This entry represents a TIR domain found in prokaryotic nucleotide-binding proteins, including CD-NTase-associated protein 12 (CAP12) and Pycsar effector proteins (E.C:3.2.2.5). Members of this entry are part of anti phage resistance systems that provide immunity against bacteriophage. CAP12 is part of the CBASS (cyclic oligonucleotide-based anti phage signaling system) and binds c-di-GMP and 3'-3'-cGAMP, cyclic nucleotides synthesized by the CD-NTase protein in response to infection that serve as specific second messenger signals to activate a diverse range of effectors, leading to bacterial cell death and thus abortive phage infection [1,2]. Pycsar effector proteins are part of the Pycsar (pyrimidine cyclase system for anti phage resistance) and are activated by cyclic nucleotides produced by the pyrimidine cyclase (PycC) in response to infection. The TIR effector domain oligomerises and functions as NADase that deplete the cell of NAD+.

1: Cyclic CMP and cyclic UMP mediate bacterial immunity against phages. Tal N, Morehouse BR, Millman A, Stokar-Avihail A, Avraham C, Fedorenko T, Yirmiya E, Herbst E, Brandis A, Mehlman T, Oppenheimer-Shaanan Y, Keszei AFA, Shao S, Amitai G, Kranzusch PJ, Sorek R; Cell. 2021;184:5728-5739. PMID:34644530

2: STING cyclic dinucleotide sensing originated in bacteria. Morehouse BR, Govande AA, Millman A, Keszei AFA, Lowey B, Ofir G, Shao S, Sorek R, Kranzusch PJ; Nature. 2020;586:429-433. PMID:32877915