A novel processive mechanism for DNA synthesis revealed by structure, modeling and mutagenesis of the accessory subunit of human mitochondrial DNA polymerase
A novel processive mechanism for DNA synthesis revealed by structure, modeling and mutagenesis of the accessory subunit of human mitochondrial DNA polymerase
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DOI：
10.1016/j.jmb.2006.02.073
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发表时间：
2006-05-19
影响因子：
5.6
通讯作者：
Kaguni, Laurie S.
中科院分区：
文献类型：
--
作者：
Fan, Li;Kim, Sangbumn;Kaguni, Laurie S.
线粒体DNA聚合酶是唯一负责复制和修复动物线粒体DNA的DNA聚合酶。在这里，我们讨论了人类全酶在核苷酸聚合中实现高加工性的分子机制。我们测定了人Pol-γ-β的晶体结构，它是与催化核心Pol-γ-α高亲和力结合的辅助亚基，以刺激其活性并增强全酶活性。我们发现，人Pol-α与IIa类氨基酰基tRNA合成酶有很高的结构相似性，并在晶体中形成二聚体。利用POL-γ-β二聚体和T7噬菌体DNA聚合酶三元复合体的结构，建立了一个人POL-γ/DNA复合体模型，该模型表明POL-γ-β与人催化核心之间存在多个亚基相互作用区域，使其能够包裹新合成的双链DNA，从而提高DNA结合亲和力和全酶加工性。用该模型解释和检验了一组新的人Pol-γ-β突变体的生化性质，并阐明了辅助亚基作为一种新型的过程性因子在刺激Pol-γ活性和提高过程性方面的作用。(C)2006爱思唯尔有限公司。保留所有权利。
Mitochondrial DNA polymerase (pol gamma) is the sole DNA polymerase responsible for replication and repair of animal mitochondrial DNA. Here, we address the molecular mechanism by which the human holoenzyme achieves high processivity in nucleotide polymerization. We have determined the crystal structure of human pol gamma-beta, the accessory subunit that binds with high affinity to the catalytic core, pol gamma-alpha, to stimulate its activity and enhance holoenzyme processivity We find that human pol gamma-beta shares a high level of structural similarity to class IIa aminoacyl tRNA synthetases, and forms a dimer in the crystal. A human pol gamma/DNA complex model was developed using the structures of the pol gamma-beta dimer and the bacteriophage T7 DNA polymerase ternary complex, which suggests multiple regions of subunit interaction between pol gamma-beta and the human catalytic core that allow it to encircle the newly synthesized double-stranded DNA, and thereby enhance DNA binding affinity and holoenzyme processivity. Biochemical properties of a novel set of human pol gamma-beta mutants are explained by and test the model, and elucidate the role of the accessory subunit as a novel type of processivity factor in stimulating pol gamma activity and in enhancing processivity. (c) 2006 Elsevier Ltd. All rights reserved.