6p7o

Structural highlights

Function

NUCC_ECOM1 CBASS (cyclic oligonucleotide-based antiphage signaling system) provides immunity against bacteriophage. The CD-NTase protein synthesizes cyclic nucleotides in response to infection; these serve as specific second messenger signals. The signals activate a diverse range of effectors, leading to bacterial cell death and thus abortive phage infection. A type III-C(AAA) CBASS system (PubMed:32839535).^{[1] [2]} A cyclic nucleotide-activated dsDNase. In the presence of 3',3',3'-cyclic AMP-AMP-AMP (cAAA), and to a lesser extent 3',3',3'-cyclic AMP-AMP-GMP (cAAG) and cyclic-di-AMP (c-di-AMP), endonucleolytically degrades dsDNA (PubMed:31932165, PubMed:31932164). Binds one cAAA in a pocket on one surface of the trimer; cAAA binding promotes hexamerization, which is necessary for nuclease activation. Also binds c-diAMP or linear di-AMP with lower affinity. The nuclease digests dsDNA to about 50 bp lengths with a 2-base 3' overhang and a consensus recognition site of 5'-Axx|T-3'. DNA has been modeled to contact a pair of juxtaposed active sites (one from each layer of the hexamer), accounting for cleavage on both strands and the 2-base overhang (PubMed:31932164).^{[3] [4]} Protects E.coli strain JP313 against bacteriophage lambda cI- infection. When the cdnC-cap7-cap6-nucC operon is transformed into a susceptible strain it confers bacteriophage immunity. Mutations in the sensor (Cap7 also called HORMA) or effector proteins (CdnC, NucC) but not the disassembly protein (Cap6 also called Trip13) no longer confer immunity. The presence of the intact operon leads to culture collapse and cell death which occurs before the phage has finished its replication cycle, thus protecting non-infected bacteria by aborting the phage infection and preventing its propagation.^{[5] [6]}

References

1. ↑ Ye Q, Lau RK, Mathews IT, Birkholz EA, Watrous JD, Azimi CS, Pogliano J, Jain M, Corbett KD. HORMA Domain Proteins and a Trip13-like ATPase Regulate Bacterial cGAS-like Enzymes to Mediate Bacteriophage Immunity. Mol Cell. 2019 Dec 31. pii: S1097-2765(19)30922-0. doi:, 10.1016/j.molcel.2019.12.009. PMID:31932165 doi:http://dx.doi.org/10.1016/j.molcel.2019.12.009
2. ↑ Millman A, Melamed S, Amitai G, Sorek R. Diversity and classification of cyclic-oligonucleotide-based anti-phage signalling systems. Nat Microbiol. 2020 Dec;5(12):1608-1615. doi: 10.1038/s41564-020-0777-y. Epub, 2020 Aug 24. PMID:32839535 doi:http://dx.doi.org/10.1038/s41564-020-0777-y
3. ↑ Lau RK, Ye Q, Birkholz EA, Berg KR, Patel L, Mathews IT, Watrous JD, Ego K, Whiteley AT, Lowey B, Mekalanos JJ, Kranzusch PJ, Jain M, Pogliano J, Corbett KD. Structure and Mechanism of a Cyclic Trinucleotide-Activated Bacterial Endonuclease Mediating Bacteriophage Immunity. Mol Cell. 2020 Jan 6. pii: S1097-2765(19)30923-2. doi:, 10.1016/j.molcel.2019.12.010. PMID:31932164 doi:http://dx.doi.org/10.1016/j.molcel.2019.12.010
4. ↑ Ye Q, Lau RK, Mathews IT, Birkholz EA, Watrous JD, Azimi CS, Pogliano J, Jain M, Corbett KD. HORMA Domain Proteins and a Trip13-like ATPase Regulate Bacterial cGAS-like Enzymes to Mediate Bacteriophage Immunity. Mol Cell. 2019 Dec 31. pii: S1097-2765(19)30922-0. doi:, 10.1016/j.molcel.2019.12.009. PMID:31932165 doi:http://dx.doi.org/10.1016/j.molcel.2019.12.009
5. ↑ Lau RK, Ye Q, Birkholz EA, Berg KR, Patel L, Mathews IT, Watrous JD, Ego K, Whiteley AT, Lowey B, Mekalanos JJ, Kranzusch PJ, Jain M, Pogliano J, Corbett KD. Structure and Mechanism of a Cyclic Trinucleotide-Activated Bacterial Endonuclease Mediating Bacteriophage Immunity. Mol Cell. 2020 Jan 6. pii: S1097-2765(19)30923-2. doi:, 10.1016/j.molcel.2019.12.010. PMID:31932164 doi:http://dx.doi.org/10.1016/j.molcel.2019.12.010
6. ↑ Ye Q, Lau RK, Mathews IT, Birkholz EA, Watrous JD, Azimi CS, Pogliano J, Jain M, Corbett KD. HORMA Domain Proteins and a Trip13-like ATPase Regulate Bacterial cGAS-like Enzymes to Mediate Bacteriophage Immunity. Mol Cell. 2019 Dec 31. pii: S1097-2765(19)30922-0. doi:, 10.1016/j.molcel.2019.12.009. PMID:31932165 doi:http://dx.doi.org/10.1016/j.molcel.2019.12.009