The amphipathic α‐helix concept

The increase in infectious diseases and bacterial resistance to antibiotics has resulted in intensive studies focusing on the use of linear, ␣-helical, cytolytic peptides from insects and mammals as potential drugs for new target sites in bacteria. Recent studies with diastereomers of the highly potent cytolytic peptides, pardaxin and melittin, indicate that ␣-helical structure is required for mammalian cells lysis but is not necessary for antibacterial activity. Thus, hydrophobicity and net positive charge of the polypeptide might confer selective antibacterial lytic activity. To test this hypothesis, a series of diastereomeric model peptides (12 amino acids long) composed of varying ratios of leucine and lysine were synthesized, and their structure and biological function were investigated. Peptide length and the position of D-amino acids were such that short peptides with stretches of only 1-3 consecutive L-amino acids that cannot form an ␣-helical structure were constructed. Circular dichroism spectroscopy showed that the peptides do not retain any detectable secondary structure in a hydrophobic environment. This enabled examination of the sole effect of hydrophobicity and positive charge on activity. The data reveal that modulating hydrophobicity and positive charge is sufficient to confer antibacterial activity and cell selectivity. A highly hydrophobic diastereomer that permeated both zwitterionic and negatively charged phospholipid vesicles, lysed eukaryotic and prokaryotic cells. In contrast, a highly positively charged diastereomer that only permeated slightly negatively charged phospholipid vesicles had low antibacterial activity and could not lyse eukaryotic cells. In the boundary between high hydrophobicity and high positive charge, the diastereomers acquired selective and potent antibacterial activity. Furthermore, they were completely resistant to human serum inactivation, which dramatically reduces the activity of native antibacterial peptides. In addition, a strong synergistic effect was observed at nonlethal concentrations of the peptides with the antibiotic tetracycline on resistant bacteria. The results are discussed in terms of proposed mechanisms of antibacterial activity, as well as a new strategy for the design of a repertoire of short, simple, and easily manipulated antibacterial peptides as potential drugs in the treatment of infectious diseases.Infectious diseases are increasing phenomena today mainly as a result of changes in the spectrum of pathogens and the increase in antibiotic-resistant pathogens. When antibiotics were first introduced, the proportion of resistant versus nonresistant pathogens was less than 1%, but this percentage has dramatically increased within 12 years of their uses. Although the number of antibacterial products available today is impressive (about 150), they cover only six different target sites and are dominated by ␤-lactams, tetracyclines, aminoglycosides, marcolides, sulfonamides, and quinolones (1). The search for new target sites has resulted in an incr...

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“…All the other peptides showed no significant hemolytic activity up to the maximum concentration tested (100 m) (Fig. 1) (22).…”

Section: Resultsmentioning

confidence: 91%

“…-K 4 L 8 but composed of only L-amino acids was found to have ϳ40% ␣-helical structure in methanol and in L-␣-dimyristoylphosphatidylcholine vesicles (22).…”

Section: Resultsmentioning

confidence: 93%

A Repertoire of Novel Antibacterial Diastereomeric Peptides with Selective Cytolytic Activity

Ziv

Hong

Shai

1997

Journal of Biological Chemistry

192

162

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“…E-mail: dathe@fmp.fta-berlin.de expected to facilitate peptide attachment at the negatively charged bacterial surface [16]. Several attempts have been described to improve antimicrobial activity and enhance selectivity by increasing the positive charge and/or helicity [17,18,5,19]. However, often enhanced activity was found to be connected with reduced selectivity.…”

Section: Introductionmentioning

confidence: 99%

Hydrophobicity, hydrophobic moment and angle subtended by charged residues modulate antibacterial and haemolytic activity of amphipathic helical peptides

Dathe¹,

Wieprecht²,

Nikolenko³

et al. 1997

FEBS Letters

374

270

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The hydrophobicity (H), hydrophobic moment (|i) and the angle subtended by the positively charged helix face () of a set of model and magainin 2 amide peptides with conserved charge and helix propensity have been shown to be effective modulators of antibacterial and haemolytic activity. Except peptides of low hydrophobicity which are inactive, changing the parameters has little influence on the activity against Gramnegative bacteria, thus revealing the dominance of electrostatic interactions for the effect. However, the increase of H, |i and <5> substantially enhances haemolytic and Gram-positive antibacterial activity and is related to a reduction of peptide specificity for Gram-negative bacteria.

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“…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].…”

mentioning

confidence: 99%

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

Béven

Castano

Dufourcq

et al. 2003

European Journal of Biochemistry

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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...

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The amphipathic α‐helix concept

Cited by 108 publications

References 18 publications

A Repertoire of Novel Antibacterial Diastereomeric Peptides with Selective Cytolytic Activity

A Repertoire of Novel Antibacterial Diastereomeric Peptides with Selective Cytolytic Activity

Hydrophobicity, hydrophobic moment and angle subtended by charged residues modulate antibacterial and haemolytic activity of amphipathic helical peptides

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

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