ELUCIDATING BINDING, FUSION AND ENTRY OF HUMAN METAPNEUMOVIRUS

Human metapneumovirus (HMPV) is a respiratory pathogen in the Paramyxoviridae family that infects nearly 100% of the world population. This enveloped RNA virus causes severe viral respiratory disease in infants, the elderly, and immunocompromised patients worldwide. Despite its prevalence and importance to human health, no therapies are available against this pathogen. Entry of paramyxoviruses into host cells generally requires the coordinated activity of the attachment glycoprotein, G, which interacts with a cell receptor, and the fusion glycoprotein, F, which promotes subsequent fusion of viral and cellular membranes. However, HMPV F is the primary viral protein mediating both binding and fusion for HMPV. Previous work that showed HMPV F mediates attachment to heparan sulfate proteoglycans (HSPGs), and some HMPV F fusion activity can be promoted by acidic pH. The work presented here provides significant advances in our understanding of the fusion and binding events during HMPV infection. We demonstrated that low pH promotes fusion in HMPV F proteins from diverse clades, challenging previously reported requirements and identifying a critical residue that enhances low pH promoted fusion. These results support our hypothesis that electrostatic interactions play a key role in HMPV F triggering and further elucidate the complexity of viral fusion proteins. Additionally, we characterized the key features of the binding interaction between HMPV and HSPGs using heparan sulfate mimetics, identifying an important sulfate modification, and demonstrated that these interactions occur at the apical surface of polarized airways tissues. We identified differences in particle binding related to the presence or absence of the HMPV G and SH glycoproteins. Lastly, we characterized paramyxovirus infection in cystic fibrosis bronchial epithelial cells, identifying a potential specific susceptibility to HMPV infection in these individuals. The work presented here contributes to our understanding of HMPV infection, from mechanisms of early events of entry to clinical scenarios