This family includes Kiwa protein KwaB from E.coli, a component of antiviral defense system Kiwa composed of KwaA and KwaB. The expression of Kiwa in E.coli (strain MG1655) confers resistance to phages lambda and SECphi18 [2]. This family also includes a phylogenetically broad range of bacteria associated with the human gut microbiome. A member of this family from Lactobacillus casei CRL 705 is part of the gene cluster involved in synthesis of bacteriocin toxin [1].

1: Identification and nucleotide sequence of genes involved in the synthesis of lactocin 705, a two-peptide bacteriocin from Lactobacillus casei CRL 705. Cuozzo SA, Sesma F, Palacios JM, de Ruiz Holgado AP, Raya RR; FEMS Microbiol Lett 2000;185:157-161. PMID:10754241

2: Systematic discovery of antiphage defense systems in the microbial pangenome. Doron S, Melamed S, Ofir G, Leavitt A, Lopatina A, Keren M, Amitai G, Sorek R; Science. 2018; [Epub ahead of print] PMID:29371424