Using novel software, scientists for the first time have been able to determine an entire structure of spherical virus without resorting to icosahedral symmetry, a technique used to simplify image reconstruction. The press office from Purdue University explains the research that was published in this week’s edition of Nature:
“While before we could only see virus parts that were symmetric, we can now see those that have non-symmetric structures, such as portions of the one our paper focuses on, the Epsilon 15 virus that attacks salmonella,” said Jiang, who recently joined Purdue’s College of Science as an assistant professor of biology. “This software will enable a substantial expansion of what we can see and study. We remain limited to observing those viruses that are identical from one individual viral particle to the next – which, sadly, is still only a small portion of the viral species that are out there. But it is a major step forward toward our goal of seeing them all…”
“Many teams were able to determine the shell’s configuration because it is a highly symmetric, regular 20-sided shape. But to do so, they essentially had to pretend the rest of the virus didn’t exist,” Jiang said. “The trouble is that its structure is a lot more complicated than that. It has a tail and an internal genome made up of strands of tightly coiled DNA that are essential to the virus’s function. We literally didn’t have the whole picture of what tools Epsilon 15 uses to infect its host.”
The newly revealed components of the viral particle possesses qualities surprising to researchers accustomed to seeing only symmetric viruses up close.
“Epsilon 15’s tail, for example, has six ‘spikes’ in it, but they aren’t arranged in a neat hexagonal ring. They’re highly deviant,” Jiang said. “Because they’re so off-kilter, only two of the spikes actually grasp the shell surface. It’s probably not very exciting news to anyone who doesn’t look at these things for a living, but what it shows us is that the viral world holds many unexpected secrets, and if we’re going to unlock them, we need to see them first.”
Probing the innards of the virus also revealed that it possesses a core, the existence of which the researchers did not suspect and the function of which they can as yet only guess at. Jiang said his team suspects the core helps ease the release of the DNA coil into the bacterium, an event akin to shooting a spool of twine attached to a grappling hook across a wall at high velocity.
The press release…