Mutational analysis of the signal-anchor domain of influenza virus neuraminidase

Abstract

Influenza virus neuraminidase (NA; EC 3.2.1.18) possesses a signal-anchor hydrophobic domain at the amino terminus. To characterize the nature of this signal-anchor domain we have introduced single amino acid changes in this domain by oligonucleotide-directed mutagenesis. Three mutant NA proteins that were synthesized contained a single charged amino acid residue in place of a hydrophobic amino acid residue at position 11, 17, or 26 of the signal-anchor domain. When the altered NA proteins were expressed in CV-1 cells, two phenotypes were observed: substitution of arginine in place of glycine at position 11 and substitution of aspartic acid for valine at position 17 did not abolish the signal, the anchor, or the transport functions. On the other hand, substitution of arginine for isoleucine at position 26 blocked the migration of the NA protein from the Golgi complex to the cell surface. Double mutants were constructed from these single point mutations and they exhibited two phenotypes: one double mutant (aspartic acid at position 17 and arginine at position 26) was present mostly in the cytoplasm and the other (arginine at positions 11 and 26) was present mostly in the rough endoplasmic reticulum. These results indicate that the hydrophobic amino acids at positions 11, 17, and 26 are required for intracellular transport. Furthermore, the accumulation of the mutant proteins in the rough endoplasmic reticulum or the Golgi apparatus suggests the existence of putative intracellular transport (or traffic) signals in the signal-anchor domain of NA.