Peptide-Lipid Huge Toroidal Pore, a New Antimicrobial Mechanism Mediated by a Lactococcal Bacteriocin, Lacticin Q

Abstract

Lacticin Q is a pore-forming bacteriocin produced by Lactococcus lactis QU 5, and its antimicrobial activity is in the nanomolar range. Lacticin Q induced calcein leakage from negatively charged liposomes. However, no morphological changes in the liposomes were observed by light scattering. Concomitantly with the calcein leakage, lacticin Q was found to translocate from the outer to the inner leaflet of the liposomes, after it initially bound to the membrane within 2 s. Lacticin Q also induced lipid flip-flop. These results reveal that the antimicrobial mechanism of lacticin Q can be described by the toroidal pore model. This is the first report of a bacteriocin of gram-positive bacteria that forms a toroidal pore. From liposomes, lacticin Q leaked fluorescence-labeled dextran with a diameter of 4.6 nm. In addition, lacticin Q caused the leakage of small proteins, such as the green fluorescent protein, from live bacterial cells. There are no other reports of antimicrobial peptides that exhibit protein leakage properties. The proposed pore formation model of lacticin Q is as follows: (i) quick binding to outer membrane leaflets; (ii) the formation of at least 4.6-nm pores, causing protein leakage with lipid flip-flop; and (iii) the migration of lacticin Q molecules from the outer to the inner membrane leaflets. Consequently, we termed the novel pore model in the antimicrobial mechanism of lacticin Q a "huge toroidal pore."

A Comparative Study of Antimicrobial Profile Having Broad Spectrum Bacteriocins Against Antibiotics

“…It causes membrane permeabilization of strains without need of any specific receptors [61]. It forms a huge toroidal spore (HTP) causing leakage of intracellular components and large molecules which results in the cell death.…”

Bacteriocins from Lactic Acid Bacteria: A Review of Biosynthesis, Mode of Action, Fermentative Production, Uses, and Prospects

“…On the other hand, the unique killing mechanism of lacticin Q, a leaderless bacteriocin, has been well characterized (Yoneyama et al 2009b). While most bacteriocins require a docking molecule for their antimicrobial action, lipid II for nisin A and other lantibiotics, and mannose ABC transporter, MptD, for pediocin PA-1/AcH and its homologue bacteriocins, lacticin Q has been found to cause high-level membrane permeabilization of target strains without the need of any specific receptors (Yoneyama et al 2009a).…”

“…thereby causing cell death (Yoneyama et al 2009b). It has been shown that the mechanism of HTP formation starts with the electrostatic interaction of the cationic lacticin Q molecules and the negatively charged membranes.…”

“…The pores formed in the membrane are short-lived because these HTPs close back as the lacticin Q molecular mass translocates itself from the outer to the inner cell membrane (Fig. 3) (Yoneyama et al 2009b). However, the killing mechanism through HTP formation of lacticin Q is selective and highly dependent on the physiological features of the outer membrane of target cells, which explains the non-toxicity of lacticin Q against Gram-negative bacteria (Yoneyama et al 2011).…”

“…Some efforts on the isolation and screening for bacteriocin-producing LAB strains have been done by the National Institute of Molecular Biology and ____________________________________________________________________________________________________________ www.philscitech.org The highly cationic lacticin Q molecules rapidly bind to the negatively charged phospholipid bilayer membrane (i) that results in the formation of HTPs coupled with membrane lipid flip-flop that causes t h e l e a k a g e o f i n t r a c e l l u l a r components, including ions, ATP, and small proteins (ii), after which, the l a c t i c i n Q m o l e c u l a r m a s s translocates itself from the outer to the inner membrane as the pore closes (iii) (Yoneyama et al 2009b). …”