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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