Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Findings uncover new details about mysterious mimivirus

29.04.2009
An international team of researchers has determined key structural features of the largest known virus, findings that could help scientists studying how the simplest life evolved and whether the unusual virus causes any human diseases.

The mimivirus has been called a possible "missing link" between viruses and living cells. It was discovered accidentally by French scientists in 1992 but wasn't confirmed to be a virus until 2003.

The virus infects amoebas, but it is thought to possibly be a human pathogen because antibodies to the virus have been discovered in pneumonia patients. However, many details about the virus remain unknown, said Michael Rossmann, Purdue University's Hanley Distinguished Professor of Biological Sciences.

Now a team of researchers from Purdue, the University of California at Irvine and the University of the Mediterranean in Marseilles, France, have thrown more light on the mimivirus' makeup.

The scientists have determined the basic design of the virus' outer shell, or capsid, and also of the hundreds of smaller units called capsomeres making up this outer shell. Findings also confirmed the existence of a starfish-shaped structure that covers a "special vertex," an opening in the capsid where genetic material leaves the virus to infect its host, and an indentation in the virus's genetic material itself is positioned opposite this opening, Rossmann said.

"The findings are important in terms of studying the evolution of cells, bacteria and viruses," said Siyang Sun, a postdoctoral research associate working in Rossmann's lab. "The mimivirus is like an intermediate between a cell and a virus. We usually think of cells as being alive and a virus is thought of as being dead because it needs a host cell to complete its life cycle. The mimivirus straddles a middle ground between viruses and living cells, perhaps redefining what a virus is.”

The virus approaches the size of bacteria and is about half of a micron in diameter, more than 10 times larger than the virus that causes the common cold and large enough to be seen with a light microscope. Other viruses are too small to be seen with conventional light microscopes.

The findings are detailed in a research paper that will appear online April 28 in the journal PLoS Biology, published by the Public Library of Science, a nonprofit organization of scientists and physicians. The paper's lead author was Chuan Xiao, a former Purdue postdoctoral research associate and now an assistant professor in the Department of Chemistry at the University of Texas at El Paso.

Researchers had previously been unable to determine the virus's structure because they had assumed that, like many other viruses, it's capsid possessed a design known as icosahedral symmetry.

Xiao discovered the true structure when he decided to try reconstructing the virus assuming it possessed not standard icosahedral symmetry but another configuration called five-fold symmetry.

"If you start out thinking the object has icosahedral symmetry, then you assume there are 60 identical pieces, and that influences how you reconstruct the virus's structure," Rossmann said.

Researchers took images of the virus using an atomic force microscope, revealing a pattern of holes regularly spaced throughout the virus's outer shell.

"The capsids of most other large, pseudo icosahedral viruses do not contain such holes, and their function is unknown," Rossmann said.

The researchers used a method called cryo-electron microscopy reconstruction to determine the structure details. The reconstruction method enables researchers to produce three-dimensional structures by combining two-dimensional pictures, much like a complete architectural drawing of a house can be assembled with two-dimensional drawings of the sides, the roof and other elements.

Using five-fold symmetry revealed that one side of the virus's capsid is slightly different than the others, whereas all sides are the same in a regular icosahedron.

An icosahegron has a roughly spherical shape containing 20 triangular facets and 60 identical subunits. Like an icosahedron, the mimivirus capsid also has 20 facets. However, unlike an icosohedron, five facets of the capsid are slightly different than the others and surround the special vertex. Icosohedra contain 12 similar vertices, whereas the mimivirus contains eleven such vertices, with the 12th being different than the others.

The new reconstructed picture of the virus matched features seen using the atomic force microscope picture, Rossmann said.

The starfish-shaped feature apparently opens up like a blooming flower when the virus is ready to infect its host amoeba, enabling the virus to eject its DNA for insertion into the host, Rossmann said.

"In addition, we think the indentation of the genetic material has something to do with how the genome comes out of the virus," he said. "There is a relationship between the shape of the genome and the special vertex."

The research, which is funded by the National Institutes of Health, is ongoing, with future work probing additional properties of the virus, particularly the structure of the starfish-shaped feature and how it functions.

The paper was written by Xiao; microscope expert Yurii G. Kuznetsov in the Department of Molecular Biology and Biochemistry at UC Irvine; Sun; postdoctoral research associates Susan L. Hafenstein and Victor A. Kostyuchenko and electron microscopist Paul R. Chipman, from Purdue; research scientist Marie Suzan-Monti and Didier Raoult, a professor of microbiology, both from the University of the Mediterranean; Alexander McPherson, a professor of molecular biology and biochemistry at UC Irvine; and Rossmann.

Writer: Emil Venere, (765) 494-4709, venere@purdue.edu
Sources: Michael Rossmann, (765) 494-4911, mr@purdue.edu
Siyang Sun, siyang@purdue.edu
Purdue News Service: (765) 494-2096; purduenews@purdue.edu

Emil Venere | EurekAlert!
Further information:
http://www.purdue.edu

More articles from Life Sciences:

nachricht Modern genetic sequencing tools give clearer picture of how corals are related
17.08.2017 | University of Washington

nachricht The irresistible fragrance of dying vinegar flies
16.08.2017 | Max-Planck-Institut für chemische Ökologie

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Gold shines through properties of nano biosensors

17.08.2017 | Physics and Astronomy

Greenland ice flow likely to speed up: New data assert glaciers move over sediment, which gets more slippery as it gets wetter

17.08.2017 | Earth Sciences

Mars 2020 mission to use smart methods to seek signs of past life

17.08.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>