Osheroff N
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee.
Pharmacol Ther. 1989;41(1-2):223-41. doi: 10.1016/0163-7258(89)90108-3.
DNA topoisomerases are complex and unique enzymes which alter the topological state of DNA without changing its chemical structure. Between the type I and II enzymes, topoisomerases carry out a multitude of reactions, including DNA binding, site specific DNA cleavage/religation, relaxation, catenation/decatenation, and knotting/unknotting of nucleic acid substrates, DNA strand transfer, and ATP hydrolysis. In vivo, topoisomerases are involved in many aspects of nucleic acid metabolism and play critical roles in maintaining chromosome and nuclear structure. Finally, these enzymes are of clinical relevance, as they appear to be the primary cellular targets for many varied classes of antineoplastic agents. Considering the importance of the topoisomerases, it is distressing that we know so little about their enzymatic mechanisms. Many major questions remain. Just a few include, "How do topoisomerases recognize their nucleic acid interaction sites?"; "What amino acid residues comprise the enzymes' active sites?"; "What are the conformational changes that accompany DNA strand passage?"; "How does phosphorylation stimulate enzyme activity?"; "How does topoisomerase function when it is part of an immobilized structure such as the nuclear matrix or the mitotic chromosome scaffold?"; and "How do antineoplastic agents interact with their topoisomerase targets and stabilize covalent enzyme.DNA cleavage products?" Clearly, before the physiological functions of the topoisomerases can be fully described, these and similar issues will have to be addressed. Hopefully, the next several years will produce answers for at least some of these important questions.
DNA拓扑异构酶是复杂而独特的酶，它们可改变DNA的拓扑状态而不改变其化学结构。在I型和II型酶之间，拓扑异构酶可进行多种反应，包括DNA结合、位点特异性DNA切割/连接、松弛、连环化/解连环化以及核酸底物的打结/解结、DNA链转移和ATP水解。在体内，拓扑异构酶参与核酸代谢的许多方面，并在维持染色体和核结构中发挥关键作用。最后，这些酶具有临床相关性，因为它们似乎是许多不同种类抗肿瘤药物的主要细胞靶点。考虑到拓扑异构酶的重要性，令人苦恼的是我们对其酶促机制了解甚少。许多主要问题仍然存在。仅举几个问题为例：“拓扑异构酶如何识别其核酸相互作用位点？”；“哪些氨基酸残基构成酶的活性位点？”；“DNA链通过时伴随的构象变化是什么？”；“磷酸化如何刺激酶活性？”；“当拓扑异构酶作为固定结构（如核基质或有丝分裂染色体支架）的一部分时，它是如何发挥功能的？”；以及“抗肿瘤药物如何与其拓扑异构酶靶点相互作用并稳定共价酶-DNA切割产物？”显然，在能够充分描述拓扑异构酶的生理功能之前，必须解决这些以及类似的问题。希望在未来几年至少能找到其中一些重要问题的答案。
