The structure and function of the SLX4 nuclease complex

我们的遗传蓝图包含在我们细胞核中的长的染色体DNA分子中。在我们的一生中，我们许多组织中的细胞不断分裂，以取代旧的和受损的细胞。这是自然衰老过程的一部分。在分裂之前，细胞必须准确复制其DNA，以防止染色体变化，这些变化可能导致包括癌症和神经变性在内的衰弱性退行性疾病，其中许多是衰老的标志。DNA复制是通过DNA聚合酶进行的，DNA聚合酶复制亲本细胞中的模板链，作为完整染色体复制和细胞分裂的一部分。由于DNA由两条DNA链组成，复制涉及这两条链的分离和复制，以及每条链在一个协调过程中的复制，需要每条链的专用因子。当DNA链被分离时，产生的结构包含解旋区域，解旋和复制正在进行的连接被称为“复制叉”。重要的是，在每一轮复制过程中，专门的复制蛋白质都会遇到DNA中的结构或损伤，从而阻止它们的进展。这些结构可能是DNA中“难以”复制的天然区域，也可能是DNA中的化学损伤区域。这种化学损伤可能是由于不断发生的正常细胞过程而自发产生的，或者它们可能是通过暴露于外部因素，例如太阳辐射（阳光）或各种环境化学试剂而造成的。此外，几种重要的抗癌药物也会产生这种损伤，充分了解细胞对这种损伤的反应可能有助于我们改进化疗。复制过程中遇到的异常必须得到修复，这通常涉及一种称为核酸内切酶的蛋白质，它可以切割异常的DNA结构。这可以发生在复制过程中，或者在DNA复制过程中产生的结构可以在复制完成后稍后解析。核酸内切酶启动这种级联修复事件，已知需要的几个关键因子是XPF-ERCC 1，SLX 1和MUS 81-EME 1蛋白。然而，最近变得明显的是，这些因子必须与一种名为SLX 4的大型“平台”蛋白质相关，该蛋白质有助于将其引导到受损的复制叉以及与修复受损DNA相关的其他结构。以高分辨率解决SLX 4复合物的三维结构将是理解其机制的关键。这反过来又将最终有助于开发新的治疗方法，以对抗与衰老相关的许多退行性疾病。它还应该改善我们对发育和恶性疾病的诊断，并提供制药和生物技术部门可以用来产生新药物和新技术的重要见解，特别是因为似乎有针对性地抑制这些修复反应可能有助于改善癌症治疗。

Our genetic blueprint is contained within long, chromosomal molecules of DNA in the nucleus of our cells. During our lifetime, the cells in many of our tissues are constantly dividing to replace old and damaged cells. This is part of the natural ageing process. Before dividing, a cell must replicate its DNA accurately to prevent chromosomal changes that could lead to debilitating degenerative diseases including cancer and neurodegeneration, many of which are hallmarks of ageing. DNA replication is performed by DNA polymerases that copy the template strands in the parent cell, as part of full chromosome duplication and cell division. Since the DNA is composed of two strands of DNA, replication involves separation and replication of these two strands, and replication of each strand in a co-ordinated process requiring dedicated factors for each strand. When the DNA strands are separated the structure produced contains unwound regions, and the junction where unwinding and replication are ongoing is named a 'replication fork'. Importantly, during every round of replication the dedicated replication proteins encounter structures or damage within the DNA that block their progress. These structures might be naturally arising regions of the DNA that are 'hard' to replicate, or they might be chemically damaged regions within DNA. Such chemical damage can arise spontaneously as a result of normal cellular processes that are constantly occurring, or they might be inflicted through exposure to external agents, for example solar radiation (sunlight) or a variety of environmental chemical agents. Moreover, this type of damage is produced is also produced by several important medicines used to treat cancer, and a full understanding of how cells respond to this damage might help us improve chemotherapy.The abnormalities encountered during replication must be repaired, and this frequently involves proteins called endonucleases, that cut abnormal DNA structures. This can occur either during the process of replication, or structures generated during DNA replication can be later resolved after replication is complete. Endonucleases initiate this cascade of repair events, and several key factors known to be required for are the XPF-ERCC1, SLX1 and MUS81-EME1 proteins. However, it has recently become apparent that these factors must be associated with a large 'platform' protein called SLX4 which helps direct it to the damaged replication forks, and other structures associated with the repair of damaged DNA. Solving the three-dimensional structure of the SLX4 complex at high resolution will be key to understanding its mechanism. This in turn will ultimately help in the development of new therapeutics combating a number of degenerative conditions associated with ageing. It should also improve our diagnosis of developmental and malignant disorders and provide important insights that the pharmaceutical and biotechnology sectors could use to generate new medicines and technologies, especially since it appears that targeted inhibition of these repair reactions might help improve cancer therapy.