A single mutation in dairy cow-associated H5N1 viruses increases receptor binding breadth

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• An unprecedented outbreak of Clade 2.3.4.4b H5N1 avian influenza virus is occurring in US dairy cows.
• Understanding viral evolution and host adaptation is critical during emerging outbreaks.

Purpose of the Study:

• To investigate if recent H5N1 viruses have altered their sialic acid receptor binding properties.
• To identify molecular mechanisms behind any observed changes in receptor binding.

Main Methods:

• Screening of recombinant hemagglutinin (HA) from historical and recent H5N1 viruses using glycan microarrays.
• Analysis of binding to glycans with terminal α2,3 and α2,6 sialic acids.
• Molecular dynamics simulations and cryo-electron microscopy (cryo-EM) structure determination.
• Site-directed mutagenesis to identify key mutations affecting binding.

Main Results:

• H5 from a recent dairy cow isolate (A/Texas/37/2024) exhibited increased binding breadth to α2,3 sialic acid glycans (avian receptor).
• No binding to α2,6 sialic acid glycans (human receptor) was detected.
• A/Texas/37/2024 H5 showed greater receptor-binding site flexibility compared to a 2022 H5N1 strain.
• A single mutation, T199I, outside the receptor-binding site, was identified as responsible for increased binding breadth by enhancing flexibility.

Conclusions:

• Recent H5N1 viruses, including those in dairy cows, are evolving broader receptor binding capabilities.
• The T199I mutation contributes to increased receptor binding site flexibility and potentially alters the host range and tropism of H5N1.
• These findings highlight the dynamic evolution of avian influenza viruses and their potential for host adaptation.