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Prx actually has a dual role in the process. Its usual job is removing
excess hydrogen peroxide from the cells by converting it to water. But
if levels get dangerously high � and Prx needs help � it becomes
inactive in its �converting� job and instead becomes a �signaler,�
telling the cell to produce or activate other proteins to help remove
the excess.
�It basically acts as a sensor and warns the cell that levels are too
high and that the cell needs to respond,� said Thomas J. J�nsson, Ph.D.,
lead author, and a post-doctoral fellow at Wake Forest. �Once that
threat is gone, Prx needs to go back to its normal state.�
But how does Prx revert back to its usual job and become active again,
so that it is available for a new wave of hydrogen peroxide? In 2003,
scientists reported that a protein known as sulfiredoxin (Srx) was
involved in the process. The goal of Lowther�s team was to use X-ray
crystallography to learn exactly what happens.
�This technology gives us a three-dimensional snapshot of how the
proteins interact,� said Lowther. �We wanted to know how Prx changes
its structure to be repaired.�
The scientists knew that the repair of Prx would involve it binding
with Srx. They also knew that the structure of Prx would need to
change because the portion of the molecule that is repaired by Srx is
initially hidden when it is in the inactive form.
�We found that the protein unfolded, flipped around and attached to
the back side of Srx, known as an �embrace,�� said Lowther. �It
basically put its arm around its buddy, which helps hold the repair
protein in place.�
J�nsson said the binding of Srx causes a chemical reaction that
repairs Prx. �The change in structure is dramatic and we found that it
is critical for the repair to take place,� he said.
The scientists said that understanding this protective mechanism that
keeps cells healthy may one day help reveal how the process goes awry
in disease. They will continue the research by studying how the
structural change may affect how Prx interacts with other proteins.
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