Viral protein in their sights: Advanced imaging reveals key structure of Ebola and other RNA viruses

Viral protein in their sights
The structure of the L-protein of vesicular stomatitis virus from electron cryomicroscopy. Credit: Simon Jenni

Viruses need us. In order to multiply, viruses have to invade a host cell and copy their genetic information. To do so, viruses encode their own replication machinery or components that subvert the host replication machinery to their advantage.

Ebola virus and rabies virus, two of the most lethal pathogens known to humans, belong to an order of RNA that share a common strategy for copying their genomes inside their hosts. Other relatives include Marburg virus, measles, mumps, respiratory syncytial virus and (VSV). Scientists study VSV, which causes acute disease in livestock but typically does not lead to illness in people, as a model for viruses that are harmful to humans.

Now a team from Harvard Medical School, using electron cryomicroscopy (imaging frozen specimens to reduce damage from electron radiation), has for the first time revealed the structure of a VSV protein at the atomic level. Called polymerase protein L, it is required for viral replication in this group of RNA viruses. The findings are published in Cell.

"We now have a better understanding of how RNA synthesis works for these viruses," said Sean Whelan, HMS professor of microbiology and immunobiology and senior author of the paper. "I think if you were trying to develop a viral-specific target to block the replication of one of these viruses, having the structure of the polymerase protein would help."

Scientists already know how these RNA viruses infect cells. They start by delivering a large protein RNA complex, which is viral RNA enclosed in a . The protein that copies viral RNA is polymerase protein L, which conducts all the enzymatic activities needed to synthesize RNA and then add a cap structure to its end to ensure it doesn't get destroyed by the cell—and to ensure that it can be translated into protein.

While researchers have known the atomic structures of the protein that coats the viral RNA, there are no data on protein L's atomic structure.

Antiviral drugs that target polymerase molecules are based in part on knowing their structure. That approach has been successful against HIV and herpes and hepatitis C viruses. But for the class of viruses known as nonsegmented negative-strand RNA viruses, finding the structure of polymerase protein L has been challenging.

The "L" stands for large. Larger proteins are often difficult to produce and to purify, Whelan said. Protein L is also flexible, with many functional fragments that are hard to isolate. The viruses evolved to make only small quantities of this protein.

Five years ago, using a lower-resolution form of electron microscopy in which the protein is visualized in the presence of negative stain, Whelan's team was able to detect at low resolution a structure that looked like a doughnut with three globular domains. Those earlier studies were informative, but the approach could not provide the atomic level of resolution the team ultimately needed.

Advances in electron cryomicroscopy encouraged them to try again. A team from Whelan's lab, working with a group led by Stephen Harrison, Giovanni Armenise - Harvard Professor of Basic Biomedical Science at HMS and a Howard Hughes Medical Institute (HHMI) investigator, was able to collect data from their viral samples that gave them much greater resolution. They also were able to align the images they collected into a three-dimensional model of polymerase protein L.

Into the density map obtained from these studies, members of the team built an atomic model of the polypeptide chain of VSV L protein. Solving this puzzle was a significant challenge and also involved the team of Nikolaus Grigorieff at HHMI's Janelia campus.

The result? An model of polymerase protein L's structure for VSV, which will form the basis for understanding the L protein of the other viruses in the order.

"The Ebola protein will look the same, the rabies protein will look the same, the other L proteins will look the same," Whelan said. "There will be some subtle differences reflecting the precise nature of amino acids, but we know that they're functionally and structurally the same."

Knowing the structure means scientists can explore how RNA synthesis is working in these viruses.

"It begins to suggest ways that we can perhaps pull apart other proteins that have not been so easy to express, such as the L protein in Ebola," Whelan said. "It doesn't mean we're going to have inhibitors immediately, but this is an important step, I think, towards that longer-term goal."


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Journal information: Cell

Citation: Viral protein in their sights: Advanced imaging reveals key structure of Ebola and other RNA viruses (2015, July 2) retrieved 23 May 2019 from https://phys.org/news/2015-07-viral-protein-sights-advanced-imaging.html
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JVK
Jul 03, 2015
Excerpt: "The Ebola protein will look the same, the rabies protein will look the same, the other L proteins will look the same," Whelan said. "There will be some subtle differences reflecting the precise nature of amino acids, but we know that they're functionally and structurally the same."

Subtle differences in amino acid substitutions differentiate the nutrient-dependent cell types of all genera. This news indirectly links viral microRNAs to entropy elasticity and genomic entropy that is prevented by the anti-entropic epigenetic effects of nutrient-dependent microRNAs which control viral replication.

Controlled replication is linked to the nutrient-dependent RNA-mediated amino acid substitutions that differentiate all cell types of all individuals of all living genera via their physiology of reproduction. The nutrient-dependent controlled physiology of reproduction enables the fixation of RNA-mediated amino acid substitutions that stabilize organized genomes.

Jul 03, 2015
"Controlled replication is linked to the nutrient-dependent RNA-mediated amino acid substitutions that differentiate all cell types of all individuals of all living genera via their physiology of reproduction. The nutrient-dependent controlled physiology of reproduction enables the fixation of RNA-mediated amino acid substitutions that stabilize organized genomes."

Where is the evidence for your statement? Without linking to your phishing blogs.


JVK
Jul 03, 2015
The experimental evidence is included in the background information linked to any aspect of what is currently known about nutrient-dependent protein folding.

What was the latest research report that you read?

Inching toward the 3D genome http://comments.s....6217.10

MicroRNA-Based Single-Gene Circuits Buffer Protein Synthesis Rates against Perturbations
http://dx.doi.org...b4001867

The structural basis of transfer RNA mimicry and conformational plasticity by a viral RNA
http://www.ncbi.n...4136544/

Who is the puppet master? Replication of a parasitic wasp-associated virus correlates with host behaviour manipulation http://rspb.royal...20142773

Jul 03, 2015
@JVK

None of the four links you provided address:"Controlled replication is linked to the nutrient-dependent RNA-mediated amino acid substitutions that differentiate all cell types of all individuals of all living genera via their physiology of reproduction. The nutrient-dependent controlled physiology of reproduction enables the fixation of RNA-mediated amino acid substitutions that stabilize organized genomes."

Try again. And avoid self-referencing.


JVK
Jul 03, 2015
http://comments.s...6219.220
Apparently, they've learned that the same set of microRNAs controls expression of the genes for rate-limiting enzymes that control the hormone production of different hormones in insects and crustaceans.

They confirmed that fact two months later.

The phylogenetic utility and functional constraint of microRNA flanking sequences http://rspb.royal...20142983

JVK
Jul 03, 2015
Have you watched this webinar yet?

Exosome Biogenesis and the Budding of Proteins and Viruses

It is now available on-demand and you can tell other biologically uninformed science idiots about it, so that they can watch it, too.

Click here: http://www.labroo...uld-jul2

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