The amino-terminal region of the neuraminidase protein from avian H5N1 influenza virus is important for its biosynthetic transport to the host cell surface

•Protein expression and trafficking of NA N-terminal mutants were investigated.•N-terminal amino acid residues 16-20 are indispensable for NA protein expression.•N-terminal amino acids 7-15 may suppress NA protein expression.•N-terminal amino acids 7-15 are critical for NA transport to the host cell surface.•Cdc42-mediated regulation of NA transport requires N-terminal amino acids 7-15.

Influenza virus neuraminidase (NA) is a major viral envelope glycoprotein, which plays a critical role in viral infection. Although NA functional domains have been determined previously, the precise role of the amino acids located at the N-terminus of avian H5N1 NA for protein expression and intracellular transport to the host plasma membrane is not fully understood. In the present study, a series of N-terminal truncation or deletion mutants of H5N1 NA were generated and their expression and intracellular trafficking were investigated.Protein expression from mutants NAΔ20, NAΔ35, NAΔ40, NAΔ7-20 and NAΔ7-35 was undetectable by immunoblotting and by performing NA activity assays. Mutants NAΔ6, NAΔ11 and NAΔ15-20 showed a marked decreased in protein expression, whereas mutants NAΔ7-15 and NAΔ15 displayed a slight increase in protein expression, compared with that of the native NA protein. These data suggest that amino acid residues 16-20 are vital for NA protein expression, while amino acids 7-15 might suppress NA protein expression. In deletion mutants NAΔ7-15 and NAΔ15 there was an accumulation of NA protein at the juxta-nuclear region, with reduced expression of NA at the cell surface. Although active Cdc42 could promote transport of wild-type NA to the host cell surface, this member of the Rho family of GTPases failed to regulate transport of mutants NAΔ7-15 and NAΔ15. The results of the study reveal that amino acid residues 7-15 of H5N1 NA are critical for its biosynthetic transport to the host cell surface.