SGM Journals

Research explained · Influenza surface proteins

How do sugars on the haemagglutinin stem affect H7N1 growth?

In an experimental H7N1 strain, removing the sugar chain at position 12 of haemagglutinin stopped the virus growing at 37 °C and reduced its growth at 33 °C. Removing the chain at position 478 had a smaller effect. Researchers tested the strain in cultured cells and embryonated chicken eggs. [1]

See original studies View the SGM research record

What happened when each sugar chain was removed

Asparagine 12
The variant failed to grow at 37 °C and grew less well at 33 °C in both cells and eggs.
The severity depended on the test temperature. [1]
Asparagine 28
The team could not recover a recombinant virus missing this chain.
The experiment produced no virus for a growth test at this site. [1]
Asparagine 478
The team recovered a virus missing this chain and measured smaller effects on growth.
The virus remained recoverable in the same system that failed to recover the position 28 variant. [1]

What is a stem glycan?

A glycan is a sugar chain. The three chains in these experiments are attached to asparagines in the stem of haemagglutinin, an influenza surface protein. The stem helps the protein change shape during the process that fuses the viral and cellular membranes. [1][2]

How does the growth result relate to fusion?

Earlier work on haemagglutinin produced in cells found that stem glycans help the protein hold the shape it needs before fusion. The later experiments measured growth of whole viruses. They also found that the recovered variants lost infectivity more readily after acid exposure than virus carrying wild-type haemagglutinin. The authors interpreted that as evidence that the sugar chains help stabilize the protein. [1][2]

Why did a study of H2 get a different result?

The H2 study removed chains at different positions and measured properties of haemagglutinin. This H7N1 study measured whether a whole virus grew. Those experiments can show which chains matter in their own systems. [1][3]

Original research

  1. Wagner et al. (2002), Journal of General Virology. N-Glycans attached to the stem domain of haemagglutinin efficiently regulate influenza A virus replication. Primary recombinant H7N1 growth and pH-stability experiments.
  2. Ohuchi et al. (1997), Journal of Virology. Oligosaccharides in the stem region maintain the influenza virus hemagglutinin in the metastable form required for fusion activity. Earlier expressed-protein study that examined fusion.
  3. Tsuchiya et al. (2002), Journal of General Virology. Role of overlapping glycosylation sequons in antigenic properties, intracellular transport and biological activities of influenza A/H2N2 virus haemagglutinin. Comparison with overlapping attachment sites on the H2 subtype.