Andres Sara N, Modesti Mauro, Tsai Chun J, Chu Gilbert, Junop Murray S
Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON L8N 3Z5, Canada.
Mol Cell. 2007 Dec 28;28(6):1093-101. doi: 10.1016/j.molcel.2007.10.024.
DNA double-strand breaks represent one of the most severe forms of DNA damage in mammalian cells. One pathway for repairing these breaks occurs via nonhomologous end-joining (NHEJ) and depends on XRCC4, LigaseIV, and Cernunnos, also called XLF. Although XLF stimulates XRCC4/LigaseIV to ligate mismatched and noncohesive DNA ends, the mechanistic basis for this function remains unclear. Here we report the structure of a partially functional 224 residue N-terminal fragment of human XLF. Despite only weak sequence similarity, XLF(1-170) shares structural homology with XRCC4(1-159). However, unlike the highly extended 130 A helical domain observed in XRCC4, XLF adopts a more compact, folded helical C-terminal region involving two turns and a twist, wrapping back to the structurally conserved N terminus. Mutational analysis of XLF and XRCC4 reveals a potential interaction interface, suggesting a mechanism for how XLF stimulates the ligation of mismatched ends.
DNA双链断裂是哺乳动物细胞中最严重的DNA损伤形式之一。修复这些断裂的一种途径是通过非同源末端连接（NHEJ），该途径依赖于XRCC4、连接酶IV和Cernunnos（也称为XLF）。虽然XLF刺激XRCC4/连接酶IV连接错配和无粘性的DNA末端，但其功能的机制基础仍不清楚。在此，我们报道了人XLF的一个部分功能的224个残基N端片段的结构。尽管序列相似性较弱，但XLF（1-170）与XRCC4（1-159）具有结构同源性。然而，与在XRCC4中观察到的高度延伸的130 Å螺旋结构域不同，XLF采用了更紧凑、折叠的螺旋C端区域，该区域包含两圈和一个扭曲，回绕到结构保守的N端。对XLF和XRCC4的突变分析揭示了一个潜在的相互作用界面，提示了XLF刺激错配末端连接的机制。
