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NSF PR 00-54 - August 9, 2000
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"Gatekeeper" Protein Is Key to Cellular Life
Researchers funded by the National Science Foundation
(NSF) and affiliated with Ohio State University have
determined that a seemingly ordinary protein called
YidC found within the membranes of bacteria
serves as a gatekeeper of sorts, allowing into the
membranes other proteins essential for the bacteria
to live. When YidC isn't present, the bacteria
dies.
The finding surprised scientists who long believed
that certain "independent" proteins were able to pass
into membranes on their own. The new discovery, reported
in this week's issue of the journal Nature,
may suggest a completely new pathway for the translocation
of proteins within basic biological units.
While YidC has been known to be present in cells
for some time, researchers were unclear as to what
role it might perform, explained Ross Dalbey, a chemist
at Ohio State University. Dalbey and student James
Samuelson were investigating the protein's role in
Escherichia coli bacteria as part of an NSF-supported
study. "The process of membrane insertion is needed
for cellular respiration in bacteria and mitochondria,
as well as for photosynthesis in chloroplasts," Dalbey
said.
The researchers hope that uncovering the function of
YidC and related proteins may offer new ways
of either enhancing cell function or in accelerating
cell death - two mechanisms essential in fighting
most diseases. "In order to exploit cellular membranes
through biotechnology for the benefit of mankind,
we need first to understand the basic processes by
which proteins are inserted into those membranes,"
explains Eve Barak, program director in NSF's division
of molecular and cellular biosciences, which funded
the research. "This research sheds important new light
on this fundamental biological function."
More startling was the discovery that several other
proteins that are remarkably similar to YidC
may play similar roles inside mitochondria and in
chloroplasts as well.
"Proteins are synthesized within the cytoplasm of the
cell but they then have to be transported, or inserted,
either across or into the membranes of organelles
within the cell to do their work," Dalbey said. These
membranes function as barriers, he said, blocking
proteins and other compounds from areas where they
don't belong.
In their work, Dalbey and Samuelson developed a strain
of E. coli in which YidC can be depleted.
They found that when the YidC was absent, proteins
could not migrate into the membranes and the bacteria
died.
They also looked at another specific protein called
Procoat that was considered "independent,"
that is, researchers believed it would insert itself
into the membrane on its own. But in bacteria lacking
YidC, even the Procoat was blocked from
entering the membrane. "To everyone's surprise, the
protein nearly everybody thought inserted spontaneously
requires YidC to succeed in entering the membrane,"
Dalbey said.
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