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首页> 外文期刊>Journal of Molecular Biology >The Prohead-I structure of bacteriophage HK97: implications for scaffold-mediated control of particle assembly and maturation.
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The Prohead-I structure of bacteriophage HK97: implications for scaffold-mediated control of particle assembly and maturation.

机译：HK97噬菌体的Prohead-I结构：对支架介导的颗粒组装和成熟控制的影响。

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摘要

Virus capsid assembly requires recruiting and organizing multiple copies of protein subunits to form a closed shell for genome packaging that leads to infectivity. Many viruses encode scaffolding proteins to shift the equilibrium toward particle formation by promoting intersubunit interactions and stabilizing assembly intermediates. Bacteriophage HK97 lacks an explicit scaffolding protein, but the capsid protein (gp5) contains a scaffold-like N-terminal segment termed the delta domain. When gp5 is expressed in Escherichia coli, the delta domain guides 420 copies of the subunit into a procapsid with T=7 laevo icosahedral symmetry named Prohead-I. Prohead-I can be disassembled and reassembled under mild conditions and it cannot mature further. When the virally encoded protease (gp4) is coexpressed with gp5, it is incorporated into the capsid and digests the delta domain followed by autoproteolysis to produce the metastable Prohead-II. Prohead-I(+P) was isolated by coexpressing gp5 and an inactive mutant of gp4. Prohead-I and Prohead-I(+P) were compared by biochemical methods, revealing that the inactive protease stabilized the capsid against disassembly by chemical or physical stress. The crystal structure of Prohead-I(+P) was determined at 5.2 A resolution, and distortions were observed in the subunit tertiary structures similar to those observed previously in Prohead-II. Prohead-I(+P) differed from Prohead-II due to the presence of the delta domain and the resulting repositioning of the N-arms, explaining why Prohead-I can be reversibly dissociated and cannot mature. Low-resolution X-ray data enhanced the density of the relatively dynamic delta domains, revealing their quaternary arrangement and suggesting how they drive proper assembly.
机译：病毒衣壳组装需要募集并组织蛋白质亚基的多个副本，以形成用于基因组包装的封闭外壳，从而导致感染。许多病毒编码支架蛋白，通过促进亚基间相互作用并稳定组装中间体，从而使平衡向颗粒形成转移。噬菌体HK97缺乏明确的支架蛋白，但衣壳蛋白（gp5）包含一个称为δ域的支架样N末端片段。当gp5在大肠杆菌中表达时，δ结构域将420个亚基拷贝导入T = 7二十面体二十面体对称的前壳体，称为Prohead-I。 Prohead-I可以在温和的条件下拆卸和重新组装，无法进一步成熟。当病毒编码的蛋白酶（gp4）与gp5共表达时，将其掺入衣壳中并消化δ结构域，然后进行自动蛋白水解以产生亚稳态的Prohead-II。通过共表达gp5和gp4的失活突变体来分离Prohead-I（+ P）。通过生物化学方法比较了Prohead-I和Prohead-I（+ P），发现无活性的蛋白酶使衣壳稳定，不会因化学或物理应力而解体。 Prohead-I（+ P）的晶体结构在5.2 A分辨率下确定，并且在亚单位三级结构中观察到畸变，类似于先前在Prohead-II中观察到的畸变。 Prohead-I（+ P）与Prohead-II有所不同，因为存在delta域并导致N臂重新定位，这说明了Prohead-I可以可逆分离并不能成熟的原因。低分辨率X射线数据增强了相对动态的δ域的密度，揭示了它们的四级排列并暗示了它们如何驱动正确的组装。

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