**组蛋白甲基转移酶**（英語：，简称为**HMT**）是包括组蛋白-赖氨酸*N*-甲基转移酶与组蛋白-精氨酸*N*-甲基转移酶在内的是一大類组蛋白修饰酶类，它们催化将一个、两个或三个甲基转移到组蛋白的赖氨酸或精氨酸残基上。被添加上的甲基基团主要位于组蛋白H3和H4的特定赖氨酸或精氨酸上。

种类
--

赖氨酸特异性组蛋白甲基转移酶类可被细分为含SET结构域的和不含SET结构域的两类。顾名思义，它们之间的区别在于存不存在SET这样一种结构域。

人类基因所编码的具有组蛋白甲基转移酶活性的蛋白质包括：

* ASH1L
* DOT1L
* EHMT1、EHMT2、EZH1、EZH2
* MLL、MLL2、MLL3、MLL4、MLL5
* NSD1
* PRDM2
* SET、SETBP1、SETD1A、SETD1B、SETD2、SETD3、SETD4、SETD5、SETD6、SETD7、SETD8、SETD9、SETDB1、SETDB2
* SETMAR、SMYD1、SMYD2、SMYD3、SMYD4、SMYD5、SUV39H1、SUV39H2、SUV420H1、SUV420H2

### 含SET结构域的赖氨酸特异性组蛋白甲基转移酶

#### 结构

影响甲基转移酶活性的结构包括：SET结构域（包括130个氨基酸）、前SET和后SET结构域。前SET区域包括半胱氨酸残基，可形成三角锌簇，紧密结合锌原子并使结构稳定。SET结构域本身包含一个富含β-股的催化核心，从而形成几个β折叠区域。 一般在前SET结构域发现的β-股将形成的β-折叠，它带有SET结构域的β-股，导致SET结构域结构的细微变化。

These small changes alter the target residue site specificity for methylation and allow the SET domain methyltransferases to target many different residues. This interplay between the pre-SET domain and the catalytic core is critical for enzyme function.

#### 催化机制

In order for the reaction to proceed, S-Adenosyl methionine (SAM) and the lysine residue of the substrate histone tail must first be bound and properly oriented in the catalytic pocket of the SET domain. Next, a nearby tyrosine residue deprotonates the ε-amino group of the lysine residue. The lysine chain then makes a nucleophilic attack on the methyl group on the sulfur atom of the SAM molecule, transferring the methyl group to the lysine side chain.

 Active site of Histone Lysine N-Methyltransferase. Lysine residue (in yellow) and S-Adenosyl methionine (SAM) (in blue) clearly visible.
### 不含SET结构域的赖氨酸特异性组蛋白甲基转移酶

Instead of SET, non-SET domain-containing histone methyltransferase utilizes the enzyme Dot1. Unlike the SET domain, which targets the lysine tail region of the histone, Dot1 methylates a lysine residue in the globular core of the histone, and is the only enzyme known to do so. A possible homolog of Dot1 was found in archaea which shows the ability to methylate archaeal histone-like protein in recent studies.

#### 结构

The N terminal of Dot1 contains the active site. A loop serving as the binding site for SAM links the N-terminal and the C-terminal domains of the Dot1 catalytic domain. The C-terminal is important for the substrate specificity and binding of Dot1 because the region carries a positive charge, allowing for a favorable interaction with the negatively charged backbone of DNA. Due to structural constraints, Dot1 is only able to methylate histone H3.

### 精氨酸特异性组蛋白甲基转移酶

There are two different types of protein arginine methyltransferases (PRMTs) and three types of methylation that can occur at arginine residues on histone tails. The first type of PRMTs (PRMT1, PRMT3, CARM1⧸PRMT4, and Rmt1⧸Hmt1) produce monomethylarginine and asymmetric dimethylarginine. The second type (JBP1⧸PRMT5) produces monomethyl or symmetric dimethylarginine. The differences in the two types of PRMTs arise from restrictions in the arginine binding pocket.

