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Proteins are complex molecules that form the main support structure
for plant and animal cells, and they also regulate biochemical
reactions. The shape and movements of a protein molecule determine its
function, and scientists have long known that proteins can't function
unless they are immersed in water.
�Protein-water interactions are a central, long-standing, unsolved
problem in protein science,� said Dongping Zhong, associate professor
of physics at Ohio State and leader of the study. �We believe that we
are making a major step to answer these fundamental questions, and the
final results will be very important for many biological applications.�
For instance, scientists could better understand how proteins fold and
mis-fold - a key to understanding certain diseases. They could also
design more effective drug molecules that link up with proteins in
just the right way.
Molecules move fast, shape-shifting in mere fractions of a second, so
the movements are hard to see.
This study marks the first time scientists have been able to map the
movements of water molecules at different sites on a much larger
protein molecule, and see how those movements influence the form and
function of the protein.
Zhong and his team took laser �snapshots� of a single myoglobin
protein - the protein that carries oxygen inside muscle tissue -
immersed in water in the laboratory. They were able to measure how
fast the water molecules were moving around the protein, and see how
those movements related to characteristics of the protein at that
moment - the electrical charge at a particular site, for instance, or
changes in the protein's shape.
Proteins can execute a movement in a few billionths of a second. Water
normally moves a thousand times faster -- on the scale of a trillionth
of a second. In previous work, the Ohio State researchers showed that
water molecules slow down substantially as they gets close to a
protein.
This new study shows that the water molecules slow even more once they
reach the protein. The water forms a very thin layer -- only three
molecules thick - around the protein, and this layer is key to
maintaining the protein's structure and flexibility, lubricating its
movements.
Their findings challenge the conventional wisdom of theorists who try
to envision what is happening on these tiny scales. Because they can't
directly see what's happening, scientists use simulations to fill the
gap.
The simulation software has improved in recent years, Zhong said. But
for two years his team has compared simulations to actual experiments,
and found that the two don't match up.
�We are pretty confident at this point that the simulations need to
change,� Zhong said. �Our experimental data provide a benchmark for
testing and improving them.�
In the future, Zhong's team will study how water affects proteins
interacting with each other, and with DNA.
�Our ultimate goal is to understand why water is so unique and
important to life,� he said.
Zhong's coauthors on the paper included Luyuan Zhang, Lijuan Wang,
Ya-Ting Kao, Weihong Qiu, Yi Yang, and Oghaghare Okobiah, all of Ohio
State . This work was supported by the National Science Foundation,
the Packard Foundation Fellowship, and the Petroleum Research Fund.
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