The recent pandemic-causing H1N1 flu virus used a new biochemical trick to spread efficiently in humans, researchers have said.
The discovery not only yields new insight into the subtle biology of flu, but also reveals another genetic marker public health officials can use to presage pandemics.
"We have found why the pandemic H1N1 virus replicated so well in humans," said Yoshihiro Kawaoka of University of Wisconsin-Madison's School of Veterinary Medicine. he H1N1 virus, Kawaoka explained, is really a combination of four different avian and swine flu viruses that have emerged during the past 90 years, and even includes genetic residue of the 1918 pandemic virus, an influenza that killed as many as 20 million people.
Typically, the presence of two amino acids- lysine and asparagines- in specific sites on a key avian protein are required for a flu virus to make the jump from an animal host and replicate efficiently in human cells.
The H1N1 virus lacked both of these amino acid building blocks, posing a puzzle for scientists.
The new study found that the lysine amino acid resides in a completely different location on the protein and is responsible for the H1N1 virus's ability to adapt to and co-opt human cells.
"This pandemic H1N1 has this mutation and is why it can replicate so well in humans. This gives us another marker to help predict the possibility of future flu pandemics," said Kawaoka.
The structural data, said Kawaoka, provides essential insight into how the virus interacts with the host cell, and could help provide a basis for antiviral agents that could be used to thwart a future flu virus that uses the same amino acid trick to infect human cells.
"Clearly, the host factors in human cells are doing something. The structure may help us better understand the interplay between the virus and the host human cell," said Kawaoka.
According to Bart L. Staker of Emerald BioStructures Inc., a member of the SSCGID, the structural data has also revealed changes in the surface shape of the avian virus protein in H1N1, which could, in turn, be responsible for thwarting factors in the human cell that would otherwise inhibit infection.
The findings were published in the Public Library of Science Pathogens.