Mapping the haemagglutinin and neuraminidase functions of the human parainfluenza virus type 3 haemagglutinin-neuraminidase protein.

Abstract

The haemagglutinin-neuraminidase protein (HN) of human parainfluenza virus type 3 is a bifunctional protein. To map the functions to the protein, three truncations of the gene were constructed by digesting the HN gene with the restriction endonucleases Hind III, Bgl II or Xbo I and inserting a stop codon. An internal deletion using Rsa I was also constructed. The four mutants were expressed in the recombinant vaccinia virus system. The expression of the mutant proteins was analysed by both Western Blot and immunoprecipitation. The products of the three truncations migrated at the molecular weights predicted for the truncated proteins. The product of the internal deletion migrated more quickly than predicted and upon sequencing revealed a frame shift mutation and, therefore, a fourth truncation. The migration of the gene product was consistent with the molecular weight predicted for this truncation. The full length HN was functional in both haemagglutination and neuraminidase assays. The four mutants were active only in the neuraminidase assay, none of them haemagglutinated Guinea pig erythrocytes. This allows us to predict that the haemagglutination region is near the carboxy-terminus of the protein while the neuraminidase region is amino-terminal of amino acid 212.