218 ◾ Fundamental Food Microbiology
bactericidal effectiveness than those with one disulfide ring (Figure 17.1). A bacteriocin with two
peptides (that have some similarities in amino acid sequence with each other) needs both peptides
for full bactericidal activity. However, each peptide has a lower bactericidal effect. The bacteriocins under “nonsubgroup” in Class II do not have any common characteristics; however, a few
can have a free thiol group (Figure 17.1). A few bacteriocins, quite different from those described
previously, are translated as probacteriocin (only the main part) without any leader peptide at the
N-terminus region. Finally, several bacteriocins of lactic acid bacteria are found to be secreted
by the Sec-dependent secretory mechanism as opposed to ABC transporter systems of the other
bacteriocins.
A comparison of the amino acid sequences of leader peptides revealed very few similarities
among both Group I and Group II bacteriocins (Table 17.3). This is more evidenced with Group
I bacteriocins. But some Group II bacteriocins have –G–G– at the C-terminus end of the leader
peptide (at –1 and –2 positions). The double glycine is the recognition site for the endopeptidase
activity of the ABC transporter to remove the leader peptide from the prebacteriocin molecule.
Because a leader peptide propels the prebacteriocin molecule toward an ABC transporter in
the membrane, it is possible that a specific amino acid sequence of a leader peptide recognizes
a specific ABC transporter system for the most efficient transport of the probacteriocin (prebacteriocin without the leader peptide) in the environment; an interchange of leader peptides
with other bacteriocins may not function very effectively. The amino acid sequences of probacteriocins (or bacteriocins) of lantibiotics have very few similarities (Table 17.4). In contrast,
bacteriocins in the cystibiotic subgroup have several sequence homologies. The most important is
the –YGNGV– sequence in the N-terminal halves of the molecules, which is known to have an
important role in the bactericidal properties of the molecules. In addition, there are at least two
cysteins, usually at positions +9 and +14, that form a disulfide bond and are important for the
bactericidal property. In several cystibiotics (e.g., pediocin AcH or PA-1, enterocin A) there are
two more cysteine molecules in the C-terminal half of the molecule (at +24 and +44 positions
Nisin A:
S
S
S
S
S
S
S
A
B
C
D
E
(3)
(7) (8)
(11) (13)
(19)
(23)
(25) (28)
(34)
(47)
S
S
Pediocin AcH:
Lactococcin B:
K-Y-Y-G-N-G-V-T-C-G-K-H-S-C-S-V-D-W-G-K-A-T-T-C-I-I-N-N-G-A-M-A-W-A-T-G-G-H-Q-G-N-H-K-C
(9)
(14)
(24)
(44)
SH
S-L-Q-Y-V-M-S-A-G-P-Y-T-W-Y-K-D-T-R-T-G-K-T-I-C-K-Q-T-I-D-T-A-S-Y-T-F-G-V-M-A-E-G-W-G-K-T-F-H
I-dhB-Ala-I-dhA-L-Ala-Abu-P-G-Ala-K-Abu-G-A-L-M-G-Ala-N-M-K-Abu-A-Abu-Ala-H-Ala-S-I-H-V-dhA-K
Figure 17.1 Sequence of three bacteriocins is presented. Sequence of nisin showing thioether rings labeled as A, B, C, D, e, and also disulfide bonds, and thiol groups in other bacteriocins of lactic acid bacteria are shown. Abu, Aminobutyrate, dhA, dehydroalanine; dhB,
didehydrobutyrine.
bactericidal effectiveness than those with one disulfide ring (Figure 17.1). A bacteriocin with two
peptides (that have some similarities in amino acid sequence with each other) needs both peptides
for full bactericidal activity. However, each peptide has a lower bactericidal effect. The bacteriocins under “nonsubgroup” in Class II do not have any common characteristics; however, a few
can have a free thiol group (Figure 17.1). A few bacteriocins, quite different from those described
previously, are translated as probacteriocin (only the main part) without any leader peptide at the
N-terminus region. Finally, several bacteriocins of lactic acid bacteria are found to be secreted
by the Sec-dependent secretory mechanism as opposed to ABC transporter systems of the other
bacteriocins.
A comparison of the amino acid sequences of leader peptides revealed very few similarities
among both Group I and Group II bacteriocins (Table 17.3). This is more evidenced with Group
I bacteriocins. But some Group II bacteriocins have –G–G– at the C-terminus end of the leader
peptide (at –1 and –2 positions). The double glycine is the recognition site for the endopeptidase
activity of the ABC transporter to remove the leader peptide from the prebacteriocin molecule.
Because a leader peptide propels the prebacteriocin molecule toward an ABC transporter in
the membrane, it is possible that a specific amino acid sequence of a leader peptide recognizes
a specific ABC transporter system for the most efficient transport of the probacteriocin (prebacteriocin without the leader peptide) in the environment; an interchange of leader peptides
with other bacteriocins may not function very effectively. The amino acid sequences of probacteriocins (or bacteriocins) of lantibiotics have very few similarities (Table 17.4). In contrast,
bacteriocins in the cystibiotic subgroup have several sequence homologies. The most important is
the –YGNGV– sequence in the N-terminal halves of the molecules, which is known to have an
important role in the bactericidal properties of the molecules. In addition, there are at least two
cysteins, usually at positions +9 and +14, that form a disulfide bond and are important for the
bactericidal property. In several cystibiotics (e.g., pediocin AcH or PA-1, enterocin A) there are
two more cysteine molecules in the C-terminal half of the molecule (at +24 and +44 positions
Nisin A:
S
S
S
S
S
S
S
A
B
C
D
E
(3)
(7) (8)
(11) (13)
(19)
(23)
(25) (28)
(34)
(47)
S
S
Pediocin AcH:
Lactococcin B:
K-Y-Y-G-N-G-V-T-C-G-K-H-S-C-S-V-D-W-G-K-A-T-T-C-I-I-N-N-G-A-M-A-W-A-T-G-G-H-Q-G-N-H-K-C
(9)
(14)
(24)
(44)
SH
S-L-Q-Y-V-M-S-A-G-P-Y-T-W-Y-K-D-T-R-T-G-K-T-I-C-K-Q-T-I-D-T-A-S-Y-T-F-G-V-M-A-E-G-W-G-K-T-F-H
I-dhB-Ala-I-dhA-L-Ala-Abu-P-G-Ala-K-Abu-G-A-L-M-G-Ala-N-M-K-Abu-A-Abu-Ala-H-Ala-S-I-H-V-dhA-K
Figure 17.1 Sequence of three bacteriocins is presented. Sequence of nisin showing thioether rings labeled as A, B, C, D, e, and also disulfide bonds, and thiol groups in other bacteriocins of lactic acid bacteria are shown. Abu, Aminobutyrate, dhA, dehydroalanine; dhB,
didehydrobutyrine.