Department of Agricultural Biotechnology, Seoul National University, Seoul 08826, Korea.
Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea.
Nucleic Acids Res. 2023 Nov 27;51(21):11941-11951. doi: 10.1093/nar/gkad951.
Bacteriophages (phages) are viruses that infect bacteria and archaea. To fend off invading phages, the hosts have evolved a variety of anti-phage defense mechanisms. Gabija is one of the most abundant prokaryotic antiviral systems and consists of two proteins, GajA and GajB. GajA has been characterized experimentally as a sequence-specific DNA endonuclease. Although GajB was previously predicted to be a UvrD-like helicase, its function is unclear. Here, we report the results of structural and functional analyses of GajB. The crystal structure of GajB revealed a UvrD-like domain architecture, including two RecA-like core and two accessory subdomains. However, local structural elements that are important for the helicase function of UvrD are not conserved in GajB. In functional assays, GajB did not unwind or bind various types of DNA substrates. We demonstrated that GajB interacts with GajA to form a heterooctameric Gabija complex, but GajB did not exhibit helicase activity when bound to GajA. These results advance our understanding of the molecular mechanism underlying Gabija anti-phage defense and highlight the role of GajB as a component of a multi-subunit antiviral complex in bacteria.
噬菌体（phages）是感染细菌和古菌的病毒。为了抵御入侵的噬菌体，宿主进化出了多种抗噬菌体防御机制。Gabija 是最丰富的原核抗病毒系统之一，由两种蛋白质 GajA 和 GajB 组成。GajA 已被实验证明是一种序列特异性 DNA 内切酶。虽然 GajB 先前被预测为 UvrD 样解旋酶，但它的功能尚不清楚。在这里，我们报告了 GajB 的结构和功能分析结果。GajB 的晶体结构揭示了一种 UvrD 样结构域架构，包括两个 RecA 样核心和两个辅助亚结构域。然而，对于 UvrD 解旋酶功能很重要的局部结构元素在 GajB 中并不保守。在功能测定中，GajB 不能解旋或结合各种类型的 DNA 底物。我们证明 GajB 与 GajA 相互作用形成异源八聚体 Gabija 复合物，但 GajB 与 GajA 结合时没有表现出解旋酶活性。这些结果增进了我们对 Gabija 抗噬菌体防御的分子机制的理解，并强调了 GajB 作为细菌中多亚基抗病毒复合物的一个组成部分的作用。
