同源DNA雙鏈之間的遺傳重組在基因組的維持和增殖中扮演一個關(guān)鍵角色,。這一過程的核心中間體是一個四通路的結(jié)合點（Holliday），連接著兩個DNA雙鏈,。這兩個鏈最終分開，形成兩個單獨的DNA雙鏈,。各種不同類型的結(jié)合點分解酶見于原核生物,、真核生物和它們的病毒,。這些核酸酶對于DNA分歧點（branchpoint）有高度選擇性。現(xiàn)在,，兩個小組描述了兩種不同的結(jié)合點分解酶的復(fù)合物的晶體結(jié)構(gòu),，這兩種分解酶分別是endonuclease 1 (phage T7) 和 endonuclease VII (phage T4),，每個都與DNA結(jié)合點結(jié)合在一起,。這兩種酶在結(jié)合時使結(jié)合點的結(jié)構(gòu)顯著扭曲。新的結(jié)構(gòu)揭示了這兩種酶何以對DNA結(jié)合點有選擇性,，也揭示了分解反應(yīng)的原理,。
原始出處:
Nature 449, 616-620 (4 October 2007) | doi:10.1038/nature06152; Received 1 June 2007; Accepted 7 August 2007; Published online 16 September 2007
Crystal structure of T4 endonuclease VII resolving a Holliday junction
Christian Biertümpfel1, Wei Yang1 & Dietrich Suck2
National Institute of Diabetes and Digestive and Kidney Diseases, Laboratory of Molecular Biology, 9000 Rockville Pike, Bethesda, Maryland 20892, USA
European Molecular Biology Laboratory, Structural and Computational Biology Programme, Meyerhofstr. 1, 69117 Heidelberg, Germany
Correspondence to: Wei Yang1Dietrich Suck2 Correspondence and requests for materials should be addressed to W.Y. (Email: [email protected]) or D.S. (Email: [email protected]).
Holliday proposed a four-way DNA junction as an intermediate in homologous recombination1, and such Holliday junctions have since been identified as a central component in DNA recombination and repair2. Phage T4 endonuclease VII (endo VII) was the first enzyme shown to resolve Holliday junctions into duplex DNAs by introducing symmetrical nicks in equivalent strands3. Several Holliday junction resolvases have since been characterized4, but an atomic structure of a resolvase complex with a Holliday junction remained elusive. Here we report the crystal structure of an inactive T4 endo VII(N62D) complexed with an immobile four-way junction with alternating arm lengths of 10 and 14 base pairs. The junction is a hybrid of the conventional square-planar and stacked-X conformation. Endo VII protrudes into the junction point from the minor groove side, opening it to a 14 Å 32 Å parallelogram. This interaction interrupts the coaxial stacking, yet every base pair surrounding the junction remains intact. Additional interactions involve the positively charged protein and DNA phosphate backbones. Each scissile phosphate that is two base pairs from the crossover interacts with a Mg2+ ion in the active site. The similar overall shape and surface charge potential of the Holliday junction resolvases endo VII, RuvC, Ydc2, Hjc and RecU, despite having different folds, active site composition and DNA sequence preference, suggest a conserved binding mode for Holliday junctions.
