the helicase subunits exchange during unwinding. Nevertheless, oligomerization of HCV helicase stimulates the ATPase activity, and it is required for the helicase activity.