Department of Biology, McMaster University, 1280 Main St. W., Hamilton, ON L8S 4K1, Canada.
Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA.
Cell Host Microbe. 2023 Mar 8;31(3):343-355.e5. doi: 10.1016/j.chom.2023.01.010.
There is strong selection for the evolution of systems that protect bacterial populations from viral attack. We report a single phage defense protein, Hna, that provides protection against diverse phages in Sinorhizobium meliloti, a nitrogen-fixing alpha-proteobacterium. Homologs of Hna are distributed widely across bacterial lineages, and a homologous protein from Escherichia coli also confers phage defense. Hna contains superfamily II helicase motifs at its N terminus and a nuclease motif at its C terminus, with mutagenesis of these motifs inactivating viral defense. Hna variably impacts phage DNA replication but consistently triggers an abortive infection response in which infected cells carrying the system die but do not release phage progeny. A similar host cell response is triggered in cells containing Hna upon expression of a phage-encoded single-stranded DNA binding protein (SSB), independent of phage infection. Thus, we conclude that Hna limits phage spread by initiating abortive infection in response to a phage protein.
存在强烈的选择压力，促使细菌群体进化出能够抵御病毒攻击的系统。我们报告了一种单一的噬菌体防御蛋白 Hna，它可以为固氮α-变形菌根瘤菌属的多种噬菌体提供保护。Hna 的同源物广泛分布于细菌谱系中，大肠杆菌的同源蛋白也具有噬菌体防御功能。Hna 的 N 端含有超家族 II 解旋酶基序，C 端含有核酸酶基序，这些基序的突变会使病毒防御失活。Hna 可改变噬菌体 DNA 的复制，但始终会引发一种无效感染反应，即携带该系统的感染细胞死亡但不会释放噬菌体后代。在含有 Hna 的细胞中，当表达噬菌体编码的单链 DNA 结合蛋白 (SSB) 时，也会触发类似的宿主细胞反应，而无需噬菌体感染。因此，我们得出结论，Hna 通过响应噬菌体蛋白引发无效感染来限制噬菌体的传播。
