no homologues were found yet in any other bacteriocin operon [40]. The Cterminus of LctM was shown to display striking homology with NisC, proposed
as a post-translational modification enzyme for nisin [118, 123]. Both the lactococcin DR and the lactocin S operons contain coding information for an ABC
transporter protein (LctT (= LcnDR3), LasT) [82, 118]. For lactocin S, the
structural lasP gene encodes a proteinase of 266 amino acid residues [82]. The
lactocin S gene cluster contains several other genes (lasN, U, V, W and orf57)
without putative function or homologous counterparts in other bacteriocin
operons [82].A similar cluster was recently identified for lacticin 481 [119]. The
proteins encoded by IctF, IctE and IctG were proposed to form an ABC transporter and should play some role in the immunity against lacticin 481.
3.5
Class II Non-Lantibiotic Bacteriocins
3.5.1
Introduction
The class II non-lantibiotic bacteriocins consist of a large heterologous group
produced by different species of the lactic acid bacteria [21]. Despite this
heterogeneity, all class II bacteriocins display a very conserved N-terminal
leader peptide and a characteristic double-glycine-type (Gly –2 Gly –1 Xaa) proteolytic processing site [21]. The conserved mechanism of secretion and
processing suggested by these findings is reflected in the organization of the
operon structures encoding these bacteriocins (Fig. 4). The genetic determinants involved in the production of several class II bacteriocins have been
genetically studied in detail (Fig. 4): lactacin F produced by Lactobacillus
johnsonii [48, 124], lactococcin G, and the lactococcin A, B and M gene cluster
of Lactococcus lactis [125–128], leucocin A-UAL produced by Leuconostoc
gelidum [42, 129] and mesentericin Y105 produced by Leuconostoc mesenteroides [124], the identical bacteriocins pediocin PA-1.0 and pediocin AcH
produced by Pediococcus acidilactici [130–132], sakacin A produced by L. sake
[133] and plantaricin A, produced by L. plantarum [49, 134] (Fig. 4).
3.5.2
The Lactococcal Bacteriocins, Lactococcin A, B and M
The lactococcin A, B, and M operon cluster on the 60-kb conjugal plasmid
p9B4–6, was the first class II bacteriocin genetic determinant to be analyzed.
Two fragments, conferring bacteriocin production and immunity, were cloned
[46, 135]. The lactococcin A operon encoded one bacteriocin (LcnA) and an
immunity protein (LciA), and expressed a high antagonistic activity against
L. lactis indicator strains.
In the lactococcin M operon, two bacteriocins (LcnM and LcnN) and one
immunity protein (LciM) were found, displaying a low antagonistic activity
against L. lactis indicator strains [46, 135]. In the lactococcin M operon, disruption of both lcnM and lcnN resulted in a non-producer phenotype. Therefore,
Antimicrobial Peptides of Lactic Acid Bacteria: Mode of Action, Genetics and Biosynthesis
31
as a post-translational modification enzyme for nisin [118, 123]. Both the lactococcin DR and the lactocin S operons contain coding information for an ABC
transporter protein (LctT (= LcnDR3), LasT) [82, 118]. For lactocin S, the
structural lasP gene encodes a proteinase of 266 amino acid residues [82]. The
lactocin S gene cluster contains several other genes (lasN, U, V, W and orf57)
without putative function or homologous counterparts in other bacteriocin
operons [82].A similar cluster was recently identified for lacticin 481 [119]. The
proteins encoded by IctF, IctE and IctG were proposed to form an ABC transporter and should play some role in the immunity against lacticin 481.
3.5
Class II Non-Lantibiotic Bacteriocins
3.5.1
Introduction
The class II non-lantibiotic bacteriocins consist of a large heterologous group
produced by different species of the lactic acid bacteria [21]. Despite this
heterogeneity, all class II bacteriocins display a very conserved N-terminal
leader peptide and a characteristic double-glycine-type (Gly –2 Gly –1 Xaa) proteolytic processing site [21]. The conserved mechanism of secretion and
processing suggested by these findings is reflected in the organization of the
operon structures encoding these bacteriocins (Fig. 4). The genetic determinants involved in the production of several class II bacteriocins have been
genetically studied in detail (Fig. 4): lactacin F produced by Lactobacillus
johnsonii [48, 124], lactococcin G, and the lactococcin A, B and M gene cluster
of Lactococcus lactis [125–128], leucocin A-UAL produced by Leuconostoc
gelidum [42, 129] and mesentericin Y105 produced by Leuconostoc mesenteroides [124], the identical bacteriocins pediocin PA-1.0 and pediocin AcH
produced by Pediococcus acidilactici [130–132], sakacin A produced by L. sake
[133] and plantaricin A, produced by L. plantarum [49, 134] (Fig. 4).
3.5.2
The Lactococcal Bacteriocins, Lactococcin A, B and M
The lactococcin A, B, and M operon cluster on the 60-kb conjugal plasmid
p9B4–6, was the first class II bacteriocin genetic determinant to be analyzed.
Two fragments, conferring bacteriocin production and immunity, were cloned
[46, 135]. The lactococcin A operon encoded one bacteriocin (LcnA) and an
immunity protein (LciA), and expressed a high antagonistic activity against
L. lactis indicator strains.
In the lactococcin M operon, two bacteriocins (LcnM and LcnN) and one
immunity protein (LciM) were found, displaying a low antagonistic activity
against L. lactis indicator strains [46, 135]. In the lactococcin M operon, disruption of both lcnM and lcnN resulted in a non-producer phenotype. Therefore,
Antimicrobial Peptides of Lactic Acid Bacteria: Mode of Action, Genetics and Biosynthesis
31