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Research explained · Influenza surface proteins

Can influenza A(H2N2) attach sugars at neighboring sites?

Yes. In lab tests of haemagglutinin, a surface protein of influenza A(H2N2), either of two neighboring amino acids could carry a sugar chain. The researchers found this pattern at two places in the protein. Removing the chains had limited effects on the transport and biological activity they measured. [1]

See original studies View the SGM research record

Which positions could carry a sugar chain?

Positions 20 and 21
The first pair of candidate sites contained two neighboring asparagines, at positions 20 and 21.
The experimental variants showed that each position could carry a chain. [1]
Positions 169 and 170
A second pair of neighboring asparagines sat farther along the protein.
Here too, either position could carry a chain in the tested variants. [1]
Transport, activity and antibody binding
Losing the tested sugar chains had limited effects on transport inside the cell and on measured biological activity.
Some variants also changed how antibodies bound to the protein. A mutation changes the amino-acid sequence itself, so the researchers could not attribute those differences to the sugar alone. [1]

What makes the sites overlap?

An N-linked glycan is a sugar chain attached to an amino acid called asparagine. A short sequence of amino acids, called a sequon, marks a possible attachment site. At the sites studied, two sequons shared part of their sequence. [1]

How could the researchers tell which sites were used?

The team made versions of haemagglutinin with one or two candidate sites disabled. The sugar chains affected how the protein moved through a gel. Comparing those patterns helped the team identify which positions could carry a chain in each variant. [1]

How did the result compare with H7N1?

In a separate experiment, researchers found that removing one stem glycan strongly impaired the growth of recombinant H7N1 virus. The H7N1 study measured whole-virus growth. The H2N2 study measured properties of the surface protein after changing a different set of sites. [1][2]

Original research

  1. 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. Primary H2N2 mutagenesis, gel-mobility and protein-function experiments.
  2. 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 experiment for comparison.