Determination of the structure of the 1918 flu virus receptor for binding protein will contribute to understanding of flu viruses and their transmission from birds to humans.

NIMR scientists have solved an 85-year old riddle by determining the structure of the Haemagglutinin (HA) of the flu virus which jumped from birds to humans in 1918 killing more than 20 million people worldwide. The work published today (5 February) in the online version of the journal Science will contribute to understanding of flu viruses and their transmission from birds to humans.

The first step in infection by flu viruses is their attachment to the cells in which they will replicate themselves. Attachment involves the Haemagglutinins spike-like molecules that project from the viruses and bind to particular receptors on the surface of cells in the body.

X-ray crystallography was used to determine the three-dimensional structure of the HA of the 1918 virus based on RNA sequences obtained in the USA from pathological specimens preserved since 1918.

Human and bird virus HAs interact with different cell receptors and therefore bird viruses do not usually infect humans. For them to be able to infect people and start widespread epidemics their HAs must normally change so that they can attach to the human receptors on the cell. The structure of the 1918 HA changed to make it capable of attaching to human cells, thus allowing human to human transmission.

NIMR Director Sir John Skehel said, "This paper is important because of the knowledge it brings about how these viruses, which originate in birds can jump to humans. This allows us to track and monitor the changes in the virus for public health purposes, although it does not allow us to predict or prevent future forms of flu."

"This tells us more about the transmission of infections from birds to humans. However, it will not have an immediate impact on the situation currently unfolding in the Far East with the chicken flu known as H5, since, from our previous work, we know that the 1918 and the H5 Hemagglutinins are quite different."