To initiate their life cycle, phages must specifically bind to the surface of their bacterial hosts. Long-tailed phages often interact with the cell surface using fibers, which are elongated intertwined trimeric structures. The folding and assembly of these complex structures generally requires the activity of an intra- or intermolecular chaperone protein. Tail fiber assembly (Tfa) proteins are a very large family of proteins that serve as chaperones for fiber folding in a wide variety of phages that infect diverse species. A recent structural study showed that the Tfa protein from Escherichia coli phage Mu (Tfa_Mu) mediates fiber folding and stays bound to the distal tip of the fiber, becoming a component of the mature phage particle. This finding revealed the potential for Tfa_Mu to also play a role in cell surface binding. To address this issue, we have here shown that Tfa_Mu binds to lipopolysaccharide (LPS), the cell surface receptor of phage Mu, with a similar strength as to the fiber itself. Furthermore, we have found that Tfa_Mu and the Tfa protein from E. coli phage P2 bind LPS with distinct specificities that mirror the host specificity of these two phages. By comparing the sequences of these two proteins, which are 93% identical, we identified a single residue that is responsible for their distinct LPS-binding behaviors. Although we have not yet found conditions under which Tfa proteins influence host range, the potential for such a role is now evident, as we have demonstrated their ability to bind LPS in a strain-specific manner.

中文翻译：

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尾巴纤维组装所需的噬菌体蛋白也专门结合到宿主细菌菌株的表面。

为了启动它们的生命周期，噬菌体必须与它们的细菌宿主表面特异性结合。长尾噬菌体经常使用纤维与细胞表面相互作用，纤维是细长的缠结三聚体结构。这些复杂结构的折叠和组装通常需要分子内或分子间伴侣蛋白的活性。尾巴纤维装配（Tfa）蛋白是一个非常大的蛋白家族，可作为伴侣伴侣在多种噬菌体中进行纤维折叠，从而感染多种物种。最近的结构研究表明，来自大肠杆菌噬菌体Mu的Tfa蛋白（Tfa _Mu）介导纤维折叠并保持与纤维末端的结合，成为成熟噬菌体颗粒的组成部分。这一发现揭示了Tfa的潜力_亩在细胞表面结合中也起作用。为了解决这个问题，我们在这里表明Tfa _Mu与噬菌体Mu的细胞表面受体脂多糖（LPS）结合，其强度与纤维本身相似。此外，我们发现Tfa _Mu和来自大肠杆菌的Tfa蛋白噬菌体P2以独特的特异性结合LPS，这反映了这两个噬菌体的宿主特异性。通过比较这两种蛋白质（93％相同）的序列，我们确定了一个负责其独特的LPS结合行为的残基。尽管我们还没有发现Tfa蛋白影响宿主范围的条件，但这种作用的潜力现在很明显，因为我们已经证明它们以菌株特异性方式结合LPS的能力。