Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada.
Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
J Bacteriol. 2021 Jan 11;203(3). doi: 10.1128/JB.00406-20.
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 phage Mu (Tfa) 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 to also play a role in cell surface binding. To address this issue, we have here shown that Tfa 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 and the Tfa protein from 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. With the growing interest in using phages to combat antibiotic-resistant infections or manipulate the human microbiome, establishing approaches for the modification of phage host range has become an important research topic. Tfa proteins are a large family of proteins known previously to function as chaperones for the folding of phage fibers, which are crucial determinants of host range for long-tailed phages. Here, we reveal that some Tfa proteins are bi-functional, with the additional activity of binding to LPS, the surface binding receptor for many phages. This discovery opens up new potential avenues for altering phage host range through engineering of the surface binding specificity of Tfa proteins.
为了启动它们的生命周期，噬菌体必须特异性地结合到它们的细菌宿主的表面。长尾噬菌体通常使用纤维与细胞表面相互作用，纤维是长而交织的三聚体结构。这些复杂结构的折叠和组装通常需要一种分子内或分子间伴侣蛋白的活性。尾丝组装（Tfa）蛋白是一个非常大的蛋白家族，作为纤维折叠的伴侣，存在于感染多种不同物种的多种噬菌体中。最近的一项结构研究表明，噬菌体 Mu 的 Tfa 蛋白（Tfa）介导纤维折叠，并与纤维的远端尖端结合，成为成熟噬菌体颗粒的一个组成部分。这一发现表明 Tfa 也有可能在细胞表面结合中发挥作用。为了解决这个问题，我们在这里表明，Tfa 与脂多糖（LPS），噬菌体 Mu 的细胞表面受体，以类似于纤维本身的强度结合。此外，我们发现 Tfa 和噬菌体 P2 的 Tfa 蛋白与 LPS 的结合具有不同的特异性，反映了这两种噬菌体的宿主特异性。通过比较这两种蛋白的序列，它们有 93%的一致性，我们确定了一个单一的残基负责它们不同的 LPS 结合行为。尽管我们还没有找到 Tfa 蛋白影响宿主范围的条件，但现在显然有这样的作用的可能性，因为我们已经证明了它们以菌株特异性的方式结合 LPS 的能力。随着使用噬菌体来对抗抗生素耐药性感染或操纵人类微生物组的兴趣日益增加，建立修饰噬菌体宿主范围的方法已成为一个重要的研究课题。Tfa 蛋白是一个已知的先前作为噬菌体纤维折叠的伴侣蛋白的大家族，而纤维是长尾噬菌体宿主范围的关键决定因素。在这里，我们揭示了一些 Tfa 蛋白具有双重功能，具有与 LPS 结合的额外活性，LPS 是许多噬菌体的表面结合受体。这一发现为通过工程改造 Tfa 蛋白的表面结合特异性来改变噬菌体宿主范围开辟了新的潜在途径。
