Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
Section of Molecular Genetics and Microbiology, University of Texas at Austin, Austin, Texas 78712.
J Biol Chem. 2011 Sep 2;286(35):30867-30877. doi: 10.1074/jbc.M111.260877. Epub 2011 Jun 25.
Podoviridae are double-stranded DNA bacteriophages that use short, non-contractile tails to adsorb to the host cell surface. Within the tail apparatus of P22-like phages, a dedicated fiber known as the "tail needle" likely functions as a cell envelope-penetrating device to promote ejection of viral DNA inside the host. In Sf6, a P22-like phage that infects Shigella flexneri, the tail needle presents a C-terminal globular knob. This knob, absent in phage P22 but shared in other members of the P22-like genus, represents the outermost exposed tip of the virion that contacts the host cell surface. Here, we report a crystal structure of the Sf6 tail needle knob determined at 1.0 Å resolution. The structure reveals a trimeric globular domain of the TNF fold structurally superimposable with that of the tail-less phage PRD1 spike protein P5 and the adenovirus knob, domains that in both viruses function in receptor binding. However, P22-like phages are not known to utilize a protein receptor and are thought to directly penetrate the host surface. At 1.0 Å resolution, we identified three equivalents of l-glutamic acid (l-Glu) bound to each subunit interface. Although intimately bound to the protein, l-Glu does not increase the structural stability of the trimer nor it affects its ability to self-trimerize in vitro. In analogy to P22 gp26, we suggest the tail needle of phage Sf6 is ejected through the bacterial cell envelope during infection and its C-terminal knob is threaded through peptidoglycan pores formed by glycan strands.
Podoviridae 是双链 DNA 噬菌体，它们使用短而不收缩的尾巴吸附在宿主细胞表面。在 P22 样噬菌体的尾部装置中，一种称为“尾针”的专用纤维可能充当细胞包膜穿透装置，以促进病毒 DNA 在宿主内的排出。在 Sf6 中，一种感染志贺氏菌的 P22 样噬菌体，尾针呈现出 C 末端球状旋钮。该旋钮在噬菌体 P22 中不存在，但在其他 P22 样属成员中共享，代表与宿主细胞表面接触的病毒粒子的最外暴露尖端。在这里，我们报告了 Sf6 尾针旋钮的晶体结构，其分辨率为 1.0 Å。该结构揭示了 TNF 折叠的三聚体球状结构域，与无尾噬菌体 PRD1 刺突蛋白 P5 和腺病毒旋钮的结构域在结构上是可叠加的，这两个结构域在两种病毒中都具有受体结合功能。然而，P22 样噬菌体不被认为利用蛋白质受体，并且被认为直接穿透宿主表面。在 1.0 Å 的分辨率下，我们确定了每个亚基界面结合的三个等价的 l-谷氨酸（l-Glu）。尽管 l-Glu 紧密结合在蛋白质上，但它既不会增加三聚体的结构稳定性，也不会影响其在体外自我三聚化的能力。与 P22 gp26 类似，我们建议噬菌体 Sf6 的尾针在感染过程中通过细菌细胞包膜射出，其 C 末端旋钮穿过糖链形成的肽聚糖孔。
