The HN glycoprotein of sendai virus: Analysis of site(s) involved in hemagglutinating and neuraminidase activities

Abstract

The HN glycoprotein of paramyxoviruses is responsible for attachment to red cell and host cell receptors and for neuraminidase activity. Several lines of evidence presented in this report are consistent with the concept that hemagglutinating and neuraminidase activities of the HN glycoprotein of the paramyxoviruses, Sendai and Newcastle disease virus, involve two distinct sites of the molecule. First, a Sendai virus mutant, temperature-sensitive ( ts) at 38° for hemagglutination and attachment to host cells was not ts for neuraminidase activity, indicating that different sites may be involved in these activities. Second, monoclonal antibodies to the HN protein were used to select antigenic variants. The variants were then reacted with antibody and tested for neuraminidase and hemagglutinating activities. The results showed that some variants were inhibited in hemagglutination but not in neuraminidase activity. Finally, an analog of N-acetylneuraminic acid (2-deoxy-2,3-dehydro- N-acetlyneuraminic acid) inhibited neuraminidase activity of Sendai virus and Newcastle disease virus by >95% at 10 −4 M. However, at 10 −2 to 10 −4 M, the analog did not inhibit hemagglutination by either virus, although it inhibited the elution of NDV and Sendai virus from agglutinated red cells. This latter observation shows that the analog does not inhibit virion binding to red cell receptors, but does inhibit the neuraminidase activity responsible for the elution process. Taken together, these data are consistent with the concept that independent sites on the HN molecule may be involved in attachment to host cells and neuraminidase activity. However, the possibility that a single active site may be involved in both activities has not been excluded.