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Free Content Editorial:[Hot Topic: Amphiphilic Peptides Structures (Guest Editors: Sarah R. Dennison & David A. Phoenix)]

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Antimicrobial peptides (AMPs) are a class of defence peptides that selectively target micro-organisms in order to protect the host. AMPs form part of the innate immune system of organisms such as plants (thormatin), insects (ceratoxin), amphibians (magainins, brevins, aureins) and mammals (indolicidin, LL-37, defensins, dermaseptin) [1-4]. Many of these peptides are cationic, composed of 10 to 45 amino acids, and adopt amphiphilic structures at the membrane interface. These peptides have a potent ability to target and kill a wide range of Gram-negative and Gram-positive bacteria [5-6], protozoa [7] parasites [7], fungi [8], viruses [9] and some tumour cells [10]. Based on this ability, AMPs are attractive propositions for development as therapeutically useful antimicrobial and anticancer agents [11].

It is generally accepted that the killing mechanisms of defence peptides involve the invasion of target cell membranes, although there remain many questions around the precise structure / function relationships involved. Membrane binding is thought to provide a key rate limiting step in these mechanisms, which can then lead to passage of the peptide through the membrane in order to attack intracellular targets or, as in most cases, membrane disruption and cell death [12]. In the opening review by Peter Bond and Syma Khalid, molecular dynamic simulations are applied to investigate the role of conformation in the activity of AMPs. More recently, course grain simulations have been used to investigate the impact of factors such as peptide concentration, lipid composition and membrane curvature and also the effect these factors have on the lytic mechanism employed by AMPs.

Whilst primary sequence data can provide key information regarding activity, a range of biophysical and molecular analysis have shown that the overall molecular architecture of AMPs is important for peptide-membrane interaction. Over 1500 AMPs have so far been identified and the majority of these peptides adopt β-sheet or α-helical structure. The paper by Kowlaski et al. characterises the antimicrobial properties of two synthetic β-sheet peptides derived from Limulus anti-lipopolysaccharides. Isothermal titration calorimetry is used to investigate the binding of the peptide to lipopolysaccharides and to investigate its potential antiseptic activity. The review paper by Christopher Dempsey and co-workers summarises a membrane model system used to investigate the thermodynamics of interfacial binding and subsequent membrane disruption by α-helical antimicrobial peptides. RTA3 and magainin analogues are used to investigate how the balance of hydrophobicity, amphiphilicity and positive charge affected binding and disruption of membranes.

Once bound, many AMPs exert their activity by disruption of bilayer structure via one of a number of mechanisms. To further understand this activity, it is therefore important to investigate the impact of the peptide on the phospholipid. The paper by Farid Sa'adedin and Jeremy Bradshaw adds an interesting aspect to the literature about the effect of the antimicrobial peptide LS3 on the phase transition temperature of model lipid membranes. Differential scanning calorimetry studies were used to investigate the effect of the peptide on the phase transition of mixtures of cis and trans isomers of phosphatidylethanolamine and the data was used to discuss the orientation of the peptide in the membrane. The work undertaken by Angeliki Damianoglou et al. uses a well characterised AMP, melittin, and the enzyme, phospholipase A2 (PLA2), to analyse peptidemembrane interactions and insertion behaviour using linear dichroism (LD) to study the orientation of the peptide in the membrane. Although LD improves our understanding of peptide-membrane interactions, this paper emphasises that such work needs to be complemented by a range of other biophysical techniques such as dynamic light scattering, circular dichroism and mass spectrometry...........
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Document Type: Research Article

Publication date: 01 November 2010

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  • Protein & Peptide Letters publishes short papers in all important aspects of protein and peptide research, including structural studies, recombinant expression, function, synthesis, enzymology, immunology, molecular modeling, drug design etc. Manuscripts must have a significant element of novelty, timeliness and urgency that merit rapid publication. Reports of crystallisation, and preliminary structure determinations of biologically important proteins are acceptable. Purely theoretical papers are also acceptable provided they provide new insight into the principles of protein/peptide structure and function.
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