Structure, assembly, and DNA packaging of the bacteriophage T4 head.
Structure, assembly, and DNA packaging of the bacteriophage T4 head.
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DOI：
10.1016/b978-0-12-394621-8.00018-2
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发表时间：
2012
影响因子：
--
通讯作者：
Rao, Venigalla B.
中科院分区：
文献类型：
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作者：
Black, Lindsay W.;Rao, Venigalla B.
噬菌体T4头是一个细长的二十面体，包裹着172kb的线性双链DNA和许多蛋白质。衣壳由三种基本蛋白质构成：gp23*，它形成六边形衣壳晶格；Gp24 *，在12个顶点中的11个形成五聚体；gp20形成独特的十二轴门静脉顶点，DNA在包装过程中通过它进入，在感染过程中通过它退出。半个多世纪的密集工作使人们对噬菌体T4头有了深入的了解。gp24的原子结构已经确定。利用gp23与gp24的相似性构建的结构模型表明，噬菌体T4主要衣壳蛋白与许多其他二十面体噬菌体具有相同的折叠。然而，T4噬菌体显示出一种不寻常的膜和门脉启动组装，形状决定了自给自足的支架核心。gp23的折叠需要两个伴侣的帮助，大肠杆菌伴侣GroEL与噬菌体编码的gp23特异性伴侣gp31一起作用。衣壳还含有两种非必需的外衣壳蛋白，Hoc和Soc，它们修饰衣壳表面。通过与邻近的gp23亚基结合，Soc强化了衣壳结构。Hoc和Soc已广泛应用于两部分肽展示文库和病原体抗原展示，包括人类免疫缺陷病毒（HIV）、脑膜炎奈瑟菌、炭疽芽孢杆菌和口蹄疫病毒。Ip1*的结构表明它是一种特异性的酶切酶的抑制剂，这种酶切酶特异性地靶向糖基化羟甲基胞嘧啶DNA。Ip1*是多个（bbb100）复制蛋白中的一个，被包装并注入了来自整个头部的DNA。广泛的诱变，结合DNA包装/终止酶蛋白gp16和gp17的原子结构，阐明了参与DNA易位和头部DNA切割的atp酶和核酸酶功能基序。T4包装机的低温电镜结构显示在门静脉顶点有gp17亚基组装的五聚体马达。单分子光镊和荧光研究表明，T4马达包装DNA的速度是已知的最高的，并且可以包装多个片段。Förster共振能量转移-荧光相关光谱研究表明，DNA在失速马达中被压缩，并且在易位过程中，端到门的距离发生变化。目前的证据表明，一个线性双组分（大端酶加门户）易位马达，其中ATP水解产生的静电力通过在紧张和放松状态之间交替的马达驱动DNA易位。
The bacteriophage T4 head is an elongated icosahedron packed with 172 kb of linear double-stranded DNA and numerous proteins. The capsid is built from three essential proteins: gp23*, which forms the hexagonal capsid lattice; gp24*, which forms pentamers at 11 of the 12 vertices; and gp20, which forms the unique dodecameric portal vertex through which DNA enters during packaging and exits during infection. Intensive work over more than half a century has led to a deep understanding of the phage T4 head. The atomic structure of gp24 has been determined. A structural model built for gp23 using its similarity to gp24 showed that the phage T4 major capsid protein has the same fold as numerous other icosahedral bacteriophages. However, phage T4 displays an unusual membrane and portal initiated assembly of a shape determining self-sufficient scaffolding core. Folding of gp23 requires the assistance of two chaperones, the Escherichia coli chaperone GroEL acting with the phage-coded gp23-specific cochaperone, gp31. The capsid also contains two nonessential outer capsid proteins, Hoc and Soc, which decorate the capsid surface. Through binding to adjacent gp23 subunits, Soc reinforces the capsid structure. Hoc and Soc have been used extensively in bipartite peptide display libraries and to display pathogen antigens, including those from human immunodeficiency virus (HIV), Neisseria meningitides, Bacillus anthracis, and foot and mouth disease virus. The structure of Ip1*, one of a number of multiple (>100) copy proteins packed and injected with DNA from the full head, shows it to be an inhibitor of one specific restriction endonuclease specifically targeting glycosylated hydroxymethyl cytosine DNA. Extensive mutagenesis, combined with atomic structures of the DNA packaging/terminase proteins gp16 and gp17, elucidated the ATPase and nuclease functional motifs involved in DNA translocation and headful DNA cutting. The cryoelectron microscopy structure of the T4 packaging machine showed a pentameric motor assembled with gp17 subunits on the portal vertex. Single molecule optical tweezers and fluorescence studies showed that the T4 motor packages DNA at the highest rate known and can package multiple segments. Förster resonance energy transfer–fluorescence correlation spectroscopy studies indicate that DNA gets compressed in the stalled motor and that the terminase-to-portal distance changes during translocation. Current evidence suggests a linear two-component (large terminase plus portal) translocation motor in which electrostatic forces generated by ATP hydrolysis drive DNA translocation by alternating the motor between tensed and relaxed states.