Six-helix bundle assembly and characterization of heptad repeat regions from the F protein of Newcastle disease virus.

Paramyxoviruses may adopt a similar fusion mechanism to other enveloped viruses, in which an anti-parallel six-helix bundle structure is formed post-fusion in the heptad repeat (HR) regions of the envelope fusion protein. In order to understand the fusion mechanism and identify fusion inhibitors of Newcastle disease virus (NDV), a member of the Paramyxoviridae family, we have developed an E. coli system that separately expresses the F protein HR1 and HR2 regions as GST fusion proteins. The purified cleaved HR1 and HR2 have subsequently been assembled into a stable six-helix bundle heterotrimer complex. Furthermore, both the GST fusion protein and the cleaved HR2 show virus-cell fusion inhibition activity (IC(50) of 1.07-2.93 microM). The solubility of the GST-HR2 fusion protein is much higher than that of the corresponding peptide. Hence this provides a plausible method for large-scale production of HR peptides as virus fusion inhibitors.