Viruses Come in Very Bizarre, Recognizable Shapes


Discovery of Armored Viruses May Inspire New Designs for Nanotechnology

Source: Science Magazine

September 22, 2000

Anyone suffering from a common cold is living proof of just how tough a virus can be. Scientists have now discovered why, at least in the case of one virus. They have found a type of virus that actually comes equipped with an "armored coat" that is made of interlocking rings of protein.

In a report, published in the Sept. 22 issue of Science, researchers say that the structure of this virus is remarkably similar to chain mail suits worn by medieval knights. The virus has been predicted but never directly observed until now. The researchers say that this discovery could have applications for the recently booming nanotechnology field.

The armored virus was detected by an international team of scientists from Stanford University, the Scripps Research Institute, the University of Pittsburgh and the University of Uppsala in Sweden.

A virus typical consists of no more than one chromosome of DNA or RNA wrapped inside a protein coat. Even though they seem like simple microbes on the surface, determining their molecular structure requires very sophisticated instrumentation. The researchers had to use special micro-imaging techniques just to analyze the outer coating of a virus called bacteriophage HK97.

From a recent press release about the study: "Bacteriophages are viruses that only infect bacteria. They come in very bizarre shapes, some of which resemble NASA-designed satellites or Martian landers. HK97 is no exception. It has an odd, balloon-shaped head attached to a short tail."

In order to analyze this strange protein exterior, both electron microscopy and X-ray crystallography were required, according to Hiro Tsuruta, a senior research associate with the Stanford Synchrotron Radiation Laboratory (SSRL) and the Department of Chemistry.

"The head of the virus is thousands of times narrower than a human hair," adds Tsuruta, a co-author of the Science study.

With the aid of a small angle X-ray diffraction instrument at SSRL, Tsuruta and his colleagues determined that HK97's head is made up of 72 protein rings - 12 pentagons and 60 hexagons - that locked together forming a protective coating surrounding the virus's DNA.

As quoted in the press release: "Its protein rings are cross-linked in a manner similar to the five-ring Olympic symbol," observes Tsuruta. "Together, the rings form a rigid, spherical cage shaped like a 20-sided soccer ball."

This unique chain-link structure makes the HK97 virus extraordinarily stable, adds Scripps biologist John E. Johnson, a co-author of the Science study.

Johnson is quoted as saying, "The head is organized exactly like medieval armor." The protective suits worn by knights in the Middle Ages were made of interwoven rings of iron. They were designed to deflect arrows yet still be able to allow maximum freedom of movement during battle.

The protein "armor" that was discovered in HK97 may have the same function - allowing the virus mobility while protecting its precious cargo of DNA.

"The virus has developed a very clever way of keeping its DNA intact," notes Tsuruta in the study.

Interwoven molecular rings - called catenanes - are a major focus of biochemical research. Johnson pointed out that HK97's catenane structure should be of particular interest for nanotechnology - where engineers and scientists are designing operational atomic scale devices.

"People are looking at viruses as containers and the chain mail structure could provide a novel way to create a container that's very thin yet stable. No one expected that proteins could do this," said Johnson, "and now we know they can."

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