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Volume 89 Issue 44 | p. 10 | News of The Week
Issue Date: October 31, 2011

Microscopy Reveals New Layout For Measles Virus

Imaging: Results suggest a role for measles matrix protein in packaging viral RNA
Department: Science & Technology
News Channels: Biological SCENE
Keywords: Measles, electron microscopy, structural biology
This video, compiled from multiple electron microscope images, shows the helical bundles made from complexes of matrix and nucleocapsid proteins.
Credit: Adapted from Proc. Natl. Acad. Sci. USA

The three-dimensional organization of measles virus appears to be different than what researchers had expected. The discovery of a protein-nucleic acid complex via electron microscopy studies could have implications for designing drugs that combat related viruses, such as respiratory syncytial virus or influenza.

Many teams have mapped the measles virus layout in the past, but they used negative-stain electron microscopy, a technique that cannot peer inside the virus in its natural state. Sarah J. Butcher of the University of Helsinki, in Finland, and colleagues at Oxford University and Finland’s University of Turku, however, looked at measles virus with cryoelectron microscopy, which doesn’t have that limitation.

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New Twist
The measles matrix protein was thought to line part of the viral inner membrane (top). New data suggest it coats the helical nucleocapsid instead (bottom). Nucleocapsid = brown, matrix = blue, membrane = red, membrane glycoproteins = purple and yellow.
Credit: Proc. Natl. Acad. Sci. USA
The measles matrix protein was thought to line the virus’s inner membrane (left). New data suggests it coats the helical nucleocapsid instead (right). Nucleocapsid=brown, matrix=blue, membrane=red, membrane glycoproteins=purple and yellow.
 
New Twist
The measles matrix protein was thought to line part of the viral inner membrane (top). New data suggest it coats the helical nucleocapsid instead (bottom). Nucleocapsid = brown, matrix = blue, membrane = red, membrane glycoproteins = purple and yellow.
Credit: Proc. Natl. Acad. Sci. USA

The team detected a never-before-seen complex between the virus’s matrix protein (Proc. Natl. Acad. Sci. USA, DOI:10.1073/pnas.1105770108), thought to play a major part in viral assembly, and its nucleocapsid, which consists of viral RNA surrounded by protective capsid proteins. Until now, the scientific consensus was that the matrix protein covered the inner part of the viral membrane. The Finland team’s data suggest that the matrix protein instead coats sections of the helical nucleocapsid, packing it into bundles resembling rotini pasta.

[+]Enlarge
Credit: Proc. Natl. Acad. Sci. USA
VIRAL SLICE This electron microscope image depicts a measles virus particle. Arrows indicate the rigatoni-like complexes of matrix and nucleocapsid proteins.
 
Credit: Proc. Natl. Acad. Sci. USA

The existence of the added coating implies that additional steps are involved in virus replication, Butcher says. “And if you’ve got more steps, you’ve got more drug targets,” she adds. Though measles virus is largely controlled with vaccines in developed nations, her team is now studying related viruses to see whether they can detect similar helical complexes.

The work “is very exciting as it seriously challenges the classical view of measles virus particle organization,” says Sonia Longhi, who studies measles virus protein structure at Aix-Marseille University and France’s National Center for Scientific Research (CNRS). “It will undoubtedly promote numerous future studies to unveil the determinants of coating and uncoating,” she adds.

 
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