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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