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Structures and mode of membrane interaction of a short Î±âhelical lytic peptide and its diastereomer determined by NMR, FTIR, and fluorescence spectroscopy
- Oren, Ziv, Ramesh, Jagannathan, Avrahami, Dorit, Suryaprakash, N., Shai, Yechiel, Jelinek, Raz
- European journal of biochemistry 2002 v.269 no.16 pp. 3869-3880
- Fourier transform infrared spectroscopy, acids, anti-infective properties, antimicrobial cationic peptides, colorimetry, diastereomers, electrostatic interactions, fluorescence, fluorescence emission spectroscopy, hemolysis, hydrophobicity, leucine, lysine, micelles, nuclear magnetic resonance spectroscopy, phospholipids, sodium dodecyl sulfate, tryptophan, zwitterions
- The interaction of many lytic cationic antimicrobial peptides with their target cells involves electrostatic interactions, hydrophobic effects, and the formation of amphipathic secondary structures, such as Î±âhelices or Î²âsheets. We have shown in previous studies that incorporating ââ30%dâamino acids into a short Î±âhelical lytic peptide composed of leucine and lysine preserved the antimicrobial activity of the parent peptide, while the hemolytic activity was abolished. However, the mechanisms underlying the unique structural features induced by incorporating dâamino acids that enable short diastereomeric antimicrobial peptides to preserve membrane binding and lytic capabilities remain unknown. Inthis study, we analyze in detail the structuresofa modelamphipathic Î±âhelical cytolytic peptide KLLLKWLL KLLKâNH2 and its diastereomeric analog and their interactions with zwitterionic and negatively charged membranes. Calculations based on highâresolution NMR experiments in dodecylphosphocholine (DPCho) and sodium dodecyl sulfate (SDS) micelles yield threeâdimensional structures of both peptides. Structural analysis reveals that the peptides have an amphipathic organization within both membranes. Specifically, the Î±âhelical structure of theLâtype peptide causes orientation of the hydrophobic andpolar amino acids onto separate surfaces, allowing interactions with both the hydrophobic core of the membrane andthe polar head group region. Significantly, despite the absence of helical structures, the diastereomer peptide analog exhibits similar segregation between the polar and hydrophobic surfaces. Further insight into the membraneâbinding properties of the peptides and their depth of penetration into the lipid bilayer has been obtained through tryptophan quenching experiments using brominated phospholipids and the recently developed lipid/polydiacetylene (PDA) colorimetric assay. The combined NMR, FTIR, fluorescence, and colorimetric studies shed light on the importance of segregation between the positive charges and the hydrophobic moieties on opposite surfaces within the peptides for facilitating membrane binding and disruption, compared to the formation of Î±âhelical or Î²âsheet structures.