Researchers have captured images of the formation of
individual viruses, offering a real-time view into the kinetics of viral
assembly. The research provides new insights into how to fight viruses and
engineer self-assembling particles.
Manoharan and his team focused on single-stranded RNA
viruses, the most abundant type of virus on the planet. In
humans, RNA viruses are responsible for, among others, West Nile fever,
gastroenteritis, hand, foot, and mouth disease, polio, and the common cold.
These viruses tend to be very simple. The virus Manoharan
and his team studied, which infects E. coli bacteria, is about 30 nanometers in
diameter and has one piece of RNA, with about 3600 nucleotides, and 180
identical proteins. The proteins arrange themselves into hexagons and pentagons
to form a soccer-ball-like structure around the RNA, called a capsid.
How those proteins manage to form that structure is
the central question in virus assembly. Until now, no one had been able to
observe viral assembly in real time because viruses and their components are very
small and their interactions are very weak.
To observe the viruses, the researchers used an
optical technique known as interferometric scattering microscopy, in which the
light scattered off an object creates a dark spot in a larger field of light. The
technique doesn't reveal the virus's structure but it does reveal its size and
how that size changes with time.
The researchers compared these observations to
previous results from simulations, which predicted two types of assembly
pathways. In one type of pathway, the proteins first stick randomly to the RNA
and then rearrange themselves into a capsid. In the second, a critical mass of
proteins, called a nucleus, must form before the capsid can grow.
See:
Posted by Dr. Tim Sandle, Pharmaceutical Microbiology
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