First-Ever Video Of Virus Assembly- Rare View Of Virus Formation
Researchers have now captured images of the formation of individual viruses- for the first time ever- offering a real-time view of the kinetics of viruses formation and its assembly. The research study provides new insights into how to fight against viruses & engineer self-assembling particles.
This study is published in the Proceedings of the National Academy of Sciences.
Vinothan Manoharan, Wagner Family Professor of Chemical Engineering and Professor of Physics- Harvard John A. Paulson School of Engineering and Applied Sciences– said that structural biology has been able to resolve the structures of viruses with amazing resolution, down to every atom in every protein; Still, we did not know how that structure assembles itself. This new technique gives the first window into how viruses assemble & also reveals the kinetics as well as the pathways in quantitative detail.
Manoharan is the co-director of the Quantitative Biology Initiative, a cross-Harvard effort that brings together biology, novel measurement techniques, statistics & mathematics to develop causal and predictive mathematical models of biological systems.
Manoharan and his research team focused on single-stranded RNA viruses (ssRNA Viruses) which are the most abundant type of virus on the planet. In humans RNA viruses are responsible for West Nile fever, polio, gastroenteritis, hand, foot, & mouth disease, and the common cold.
RNA viruses tend to be very simple. Manoharan and his research team studied the virus, which infects E. coli bacteria, is about 30 nm in diameter & has one piece of RNA, with about 3600 nucleotides, & 180 identical proteins. These proteins arrange themselves into hexagons & pentagons to form a soccer-ball-like structure around the RNA which is called a capsid.
Researchers Record First-Ever Video Of Virus Assembly
The dark spots seen above are individual viruses. The spots grow darker as more and more proteins attach to the RNA strand. (Video courtesy of Manoharan lab)
How did those proteins manage to form those structures? Till now, no one had been able to observe viral assembly in real-time because viruses & their components are very small where their interaction is very weak.
To observe the viruses, the scientists used an optical technique known as interferometric scattering microscopy. This is a technique where the light scattered off an object creates a dark spot in a larger field of light. This technique does not reveal the virus’s structure but it does reveal its size & how that size changes with time.
Scientists attached viral RNA strands to a substrate, like stems of a flower, & flowed proteins over the surface. Then, by using the interferometric microscope, researchers watched as dark spots appeared & grew steadily darker until they were the size of full-grown viruses. And by recording intensities of those growing spots, the team could actually determine how many proteins were actually attaching to each RNA strand over time.
Manoharan said one thing the team noticed immediately is that the intensity of all the spots started low & then shot up to the intensity of a full virus. And that shooting up happened at different times. Some of the capsids assembled in under a minute, some took 2 or 3mins & some took more than 5mins. But once they started assembling, they did not backtrack. They grew & grew and then they were done, he explained.
The team compared these observations to that of the previous results from simulations, which predicted 2 types of assembly pathways. In the first type of pathway, the proteins first stick randomly to the RNA & then rearrange themselves into a capsid. And in the second, a critical mass of proteins, called a nucleus, must form before the capsid can grow.
The experimental results matched the second pathway & ruled out the first. Nucleus actually forms at different times for different viruses; And once it does, the viruses grow quickly & does not stop until it reaches its right size.
The team also noticed that the viruses tended to misassemble more often when there were more proteins flowing over the substrates.
Viruses that assemble in this way will have to balance the formation of the nuclei with the growth of the capsid. And if the nuclei form too quickly, complete capsids cannot grow. This observation might give us some insights into how to derail the assembly of these pathogenic viruses, said Manoharan.
How these individual proteins come together to form the nucleus is still an open question but now that experimentalists have identified the pathway, scientists can develop new models that can explore assembly within that pathway. And those models might also be useful for the designing of nanomaterials – that assemble themselves.
It is a good example of quantitative biology, in that we actually have the experimental results which can be described by a mathematical model, said Manoharan.
The research was co-authored by Aaron M. Goldfain & Rees F. Garmann. This study was supported by the National Science Foundation, the National Institutes of Health, and the Simons Foundation.
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