The x-ray structure of a complex of sialic acid (Neu5Ac) with neuraminidase N9 subtype from A͞tern͞ Australia͞G70C͞75 inf luenza virus at 4°C has revealed the location of a second Neu5Ac binding site on the surface of the enzyme. At 18°C, only the enzyme active site contains bound Neu5Ac. Neu5Ac binds in the second site in the chair conformation in a similar way to which it binds to hemagglutinin. The residues that interact with Neu5Ac at this second site are mostly conserved in avian strains, but not in human and swine strains, indicating that it has some as-yet-unknown biological function in birds.

The polypeptides of the trimeric seed storage protein phaseolin comprise two structurally similar units each made up of a beta‐barrel and an alpha‐helical domain. The beta‐barrel has the ‘jelly‐roll’ folding topology of the viral coat proteins and the alpha‐helical domain shows structural similarity to the helix‐turn‐helix motif found in certain DNA‐binding proteins.

No abstract