Structural insight into human N6amt1-Trm112 complex functioning as a protein methyltransferase
Structural insight into human N6amt1-Trm112 complex functioning as a protein methyltransferase
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人类 N6amt1-Trm112 复合物作为蛋白质甲基转移酶的结构见解
DOI：
10.1038/s41421-019-0121-y
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发表时间：
2019-09-10
期刊：
影响因子：
33.5
通讯作者：
Ding, Jianping
中科院分区：
文献类型：
--
作者：
Li, Wenjing;Shi, Yu;Ding, Jianping
DNA甲基化在许多生物体中是一种重要的表观遗传修饰，可发生在胞嘧啶或腺嘌呤上。N-6-甲基腺嘌呤(6 MA)广泛存在于细菌基因组中，在细菌限制性内切酶修饰系统中起着至关重要的作用。最近，从单细胞生物到后生动物的各种真核生物的基因组中也有报道存在6 mA。人类N6amt1最初被报道为eRF1的谷氨酰胺MTase，但关于它是否为6 mA DNA MTase的报道存在争议。本文报道了人N6amt1-Trm112与辅因子SAM形成的络合物的晶体结构。结构分析表明，Trm112与N6amt1的疏水表面结合以稳定其结构，但不直接促进底物结合和催化。N6amt1的活性部位和潜在底物结合部位主要是负电荷，因此不适合DNA结合。生化数据证实，该复合体不能结合DNA，对DNA没有MTase活性，但对eRF1的Gln185甲基化具有活性。我们的结构和生化数据共同证明了N6amt1是一个真正的蛋白质MTase，而不是DNA MTase。
DNA methylation is an important epigenetic modification in many organisms and can occur on cytosine or adenine. N-6-methyladenine (6mA) exists widespreadly in bacterial genomes, which plays a vital role in the bacterial restriction-modification system. Recently, 6mA has also been reported to exist in the genomes of a variety of eukaryotes from unicellular organisms to metazoans. There were controversial reports on whether human N6amt1, which was originally reported as a glutamine MTase for eRF1, is a putative 6mA DNA MTase. We report here the crystal structure of human N6amt1-Trm112 in complex with cofactor SAM. Structural analysis shows that Trm112 binds to a hydrophobic surface of N6amt1 to stabilize its structure but does not directly contribute to substrate binding and catalysis. The active site and potential substrate-binding site of N6amt1 are dominantly negatively charged and thus are unsuitable for DNA binding. The biochemical data confirm that the complex cannot bind DNA and has no MTase activity for DNA, but exhibits activity for the methylation of Gln185 of eRF1. Our structural and biochemical data together demonstrate that N6amt1 is a bona fide protein MTase rather than a DNA MTase.