Xie Ping
Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190 China.
Cell Mol Bioeng. 2018 Dec 5;12(2):179-191. doi: 10.1007/s12195-018-00563-y. eCollection 2019 Apr.
AddAB enzyme is a helicase-nuclease complex that initiates recombinational repair of double-stranded DNA breaks. It catalyzes processive DNA unwinding and concomitant resection of the unwound strands, which are modulated by the recognition of a recombination hotspot called Chi in the 3'-terminated strand. Despite extensive structural, biochemical and single molecule studies, the detailed molecular mechanism of DNA unwinding by the complex and modulation by Chi sequence remains unclear.
A model of DNA unwinding by the AddAB complex and modulation by Chi recognition was presented, based on which the dynamics of AddAB complex was studied analytically.
The theoretical results explain well the available experimental data on effect of DNA sequence on velocity, effect of Chi recognition on velocity, static disorder peculiar to the AddAB complex, and dynamics of pausing of wild-type and mutant AddAB complexes occurring at Chi or Chi-like sequence. Predictions were provided. Comparisons of AddAB complex with other helicase-nuclease complexes such as RecBCD and AdnAB were made.
The study has strong implications for the molecular mechanism of DNA unwinding by the AddAB complex. The intriguing issues are addressed of why Chi recognition is an inefficient process, how AddAB complex pauses upon recognizing Chi sequence, how the paused state transits to the translocating state, why the mutant AddAB with a stronger affinity to Chi sequence has a shorter pausing lifetime, why the pausing lifetime is sensitive to the solution temperature, and so on.
AddAB酶是一种解旋酶-核酸酶复合物，可启动双链DNA断裂的重组修复。它催化持续性的DNA解旋以及对解旋链的伴随切除，这一过程受到3'端链中一个名为Chi的重组热点识别的调控。尽管进行了广泛的结构、生化和单分子研究，但该复合物解旋DNA以及受Chi序列调控的详细分子机制仍不清楚。
提出了AddAB复合物解旋DNA及受Chi识别调控的模型，并在此基础上对AddAB复合物的动力学进行了分析研究。
理论结果很好地解释了关于DNA序列对速度的影响、Chi识别对速度的影响、AddAB复合物特有的静态无序以及野生型和突变型AddAB复合物在Chi或类Chi序列处暂停的动力学等现有实验数据。给出了预测结果。对AddAB复合物与其他解旋酶-核酸酶复合物（如RecBCD和AdnAB）进行了比较。
该研究对AddAB复合物解旋DNA的分子机制具有重要意义。探讨了一些有趣的问题，如为什么Chi识别是一个低效过程、AddAB复合物在识别Chi序列时如何暂停、暂停状态如何转变为转运状态、为什么对Chi序列亲和力更强的突变型AddAB的暂停寿命更短、为什么暂停寿命对溶液温度敏感等等。
