Sam My D, Cascio Duilio, Johnson Reid C, Clubb Robert T
Department of Chemistry and Biochemistry and the UCLA-DOE Institute for Genomics and Proteomics, University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, CA 90095-1570, USA.
J Mol Biol. 2004 Apr 23;338(2):229-40. doi: 10.1016/j.jmb.2004.02.053.
The excisionase (Xis) protein from bacteriophage lambda is the best characterized member of a large family of recombination directionality factors that control integrase-mediated DNA rearrangements. It triggers phage excision by cooperatively binding to sites X1 and X2 within the phage, bending DNA significantly and recruiting the phage-encoded integrase (Int) protein to site P2. We have determined the co-crystal structure of Xis with its X2 DNA-binding site at 1.7A resolution. Xis forms a unique winged-helix motif that interacts with the major and minor grooves of its binding site using an alpha-helix and an ordered beta-hairpin (wing), respectively. Recognition is achieved through an elaborate water-mediated hydrogen-bonding network at the major groove interface, while the preformed hairpin forms largely non-specific interactions with the minor groove. The structure of the complex provides insights into how Xis recruits Int cooperatively, and suggests a plausible mechanism by which it may distort longer DNA fragments significantly. It reveals a surface on the protein that is likely to mediate Xis-Xis interactions required for its cooperative binding to DNA.
来自噬菌体λ的切除酶（Xis）蛋白是一大类重组方向性因子中特征最为明确的成员，这些因子控制整合酶介导的DNA重排。它通过协同结合噬菌体中的X1和X2位点来触发噬菌体切除，使DNA发生显著弯曲，并将噬菌体编码的整合酶（Int）蛋白招募到P2位点。我们已经确定了Xis与其X2 DNA结合位点的共晶体结构，分辨率为1.7埃。Xis形成了一个独特的翼状螺旋基序，分别使用一个α螺旋和一个有序的β发夹（翼）与结合位点的大沟和小沟相互作用。通过在大沟界面处精心构建的水介导氢键网络实现识别，而预先形成的发夹则与小沟形成 largely 非特异性相互作用。该复合物的结构为Xis如何协同招募Int提供了见解，并提出了一种它可能显著扭曲更长DNA片段的合理机制。它揭示了蛋白质上一个可能介导Xis与Xis相互作用的表面，这种相互作用是其与DNA协同结合所必需的。
