Jiang Tao, Zhou Xinfeng, Taghizadeh Koli, Dong Min, Dedon Peter C
Biological Engineering Division and Center for Environmental Health Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Proc Natl Acad Sci U S A. 2007 Jan 2;104(1):60-5. doi: 10.1073/pnas.0606775103. Epub 2006 Dec 26.
The posttranslational modification of histone and other chromatin proteins has a well recognized but poorly defined role in the physiology of gene expression. With implications for interfering with these epigenetic mechanisms, we now report the existence of a relatively abundant secondary modification of chromatin proteins, the N(6)-formylation of lysine that appears to be uniquely associated with histone and other nuclear proteins. Using both radiolabeling and sensitive bioanalytical methods, we demonstrate that the formyl moiety of 3'-formylphosphate residues arising from 5'-oxidation of deoxyribose in DNA, caused by the enediyne neocarzinostatin, for example, acylate the N(6)-amino groups of lysine side chains. A liquid chromatography (LC)-tandem mass spectrometry (MS) method was developed to quantify the resulting N(6)-formyl-lysine residues, which were observed to be present in unperturbed cells and all sources of histone proteins to the extent of 0.04-0.1% of all lysines in acid-soluble chromatin proteins including histones. Cells treated with neocarzinostatin showed a clear dose-response relationship for the formation of N(6)-formyl-lysine, with this nucleosome linker-selective DNA-cleaving agent causing selective N(6)-formylation of the linker histone H1. The N(6)-formyl-lysine residue appears to represent an endogenous histone secondary modification, one that bears chemical similarity to lysine N(6)-acetylation recognized as an important determinant of gene expression in mammalian cells. The N(6)-formyl modification of lysine may interfere with the signaling functions of lysine acetylation and methylation and thus contribute to the pathophysiology of oxidative and nitrosative stress.
组蛋白和其他染色质蛋白的翻译后修饰在基因表达生理过程中的作用已得到广泛认可，但尚未明确界定。鉴于这些表观遗传机制可能受到干扰，我们现在报告染色质蛋白存在一种相对丰富的二级修饰，即赖氨酸的N(6)-甲酰化，这种修饰似乎与组蛋白和其他核蛋白具有独特关联。我们使用放射性标记和灵敏的生物分析方法证明，例如由烯二炔新制癌菌素引起的DNA中脱氧核糖5'-氧化产生的3'-甲酰磷酸残基的甲酰基部分，会酰化赖氨酸侧链的N(6)-氨基。我们开发了一种液相色谱（LC）-串联质谱（MS）方法来定量所得的N(6)-甲酰赖氨酸残基，发现在未受干扰的细胞以及所有组蛋白来源中，酸溶性染色质蛋白（包括组蛋白）中所有赖氨酸的0.04 - 0.1%存在这种残基。用新制癌菌素处理的细胞在N(6)-甲酰赖氨酸形成方面呈现明显的剂量反应关系，这种核小体连接子选择性DNA切割剂会导致连接子组蛋白H1发生选择性N(6)-甲酰化。N(6)-甲酰赖氨酸残基似乎代表一种内源性组蛋白二级修饰，它在化学性质上与赖氨酸N(6)-乙酰化相似，而赖氨酸N(6)-乙酰化被认为是哺乳动物细胞基因表达的重要决定因素。赖氨酸的N(6)-甲酰化修饰可能会干扰赖氨酸乙酰化和甲基化的信号功能，从而导致氧化应激和亚硝化应激的病理生理过程。
