Findings Reinforce Theories About How Viruses Evolve.

(From AScribe)

WEST LAFAYETTE, Ind. -- Two viruses that split from a common ancestor possibly a billion years ago still have the same protein "fold" in their outer shells, shedding light on how viruses evolved, Purdue University researchers have found.

The outer shells - or capsids - of viruses contain proteins, which are made of a string of building blocks called amino acids. Proteins fold into specific shapes, depending on the sequence of amino acids.

The team of structural biologists has determined that the phi 29 virus, which attacks the soil bacterium bacillus subtilis, possesses the same protein fold in its capsid as the fold found in the HK97 virus, which infects E. coli bacteria.

"These findings are made possible by studying the capsid structure in nearly atomic-scale detail," said Marc C. Morais, a postdoctoral researcher in the laboratory of Michael Rossmann, the Hanley Distinguished Professor of Biological Sciences in Purdue's College of Science.

The researchers used a powerful imaging tool called cryo-electron microscopy to determine the three-dimensional structure of phi 29 down to a resolution of 7.9 angstroms. An angstrom is one ten-billionth of a meter, or roughly one-millionth as wide as a human hair.

"What we're seeing is helping to confirm ideas about how viruses evolve," Morais said. "Other researchers previously discovered that seemingly unrelated viruses that infect mammals use the same capsid fold. Our new findings point to a similar phenomenon in bacteriophages, or viruses that infect bacteria."