阿卜杜拉国王科技大学Alfredo De Biasio小组近日取得一项新成果。经过不懈努力，他们报道了复制解旋酶解绕DNA的结构动力学。这一研究成果于2025年3月19日发表在国际顶尖学术期刊《自然》上。

通过低温电子显微镜（cryo-EM），研究人员发现猿猴病毒40大肿瘤抗原（LTag）解旋酶在复制起点以头对头六聚体的形式组装，在两个对称位置熔化DNA以建立双向复制叉。通过持续的异质性分析，研究团队描述了催化条件下分叉DNA上LTag的构象景观，证明了驱动DNA易位和解绕的协调运动。课题组研究人员表明，解旋酶将跟踪链拉过沿中心通道排列的DNA结合环，同时将非跟踪链引导出后方，这是一个循环过程。ATP水解起着“熵开关”的作用，去除易位障碍，而不是直接为DNA运动提供动力。它们的结构显示了核苷酸周转和亚基运动之间的变构耦合，使DNA解绕，同时为分离的链保持专用的退出路径。这些发现为从病毒到真核系统的复制叉的建立和发展提供了一个全面的模型。更广泛地说，他们介绍了ATP依赖酶通过熵驱动变构实现有效机械功的机制的基本原理。

研究人员表示，六聚体解旋酶是核苷酸驱动的分子机器，它解除DNA，启动生命所有领域的复制。尽管经过了几十年的深入研究，它们功能的几个关键方面仍未得到解决：DNA链分离的位置和机制，解绕繁殖的机制，以及核苷酸水解与DNA运动之间的动态关系。

附：英文原文

Title: Structural dynamics of DNA unwinding by a replicative helicase

Author: Shahid, Taha, Danazumi, Ammar U., Tehseen, Muhammad, Alhudhali, Lubna, Clark, Alice R., Savva, Christos G., Hamdan, Samir M., De Biasio, Alfredo

Issue&Volume: 2025-03-19

Abstract: Hexameric helicases are nucleotide-driven molecular machines that unwind DNA to initiate replication across all domains of life. Despite decades of intensive study, several critical aspects of their function remain unresolved1: the site and mechanism of DNA strand separation, the mechanics of unwinding propagation, and the dynamic relationship between nucleotide hydrolysis and DNA movement. Here, using cryo-electron microscopy (cryo-EM), we show that the simian virus 40 large tumour antigen (LTag) helicase assembles in the form of head-to-head hexamers at replication origins, melting DNA at two symmetrically positioned sites to establish bidirectional replication forks. Through continuous heterogeneity analysis2, we characterize the conformational landscape of LTag on forked DNA under catalytic conditions, demonstrating coordinated motions that drive DNA translocation and unwinding. We show that the helicase pulls the tracking strand through DNA-binding loops lining the central channel, while directing the non-tracking strand out of the rear, in a cyclic process. ATP hydrolysis functions as an ‘entropy switch’, removing blocks to translocation rather than directly powering DNA movement. Our structures show the allosteric couplings between nucleotide turnover and subunit motions that enable DNA unwinding while maintaining dedicated exit paths for the separated strands. These findings provide a comprehensive model for replication fork establishment and progression that extends from viral to eukaryotic systems. More broadly, they introduce fundamental principles of the mechanism by which ATP-dependent enzymes achieve efficient mechanical work through entropy-driven allostery.

DOI: 10.1038/s41586-025-08766-w

Source: https://www.nature.com/articles/s41586-025-08766-w