title: Novel Immunity Proteins Associated with Colicin M-like Bacteriocins Exhibit Promiscuous Protection inPseudomonas.
abstract: Bacteriocins related to colicin M, acting via cleavage of the cell wall precursor lipid II, have been characterized in γ- and β-proteobacteria. Depending on the species, immunity is provided by either an inner membrane-anchored periplasmic protein or by an integral membrane protein. InPseudomonashowever, the immunity partner of colicin M-like bacteriocins remains unknown. Based on anin silicoanalysis in pseudomonad genomes, we here identify a gene encoding a putative immunity partner that represents a novel type of integral membrane protein (PmiA,Pseudomonascolicin M-like immunity type A). By heterologous expression ofpmiAgenes in susceptible strains, we show that immunity to colicin M-like bacteriocins is indeed provided by the cognate PmiA. Sequence homology among PmiA proteins is essentially absent, except for a short motif with a conserved periplasm-exposed aspartate residue. However, PmiA's protective function is not abolished by changing this acidic residue to the uncharged alanine. Immunity by PmiAs appears promiscuous to the extent that PmiA homologs from a clade sharing <40% pairwise amino acid identity, equally provide protection against the bacteriocin linked to the original PmiA. This study shows that multiple immunity factors have evolved independently to silence lipid II-targeting enzymatic bacteriocins. Their relaxed bacteriocin immunization capacity contrasts to the strict specificity of immunity proteins shielding the enzymatic domain of nuclease bacteriocins. The nature of associated immune functions needs consideration when using such natural protein antibiotics or designing novel variants.
authors.affiliation: Centre of Microbial and Plant Genetics, KU LeuvenHeverlee, Belgium; National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of HealthBethesda, MD, USA.
authors.forename: Maarten G K
authors.initials: MG
authors.lastname: Ghequire
authors.affiliation: Centre of Microbial and Plant Genetics, KU Leuven Heverlee, Belgium.
authors.forename: Lieselore
authors.initials: L
authors.lastname: Kemland
authors.affiliation: Centre of Microbial and Plant Genetics, KU Leuven Heverlee, Belgium.
authors.forename: René
authors.initials: R
authors.lastname: De Mot
keywords: PmiA; PmiB; colicin M; lipid II; peptidoglycan; pyocin