The Abi Proteins and Their Involvement in Bacteriocin Self-Immunity

Abstract

The Abi protein family consists of putative membrane-bound metalloproteases. While they are involved in membrane anchoring of proteins in eukaryotes, little is known about their function in prokaryotes. In some known bacteriocin loci, Abi genes have been found downstream of bacteriocin structural genes (e.g., pln locus from Lactobacillus plantarum and sag locus from Streptococcus pyogenes), where they probably are involved in self-immunity. By modifying the profile hidden Markov model used to select Abi proteins in the Pfam protein family database, we show that this family is larger than presently recognized. Using bacteriocin-associated Abi genes as a means to search for novel bacteriocins in sequenced genomes, seven new bacteriocin-like loci were identified in Gram-positive bacteria. One such locus, from Lactobacillus sakei 23K, was selected for further experimental study, and it was confirmed that the bacteriocin-like genes (skkAB) exhibited antimicrobial activity when expressed in a heterologous host and that the associated Abi gene (skkI) conferred immunity against the cognate bacteriocin. Similar investigation of the Abi gene plnI and the Abi-like gene plnL from L. plantarum also confirmed their involvement in immunity to their cognate bacteriocins (PlnEF and PlnJK, respectively). Interestingly, the immunity genes from these three systems conferred a high degree of crossimmunity against each other's bacteriocins, suggesting the recognition of a common receptor. Site-directed mutagenesis demonstrated that the conserved motifs constituting the putative proteolytic active site of the Abi proteins are essential for the immunity function of SkkI, and to our knowledge, this represents a new concept in self-immunity.

Cysteine S -glycosylation, a new post-translational modification found in glycopeptide bacteriocins

“…chymotrypsin cleavage at Tyr16 (Table S1). Proteolysis is an established mechanism of bacteriocin resistance and immunity [32].…”

A Conserved Streptococcal Membrane Protein, LsrS, Exhibits a Receptor-Like Function for Lantibiotics

“…Members of the CPBP family are involved in diverse biological functions. For example, Kjos et al have shown that SkkI functions as a bacteriocin immunity protein for sakacin secreted by Lactobacillus plantarum (71). These authors have also shown that protease activity is necessary for the immunity function.…”

Comparative genome analysis of Streptococcus iniae DX09 reveals new insights into niche adaptation and competitive host colonisation ability

“…The mccF_like gene belongs to the Peptidase_S66 superfamily and encodes a microcin C7 self-immunity protein resistant to microcin C7 (MccF) [44]. The Abi _like protein belongs to the Abi family (also known as the CAAX prenyl protease family) consisting of putative membrane-bound metalloproteases [45]. In general, Abi is located downstream of bacteriocin structural genes, where it may be involved in selfimmunity [45].…”

“…The Abi _like protein belongs to the Abi family (also known as the CAAX prenyl protease family) consisting of putative membrane-bound metalloproteases [45]. In general, Abi is located downstream of bacteriocin structural genes, where it may be involved in selfimmunity [45]. Within PZ-II, a number of membranerelated proteins containing several transmembrane regions and a PadR family transcriptional regulator were identified upstream of mccF_like and Abi_like proteins.…”

“…A novel bacteriocin-like locus was identified in this region of PZ-II. Bacteriocin-associated genes can be effectively utilized as a means to determine unknown bacteriocins in sequenced bacterial genomes [45]. Other genes located in PZ-II, such as YbaK-like and Nramp, encode bacterial prolyl-tRNA synthetase and natural resistance-associated macrophage protein, respectively, both of which are potential contributors to bacterial survival.…”