March 3 , 2008
3pm in Howey Physics Lecture Room 5

 

Alex Evilevitch
Department of Physical Chemistry
Lund University, Sweden

 

"Biophysics of Viral Infectivity:

Matching Genome Length and Virus Size"

 

Viruses are among the simplest biological objects. They typically consist of a container, the capsid, which holds the viral genome. The viral genome is a long, charged molecule of RNA or DNA enclosed in the rigid protein shell of the capsid. This physical situation implies that the genome is highly stressed. This work involves a biophysical approach to understand as broadly as possible the state of stress of a long, semi-flexible chain, whose length is hundreds of times larger than the dimension of the viral capsid. We provide the first experimental evidence that viruses use the internal pressure built up by packaging their DNA inside the capsid to “shoot” their genomes into host cells. By balancing DNA ejecting force from viral capsids with an osmotic force resisting genome ejection, we estimated the internal DNA pressure in phage to be tens of atmospheres. Furthermore, by investigating the correlation between packaged DNA length in phage and capsid strength in response to nano-indentation with an AFM tip, we showed that the size of the genome must be consistent with the size of the shell and that it is the key to both viral infectivity and virion stability. This work provides a general mechanism of viral infection and suggests alternative future strategies to interfere with it.