Laboratoire de Microbiologie et Génétique Moléculaires, Centre National de la Recherche Scientifique-UMR 5100, Université Paul Sabatier, Toulouse, France.
Genome Biol Evol. 2011;3:674-86. doi: 10.1093/gbe/evr059. Epub 2011 Jul 11.
The tail fiber adhesins are the primary determinants of host range in the T4-type bacteriophages. Among the indispensable virion components, the sequences of the long tail fiber genes and their associated adhesins are among the most variable. The predominant form of the adhesin in the T4-type phages is not even the version of the gene encoded by T4, the archetype of the superfamily, but rather a small unrelated protein (gp38) encoded by closely related phages such as T2 and T6. This gp38 adhesin has a modular design: its N-terminal attachment domain binds at the tip of the tail fiber, whereas the C-terminal specificity domain determines its host receptor affinity. This specificity domain has a series of four hypervariable segments (HVSs) that are separated by a set of highly conserved glycine-rich motifs (GRMs) that apparently form the domain's conserved structural core. The role of gp38's various components was examined by a comparative analysis of a large series of gp38 adhesins from T-even superfamily phages with differing host specificities. A deletion analysis revealed that the individual HVSs and GRMs are essential to the T6 adhesin's function and suggests that these different components all act in synergy to mediate adsorption. The evolutionary advantages of the modular design of the adhesin involving both conserved structural elements and multiple independent and easily interchanged specificity determinants are discussed.
尾丝附属蛋白是 T4 型噬菌体决定宿主范围的主要因素。在必不可少的病毒粒子成分中，长尾丝基因的序列及其相关的附属蛋白是最易变的。在 T4 型噬菌体中，主要的附属蛋白形式甚至不是超级家族原型 T4 编码的基因版本，而是由密切相关的噬菌体（如 T2 和 T6）编码的一种小型无关蛋白（gp38）。这种 gp38 附属蛋白具有模块化设计：其 N 端附着域结合在尾丝的尖端，而 C 端特异性域决定其宿主受体亲和力。该特异性域具有一系列四个超变区（HVS），它们由一组高度保守的富含甘氨酸的基序（GRMs）分隔，这些基序显然构成了该结构域的保守结构核心。通过对具有不同宿主特异性的 T 偶数超级家族噬菌体的大量 gp38 附属蛋白进行比较分析，研究了 gp38 的各种成分的作用。缺失分析表明，各个 HVS 和 GRM 对于 T6 附属蛋白的功能都是必不可少的，并表明这些不同的成分都协同作用以介导吸附。讨论了涉及保守结构元件和多个独立且易于互换的特异性决定因素的附属蛋白的模块化设计的进化优势。
