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<p>Nucleic acid degradation is a common strategy for prokaryotic anti-phage systems, as exemplified by the CRISPR-Cas system. The PD-(D/E)-XK nucleases constitute a widely distributed family in these defenses. Notably, most members exhibit a single nuclease domain, while variants containing dual nuclease domains within a single polypeptide remain underexplored, and their molecular mechanisms largely obscure. Here, we biochemically and functionally study a single-protein system containing an uncharacterized PD-(D/E)-XK defense protein (Upx). As revealed by single-particle electron cryo-microscopy (cryo-EM) structure, the C-terminal domain (CTD) harboring the conserved PD-(D/E)XK catalytic core is buttressed by the N-terminal domain (NTD) and the middle domain (MD). Functional assays demonstrate that the nucleic acid binding capability of the CTD is enhanced by the MD. The NTD also displays a noncanonical, basal exonuclease activity that is auto-inhibited by MD. IP-MS experiments identify Upx-interacting phage proteins, and substrate profiling defines its physiological preferences, collectively pointing to its potential physiological targets. Notably, the phage protein gp16 was found to relieve MD-mediated inhibition of the NTD, suggesting a virus-triggered mechanism for activating Upx’s dual nuclease activity. Together, these findings establish Upx as a single-protein dual-nuclease anti-phage system, expanding our understanding of bacterial immunity and informing antiviral strategy development.</p>

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Structural and mechanistic insights into the dual-nuclease defense protein Upx as an anti-phage system

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月9日

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  • Ruimin Zhou,
  • Yingcan Liu,
  • Qian Zhang,
  • Zhenning Yin,
  • Jiajing Tong,
  • Chendi Zhang,
  • Lingling Zhang,
  • Xuzichao Li,
  • Yanhao Zhao,
  • Shuqin Zhang,
  • Zhikun Liu,
  • Weichang Chen,
  • Nan Ji,
  • Heng Zhang,
  • Zhuang Li,
  • Hang Yin,
  • Shengkai Zuo,
  • Yong Wei

摘要

Nucleic acid degradation is a common strategy for prokaryotic anti-phage systems, as exemplified by the CRISPR-Cas system. The PD-(D/E)-XK nucleases constitute a widely distributed family in these defenses. Notably, most members exhibit a single nuclease domain, while variants containing dual nuclease domains within a single polypeptide remain underexplored, and their molecular mechanisms largely obscure. Here, we biochemically and functionally study a single-protein system containing an uncharacterized PD-(D/E)-XK defense protein (Upx). As revealed by single-particle electron cryo-microscopy (cryo-EM) structure, the C-terminal domain (CTD) harboring the conserved PD-(D/E)XK catalytic core is buttressed by the N-terminal domain (NTD) and the middle domain (MD). Functional assays demonstrate that the nucleic acid binding capability of the CTD is enhanced by the MD. The NTD also displays a noncanonical, basal exonuclease activity that is auto-inhibited by MD. IP-MS experiments identify Upx-interacting phage proteins, and substrate profiling defines its physiological preferences, collectively pointing to its potential physiological targets. Notably, the phage protein gp16 was found to relieve MD-mediated inhibition of the NTD, suggesting a virus-triggered mechanism for activating Upx’s dual nuclease activity. Together, these findings establish Upx as a single-protein dual-nuclease anti-phage system, expanding our understanding of bacterial immunity and informing antiviral strategy development.