Unveiling the multifaceted domain polymorphism of the Menshen antiphage system

Recent advances have significantly enriched our understanding of complex bacteria-phage interactions. To date, over one hundred bacterial antiphage systems have been identified, yet the mechanisms of many, including the recently discovered Menshen system, remain elusive. We employed comparative genomics and protein bioinformatics for a systematic investigation of the Menshen system, focusing on its organization, structure, function, and evolution. By delineating six primary domain determinants and predicting their functions, we propose that the three components (NsnA-B-C) of Menshen likely act as sensor, transducer, and effector modules, respectively. Notably, we unveil remarkable polymorphism in domain composition within both NsnA and NsnC. NsnA proteins universally share ParB-DUF262 and DNA-binding ParBDB domains, and often include additional DNA-binding modules at their N-termini. NsnC effectors exhibit diverse inactive PIN (inPIN)-like domains for target recognition in their N-termini, and multiple nuclease domains for toxicity in their C-termini. We demonstrate that this multifaceted polymorphism results from the independent integration of various sensor domains into NsnA, alongside constant shuffling and diversification of the inPIN and effector domains in NsnC. These findings not only elucidate the functional diversity and inter-subunit interactions of the Menshen system, but also underscore its exceptional capacity for adaptability and versatility in the ongoing arms race between bacteria and phages.