If the genome is the parts list of the human cell, certain proteins are the production managers, activating and deactivating genes as needed. Researchers funded by the National Institute of General Medical Sciences (NIGMS), part of the National Institutes of Health, now have a clearer understanding of how a key protein controls gene activity and how mutations in the protein may cause disease. The work could provide new avenues to design drugs aimed at cancer, diabetes, HIV, and heart disease.

The research appears in the Feb. 14, 2008, issue of the journal Nature. The lead authors include Philip Cole, M.D., Ph.D., of the Johns Hopkins University School of Medicine in Baltimore, Md., and Ronen Marmorstein, Ph.D., of the Wistar Institute in Philadelphia, Pa.

The researchers focused on a protein called p300/CBP that belongs to a family of enzymes known as histone acetyltransferases, or HATs. These enzymes activate genes by attaching chemicals called acetyl groups to histones, the spool-like proteins that hold DNA in a tightly wound form.

Mutations in p300/CBP are associated with a variety of cancers, including those of the colon, breast, pancreas, and prostate. Scientists think that a substance that selectively inhibits p300/CBP might be the basis for an anticancer agent.

Nearly 10 years ago, Cole and his colleagues designed a p300/CBP inhibitor. But the inhibitor is not active in the human body, so it has been used exclusively as a research tool.

In the new study, the researchers combined X-ray crystallography with detailed enzymology to understand how p300/CBP works.

Their three-dimensional crystal structure provides an image of how a key part of p300/CBP binds to the inhibitor. Their studies of numerous mutant versions of the enzyme reveal which amino acids in p300/CBP are essential for its activity.

The work has many clinical implications. Understanding the structure and behavior of p300/CBP will help researchers design a p300/CBP inhibitor that might function in human cells as an anticancer drug.

Proper functioning of p300/CBP is critical for insulin regulation and the health of heart cells. As a result, compounds that can regulate p300/CBP activity might be useful in the therapy of diabetes and heart disease.

In addition, HAT activity is necessary for the multiplication of HIV, leading at least one scientific group to suggest that targeting HATs or similar enzymes might be an new way to thwart the virus.

Finally, the article also shows that some p300/CBP mutations previously associated with certain cancers lie right where p300/CBP contacts the inhibitor. Studying how these mutations alter the enzyme's function should shed light on why the mutations can lead to disease.

"This work illustrates how enzymology and structural biology can combine to yield both fundamental and practical insights about an important biomedical problem. The studies provide a new framework for understanding p300/CBP in health and disease," said Jeremy M. Berg, NIGMS Director.


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