Smits Callum, Chechik Maria, Kovalevskiy Oleg V, Shevtsov Mikhail B, Foster Andrew W, Alonso Juan C, Antson Alfred A
York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5YW, UK.
EMBO Rep. 2009 Jun;10(6):592-8. doi: 10.1038/embor.2009.53. Epub 2009 May 15.
The DNA-packaging motor in tailed bacteriophages requires nuclease activity to ensure that the genome is packaged correctly. This nuclease activity is tightly regulated as the enzyme is inactive for the duration of DNA translocation. Here, we report the X-ray structure of the large terminase nuclease domain from bacteriophage SPP1. Similarity with the RNase H family endonucleases allowed interactions with the DNA to be predicted. A structure-based alignment with the distantly related T4 gp17 terminase shows the conservation of an extended beta-sheet and an auxiliary beta-hairpin that are not found in other RNase H family proteins. The model with DNA suggests that the beta-hairpin partly blocks the active site, and in vivo activity assays show that the nuclease domain is not functional in the absence of the ATPase domain. Here, we propose that the nuclease activity is regulated by movement of the beta-hairpin, altering active site access and the orientation of catalytically essential residues.
有尾噬菌体中的DNA包装马达需要核酸酶活性来确保基因组被正确包装。由于该酶在DNA转运过程中无活性，所以这种核酸酶活性受到严格调控。在此，我们报道了噬菌体SPP1的大型末端酶核酸酶结构域的X射线结构。与核糖核酸酶H家族内切核酸酶的相似性使得可以预测其与DNA的相互作用。与远亲T4 gp17末端酶基于结构的比对显示，存在一个在其他核糖核酸酶H家族蛋白中未发现的延伸β折叠和一个辅助β发夹结构的保守性。与DNA的模型表明，β发夹部分阻断了活性位点，体内活性测定表明，在没有ATP酶结构域的情况下，核酸酶结构域无功能。在此，我们提出核酸酶活性受β发夹移动的调控，改变活性位点的可及性以及催化必需残基的方向。
