Structural and Mechanistic Analyses Reveal a Unique Cas4-like Protein in the Mimivirus Virophage Resistance Element System
Chao Dou,
Mingjing Yu,
Yijun Gu,
Jinjing Wang,
Kun Yin,
Chunlai Nie,
Xiaofeng Zhu,
Shiqian Qi,
Yuquan Wei,
Wei Cheng
Affiliations
Chao Dou
Division of Respiratory and Critical Care Medicine, State Key Laboratory of Biotherapy, West China Hospital of Sichuan University and Collaborative Innovation Center of Biotherapy, 17th, 3rd Section, Southern Renmin Road, Chengdu, 610041, China
Mingjing Yu
Division of Respiratory and Critical Care Medicine, State Key Laboratory of Biotherapy, West China Hospital of Sichuan University and Collaborative Innovation Center of Biotherapy, 17th, 3rd Section, Southern Renmin Road, Chengdu, 610041, China
Division of Respiratory and Critical Care Medicine, State Key Laboratory of Biotherapy, West China Hospital of Sichuan University and Collaborative Innovation Center of Biotherapy, 17th, 3rd Section, Southern Renmin Road, Chengdu, 610041, China
Kun Yin
Shandong Academy of Medical Sciences, Shandong Institute of Parasitic Disease, Jining, Shandong 272033, China
Chunlai Nie
Division of Respiratory and Critical Care Medicine, State Key Laboratory of Biotherapy, West China Hospital of Sichuan University and Collaborative Innovation Center of Biotherapy, 17th, 3rd Section, Southern Renmin Road, Chengdu, 610041, China
Xiaofeng Zhu
Division of Respiratory and Critical Care Medicine, State Key Laboratory of Biotherapy, West China Hospital of Sichuan University and Collaborative Innovation Center of Biotherapy, 17th, 3rd Section, Southern Renmin Road, Chengdu, 610041, China
Shiqian Qi
Division of Respiratory and Critical Care Medicine, State Key Laboratory of Biotherapy, West China Hospital of Sichuan University and Collaborative Innovation Center of Biotherapy, 17th, 3rd Section, Southern Renmin Road, Chengdu, 610041, China
Yuquan Wei
Division of Respiratory and Critical Care Medicine, State Key Laboratory of Biotherapy, West China Hospital of Sichuan University and Collaborative Innovation Center of Biotherapy, 17th, 3rd Section, Southern Renmin Road, Chengdu, 610041, China
Wei Cheng
Division of Respiratory and Critical Care Medicine, State Key Laboratory of Biotherapy, West China Hospital of Sichuan University and Collaborative Innovation Center of Biotherapy, 17th, 3rd Section, Southern Renmin Road, Chengdu, 610041, China; Corresponding author
Summary: A clustered regularly interspaced short palindromic repeats (CRISPR)-like “mimivirus virophage resistance element” (MIMIVIRE) system, which contains specific cascade genes and a CRISPR array against virophages, was reported in mimiviruses. An essential component of the MIMIVIRE system is R354, encoding a nuclease and a likely functional homolog of Cas4. Here we show that R354 is a dual nuclease with both exonuclease and endonuclease activities. Structural analysis revealed that the catalytic core domain of R354 is similar to those of Cas4 and λ exonuclease despite their low sequence identity. R354 forms a homodimer that is important for its exonuclease but not endonuclease activity. Structural comparisons between the active and semi-active states of R354 demonstrated that an activation loop adjacent to the catalytic site is critical for enzymatic activity. Overall, the results suggest that R354 belongs to a novel MIMIVIRE system involved in innate virus immunity and provides a template for the identification of new CRISPR systems in other species. : Virology; Structural Biology; Protein Structure Aspects Subject Areas: Virology, Structural Biology, Protein Structure Aspects
