INTERACTION BETWEEN THE HEMAGGLUTININ-NEURAMINIDASE AND FUSION GLYCOPROTEINS OF HUMAN PARAINFLUENZA VIRUS TYPE III REGULATES VIRAL GROWTH IN VIVO.

• TR Number: 753
• Keywords: AIR-100 vs. cell lines, bronchiolitis, croup, EpiAirway (AIR-100), fusion protein, glycoproteins, hemagglutinin-neuraminidase, human parainfluenza virus type 3 (HPIV3), pneumonia

Paramyxoviruses, enveloped RNA viruses that include human parainfluenza virus type 3 (HPIV3), cause the majority of childhood viral pneumonia. HPIV3 infection starts when the viral receptor-binding protein engages sialic acid receptors in the lung and the viral envelope fuses with the target cell membrane. Fusion/entry requires interaction between two viral surface glycoproteins: tetrameric hemagglutmin-neuraminidase (HN) and fusion protein (F). In this report, we define structural corre­lates of the HN features that permit infection in vivo. We have shown that viruses with an HN-F that promotes growth in cul­tured immortalized cells are impaired in differentiated human airway epithelial cell cultures (HAE) and in vivo and evolve in HAE into viable viruses with less fusogenlc HN-F. In this report, we identify specific structural features of the HN dimer inter­face that modulate HN-F interaction and fusion triggering and directly impact infection. Crystal structures of HN, which pro­motes viral growth in vivo, show a diminished interface in the HN dimer compared to the reference strain’s HN, consistent with biochemical and biological data indicating decreased dimerization and decreased interaction with F protein. The crystallographic data suggest a structural explanation for the HN’s altered ability to activate F and reveal properties that are critical for infection in vivo.