OCT 04, 2019 1:46 PM PDT

Scientists Capture Video of a Virus Forming

WRITTEN BY: Carmen Leitch

In a first, scientists have captured video of individual viruses as they form, illustrating viral assembly. This work can help us learn more about how we can combat viruses, and how to engineer nanoparticles that can assemble themselves. This work focused on simple single-stranded viruses that are made of RNA, which are the most common kind of virus that we know of; these viruses cause the common cold, West Nile, gastroenteritis, and polio, among others infections. The findings have been reported in the Proceedings of the National Academy of Sciences (PNAS).

A 3D graphical representation of a tightly packed icosahedral poliovirus particle / Credit: CDC/ Sarah Poser

"Structural biology has been able to resolve the structure of viruses with amazing resolution, down to every atom in every protein," said Vinothan Manoharan, the Wagner Family Professor of Chemical Engineering and Professor of Physics at the Harvard John A. Paulson School of Engineering and Applied Sciences. "But we still didn't know how that structure assembles itself. Our technique gives the first window into how viruses assemble and reveals the kinetics and pathways in quantitative detail."

RNA viruses are typically simple structures. Manoharan’s team focused on one that can infect a bacterium. It’s a single strand of RNA that’s around 30 nanometers in diameter, and it can generate 180 identical proteins. These proteins can arrange themselves into pentagons and hexagons, forming a capsid - a protective structure that encases the viral RNA.

Until now, no one has visualized the formation of the structure. Viruses have tiny components and have been challenging to observe in real-time. Scientists turned to a tool called interferometric scattering microscopy; in it, light scatters off an object and makes a dark spot against a bright field. The physical structure of the virus can’t be seen directly, but the changes in its size can be visualized over time, as shown in the video.

In this work, strands of virus were attached to a substrate while the scientists moved proteins over the surface. With the interferometric microscope, they could watch as dark spots arose and grew darker until they reached the size of a fully-formed virus. The intensity of the darkness could be measured, enabling the scientists to calculate the number of proteins attaching to the strands of viral RNA over time.

"One thing we noticed immediately is that the intensity of all the spots started low and then shot up to the intensity of a full virus," Manoharan noted. "That shooting up happened at different times. Some capsids assembled in under a minute, some took two or three, and some took more than five. But once they started assembling, they didn't backtrack. They grew and grew, and then they were done."

Their results were compared to two other simulations with different predictions. The first one was ruled out, but the second predicted pathway agreed with their observations; the proteins form a critical mass called a nucleus before the capsid can form. Once the nucleus is generated, which happens at different times with different viruses, the growth of the virus continues until the correct size is reached. The scientists also noticed that if more proteins are moving on the substrate, the assembly can go awry.

"Viruses that assemble in this way have to balance the formation of nuclei with the growth of the capsid. If nuclei form too quickly, complete capsids can't grow. That observation might give us some insights into how to derail the assembly of pathogenic viruses," Manoharan explained.

Now that the assembly pathway has been revealed, scientists can explore more questions and learn more about how to model the mechanisms. This work could also be useful in the design of nanomaterials.

"This is a good example of quantitative biology, in that we have experimental results that can be described by a mathematical model," said Manoharan.

Learn more about viruses from the video.


Sources: AAAS/Eurekalert! via Harvard John A. Paulson School of Engineering and Applied Sciences, PNAS

About the Author
  • Experienced research scientist and technical expert with authorships on over 30 peer-reviewed publications, traveler to over 70 countries, published photographer and internationally-exhibited painter, volunteer trained in disaster-response, CPR and DV counseling.
You May Also Like
OCT 25, 2020
Microbiology
Over Time, Plague Infections Spread Faster
OCT 25, 2020
Over Time, Plague Infections Spread Faster
From the time of the Black Death, around 1348 and the Great Plague of 1665, epidemics of plague occurred in Europe. Rese ...
NOV 24, 2020
Immunology
Dirty Sheets Make Babies Healthier
NOV 24, 2020
Dirty Sheets Make Babies Healthier
Microbiologists have established that the development of infants’ immune systems is intricately linked to the dive ...
DEC 11, 2020
Microbiology
When Microbes Battle for Survival, the Weakest Can Win
DEC 11, 2020
When Microbes Battle for Survival, the Weakest Can Win
Our world is filled with different types of bacteria, and they have to coexist with one another. They have to compete fo ...
DEC 18, 2020
Microbiology
Wildfire Health Hazards Include Airborne Microbes
DEC 18, 2020
Wildfire Health Hazards Include Airborne Microbes
Research has shown that air pollution & smoke can have serious detrimental health effects. Now scientists have revealed ...
DEC 21, 2020
Microbiology
The Food Mom Eats Affects the Microbes in Her Breast Milk
DEC 21, 2020
The Food Mom Eats Affects the Microbes in Her Breast Milk
Although baby formula is a completely acceptable alternative for women that have trouble lactating, human milk is still ...
DEC 21, 2020
Genetics & Genomics
Tracing the Evolution of a Deadly Microbe
DEC 21, 2020
Tracing the Evolution of a Deadly Microbe
Salmonella are human & animal bacterial pathogens that are found everywhere. When the bacterium infects a person, it cau ...
Loading Comments...