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2.4.1 Mode of action
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Chapter II Review of Literature
Although the mode of activity of bacteriocins can differ, the cell envelope is commonly
their target. The majority is active by inducing membrane permeabilization. This is reflected
by the fact that Class II bacteriocins have an amphiphilic helical structure, which allows them
to insert into the membrane of the target cell, leading to depolarization and death (Fig. 2.3),
(Cotter et al., 2005). To form the core of the pores, this structure is believed to face with the
polar side towards the centre of the
channel, while the non-polar side faces the
hydrophobic phase of the phospholipid
bilayer (Diep et al., 2002).
This creation of pores in the membrane of
their target cells results in dissipation of
the proton motive force, intracellular ATP
depletion and leakage of nutrients and
metabolites (Deegan et al., 2006). Moreover,
to form a pore, interactions with the cytoplasmic membrane Source: of the Oscariz target and Pisabarro, cell are 2001necessary.
Initial electrostatic interactions between the positively charged peptide and anionic lipids, which
are in large quantities present in the membranes of Gram-positive bacteria, play a role to some
extent in this mode of action. Thus, the sensitivity to bacteriocins depends partly on the
physiological state of the cell (Eijsink et al., 2002). Up to this stage, it is not entirely clear
whether bacteriocins act through receptors in the target cell membrane or if there is specificity in
possible receptors.
Fig: 2.2 Killing mechanism propose for
bacteriocin