Predicted to function as a sensor domain, sensing nucleotides or nucleotide derivatives generated by SMODS and other nucleotide synthetase domains [1]. This domain has been characterised in CD-NTase-associated protein 4 (Cap4), the founding member of a major family of downstream receptors that specifically respond to nucleotide second messenger signals in CBASS immunity, a bacterial system that provides immunity against bacteriophage [2,3]. SAVED exhibits divergence in its nucleotide binding pocket which enables the recognition of a wide range of CD-NTase products such as bacterial second messengers with alternative ring size, nucleobase, and 3'-5' or 2'-5' phosphodiester linkages [2]. The sensing of ligands by SAVED activates effectors that are essential for CBASS-mediated protection of bacteria from phage infection.

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: CBASS Immunity Uses CARF-Related Effectors to Sense 3'-5'- and 2'-5'-Linked Cyclic Oligonucleotide Signals and Protect Bacteria from Phage Infection. Lowey B, Whiteley AT, Keszei AFA, Morehouse BR, Mathews IT, Antine SP, Cabrera VJ, Kashin D, Niemann P, Jain M, Schwede F, Mekalanos JJ, Shao S, Lee ASY, Kranzusch PJ; Cell. 2020; [Epub ahead of print] PMID:32544385

3: 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