In the non-homologous end-joining (NHEJ) of a DNA double-strand break, DNA ends are bound and protected by DNA-PK, which synapses across the break to tether the broken ends and initiate repair. There is little clarity surrounding the nature of the synaptic complex and the mechanism governing the transition to repair. We report an integrative structure of the synaptic complex at a precision of 13.5 Å, revealing a symmetric head-to-head arrangement with a large offset in the DNA ends and an extensive end-protection mechanism involving a previously uncharacterized plug domain. Hydrogen/deuterium exchange mass spectrometry identifies an allosteric pathway connecting DNA end-binding with the kinase domain that places DNA-PK under tension in the kinase-active state. We present a model for the transition from end-protection to repair, where the synaptic complex supports hierarchical processing of the ends and scaffold assembly, requiring displacement of the catalytic subunit and tension release through kinase activity.

在 DNA 双链断裂的非同源末端连接 (NHEJ) 中，DNA 末端受到 DNA-PK 的束缚和保护，DNA-PK 在断裂处突触以连接断裂末端并启动修复。围绕突触复合体的性质和控制过渡到修复的机制几乎没有明确的认识。我们以 13.5 Å 的精度报告了突触复合体的综合结构，揭示了对称的头对头排列，在 DNA 末端有很大的偏移，以及广泛的末端保护机制，涉及以前未表征的插头域。氢/氘交换质谱确定了连接 DNA 末端结合与激酶结构域的变构通路，该通路将 DNA-PK 置于激酶活性状态的张力下。我们提出了一个从末端保护过渡到修复的模型，