#### 结构

The catalytic domain of PRMTs consists of a SAM binding domain and substrate binding domain (about 310 amino acids in total). Each PRMT has a unique N-terminal region and a catalytic core. The arginine residue and SAM must be correctly oriented within the binding pocket. SAM is secured inside the pocket by a hydrophobic interaction between an adenine ring and a phenyl ring of a phenylalanine.

#### 催化机制

A glutamate on a nearby loop interacts with nitrogens on the target arginine residue. This interaction redistributes the positive charge and leads to the deprotonation of one nitrogen group, which can then make a nucleophilic attack on the methyl group of SAM. Differences between the two types of PRMTs determine the next methylation step: either catalyzing the dimethylation of one nitrogen or allowing the symmetric methylation of both groups. However, in both cases the proton stripped from the nitrogen is dispersed through a histidine–aspartate proton relay system and released into the surrounding matrix.

在基因调控中的作用
---------

Histone methylation plays an important role in epigenetic gene regulation. Methylated histones can either repress or activate transcription as different experimental findings suggest. For example, it is likely that the methylation of lysine 9 on histone H3 (H3K9me3) in the promoter region of genes prevents excessive expression of these genes and, therefore, delays cell cycle transition and/or proliferation. See Histone#Chromatin regulation.

疾病的相关性
------

Abnormal expression or activity of methylation-regulating enzymes has been noted in some types of human cancers, suggesting associations between histone methylation and malignant transformation of cells or formation of tumors. In recent years, epigenetic modification of the histone proteins, especially the methylation of the histone H3, in cancer development has been an area of emerging research. It is now generally accepted that in addition to genetic aberrations, cancer can be initiated by epigenetic changes in which gene expression is altered without genomic abnormalities. These epigenetic changes include loss or gain of methylations in both DNA and histone proteins.

There is not yet compelling evidence that suggests cancers develop purely by abnormalities in histone methylation or its signaling pathways, however they may be a contributing factor. For example, down-regulation of methylation of lysine 9 on histone 3 (H3K9me3) has been observed in several types of human cancer (such as colorectal cancer, ovarian cancer, and lung cancer), which arise from either the deficiency of H3K9 methyltransferases or elevated activity or expression of H3K9 demethylases.

