Family of bacterial HORMA domains found in conserved genome contexts with Pch2/TRIP13 P-loop NTPases. Acts as a 'third component' in broad class of conflict systems reliant on the production of second messenger nucleotide or nucleotide derivatives. Together with Pch2/TRIP13, could act as co-effectors or in regulation of other effectors of the systems [1]. It is found in proteins from the CBASS (cyclic oligonucleotide-based antiphage signaling system), a system that provides immunity against bacteriophage. This domain is found in CD-NTase-associated protein 7 (Cap7) from E.coli, that acts as a sensor protein of CBSS and binds to a closure peptide allowing it to activate the CD-NTase CdnC for second messenger synthesis and, therefore, it activates a diverse range of effectors [2,3].

1: Comparative genomic analyses reveal a vast, novel network of nucleotide-centric systems in biological conflicts, immunity and signaling. Burroughs AM, Zhang D, Schaffer DE, Iyer LM, Aravind L; Nucleic Acids Res. 2015;43:10633-10654. PMID:26590262

2: Diversity and classification of cyclic-oligonucleotide-based anti-phage signalling systems. Millman A, Melamed S, Amitai G, Sorek R; Nat Microbiol. 2020;5:1608-1615. PMID:32839535

3: HORMA Domain Proteins and a Trip13-like ATPase Regulate Bacterial cGAS-like Enzymes to Mediate Bacteriophage Immunity. Ye Q, Lau RK, Mathews IT, Birkholz EA, Watrous JD, Azimi CS, Pogliano J, Jain M, Corbett KD; Mol Cell. 2020;77:709-722. PMID:31932165