Completion of the current genetic view of the lactococcin system was provided by Stoddard et al. [126]. The production of a bacteriocin of L. lactis subsp.
lactis biovar diacetylactis WM4 was linked to a 131-kb plasmid pNP2 [137].
DNA sequence of a 5.6-kb AvaII fragment of pNP2 revealed two large open
reading frames upstream from the lcnA and lciA genes, designated as lcnD
(716 amino acids) and lcnC (474 amino acids) [126]. Tn5 insertional mutagenesis of both lcnD and lcnC disrupted lactococcin A production without
affecting immunity [126]. LcnC displayed highest homology with the HlyB-like
family of ATP-dependent membrane translocators (Stoddard et al., 1992). It
contains a highly conserved ATP-binding site and six N-terminal hydrophobic
domains, which could promote integration in the cytoplasmic membrane. LcnD
showed structural similarities to proteins of the HlyD and PrtE secretion
systems of E. coli [126]. The carboxy-terminal part of LcnD was also encoded by
the partial open reading frames upstream from the structural IcnA and IcnM
genes of the 60-kb plasmid p9B4–6 [127]. The three lactococcin operons were
preceded by conserved and functional promoter regions. The promoter upstream from lcnA, overlapped with a 19-bp inverted repeat. This palindromic
sequence with a DG = –9.9 kcal/mol could form a hairpin and therefore may
resemble an SOS box for binding of the Escherichia coli RecA-sensitive LexA
repressor [125]. However, lcnA has not been found to be inducible [125].
Stoddard et al. [126] noted that there were no obvious transcription terminators
positioned between lcnC and lcnA, suggesting a possible read through in the
lcnA/lciA operon, and speculated that besides a large transcript covering all
four genes, a smaller transcript spanning lcnA and lciA was produced.
The transporter proteins LcnD and LcnC were shown to be essential for
lactococcin A production but not for immunity [126]. Secretion systems based
on such ATP-binding exporters have been reported for both Gram-negative and
Gram-positive bacteria for export of extracellular proteins whose secretion
does not depend on the general signal peptide-dependent export pathway [111,
138]. Such examples for Gram-negative bacteria include the haemolysin and
colicin V proteins of E. coli [139, 140] cydolysin produced by Bordetella pertussis [141], leucotoxin produced by Pasteurella haemolytica [142], and metalloproteases B and C of Erwinia chrysanthemi [143]. For Gram-positive bacteria,
these proteins have been described for ATP-dependent membrane translocation, for instance required for competence in Streptococcus pneumoniae [144].
It was therefore likely that a universal export apparatus, involved in class II
bacteriocin secretion could consist of these two exporter proteins. Genetic analysis revealed that in the case of the identical Pediococcus bacteriocins, pediocin
PA-1.0/AcH, the Lactococcus bacteriocin lactococcin G, the Leuconostoc bacteriocin mesentericin Y105, and the Lactobacillus bacteriocins sakacin A and
plantaricin A an ATP-dependent ABC exporter apparatus was encoded adjacent
to the bacteriocin operon [124, 127, 128, 130–132, 136, 145, 146] (Fig. 4).
Antimicrobial Peptides of Lactic Acid Bacteria: Mode of Action, Genetics and Biosynthesis
33
lactis biovar diacetylactis WM4 was linked to a 131-kb plasmid pNP2 [137].
DNA sequence of a 5.6-kb AvaII fragment of pNP2 revealed two large open
reading frames upstream from the lcnA and lciA genes, designated as lcnD
(716 amino acids) and lcnC (474 amino acids) [126]. Tn5 insertional mutagenesis of both lcnD and lcnC disrupted lactococcin A production without
affecting immunity [126]. LcnC displayed highest homology with the HlyB-like
family of ATP-dependent membrane translocators (Stoddard et al., 1992). It
contains a highly conserved ATP-binding site and six N-terminal hydrophobic
domains, which could promote integration in the cytoplasmic membrane. LcnD
showed structural similarities to proteins of the HlyD and PrtE secretion
systems of E. coli [126]. The carboxy-terminal part of LcnD was also encoded by
the partial open reading frames upstream from the structural IcnA and IcnM
genes of the 60-kb plasmid p9B4–6 [127]. The three lactococcin operons were
preceded by conserved and functional promoter regions. The promoter upstream from lcnA, overlapped with a 19-bp inverted repeat. This palindromic
sequence with a DG = –9.9 kcal/mol could form a hairpin and therefore may
resemble an SOS box for binding of the Escherichia coli RecA-sensitive LexA
repressor [125]. However, lcnA has not been found to be inducible [125].
Stoddard et al. [126] noted that there were no obvious transcription terminators
positioned between lcnC and lcnA, suggesting a possible read through in the
lcnA/lciA operon, and speculated that besides a large transcript covering all
four genes, a smaller transcript spanning lcnA and lciA was produced.
The transporter proteins LcnD and LcnC were shown to be essential for
lactococcin A production but not for immunity [126]. Secretion systems based
on such ATP-binding exporters have been reported for both Gram-negative and
Gram-positive bacteria for export of extracellular proteins whose secretion
does not depend on the general signal peptide-dependent export pathway [111,
138]. Such examples for Gram-negative bacteria include the haemolysin and
colicin V proteins of E. coli [139, 140] cydolysin produced by Bordetella pertussis [141], leucotoxin produced by Pasteurella haemolytica [142], and metalloproteases B and C of Erwinia chrysanthemi [143]. For Gram-positive bacteria,
these proteins have been described for ATP-dependent membrane translocation, for instance required for competence in Streptococcus pneumoniae [144].
It was therefore likely that a universal export apparatus, involved in class II
bacteriocin secretion could consist of these two exporter proteins. Genetic analysis revealed that in the case of the identical Pediococcus bacteriocins, pediocin
PA-1.0/AcH, the Lactococcus bacteriocin lactococcin G, the Leuconostoc bacteriocin mesentericin Y105, and the Lactobacillus bacteriocins sakacin A and
plantaricin A an ATP-dependent ABC exporter apparatus was encoded adjacent
to the bacteriocin operon [124, 127, 128, 130–132, 136, 145, 146] (Fig. 4).
Antimicrobial Peptides of Lactic Acid Bacteria: Mode of Action, Genetics and Biosynthesis
33