Abstract
Influenza A virus (IAV) neuraminidase (NA) receptor-destroying activity and hemagglutinin (HA) receptor-binding affinity need to be balanced with the host receptor repertoire for optimal viral fitness. NAs of avian, but not human viruses, contain a functional 2nd sialic acid (SIA)-binding site (2SBS) adjacent to the catalytic site, which contributes to sialidase activity against multivalent substrates. The receptor-binding specificity and potentially crucial contribution of the 2SBS to the HA-NA balance of virus particles is, however, poorly characterized. Here, we elucidated the receptor-binding specificity of the 2SBS of N2 NA and established an important role for this site in the virion HA-NA-receptor balance. NAs of H2N2/1957 pandemic virus with or without a functional 2SBS and viruses containing this NA were analysed. Avian-like N2, with a restored 2SBS due to an amino acid substitution at position 367, was more active than human N2 on multivalent substrates containing α2,3-linked SIAs, corresponding with the pronounced binding-specificity of avian-like N2 for these receptors. When introduced into human viruses, avian-like N2 gave rise to altered plaque morphology and decreased replication compared to human N2. An opposite replication phenotype was observed when N2 was combined with avian-like HA. Specific bio-layer interferometry assays revealed a clear effect of the 2SBS on the dynamic interaction of virus particles with receptors. The absence or presence of a functional 2SBS affected virion-receptor binding and receptor cleavage required for particle movement on a receptor-coated surface and subsequent NA-dependent self-elution. The contribution of the 2SBS to virus-receptor interactions depended on the receptor-binding properties of HA and the identity of the receptors used. We conclude that the 2SBS is an important and underappreciated determinant of the HA-NA-receptor balance. The rapid loss of a functional 2SBS in pandemic viruses may have served to balance the novel host receptor-repertoire and altered receptor-binding properties of the corresponding HA protein.
Highlights
Influenza A virus (IAV) particles contain hemagglutinin (HA) and neuraminidase (NA) glycoproteins
By using novel assays, we established an important role for this site in the HA-NA-receptor balance of virus particles as it contributes to receptor binding and cleavage by virions, the latter of which is required for virion movement and self-elution from receptors
In NA of A/Singapore/1/1957 (H2N2) pandemic virus one of the SIAcontact residues in the 2nd sialic acid (SIA)-binding site (2SBS) is mutated compared to the avian consensus sequence (S367N, S3 Fig)
Summary
Influenza A virus (IAV) particles contain hemagglutinin (HA) and neuraminidase (NA) glycoproteins. HA functions as a sialic acid (SIA)-binding and fusion protein. NA has receptordestroying activity by cleaving SIAs from sialoglycans. The HA and NA protein functionalities are critical for host tropism, and need to be well balanced in relation to the host receptor repertoire for optimal in vivo viral fitness [1,2,3]. An optimal HA-NA balance is hypothesized to allow virions to penetrate the heavily sialylated mucus layer, to attach to host cells prior to virus entry, and to be released from cells after assembly [4,5,6,7]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.