Identification of proteins from the SECphi18 bacteriophage recognized by the KpAvs2 bacterial defense system during infection of Escherichia coli.

Antiviral STANDs (Avs) are bacterial anti-phage proteins that are considered as the evolutionary ancestors of immune pattern-recognition receptors of the NLR family. Following the recognition of a conserved phage protein, Avs proteins exhibit cellular toxicity and abort phage propagation by killing the infected cell. Type 2 Avs proteins (Avs2) were suggested to recognize the large terminase subunit of the phage by direct binding as a signature of phage infection based on co-expression assays. Here, we analyzed the binding partners of a type 2 Avs protein from Klebsiella pneumoniae (KpAvs2) expressed in Escherichia coli during SECphi18 phage infection and showed that rather than the large terminase subunit, KpAvs2 binds a small phage protein of unknown function during infection.