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Researchers have learned how the bacterial
virus, bacteriophage T4, attacks its host,
the E. coli bacterium. This discovery
could eventually lead to a new class of
antibiotics.
Funded primarily by the National Science
Foundation and published in the January
31, 2002 issue of the journal Nature,
the research describes for the first time
how the virus uses a needle-like, biochemical
puncturing device to invade its host.
"We show, in its entirety, a complex machine
that allows a virus to efficiently infect
its unfortunate host cell, the E. coli.
The baseplate portion of the virus tail
is essential in this process," says lead
researcher Michael Rossmann of Purdue
University. Rossmann conducted the research
with colleagues Shuji Kanamaru, Petr Leiman,
and Paul Chipman of Purdue University,
Victor Kostyuchenko and Vadim Mesyanzhinov
of the Shemyakin-Ovchinnikov Institute
of Bioorganic Chemistry (Russia), and
Fumio Arisaka of the Tokyo Institute of
Technology (Japan).
Because of increasing resistance of infectious
bacteria to pharmaceutical antibiotics
like penicillin, new antibiotic tools
are needed. Bacteriophages may play a
future role in controlling disease-causing
bacteria. "Knowing the exact mechanism
of T4 bacteriophage infectivity is a significant
breakthrough. This information could eventually
help in creating "designer viruses" that
could be the next class of antibiotics,"
said Kamal Shukla, the NSF project officer
for this research.
Although only about a hundred nanometers
in length and width, bacteriophage T4
is considered the "Tyrannosaurus rex"
of bacteriophages as it is one of the
largest of the bacterial viruses. It is
also a "tailed virus" because it has a
tail with fibers that are used to grip
its host. The tailed viruses are very
common; up to one billion phages can exist
in a milliliter of freshwater.
The T4 virus consists of a head, tail,
baseplate, and tail fibers - six that
are long, and six that are short. The
long fibers first find the E. coli
and make a loose attachment; then the
short fibers fasten to get a tighter grip.
The baseplate is the "nerve center" of
the virus. When the long and short fibers
attach to E. coli, the baseplate
transmits this message to the tail, which
contracts like a muscle. The baseplate
both controls the needlepoint of the tail
and the cutting enzyme that make a tiny,
nanometer-sized hole through the cell
wall of the E. coli. The viral
DNA is then squeezed through the tail
into the host. The E. coli, thus
infected, starts to make only new phage
particles and ultimately dies. "Our research
described for the first time the structure
of phage baseplate proteins and their
role in cutting through the host cell
wall," said Rossmann.
For more information, see: http://news.uns.purdue.edu/UNS/
html4ever/020130.Rossmann.T4.html |
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"T4 bacteriophage is a virus that consists
of an icosahedral (20 sided) head, contacting
tail, six short and six long fibers for
attaching to its E. coli victim,
and a base plate that is the nerve center
for communicating between the fibers and
the tail."
Credit: The figure has been adapted
by Petr Leiman (Purdue University) from
a drawing by Fred Eiserling (UCLA).
Select image for larger version
(Size: 63KB)
"A reconstructed computer image generated
by the SPIDER software (created by Joachim
Frank and colleagues at New York University)
from 418 frozen hydrated electron images
that shows the protein structure of the
baseplate - tail tube assembly. The area
labeled (gp27-gp5*-gp5C)3 is
the needlepoint that penetrates the E.
coli cell wall. The cutting enzyme
activity is located around the middle
of the needle. Figure a is a stereo
view of the surface of the assembly and
Figure b is a cross section of
the assembly on an atomic scale. The 100
Angstrom scale corresponds to one millionth
of a cm."
Credit: Rossmann and coworkers of
Purdue University, Arisaka and coworkers
of the Tokyo Institute of Technology,
and Mesyanzhinov and coworkers of the
Shemyakin-Ovchinnikov Institute of Moscow.
Reprinted with the permission of Nature.
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