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首页> 外文期刊>Journal of Molecular Biology >Structure-function analysis of the DNA translocating portal of the bacteriophage T4 packaging machine
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Structure-function analysis of the DNA translocating portal of the bacteriophage T4 packaging machine

机译：T4噬菌体包装机DNA易位门户的结构功能分析

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摘要

Tailed bacteriophages and herpesviruses consist of a structurally well conserved dodecameric portal at a special 5-fold vertex of the capsid. The portal plays critical roles in head assembly, genome packaging, neck/tail attachment, and genome ejection. Although the structures of portals from phages φ29, SPP1, and P22 have been determined, their mechanistic roles have not been well understood. Structural analysis of phage T4 portal (gp20) has been hampered because of its unusual interaction with the Escherichia coli inner membrane. Here, we predict atomic models for the T4 portal monomer and dodecamer, and we fit the dodecamer into the cryo-electron microscopy density of the phage portal vertex. The core structure, like that from other phages, is cone shaped with the wider end containing the "wing" and "crown" domains inside the phage head. A long "stem" encloses a central channel, and a narrow "stalk" protrudes outside the capsid. A biochemical approach was developed to analyze portal function by incorporating plasmid-expressed portal protein into phage heads and determining the effect of mutations on head assembly, DNA translocation, and virion production. We found that the protruding loops of the stalk domain are involved in assembling the DNA packaging motor. A loop that connects the stalk to the channel might be required for communication between the motor and the portal. The "tunnel" loops that project into the channel are essential for sealing the packaged head. These studies established that the portal is required throughout the DNA packaging process, with different domains participating at different stages of genome packaging.
机译：尾状噬菌体和疱疹病毒由位于衣壳特殊5倍顶点处的结构良好保守的十二聚体门户组成。该门户在头部组装，基因组包装，颈部/尾巴附着和基因组弹出中起着关键作用。尽管已经确定了来自噬菌体φ29，SPP1和P22的门的结构，但是它们的机械作用尚未得到很好的理解。噬菌体T4门户（gp20）的结构分析因其与大肠杆菌内膜的异常相互作用而受到阻碍。在这里，我们预测了T4门槛单体和十二聚体的原子模型，并将十二聚体适合于噬菌体入口顶点的低温电子显微镜密度。与其他噬菌体一样，其核心结构呈锥形，其末端较宽，在噬菌体头部内部包含“侧翼”和“冠状”结构域。长的“茎”围绕着中央通道，而狭窄的“茎”则突出到衣壳外部。通过将表达质粒的门户蛋白掺入噬菌体头部并确定突变对头部组装，DNA易位和病毒体生产的影响，开发了一种生物化学方法来分析门户功能。我们发现茎域的突出环参与组装DNA包装电机。马达和门户之间的通信可能需要将茎杆连接到通道的环路。突出到通道中的“隧道”回路对于密封已包装的喷头至关重要。这些研究确定了门户在整个DNA包装过程中都是必需的，不同的域参与了基因组包装的不同阶段。

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