Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-2032, USA.
Proc Natl Acad Sci U S A. 2012 Aug 28;109(35):14001-6. doi: 10.1073/pnas.1207730109. Epub 2012 Aug 13.
The Podoviridae phage C1 was one of the earliest isolated bacteriophages and the first virus documented to be active against streptococci. The icosahedral and asymmetric reconstructions of the virus were calculated using cryo-electron microscopy. The capsid protein has an HK97 fold arranged into a T = 4 icosahedral lattice. The C1 tail is terminated with a ϕ29-like knob, surrounded by a skirt of twelve long appendages with novel morphology. Several C1 structural proteins have been identified, including a candidate for an appendage. The crystal structure of the knob has an N-terminal domain with a fold observed previously in tube forming proteins of Siphoviridae and Myoviridae phages. The structure of C1 suggests the mechanisms by which the virus digests the cell wall and ejects its genome. Although there is little sequence similarity to other phages, conservation of the structural proteins demonstrates a common origin of the head and tail, but more recent evolution of the appendages.
Podoviridae 噬菌体 C1 是最早分离到的噬菌体之一，也是最早被证实可有效对抗链球菌的病毒。该病毒的二十面体和非对称结构使用低温电子显微镜进行了计算。衣壳蛋白具有 HK97 折叠结构，排列成 T=4 的二十面体晶格。C1 尾部末端带有类似 ϕ29 的球头，周围环绕着带有独特形态的十二个长附属物裙。已经鉴定出几种 C1 结构蛋白，包括一个附属物的候选蛋白。球头的晶体结构具有一个 N 端结构域，其折叠形式以前在长尾噬菌体科和肌尾噬菌体科的管状形成蛋白中观察到过。C1 的结构表明了病毒消化细胞壁并排出其基因组的机制。尽管与其他噬菌体的序列相似性很小，但结构蛋白的保守性证明了头部和尾部的共同起源，但附属物的进化较为近期。
