High-resolution crystal structure of the restriction-modification controller protein C.Ahdl from Aeromonas hydrophila
High-resolution crystal structure of the restriction-modification controller protein C.Ahdl from Aeromonas hydrophila
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DOI：
10.1016/j.jmb.2004.12.025
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发表时间：
2005-02-25
影响因子：
5.6
通讯作者：
Kneale, GG
中科院分区：
文献类型：
--
作者：
McGeehan, JE;Streeter, SD;Kneale, GG
限制性内切酶修饰(R-M)系统用于保护宿主细菌免受噬菌体入侵。多组分系统包括识别和甲基化特定DNA序列的甲基转移酶，以及识别相同序列并在该位置内或附近切割的内切酶。核酸内切酶只会切割特定位点上未甲基化的DNA，从而保护宿主DNA，而切割非宿主DNA。然而，在DNA复制之后，内切酶的表达必须推迟，直到宿主DNA适当甲基化。在许多R-M系统中，这种调节是通过控制蛋白或C蛋白在转录水平上实现的。我们已经用硒蛋氨酸MAD解决了R-M控制蛋白C.AhdI的第一个X射线结构，分辨率为1.69埃。C.AhdI是IIH R-M系统的一部分，来自病原体嗜水气单胞菌。该结构揭示了一个包含经典螺旋-转角-螺旋(HTH)结构域的All-a蛋白，并可归入XRE转录调节家族。与其单体结构同系物不同，延伸的螺旋产生一个界面，导致游离蛋白质的二聚化。二聚体是静电极化的，带正电荷的表面对应于HTH结构域的DNA识别螺旋的位置。与三元复合体结构的比较表明，C.AhdI通过与RNA聚合酶的α(70)亚基直接接触而激活转录。(C)2004爱思唯尔有限公司。保留所有权利。
Restriction-modification (R-M) systems serve to protect the host bacterium from invading bacteriophage. The multi-component system includes a methyltransferase, which recognizes and methylates a specific DNA sequence, and an endonuclease which recognises the same sequence and cleaves within or close to this site. The endonuclease will only cleave DNA that is unmethylated at the specific site, thus host DNA is protected while non-host DNA is cleaved. However, following DNA replication, expression of the endonuclease must be delayed until the host DNA is appropriately methylated. In many R-M systems, this regulation is achieved at the transcriptional level via the controller protein, or C-protein. We have solved the first X-ray structure of an R-M controller protein, C.AhdI, to 1.69 Angstrom resolution using selenomethionine MAD. C.AhdI is part of a Type IIH R-M.system from the pathogen Aeromonas hydrophila. The structure reveals an all-a protein that contains a classical helix-turn-helix (HTH) domain and can be assigned to the Xre family of transcriptional regulators. Unlike its monomeric structural homologues, an extended helix generates an interface that results in dimerisation of the free protein. The dimer is electrostatically polarised and a positively charged surface corresponds to the position of the DNA recognition helices of the HTH domain. Comparison with the structure of the cl ternary complex suggests that C.AhdI activates transcription through direct contact with the alpha(70) subunit of RNA polymerase. (C) 2004 Elsevier Ltd. All rights reserved.