Affiliation:
1. Laboratory of Microbial Gene Technology and Food Microbiology
2. Section for Biostatistics, Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, N-1432 Ås, Norway
Abstract
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 cross-immunity 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.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
87 articles.
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