Research Points Way to Development of Designer Proteins
PULLMAN, Wash. -- In the brave new world of industrial genetics,
a major obstacle has been that the high temperatures needed for
commercial production destroy the proteins that make the system
work. Now, Washington State University researcher Margaret E. Black
and colleagues at the Fred Hutchinson Cancer Research Center and
the University of Washington have invented a way to boost the
thermal stability of proteins.
Their process could lead to the rapid development of "designer"
proteins such as pollution-degrading enzymes and anticancer agents.
Their research is reported in a paper published May 6 in the
prestigious journal Science.
Designer proteins are customized versions of naturally occurring
proteins. Just as a van owner might add a biodiesel engine or a GPS
system to the vehicle, a molecular biologist can modify a protein
to make it perform in ways the original protein did not.
Black and her colleagues customized a protein to make it work at a
higher temperature than it normally would, thus enhancing its
potential to fight cancer. They did it through "computational
design," the use of a computer program that let them target
specific parts of the protein and make only those changes most
likely to create the effect they wanted.
According to Black, an associate professor in WSU's Department of
Pharmaceutical Sciences, computational design could cut years off
the time needed to make useful new versions of a protein.
Until now, designer proteins were made by a labor-intensive process
of creating mutations in the original protein and then screening
them to find one that might be useful. Improving a protein's
thermal stability has been especially difficult because there has
been no way of knowing what part of the protein to change. Most
investigators make mutations in the active site or "business end"
of the protein in order to alter how the enzyme works.
Black and her colleagues wanted to increase the enzyme's stability
at high temperatures, without changing its activity. Computational
design let them protect the active site while altering other
features.
The protein they worked with is an enzyme called yeast cytosine
deaminase or yCD. Black has studied yCD for years because of its
potential as a cancer therapy. One of her toughest challenges has
been its preference for cool temperatures. The native form of yCD
doesn't work well at human body temperature. The form of yCD
created through computational design works as well at 98.6 degrees
as it does at room temperature. It also has a shelf-life 30 times
longer than that of the native protein.
Black's co-author Barry Stoddard of the Fred Hutchinson Cancer
Research Center said this is the first time computational design
has been used to improve an enzyme's ability to work at higher
temperatures. He expects the process to save labor, time and
expense in a wide range of industrial bioengineering
applications.
"It's been an amazing project," Black said. She is now testing the
customized yCD for its ability to kill rat tumor cells.
The paper, "Computational Thermostabilization of an Enzyme," was authored by Aaron Korkegian, Margaret E. Black, David Baker and Barry L. Stoddard. The research was funded by the National Institutes of Health.