The mode of action of the lantibiotic lacticin 3147 – a complex mechanism involving specific interaction of two peptides and the cell wall precursor lipid II

Abstract

Lacticin 3147 is a two-peptide lantibiotic produced by Lactococcus lactis in which both peptides, LtnA1 and LtnA2, interact synergistically to produce antibiotic activities in the nanomolar concentration range; the individual peptides possess marginal (LtnA1) or no activity (LtnA2). We analysed the molecular basis for the synergism and found the cell wall precursor lipid II to play a crucial role as a target molecule. Tryptophan fluorescence measurements identified LtnA1, which is structurally similar to the lantibiotic mersacidin, as the lipid II binding component. However, LtnA1 on its own was not able to substantially inhibit cell wall biosynthesis in vitro; for full inhibition, LtnA2 was necessary. Both peptides together caused rapid K(+) leakage from intact cells; in model membranes supplemented with lipid II, the formation of defined pores with a diameter of 0.6 nm was observed. We propose a mode of action model in which LtnA1 first interacts specifically with lipid II in the outer leaflet of the bacterial cytoplasmic membrane. The resulting lipid II:LtnA1 complex is then able to recruit LtnA2 which leads to a high-affinity, three-component complex and subsequently inhibition of cell wall biosynthesis combined with pore formation.

The Lantibiotic NAI-107 Binds to Bactoprenol-bound Cell Wall Precursors and Impairs Membrane Functions

“…The latter mechanism is known from some two-peptide lantibiotics, such as lacticin 3147, where significant antibiotic activity is only achieved through the cooperative action of two peptides. Peptide A contains a mersacidin-like lipid II binding motif and binds to the CW precursor; the second peptide is then able to dock to the peptide⅐lipid II complex, allowing the complex to insert into the membrane to form a defined pore (56). We did not find evidence for a dimerization in solution, but the data showed clear evidence for two separate events in NAI-107⅐lipid II binding, a relatively strong initial interaction leading to the disappearance of free lipid II resonances and a weaker subsequent interaction leading to the appearance of bound lipid II and NAI-107 resonances (supplemental Fig.…”

Discovery and in vitro biosynthesis of haloduracin, a two-component lantibiotic

“…The biological activity displayed by these mature products depended on the presence of both modified peptides in the bioassay. Ltn␣ of lacticin 3147 and BHT␣ exhibit low level antibacterial activity by themselves, presumably by weak binding to lipid II (12,30). It is possible that Hal␣ may also demonstrate biological activity at higher concentrations, but so far we have been limited in the accessible concentrations of in vitro product because of its poor solubility.…”

“…A recent study on the mode of action of lacticin 3147 demonstrated that Ltn␣ binds to the peptidoglycan precursor lipid II (12), a result that was anticipated because of the structural similarity between Ltn␣ and mersacidin, which also binds to lipid II (13). However, in order for lacticin 3147 to inhibit cell wall biosynthesis and form small pores in the cell membrane, Ltn␤ is also necessary, leading to a proposed model in which the lipid II:Ltn␣ complex recruits Ltn␤ to form an active complex (12,14).…”

Fundamental functionality: recent developments in understanding the structure–activity relationships of lantibiotic peptides

“…6 Two-component lantibiotics may exert only one of these modes of action (binding to lipid II) when administered independently and both modes of action when used together (lipid II binding and pore formation). 9 There are still fundamental challenges to the successful utilization of many lantibiotics as therapeutic agents. Thus far, their use has been limited to topical applications, as many of these peptides are prone to degradation by enzymes present in the gastrointestinal tract.…”