Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario, Canada.
J Bacteriol. 2013 Dec;195(24):5461-8. doi: 10.1128/JB.00805-13. Epub 2013 Oct 4.
A variety of bacterial pathogenicity determinants, including the type VI secretion system and the virulence cassettes from Photorhabdus and Serratia, share an evolutionary origin with contractile-tailed myophages. The well-characterized Escherichia coli phage P2 provides an excellent system for studies related to these systems, as its protein composition appears to represent the "minimal" myophage tail. In this study, we used nuclear magnetic resonance (NMR) spectroscopy to determine the solution structure of gpX, a 68-residue tail baseplate protein. Although the sequence and structure of gpX are similar to those of LysM domains, which are a large family associated with peptidoglycan binding, we did not detect a peptidoglycan-binding activity for gpX. However, bioinformatic analysis revealed that half of all myophages, including all that possess phage T4-like baseplates, encode a tail protein with a LysM-like domain, emphasizing a widespread role for this domain in baseplate function. While phage P2 gpX comprises only a single LysM domain, many myophages display LysM domain fusions with other tail proteins, such as the DNA circulation protein found in Mu-like phages and gp53 of T4-like phages. Electron microscopy of P2 phage particles with an incorporated gpX-maltose binding protein fusion revealed that gpX is located at the top of the baseplate, near the junction of the baseplate and tail tube. gpW, the orthologue of phage T4 gp25, was also found to localize to this region. A general colocalization of LysM-like domains and gpW homologues in diverse phages is supported by our bioinformatic analysis.
多种细菌致病性决定因素，包括来自 Photorhabdus 和 Serratia 的 VI 型分泌系统和毒力盒，与收缩长尾噬菌体具有共同的进化起源。研究这些系统的一个很好的模型是特征明确的大肠杆菌噬菌体 P2，因为它的蛋白质组成似乎代表了最小的噬菌体尾部。在这项研究中，我们使用核磁共振（NMR）光谱学来确定 68 个残基尾部基板蛋白 gpX 的溶液结构。尽管 gpX 的序列和结构与 LysM 结构域相似，LysM 结构域是与肽聚糖结合相关的一个大家族，但我们没有检测到 gpX 与肽聚糖结合的活性。然而，生物信息学分析表明，所有的噬菌体中有一半，包括所有具有噬菌体 T4 样基板的噬菌体，都编码一个带有 LysM 样结构域的尾部蛋白，这强调了这个结构域在基板功能中的广泛作用。虽然噬菌体 P2 的 gpX 只包含一个 LysM 结构域，但许多噬菌体显示出 LysM 结构域与其他尾部蛋白的融合，例如 Mu 样噬菌体中的 DNA 循环蛋白和 T4 样噬菌体中的 gp53。与掺入的 gpX-麦芽糖结合蛋白融合的 P2 噬菌体颗粒的电子显微镜显示，gpX 位于基板的顶部，靠近基板和尾部管的连接处。噬菌体 T4 的 gp25 同源物 gpW 也被发现定位于该区域。我们的生物信息学分析支持了 LysM 样结构域和 gpW 同源物在多种噬菌体中普遍共定位的观点。
