Chemical Biology Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia.
Department of Medical Biology, University of Melbourne, Parkville, Victoria, Australia.
Biochem Soc Trans. 2022 Feb 28;50(1):459-22W. doi: 10.1042/BST20210799.
The majority of phages, viruses that infect prokaryotes, inject their genomic material into their host through a tubular assembly known as a tail. Despite the genomic diversity of tailed phages, only three morphological archetypes have been described: contractile tails of Myoviridae-like phages; short non-contractile tails of Podoviridae-like phages; and long and flexible non-contractile tails of Siphoviridae-like phages. While early cryo-electron microscopy (cryo-EM) work elucidated the organisation of the syringe-like injection mechanism of contractile tails, the intrinsic flexibility of the long non-contractile tails prevented high-resolution structural determination. In 2020, four cryo-EM structures of Siphoviridae-like tail tubes were solved and revealed common themes and divergences. The central tube is structurally conserved and homologous to the hexameric rings of the tail tube protein (TTP) also found in contractile tails, bacterial pyocins, and type VI secretion systems. The interior surface of the tube presents analogous motifs of negatively charged amino acids proposed to facilitate ratcheting of the DNA during genome ejection. The lack of a conformational change upon genome ejection implicates the tape measure protein in triggering genome release. A distinctive feature of Siphoviridae-like tails is their flexibility. This results from loose inter-ring connections that can asymmetrically stretch on one side to allow bending and flexing of the tube without breaking. The outer surface of the tube differs greatly and may be smooth or rugged due to additional Ig-like domains in TTP. Some of these variable domains may contribute to adsorption of the phage to prokaryotic and eukaryotic cell surfaces affecting tropism and virulence.
大多数噬菌体是感染原核生物的病毒，它们通过一种称为尾部的管状结构将其基因组物质注入宿主。尽管长尾噬菌体具有基因组多样性，但只描述了三种形态原型：类似于肌病毒科噬菌体的收缩性尾部；类似于短尾病毒科噬菌体的短非收缩性尾部；以及类似于丝状病毒科噬菌体的长而灵活的非收缩性尾部。虽然早期的冷冻电子显微镜（cryo-EM）工作阐明了收缩性尾部注射机制的注射器样结构的组织，但长的非收缩性尾部的固有柔韧性阻止了高分辨率结构的确定。2020 年，解决了四个类似丝状病毒科尾部管的 cryo-EM 结构，并揭示了共同的主题和差异。中央管在结构上是保守的，与收缩性尾部、细菌噬菌体和 VI 型分泌系统中发现的尾部管蛋白（TTP）的六聚体环同源。管的内表面呈现出带负电荷的氨基酸的类似基序，据推测这些基序有助于在基因组排出过程中对 DNA 进行棘轮运动。在基因组排出时没有构象变化表明卷尺蛋白在触发基因组释放中起作用。丝状病毒科尾部的一个独特特征是其灵活性。这是由于环之间的连接松散，在一侧可以不对称地拉伸，从而使管弯曲和弯曲而不会断裂。管的外表面差异很大，由于 TTP 中存在额外的 Ig 样结构域，可能是光滑的或崎岖不平的。这些可变结构域中的一些可能有助于噬菌体吸附到原核和真核细胞表面，从而影响趋向性和毒力。
