No, I'm not talking about a computer virus here, but about a real one, the Epsilon 15, which attacks the bacterium Salmonella. By writing a few lines of computer code, biologists from Purdue University have found a way to control a high-resolution microscope. This led them to look inside a virus and at its whole structure. While previous teams were able to visualize the highly symmetric outer shell of other viruses, these researchers were able to see the whole structure of Epsilon 15, including its tail, its genome and even its core. This better knowledge of viruses which attack bacteria could lead to great advances in medicine, especially when antibiotics become inefficient because bacteria resist to them. Read more...
Here is a part of the introduction of the Purdue University news release.
With a few deft lines of computer code, Purdue University's Wen Jiang and his research group have created a powerful new tool for lab research that should allow scientists to obtain high-resolution images of some of the world's smallest biological entities -- the viruses.
So what have they done?
Developing the software package enabled the team to examine the Epsilon 15 virus, a "bacteriophage" that infects the salmonella bacterium, and to resolve features as small as 9.5 angstroms across - less than a billionth of a meter. Until now, the high-resolution device, called a cryo-electron microscope, used to examine such objects could only examine the virus's outer shell.
But with this new software, they saw more than the shell. Below is an image showing the detailed structure of Epsilon 15. "From the left-side cross section of the viral particle's interior, obtained with an advanced magnifier called a cryo-electron microscope, a team including Purdue structural biologist Wen Jiang was able to generate the right-side computer graphic highlighting the salient features of the virus" (Credit: Jiang Laboratories, Purdue University/Nature).
And on the image below, you can see the major elements of Epsilon 15, including the tail hub, the tail spikes and the big mass of dsDNA -- double-stranded DNA (Credit: Jiang Laboratories, Purdue University/Nature).
Here are more explanations about the structure of the virus.
"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."
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.
If you're interested by the subject, this research work appears on the cover story of the February 3, 2006 issue of Nature under the title "Structure of epsilon15 bacteriophage reveals genome organization and DNA packaging/injection apparatus" (Volume 439, Number 7076, Page 612). Here are several links to the Editor's summary, the abstract and to some additional figures.
But Nature also gives us access to other documents, such as this PowerPoint presentation (8 pages, 11,9 MB) which tells us that the shell proteins of various bacteriophages share similar fold, as you can see on the picture below, which among others, depicts the "cryo-EM structures of Epsilon15, P22, Herpes and phi29, and crystal structures of HK97 and T4" (Credit: Jiang Laboratories, Purdue University/Nature).
You also might want to watch this movie (1 minute and 37 seconds, 33 MB) from which the second image on this note has been extracted. And please note that this movie was realized with the help of Matt Dougherty, Director of Scientific Animation at the National Center for Macromolecular Imaging.
Finally, here is a last quote from Wen Jiang.
"Phages are useful to know about because they attack bacteria, and bacteria are staging a worrisome comeback in human health terms because they are growing resistant to our antibiotics -- sometimes faster than medicine can keep up. We need a new way to attack bacteria once they mutate, and if we can employ phages to do our work for us, it could be a great advance for medicine."
Now, we just have to hope that this research will soon contribute to the fight against viral disease.
Sources: Purdue University news release, February 1, 2006; Nature, February 3, 2006; and various web sites
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