title: Interfacial properties and structural analysis of the antimicrobial peptide NK-2.
abstract: 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). The amphiphilic molecule NK-2 is surface active and forms a Gibbs monolayer at the air-buffer interface. In contrast, no adsorption was observed if NK-2 is dissolved in water. During the adsorption process in buffer solutions, NK-2 undergoes a conformational transition from random coil in bulk to alpha-helix at the interface. This change of the peptide's secondary structure is known to be associated with its antimicrobial activity. A comparison of the experimental IRRA spectra with the simulated spectra indicates that the adsorbed NK-2 alpha-helix lies flat at the interface. This is confirmed by XR measurements which show that the thickness of the NK-2 layer is approximately 17 A, which is the average diameter of a alpha-helix, indicating that only a monomolecular adsorption layer is formed.
authors.affiliation: Max Planck Institute of Colloids and Interfaces, Research Campus Golm, Am Mühlenberg 1, 14476 Potsdam, Germany. claudia.olak@mpikg.mpg.de
authors.forename: Claudia
authors.initials: C
authors.lastname: Olak
authors.forename: Annabel
authors.initials: A
authors.lastname: Muenter
authors.forename: Jörg
authors.initials: J
authors.lastname: Andrä
authors.forename: Gerald
authors.initials: G
authors.lastname: Brezesinski
mesh_terms: D000388:Air; D023181:Antimicrobial Cationic Peptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D002021:Buffers; D002942:Circular Dichroism; D008823:Micelles; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared; D013499:Surface Properties; D014270:Trifluoroethanol / Q000378:metabolism; D014867:Water / Q000737:chemistry; D014965:X-Rays
chemical_list: D023181:Antimicrobial Cationic Peptides; D002021:Buffers; D008823:Micelles; D010455:Peptides; C475945:peptide NK-2; D014867:Water; D014270:Trifluoroethanol