Phage prohead proteases activate CBASS antiphage immunity (Science)

A Science paper by Samuel J. Hobbs and Philip J. Kranzusch reports that phage prohead protease activity activates the CD-NTase enzymes of bacterial CBASS defence: the authors reconstitute CBASS recognition of phage T4 in vitro, identify cleavage of a CD-NTase activation loop as the trigger of immune signal synthesis, and show that phage prohead proteases activate CBASS in vivo, explaining how immunity is initiated late during infection. Structure-based analyses identify activation loops in clade A, D and G CD-NTases.