Lipopolysaccharide interaction is decisive for the activity of the antimicrobial peptide NK-2 against Escherichia coli and Proteus mirabilis.

Phosphatidylglycerol is a widely used mimetic to study the effects of AMPs (antimicrobial peptides) on the bacterial cytoplasmic membrane. However, the antibacterial activities of novel NK-2-derived AMPs could not be sufficiently explained by using this simple model system. Since the LPS (lipopolysaccharide)-containing outer membrane is the first barrier of Gram-negative bacteria, in the present study we investigated interactions of NK-2 and a shortened variant with viable Escherichia coli WBB01 and Proteus mirabilis R45, and with model membranes composed of LPS isolated from these two strains.

Interfacial properties and structural analysis of the antimicrobial peptide NK-2.

The structure of the antimicrobial peptide NK-2 has been studied at the air-water interface and in different solutions using spectroscopic methods such as circular dichroism (CD) and infrared reflection absorption spectroscopy (IRRAS) as well as specular X-ray reflectivity (XR). NK-2 adopts an unordered structure in water, buffer, and in the presence of monomeric cationic and noncharged amphiphiles. However, it forms a stable alpha-helix in 2,2,2-trifluoroethanol (TFE) and in micellar solutions of anionic, cationic as well as nonionic amphiphiles, whereas only in sodium dodecyl sulfonate solutions the alpha-helical structure can also be found below the critical micellar concentration (cmc).

Rationale for the design of shortened derivatives of the NK-lysin-derived antimicrobial peptide NK-2 with improved activity against Gram-negative pathogens.

The peptide NK-2 is an effective antimicrobial agent with low hemolytic and cytotoxic activities and is thus a promising candidate for clinical applications. It comprises the alpha-helical, cationic core region of porcine NK-lysin a homolog of human granulysin and of amoebapores of pathogenic amoeba. Here we visualized the impact of NK-2 on Escherichia coli by electron microscopy and used NK-2 as a template for sequence variations to improve the peptide stability and activity and to gain insight into the structure/function relationships.