1.B.162. The Cyclic oligonucleotide-based Antiphage Signaling System (CBASS) Family
Cyclic oligonucleotide-based antiphage signaling systems (CBASS) are encoded by antiviral defense operons that protect bacteria from phage replication. Duncan-Lowey et al. 2021 iendtified a widespread class of CBASS transmembrane (TM) effector proteins that respond to antiviral nucleotide signals and limit phage propagation through direct membrane disruption. Crystal structures of the Yersinia TM effector, Cap15, revealed a compact 8-stranded beta-barrel scaffold that forms a cyclic dinucleotide receptor domain that oligomerizes upon activation. They demonstrated that activated Cap15 relocalizes throughout the cell and specifically induces rupture of the inner membrane. Screening for active effectors, they identified the functions of distinct families of CBASS TM effectors and demonstrated that cell death via disruption of inner-membrane integrity is a common mechanism of defense. These results reveal the function of the most prominent class of effector protein in CBASS immunity and define disruption of the inner membrane as a widespread strategy of abortive infection in bacterial phage defense (Duncan-Lowey et al. 2021).
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Cap15, chains A and B, of 131 aas, have been solved and revealed a compact 8 stranded β-barrel. It allows the bacteria to disrupt the inner membrane to protect itself from the virus (see family description) (Duncan-Lowey et al. 2021). It resembles the short soluble region of about 160 aas between TMSs 2 and 3 in the K+ channel with a Uniprot ID of F7Q1W9 and a TC# of 1.A.1.2.39.
Cap15 of Haloplasma contractile
Uncharacterized protein of 255 aas and 3 N-terminal TMSs.
UP of Kordia antarctica
pancortin-3 of 198 aas and 2 or 3 N-terminal TMSs.
Pancortin-3 of E. coli
Uncharacterized protein of 183 aas and 3 TMSs, 2 at the N-terminus of the protein and one in the middle of the protein.
UP of Acholeplasmatales bacterium (gut metagenome)
Uncharacterized protein of 196 aas with two N-terminal TMSs.
UP of Sunxiuqinia elliptica
Uncharacterized protein of 225 aas and 2 N-terminal TMSs.
UP of Blastomonas natatoria
Uncharacterized protein of 205 aas and 2 N-terminal TMSs.
UP of Methylobacterium sp. WL116
Uncharacterized protein with two N-terminal TMSs.
UP of Thalassospira xiamenensis
Uncharacterized protein of 228 aas and 2 or 3 TMSs.
UP of Zoogloea oleivorans
Uncharacterized protein of 250 aas and 2 or 3 TMSs.
UP of Tautonia marina