进一步研究
-----

组蛋白甲基转移酶可以用作癌症的诊断和预后的生物标志物。 另外，关于组蛋白甲基转移酶在细胞的恶性转化，组织的癌发生和肿瘤发生中的功能和调节仍然存在许多问题。

另见
--

* 组蛋白修饰酶类（英语：）
* 组蛋白乙酰转移酶（HAT）
* 组蛋白脱乙酰酶（HDAC）
* 组蛋白甲基化
* 核小體
* 染色质

参考文献
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1. 1 2 3  Wood A.. Conaway JW, Conaway RC (编).. Advances in Protein Chemistry **67**. Amsterdam: Elsevier Academic Press. 2004: 201–222. ISBN 0-12-034267-7. doi:10.1016/S0065-3233(04)67008-2.
2. ↑  Trievel RC, Beach BM, Dirk LM, Houtz RL, Hurley JH.. Cell. October 2002, **111** (1): 91–103. PMID 12372303. doi:10.1016/S0092-8674(02)01000-0.
3. ↑  Min J, Feng Q, Li Z, Zhang Y, Xu RM.. Cell. March 2003, **112** (5): 711–23. PMID 12628190. doi:10.1016/S0092-8674(03)00114-4.
4. ↑  Chen D, Ma H, Hong H, Koh SS, Huang SM, Schurter BT, Aswad DW, Stallcup MR.. Science. June 1999, **284** (5423): 2174–7. PMID 10381882. doi:10.1126/science.284.5423.2174.
5. ↑  Gary JD, Lin WJ, Yang MC, Herschman HR, Clarke S.. J. Biol. Chem. May 1996, **271** (21): 12585–94. PMID 8647869. doi:10.1074/jbc.271.21.12585.
6. ↑  McBride AE, Weiss VH, Kim HK, Hogle JM, Silver PA.. J. Biol. Chem. February 2000, **275** (5): 3128–36. PMID 10652296. doi:10.1074/jbc.275.5.3128.
7. 1 2 3 4
8. ↑
9. 1 2
10. ↑  McBride AE, Silver PA.. Cell. July 2001, **106** (1): 5–8. PMID 11461695. doi:10.1016/S0092-8674(01)00423-8.
11. ↑  Fersht AR, Sperling J.. J. Mol. Biol. February 1973, **74** (2): 137–49. PMID 4689953. doi:10.1016/0022-2836(73)90103-4.
12. 1 2 3 4 5  Chen F, Kan H, Castranova V.. Tollefsbol TO (编).. Boston: Academic Press. 2010: 149–157. ISBN 0-12-375709-6. doi:10.1016/B978-0-12-375709-8.00010-1.
13. ↑  Espino PS, Drobic B, Dunn KL, Davie JR.. J. Cell. Biochem. April 2005, **94** (6): 1088–102. PMID 15723344. doi:10.1002/jcb.20387.
14. ↑  Hamamoto R, Furukawa Y, Morita M, Iimura Y, Silva FP, Li M, Yagyu R, Nakamura Y.. Nat. Cell Biol. August 2004, **6** (8): 731–40. PMID 15235609. doi:10.1038/ncb1151.

深入阅读
----

* Trievel RC.. Crit. Rev. Eukaryot. Gene Expr. 2004, **14** (3): 147–69. PMID 15248813. doi:10.1615/CritRevEukaryotGeneExpr.v14.i3.10.
* Conde F, Refolio E, Cordón-Preciado V, Cortés-Ledesma F, Aragón L, Aguilera A, San-Segundo PA.. Genetics. June 2009, **182** (2): 437–46. PMC 2691753 可免费查阅. PMID 19332880. doi:10.1534/genetics.109.101899.

外部链接
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* GeneReviews/NCBI/NIH/UW entry on Kleefstra Syndrome
* 醫學主題詞表（MeSH）：*Histone-Lysine+N-Methyltransferase*
* 醫學主題詞表（MeSH）：*Protein-Arginine+N-Methyltransferase*


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| * 
* 论
* 编
转移酶: C1基转移酶类（EC 2.1） |
| --- |
|  |
| 2.1.1：甲基转移酶类 | 

|  |  |
| --- | --- |
| N- | 
* 组胺N-甲基转移酶
* 苯乙醇胺N-甲基转移酶
* 色胺N-甲基转移酶
* 磷脂酰乙醇胺N-甲基转移酶

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|  |
| O- | 
* 乙酰复合胺O-甲基转移酶
* 邻苯二酚O-甲基转移酶

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|  |
| 同型半胱氨酸 | 
* 甜菜碱同型半胱氨酸甲基转移酶
* 同型半胱氨酸甲基转移酶
* 甲硫氨酸合成酶

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|  |
| 其他 | 
* 磷脂酰乙醇胺甲基转移酶
* DNMT3B
* 组蛋白甲基转移酶
* 胸腺嘧啶核苷酸合酶
* DNA甲基转移酶
* 硫嘌呤甲基转移酶

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|  |
| 2.1.2：羟甲基、甲酰基及相关转移酶类 | 

|  |  |
| --- | --- |
| 羟甲基转移酶类 | 
* 丝氨酸羟甲基转移酶
* 3-甲基-2-氧代丁酸羟甲基转移酶

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|  |
| 甲酰基转移酶类 | 
* 磷酸核糖基甘氨酰胺甲酰基转移酶
* 肌苷一磷酸合成酶

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|  |
| 其他 | 
* 谷氨酸亚甲胺转移酶
* 氨基甲基转移酶

