Novel insights into the host cell glycan binding profile of human metapneumovirus.

Numerous viruses have been found to exploit glycoconjugates expressed on human cells as their initial attachment factor for viral entry and infection. The virus-cell glycointeractome, when characterized, may serve as a template for antiviral drug design. Heparan sulfate proteoglycans extensively decorate the human cell surface and were previously described as a primary receptor for human metapneumovirus (HMPV). After respiratory syncytial virus, HMPV is the second most prevalent respiratory pathogen causing respiratory tract infection in young children. To date, there is neither vaccine nor drug available to prevent or treat HMPV infection. Using a multidisciplinary approach, we report for the first time the glycointeractome of the HMPV fusion (F) protein, a viral surface glycoprotein that is essential for target-cell recognition, attachment, and entry. Our glycan microarray and surface plasmon resonance results suggest that Galß1-3/4GlcNAc moieties that may be sialylated or fucosylated are readily recognized by HMPV F. The bound motifs are highly similar to the N-linked and O-linked glycans primarily expressed on the human lung epithelium. We demonstrate that the identified glycans have the potential to compete with the cellular receptors used for HMPV entry and consequently block HMPV infection. We found that lacto-N-neotetraose demonstrated the strongest HMPV binding inhibition in a cell infection assay. Our current findings offer an encouraging and novel avenue for the design of anti-HMPV drug candidates using oligosaccharide templates.IMPORTANCEAll cells are decorated with a dense coat of sugars that makes a sugar code. Many respiratory viruses exploit this sugar code by binding to these sugars to cause infection. Human metapneumovirus is a leading cause for acute respiratory tract infections. Despite its medical importance, there is no vaccine or antiviral drug available to prevent or treat human metapneumovirus infection. This study investigates how human metapneumovirus binds to sugars in order to more efficiently infect the human host. We found that human metapneumovirus binds to a diverse range of sugars and demonstrated that these sugars can ultimately block viral infection. Understanding how viruses can take advantage of the sugar code on our cells could identify new intervention and treatment strategies to combat viral disease.

A neutralizing single-domain antibody that targets the trimer interface of the human metapneumovirus fusion protein.

IMPORTANCE: Human metapneumovirus (hMPV) is an important respiratory pathogen for which no licensed antivirals or vaccines exist. Single-domain antibodies represent promising antiviral biologics that can be easily produced and formatted. We describe the isolation and detailed characterization of two hMPV-neutralizing single-domain antibodies that are directed against the fusion protein F. One of these single-domain antibodies broadly neutralizes hMPV A and B strains, can prevent proteolytic maturation of F, and binds to an epitope in the F trimer interface. This suggests that hMPV pre-F undergoes trimer opening or "breathing" on infectious virions, exposing a vulnerable site for neutralizing antibodies. Finally, we show that this single-domain antibody, fused to a human IgG1 Fc, can protect cotton rats against hMPV replication, an important finding for potential future clinical applications.