最新Nature：浙江大学等两篇文章解析DNA聚合酶

　　

生物通报道：来自美国纽约西奈山医学院（Mount Sinai School of Medicine），NIH分子生物学实验室两处的研究人员在昨日（6月24日）出版的Nature杂志上公布了DNA聚合酶η的晶体结构，同期Nature配发的News & Views文章中，Suse Broyde 和 Dinshaw Patel讨论了Polη的结构与所报道的其他Y-家族DNA聚合酶结构的相符性问题。

DNA经常遭受内源和外界环境因子的攻击，造成DNA损伤，大部分的损伤是可以被无误的DNA修复机制消除的，但也有一些损伤会因为在复制过程中没有被修复而在染色体上继续存在，如发生在S期的损伤、一些比较大的损伤、染色体组上的损伤和一些不容易被修复的损伤会，此时DNA聚合酶会在损伤处停顿，DNA复制不能正常进行，从而影响细胞的分裂，更为严重的会导致细胞的死亡。

为了应对这些损伤，细胞发展了一种损伤耐受机制，其中DNA聚合酶η (Polη)就是其中一种重要的损伤合成酶，在6月24日出版的Nature杂志上，两个研究小组破解了Polη的晶体结构，这对于解释像是着色性干皮病之类的疾病的机理具有重要的意义。

第一篇文章中，来自NIH分子生物学实验室，浙江大学等处的研究人员解析了人类DNA聚合酶η的结构和功能，确定了人体DNA聚合酶η的催化区域的结构。这显示了尺寸较大的胸腺嘧啶二聚物在一个异常大的活性点上是怎样被容纳的、以及病灶是怎样通过在其他聚合酶中不存在的相互作用来稳定的。

另外一项研究中，研究人员破解的是酵母DNA聚合酶η的结构，在这些研究中，研究人员发现“着色性干皮病”患者的“错义突变”被发现会破坏聚合酶在正常B形式中维持受损DNA的能力。

紫外线的穿透辐射诱导皮肤细胞中的DNA病灶，它们会阻止DNA复制和引起能发展成癌症的突变。身体应对这种损伤的一种方式涉及专门化的DNA聚合酶，以此来绕过这样的病灶。Polη通过复制含有胸腺嘧啶二聚物的DNA来做这件事，而这种酶的失活导致着色性干皮病的一个变种和皮肤癌的高发病率。

（生物通：万纹）

原文摘要：

Structural basis for the suppression of skin cancers by DNA polymerase η


DNA polymerase η (Polη) is unique among eukaryotic polymerases in its proficient ability for error-free replication through ultraviolet-induced cyclobutane pyrimidine dimers, and inactivation of Polη (also known as POLH) in humans causes the variant form of xeroderma pigmentosum (XPV). We present the crystal structures of Saccharomyces cerevisiae Polη (also known as RAD30) in ternary complex with a cis-syn thymine-thymine (T-T) dimer and with undamaged DNA. The structures reveal that the ability of Polη to replicate efficiently through the ultraviolet-induced lesion derives from a simple and yet elegant mechanism, wherein the two Ts of the T-T dimer are accommodated in an active site cleft that is much more open than in other polymerases. We also show by structural, biochemical and genetic analysis that the two Ts are maintained in a stable configuration in the active site via interactions with Gln 55, Arg 73 and Met 74. Together, these features define the basis for Polη’s action on ultraviolet-damaged DNA that is crucial in suppressing the mutagenic and carcinogenic consequences of sun exposure, thereby reducing the incidence of skin cancers in humans.

Structure and mechanism of human DNA polymerase η

The variant form of the human syndrome xeroderma pigmentosum (XPV) is caused by a deficiency in DNA polymerase η (Polη), a DNA polymerase that enables replication through ultraviolet-induced pyrimidine dimers. Here we report high-resolution crystal structures of human Polη at four consecutive steps during DNA synthesis through cis-syn cyclobutane thymine dimers. Polη acts like a ‘molecular splint’ to stabilize damaged DNA in a normal B-form conformation. An enlarged active site accommodates the thymine dimer with excellent stereochemistry for two-metal ion catalysis. Two residues conserved among Polη orthologues form specific hydrogen bonds with the lesion and the incoming nucleotide to assist translesion synthesis. On the basis of the structures, eight Polη missense mutations causing XPV can be rationalized as undermining the molecular splint or perturbing the active-site alignment. The structures also provide an insight into the role of Polη in replicating through D loop and DNA fragile sites.