Fundamental Food Microbiology, Third Edition - Fuad Fathir

234 FUNDAMENTAL FOOD MICROBIOLOGY
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 little
similarities among both Group I and Group II bacteriocins (Table 16.4). 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
little similarities (Table 16.5). 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
Table 16.4 Amino Acid Sequences of Leader Peptides of
Bacteriocins of Lactic Acid Bacteria
Bacteriocin Amino Acid Sequence
Nisin A (23) MSTKDFNLDLVSVSKKDSGASPR
Lacticin 481 (24) MKEQNSFLLQEVTESELDLILGA
Pediocin AcH (18) MKKIEKLTEKEMANIIGG
Leucocin A (24) MMNMKPTESYEQLDNSALEQVVGG
Sakacin P (18) MEKFIELSLKEVTAITGG
Lactococcin A (21) MKNQLNFNIVSDEELSEANGG
Note: Numbers in parentheses are the number of amino acids. The last
amino acid at the carboxyl end (right) is designated as –1. Class
II bacteriocins have GG at positions –1 and –2.
Table 16.5 Amino Acid Sequences of Probacteriocins of Lactic Acid Bacteria
Probacteriocin Amino Acid Sequence
Nisin A (34) ITSISLCTPGCKTGALMGCNMKTATCHCSIHVSK
Lacticin 481 (27) KGGSGVIHTISHECNMNSWQFVFTCCS
Pediocin AcH (44) KYYGNGVTCGKHSCSVDWGKATTCIINNGAMAWATGGHQGNHKC
Leucocin A (37) KYYGNGVHCTKSGCSVNWGEAFSAGVHRLANGGNGFW
Sakacin P (43) KYYGNGVHCGKHSCTVDWGTAIGNIGNNAAANWATGGNAGWNK
Lactococcin A (55) KLTFIQSTAAGDLYYNNTNTHKYVYQQTQNAFGAAANTIVNGWMGGAAGGFGLHH
Note: Numbers in parentheses are number of amino acids. The first N-terminal amino acid
at the left is designated as +1. Y G N G V and cysteines in cystibiotics are indicated
in bold letters.