Structure and Energetics of Encapsidated DNA in Bacteriophage HK97 Studied by Scanning Calorimetry and Cryo-electron Microscopy
Structure and Energetics of Encapsidated DNA in Bacteriophage HK97 Studied by Scanning Calorimetry and Cryo-electron Microscopy
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DOI：
10.1016/j.jmb.2009.06.035
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发表时间：
2009-08-14
影响因子：
5.6
通讯作者：
Steven, Alasdair C.
中科院分区：
文献类型：
--
作者：
Duda, Robert L.;Ross, Philip D.;Steven, Alasdair C.
噬菌体对双链体DNA的包封代表了基因组浓缩的极端情况，达到DNA的近结晶浓度。鉴于其衣壳结构的详细知识，HK 97系统非常适合于研究这种现象。为了表征所涉及的相互作用，我们结合量热法与低温电子显微镜和天然凝胶电泳。我们发现，在其他的DNA，HK 97 DNA组织在同轴缠绕嵌套壳。当在含有1 mm Mg 2+的缓冲液中扫描DNA填充的衣壳（头部）时，DNA解链和衣壳变性都有助于在82 ℃和96 ℃之间的复杂热曲线。在其他条件下（不存在Mg 2+和较低的离子强度），DNA解链转移到较低的温度，这两个事件得到解决。头部在远低于DNA解链或衣壳变性开始的温度下释放它们的DNA。我们认为，在加热时，内部压力增加，导致DNA退出-可能通过门户网站的顶点，而衣壳，虽然基本上是完整的，维持局部损伤，导致更早发生的热变性。头部在结构上与空衣壳的蛋白质外壳的曲率不同，这种变化可归因于DNA施加的向外压力。我们建议，这种转变是由门户网站，是嵌入在衣壳壁，因此门户网站的结构和它的相互作用与终止酶，包装酶，被改变，从而发出信号，包装是在或接近完成。爱思唯尔有限公司出版
Encapsidation of duplex DNA by bacteriophages represents an extreme case of genome condensation, reaching near-crystalline concentrations of DNA. The HK97 system is well suited to study this phenomenon in view of the detailed knowledge of its capsid structure. To characterize the interactions involved, we combined calorimetry with cryo-electron microscopy and native gel electrophoresis. We found that, as in other phages, HK97 DNA is organized in coaxially wound nested shells. When DNA-filled capsids (heads) are scanned in buffer containing 1 mm Mg2+, DNA melting and capsid denaturation both contribute to the complex thermal profile between 82 degrees C and 96 degrees C. In other conditions (absence of Mg2+ and lower ionic strength), DNA melting shifts to lower temperatures and the two events are resolved. Heads release their DNA at temperatures well below the onset of DNA melting or capsid denaturation. We suggest that, on heating, the internal pressure increases, causing the DNA to exit-probably via the portal vertex-while the capsid, although largely intact, sustains local damage that leads to an earlier onset of thermal denaturation. Heads differ structurally from empty capsids in the curvature of their protein shell, a change attributable to outwards pressure exerted by the DNA. We propose that this transition is sensed by the portal that is embedded in the capsid wall, whereupon the structure of the portal and its interactions with terminase, the packaging enzyme, are altered, thus signaling that packaging is at or approaching completion. Published by Elsevier Ltd.