The antibiotic activity of cationic linear amphipathic peptides: lessons from the action of leucine/lysine copolymers on bacteria of the class Mollicutes

Abstract

Peptides composed of leucyl and lysyl residues (ÔLK peptidesÕ) with different compositions and sequences were compared for their antibacterial activities using cell wall-less bacteria of the class Mollicutes (acholeplasmas, mycoplasmas and spiroplasmas) as targets. The antibacterial activity of the amphipathic a-helical peptides varied with their size, 15 residues being the optimal length, independent of the membrane hydrophobic core thickness and the amount of cholesterol. The 15-residue ideally amphipathic a helix with a +5 positive net charge (KLLKLLLKLLLKLLK) had the strongest antibacterial activity, similar to that of melittin. In contrast, scrambled peptides devoid of amphipathy and the less hydrophobic b-sheeted peptides [(LK) n K], even those 15-residue long, were far less potent than the helical ones. Furthermore, the growth inhibitory activity of the peptides was correlated with their ability to abolish membrane potential. These data are fully consistent with a predominantly flat orientation of LK peptides at the lipid/ water interface and strongly supports that these peptides and probably the linear polycationic amphipathic defence peptides act on bacterial membranes in four main steps according to the ÔcarpetÕ model: (a) interfacial partitioning with accumulation of monomers on the target membrane (limiting step); (b) peptide structural changes (conformation, aggregation, and orientation) induced by interactions with the lipid bilayer (as already shown with liposomes and erythrocytes); (c) plasma membrane permeabilization/ depolarization via a detergent-like effect; and (d) rapid bacterial cell death if the extent of depolarization is maintained above a critical threshold.Keywords: amphipathic peptides; antibacterial activity; bacterial cell death; membrane depolarization; mollicutes.The amphipathic a helix concept helps in understanding the behaviour of very different classes of proteins and peptides, especially those acting on membranes [1][2][3][4]. This concept, which has been useful in the field of peptidic cytotoxins to develop new analogues, and to better understand their mode of action [5][6][7], is still the basis for the rational design of new antimicrobial compounds, i.e. analogues or chimeras of natural products [8], or radically new molecules [9,10].The need to understand their mode of action and improve their efficacy and/or selectivity towards microorganisms led to the synthesis of new active peptides, made possible largely by the progress in solid state synthesis. As a result, a large wealth of information was obtained on many natural peptides endowed with cytotoxic (including antimicrobial) activity. However, answers are still missing regarding: (a) the requirements for optimized activity and selectivity; and (b) the mechanisms of action, especially in bacterial cells. In an effort of rationalization, a minimalistic approach was initiated by the pioneering work of De Grado and Lear [11] using residue substitutions or designing simplified sequences [2,[12][13][14]. Using the very mini...

Latarcins: versatile spider venom peptides

“…It is interesting to note that similar conclusions were drawn for CT The following LP were taken into account: Ltc 1, 2a, 3a, 3b, 4a, 4b, 5, 6a, and 7, nine molecules in total Antibacterial activity is assumed to be a value reciprocal to MIC, and the values of MIC were taken from [28] a Full charge at pH 7 (as reported in Table 1) b The number of positively charged residues (Arg and Lys, reported in Table 1) c The result is obtained taking into account only the number of negatively charged residues d In the DG scale (see details in Table 3) e In the DG scale (the values in the brackets correspond to the conditions of protonation of Asp, Glu, and His residues) f Hydrophobicity was assumed to be the value proportional to the reciprocal of the concentration of AMP necessary to disrupt planar membranes composed from DPhPC; see Table 3 for the values [108,112] and linear AMP of different origin [113,114]. Of note, for LP an optimal charge, required to reach the maximal antimicrobial effect, depends on the overall length of the peptide [115,116] and distribution of charged residues along the amino acid sequence [37]. Due to basicity of peptidoglycan stem [117], the diffusion of polypeptides, bearing negatively charged residues, can be arrested [108].…”

Membranolytic Activity of Bile Salts: Influence of Biological Membrane Properties and Composition

“…The reason why some commercial bile acid formulations contain lipids lies in the fact that the membranolytic activities of the detergents in the mixed system is strongly reduced, and thus the used detergents become less haemolytic [15,41]. On the other hand, membranolysis of bacterial membranes is a key strategy for the development of antimicrobial components [52,53]. The mechanism of membranolysis of e.g.…”

Synthetic Biology Triggers New Era of Antibiotics Development

“…Thus, numerous studies were carried out by amino acid replacement or rearrangement to generate improved AMPs (Park et al 2003 ) , such as commonly known leu/lys (Beven et al 2003 ) or gly/leu (Sousa et al 2009 ) rich peptides. The leu/lys model (referred as LK model) has strong capacity to form helix structure and was proved to be an excellent model for peptide development (Beven et al 2003 ) . Due to the important role of tryptophan for strengthening the interaction of peptide and target membrane, Kang et al .…”