Scientists have obtained the first detailed molecular structure of a member of the Tet family of enzymes. The finding is important for the field of epigenetics because Tet enzymes chemically modify DNA, changing signposts that tell the cell's machinery "this gene is shut off" into other signs that say "ready for a change." Tet enzymes' roles have come to light only in the last five years; they are needed for stem cells to maintain their multipotent state, and are involved in early embryonic and brain development and in cancer. The results, which could help scientists understand how Tet enzymes are regulated and look for drugs that manipulate them, were published online on December 25, 2013 in Nature. Researchers led by Xiaodong Cheng, Ph.D., determined the structure of a Tet family member from Naegleria gruberi by X-ray crystallography. The structure shows how the enzyme interacts with its target DNA (see image courtesy of Dr. Xiaodong Cheng, Emory University), bending the double helix and flipping out the base that is to be modified. "This base flipping mechanism is also used by other enzymes that modify and repair DNA, but we can see from the structure that the Tet family enzymes interact with the DNA in a distinct way," Dr. Cheng says. Dr. Cheng is professor of biochemistry at Emory University School of Medicine and a Georgia Research Alliance Eminent Scholar. The first author of the paper is research associate Hideharu Hashimoto, Ph.D. A team led by Yu Zheng, Ph.D., a senior research scientist at New England Biolabs, contributed to the paper by analyzing the enzymatic activity of Tet using liquid chromatography–mass spectrometry. Using oxygen, Tet enzymes change 5-methylcytosine into 5-hydroxymethylcytosine and other oxidized forms of methylcytosine.
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