Effects of heptad repeat regions of f protein on the specific membrane fusion in paramyxoviruses.

Objectives: To identify the effects of heptad repeat regions (HR1 and HR2) of F on the specific membrane fusion in paramyxoviruses.

Methods: Site-directed mutagenesis was used to create same enzyme sites on the F genes of Newcastle disease virus (NDV) and human parainfluenza virus (hPIV). Gene recombination was used to get chimeric F proteins NDV C-HR1 and hPIV C-HR1 by exchanging HR1 fragments each other; NDV C-HR2 and hPIV C-HR2 were also obtained by the same way. All the chimeric F proteins were co-expressed with their homologous or heterogeneous HN in eukaryocytes. Cell fusion functions were assayed by Giemsa staining and reporter gene method. The expression efficiencies of F proteins were assayed with fluorescence-activated cell sorter (FACS).

Results: NDV C-HR1 and hPIV C-HR1 had 53.91 and 83.15% of fusion activities, and NDV C-HR2 and hPIV C-HR2 had 107.23 and 12.01% of fusion activities, respectively, as compared with their relevant wild types. The analysis of FACS indicated that the expression efficiencies of all the chimeric F proteins except NDV C-HR2 were lower than those of their relevant wild types.

Conclusions: HR1 of NDV F might be important for its specific membrane fusion, but HR2 of NDV F may not; both HR1 and HR2 of hPIV F may be important for its specific membrane fusion.