Distributive Processing by the Iron(II)/α-Ketoglutarate-Dependent Catalytic Domains of the TET Enzymes Is Consistent with Epigenetic Roles for Oxidized 5-Methylcytosine Bases

详细信息    查看全文

• 作者：Esta Tamanaha ; Shengxi Guan ; Katherine Marks ; Lana Saleh
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：August 3, 2016
• 年：2016
• 卷：138
• 期：30
• 页码：9345-9348
• 全文大小：345K
• 年卷期：0
• ISSN：1520-5126

文摘

The ten-eleven translocation (TET) proteins catalyze oxidation of 5-methylcytosine (^5mC) residues in nucleic acids to 5-hydroxymethylcytosine (^5hmC), 5-formylcytosine (^5fC), and 5-carboxycytosine (^5caC). These nucleotide bases have been implicated as intermediates on the path to active demethylation, but recent reports have suggested that they might have specific regulatory roles in their own right. In this study, we present kinetic evidence showing that the catalytic domains (CDs) of TET2 and TET1 from mouse and their homologue from Naegleria gruberi, the full-length protein NgTET1, are distributive in both chemical and physical senses, as they carry out successive oxidations of a single ^5mC and multiple ^5mC residues along a polymethylated DNA substrate. We present data showing that the enzyme neither retains ^5hmC/^5fC intermediates of preceding oxidations nor slides along a DNA substrate (without releasing it) to process an adjacent ^5mC residue. These findings contradict a recent report by Crawford et al. ( J. Am. Chem. Soc. 2016, 138, 730) claiming that oxidation of ^5mC by CD of mouse TET2 is chemically processive (iterative). We further elaborate that this distributive mechanism is maintained for TETs in two evolutionarily distant homologues and posit that this mode of function allows the introduction of ^5mC forms as epigenetic markers along the DNA.