In the background, cryo-electron micrographs of purified viruses with their inner structure bubbling from radiation damage. Overlaid, (left) 3D computer reconstruction of a virus’s outer shell and tail in gray, with the inner structure in magenta; (right) blow-up of the inner viral structure in magenta. |
Scientists
have long tried to visualize smaller and smaller structures to provide
insights into the inner workings of human cells, bacteria and viruses.
Now, researchers at the National Institute of Arthritis and
Musculoskeletal and Skin Diseases (NIAMS), part of the National
Institutes of Health, have developed a new way to see structures within
viruses that were not clearly seen before.
Since
the discovery of the microscope, scientists have tried to visualize
smaller and smaller structures to provide insights into the inner
workings of human cells, bacteria and viruses. Now, researchers at the
National Institute of Arthritis and Musculoskeletal and Skin Diseases
(NIAMS), part of the National Institutes of Health, have developed a new
way to see structures within viruses that were not clearly seen before.
Their findings are reported in the Jan. 13 issue of Science.
Cryo-electron
microscopy (cryo-EM) is a technique that allows scientists to image
very small particles, like structures on the surface of viruses. This
method has been useful in helping researchers understand how vaccines
work. But, despite the success of cryo-EM, scientists have been unable
to clearly visualize structures inside of viruses, because radiation is
used to image them. “With lower doses of radiation, it is not possible
to see inside the organism,” said lead author Dr. Alasdair Steven of the
NIAMS Laboratory of Structural Biology Research. “However, higher doses
of radiation damage the virus, destroying the very structures that we
would like to view.”
Working
in collaboration with the group of Dr. Lindsay Black at the University
of Maryland Medical School, Baltimore, Steven and his team were able to
turn the problem of radiation damage into an asset. Viruses, one of the
simplest life forms, are made up of nucleic acids (DNA or RNA) and the
proteins encoded by the nucleic acid instruction manual. The researchers
realized that proteins inside the virus are more sensitive to damage
than DNA.
“We
first used low doses of radiation and recorded images in which the
inner structure of the virus was invisible,” said Steven. “Next, we used
high doses of radiation, and found that the inner structure could be
seen as a cylinder of bubbles.” While the inner structure was damaged,
the team was able to superimpose the images, using three-dimensional
computer reconstruction. As a result, they were able to clearly
visualize the viral structure. The investigators call this technique
bubblegram imaging.
Moving
forward, the team members anticipate many uses of bubblegram imaging.
Ideally, this technique will allow a better understanding of the inner
workings of viruses, providing more opportunities for developing novel
therapies. Beyond studying viral structure, cryo-EM could be used to
visualize interactions of proteins with DNA in human cells. One exciting
prospect lies in using this approach to visualize differences in cancer
vs. non-cancer cells. “This new cryo-EM procedure renders previously
invisible proteins visible and, thus, will provide new understanding of
cell biology,” said Steven.