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|  |
| 2.1.3：羧基及氨基甲酰基转移酶类 | 

|  |  |
| --- | --- |
| 羧基转移酶类 | 
* 甲基丙二酰辅酶 A羧基转移酶

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|  |
| 氨基甲酰基转移酶类 | 
* 天冬氨酸转氨甲酰酶
* 鸟氨酸氨甲酰转移酶
* 草氨酸氨甲酰转移酶
* 腐胺氨甲酰转移酶
* 3-羟甲基噻吩氨甲酰转移酶
* 赖氨酸氨甲酰转移酶
* N-乙酰鸟氨酸氨甲酰转移酶

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|  |
| 2.1.4：脒基转移酶类 | 
* 甘氨酸脒基转移酶

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|  |
| 
* *EC 1.1/2/3/4/5/6/7/8/9/10/11/12/13/14/15/16/17/18/19/20/21/22 · 2.1/2/3/4/5/6/7(2.7.10/11-12)/8/9 · 3.1/2/3/4(3.4.21/22/23/24)/5/6/7/8/9/10/11/12/13 · 4.1/2/3/4/5/6 · 5.1/2/3/4/5/99 · 6.1-3（英语：）/4/5-6*

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| 

| * 
* 论
* 编
转录（细菌（英语：）、真核） |
| --- |
|  |
| 转录调控 | 

|  |  |
| --- | --- |
| 原核 | 
* 操縱子
	+ 乳糖操縱子
	+ 色氨酸操纵子
	+ gab操纵子（英语：）
	+ 半乳糖操纵子（英语：）
* 阻遏蛋白
	+ 乳糖抑制子
	+ 色氨酸阻遏因子（英语：）

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|  |
| 真核 | 

|  |  |
| --- | --- |
| 組蛋白修飾 | 
* 组蛋白甲基化
* 組蛋白乙醯化
* 組蛋白修飾酶
	+ 组蛋白甲基转移酶（EZH2）
	+ 组蛋白脱甲基酶（英语：）
	+ 组蛋白乙酰转移酶
	+ 组蛋白脱乙酰化酶 HDAC1（英语：）

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|  |
| DNA甲基化 | 
* DNA甲基转移酶（英语：）

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|  |
| 其他染色质重塑（英语：）酶 | 
* CHD7（英语：）

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|  |
| 兼有 | 
* 转录共调控因子（英语：）
	+ 辅激活物（英语：）
	+ 辅阻遏物（英语：）
* 诱导物（英语：）

 |

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|  |
| 启动 | 
* 啟動子
	+ 普里布諾盒
	+ TATA盒
	+ BRE（英语：）
	+ CAAT盒（英语：）
	+ 响应元件
* 增强子
	+ E-盒
	+ 响应元件
* 绝缘子
* 沉默子

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|  |
| 起始（细菌、真核） | 
* 转录起始位点

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|  |
| 延伸 | 
* 细菌 RNA聚合酶：rpoB
* 真核 RNA聚合酶：RNA聚合酶Ⅱ

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|  |
| 终止（细菌、 真核) | 
* 終止子
* 内在终止（英语：）
* ρ因子

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|  |
| *另见：转录与转录后修饰疾病*

| * 
* 论
* 编
遗传学索引 |
| --- |
|  |
| 描述 | 
* 生化
* 基因表达
* DNA
	+ 复制
	+ 蛋白
	+ 基因重组
	+ 修复
* 转录
	+ 转录因子与细胞内受体
	+ 辅调节因子
	+ RNA
	+ 重复序列
	+ 转录后修饰
* 翻译
	+ 核糖体亚基
	+ 翻译后修饰
	+ 分拣蛋白（英语：）
* DNA结合蛋白（英语：）/RNA结合蛋白（英语：）
	+ 核糖核蛋白)
* 蛋白质
	+ 结构域
	+ 结构
		- 1°
		- 2°
		- 2+°
		- 3°
		- 4°

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|  |
| 疾病 | 
* Replication and repair（英语：）
* Transcription factor（英语：）
* 转录相关疾病（英语：）
* 轉譯相關疾病

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