But the hemagglutinin is not the only protein on the surface of the influenza virus particle. The other protein, neuraminidase, plays an essential role in the life cycle of the virus and has its own interesting history. According to Graeme Laver:
Gottschalk discovered that the reaction product produced by the RDE was sialic
acid (N-acetyl neuraminic acid) and that RDE
is a sialidase or neuraminidase. Then Graeme explained how the activities of neuraminidase and hemagglutinin were distinguished:
The structure of neuraminidase was solved in 1983 by J. N. Varghese, W. G. Laver and P. M. Colman (Nature 303:35-40). In the same issue of Nature Don Wiley commented on the structure writing that: "Viewed from above the head, each monomer consists of six of the four-stranded sheets arrayed like the petals of a flower but twisted like the blades of a pinwheel. A new category of tertiary structure is born".
Neuraminidase belongs to the class of proteins embedded in the membrane at the amino terminus. The box-like head of the neuraminidase is connected to a stalk that comprises the amino terminal part of the protein and includes the membrane-spanning domain. The stalk had been removed by protease treatment for crystallization and its structure remains unknown.
The structures of the plant RNA viruses and the picornaviruses had been remarkable in their similarity, not so the hemagglutinin and neuraminidase. Don Wiley wrote: "The topology of folding in the NA is quite unrelated to that in the HA, however, so suggestions that the two sialic acid-binding proteins of the virus may have evolved from a common ancestor can safely be dismissed".
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| Introduction | Some historical highlights: structural virology and virology |
| Solving the Structure of Icosahedral Plant Viruses | Picornavirus Structure | Poliovirus | Polio
The Influenza Virus Hemagglutinin | The Influenza Virus Neuraminidase |
Issues of Science and Society |contributors|