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In a study to be published in the Journal of Molecular Biology,
doctoral student Zhilei Chen and Huimin Zhao, a professor of
chemical and biomolecular engineering, describe what they call a
"simple and efficient method for creation of novel protein functions
in an existing protein scaffold." In doing so, Zhao and Chen
skirted the two time-and-labor-consuming approaches tried repeatedly
in the past decade: rational design, which requires extensive
knowledge of protein folding, structure, function and dynamics; and
directed evolution, which mimics natural evolution in a test tube
but may require the screening of an astronomical number of mutants
for the creation of new protein functions.
"We now provide one possible solution to a long-lasting barrier
that is important in the protein engineering area -- that is the
creation of the new protein functions," Zhao said. "Our approach is
to build a bridge between the existing protein function to the
target new function by adding some intermediate functions followed
by stepwise directed evolution of these intermediate functions. If
done, it gives you the ability to create protein functions for any
purpose you want -- as a catalyst to create new chemicals that might
be useful in such things as therapeutics, for example."
By way of in vitro coevolution, the researchers gradually changed
the function of the human estrogen receptor alpha, a nuclear hormone
receptor mostly expressed in the prostate, ovary and urinary tract.
What they did was modify the estrogen receptor in a stepwise
fashion, Zhao said. They used testosterone and progesterone to build
the bridge.
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 The receptor was gradually altered to accept one steroid, then
another, until accepting the desired one -- corticosterone, a potent
glucocoticoid. In total, Zhao and Chen did four rounds of random
mutagenesis and screened about 1 million mutants before they found
two estrogen receptor mutants that can be activated by
corticosterone. The whole process was done in a couple of months.
The authors conclude that their new method may provide "a general
approach to engineering biomolecules and biosystems such as
receptors, enzymes, antibodies, ribosymes, DNAzymes and viruses with
novel functions."
Zhao is a member of the Institute for Genomic Biology and the
Center for Biophysics and Computational Biology at Illinois. He also
is an affiliate in the chemistry and bioengineering departments.
A National Science Foundation Faculty Early Career Development
Award to Zhao helped fund the research.
[Provided by Jim Barlow, life sciences editor,
University of Illinois at
Urbana-Champaign]
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