DNA pressure stabilizes vessel of transport
Researchers at the Vrije Universiteit, the FOM Foundation and the Lund University in Sweden have measured the flexibility and the strength of a DNA-filled virus shell. They discovered that the shell doubled its strength, only when the virus shell was filled for over 95 percent. When the shell was less than 95 percent DNA-filled, it seemed empty. The findings will lead to more understanding of virus multiplication. The researchers had their findings published in the renowned journal Proceedings of the National Academy of Sciences (PNAS) on 5 June 2007.
A virus is an amount of genetic material that is embedded in a protein shell, called capsid. All viruses have a protein shell like that, particularly for protecting themselves during transport from one host to another. In addition to this, the closed shell also functions sometimes as a high-pressure vessel, which contains the essential energy for entering the host. So, viruses are unable to contaminating without a shell. The pressure is high in the small protein shell: about 60 atmosphere.
Prior to this scientists at the Vrije Universteit and the FOM Foundation have been investigating the flexibility and strength of an empty protein shell (see also Flexibele 'viruscontainer' mogelijk bruikbaar als nanotransporter . And now they have examined the DNA-filled protein shells: what is the influence of the DNA length in the protein shell on the rigidity of its shell? Therefore, they have used a bacteriophage, a small virus that contaminates only bacteria. Scientists use this virus many times as a model for research. There are short lengths variants of DNA strands of this virus. The researchers expected that ‘packaging’ the DNA in the protein shell would increase the pressure on the shell significantly, the more DNA the shell contained. The larger the packaged DNA chain, the more it will be folded up and the more the parts of the chain will reject one another. To the researchers’ surprise the pressure in the shell was hardly felt when there was a pressure on the virus shell by using a needle of an Atomic Force Microscope (AFM). Even when the DNA chain reached about 95 percent of its standard length, the rigidity of the filled protein shell was still equal to that of an empty shell. The DNA then behaved like a liquid crystal. Only when the shell was one hundred percent DNA-filled, the increased pressure was noticeable and the rigidity of the shell doubled. The repulsion between the parts of the DNA chain became then really tangible. On the basis of these results the researchers have concluded that the maximum amount of DNA that a protein shell may contain is exactly in balance with the strength that the shell is able to resist. Or, the bacteriophage is only functioning optimally when the protein shell is filled one hundred percent.
So, a completely DNA-filled protein shell appears to react differently than an empty shell. That puts a different light on the working of viruses. The next question that the researchers occupying themselves with, concerns the influence of the vicinity of the virus. What happens in a saline solution? Furthermore, the researchers will also have a try at making a transcription on viruses that can contaminate people.
For more information,please contact Dr. Gijs Wuite, vrije Universiteit Amsterdam, phone: (020) 598 79 87.