PDF(Pubmed)
Abstract：
The large dsDNA viruses replicate their DNA as concatemers consisting of multiple covalently linked genomes. Genome packaging is catalyzed by a terminase enzyme that excises individual genomes from concatemers and packages them into preassembled procapsids. These disparate tasks are catalyzed by terminase alternating between two distinct states-a stable nuclease that excises individual genomes and a dynamic motor that translocates DNA into the procapsid. It was proposed that bacteriophage λ terminase assembles as an anti-parallel dimer-of-dimers nuclease complex at the packaging initiation site. In contrast, all characterized packaging motors are composed of five terminase subunits bound to the procapsid in a parallel orientation. Here, we describe biophysical and structural characterization of the λ holoenzyme complex assembled in solution. Analytical ultracentrifugation, small angle X-ray scattering, and native mass spectrometry indicate that 5 subunits assemble a cone-shaped terminase complex. Classification of cryoEM images reveals starfish-like rings with skewed pentameric symmetry and one special subunit. We propose a model wherein nuclease domains of two subunits alternate between a dimeric head-to-head arrangement for genome maturation and a fully parallel arrangement during genome packaging. Given that genome packaging is strongly conserved in both prokaryotic and eukaryotic viruses, the results have broad biological implications.
摘要：
大型dsDNA病毒将其DNA复制为由多个共价连接的基因组组成的多联体。基因组包装由末端酶催化，该酶从串联体中切除单个基因组并将其包装成预组装的原衣壳。这些不同的任务由在两种不同状态之间交替的终止酶催化-一种稳定的核酸酶，其切除单个基因组和一种动态马达，其将DNA易位到衣壳中。有人提出，噬菌体λ末端酶在包装起始位点组装为反平行的二聚体-二聚体核酸酶复合物。相比之下,所有具有特征的包装马达都由以平行方向与原衣壳结合的五个末端酶亚基组成。这里,我们描述了在溶液中组装的λ全酶复合物的生物物理和结构表征。分析超速离心，小角度X射线散射，和天然质谱表明5个亚基组装了一个锥形的末端酶复合物。冷冻EM图像的分类揭示了具有偏斜的五聚体对称性和一个特殊亚基的海星状环。我们提出了一个模型，其中两个亚基的核酸酶结构域在基因组成熟的二聚体头对头排列和基因组包装期间的完全平行排列之间交替。鉴于基因组包装在原核和真核病毒中都非常保守，结果具有广泛的生物学意义。
