Identification of amino acids involved in the sialidase activity of the mumps virus hemagglutinin-neuraminadase protein.

We previously described sialidase-deficient variants of the O'Take strain of mumps virus obtained by growth under the selective pressure of the competitive sialidase inhibitor 2-deoxy-2,3-dehydro-N-acetylneuraminic acid (DANA). In this report, we describe the production of a sialidase-deficient variant of the RW strain of mumps virus using an identical selection protocol. The biologic activities of the RW variant, RW(DANA)v1, were identical to those described for O'Take-(DANA)v1 and included a lack of detectable sialidase activity, unchanged hemagglutination activity, and expression of cell-to-cell fusion in infected cell monolayers. Analysis of the structural proteins of each virus by both two-dimensional tryptic peptide mapping and monoclonal antibody binding assays suggested that limited changes occurred in the hemagglutinin-neuraminidase (HN) proteins and that only the HN proteins were altered. The complete nucleotide sequence of the RW(DANA)v1 HN was determined and compared to the HN sequence of the RW parent. Two nucleotide differences accounting for two nonconservative amino acid differences were noted; an lle to a Thr at amino acid 181 and a Gln to Lys at amino acid 261 from RW to RW(DANA)v1, respectively. By comparing the data presented here with those reported for several other paramyxoviruses, we tentatively identify amino acid 181 as a critical residue in the active site of the mumps virus sialidase enzyme.