Three-dimensional structure/hydrophobicity of latarcins specifies their mode of membrane activity.

Latarcins, linear peptides from the Lachesana tarabaevi spider venom, exhibit a broad-spectrum antimicrobial activity, likely acting on the bacterial cytoplasmic membrane. We study their spatial structures and interaction with model membranes by a combination of experimental and theoretical methods to reveal the structure-activity relationship. In this work, a 26 amino acid peptide, Ltcl, was investigated. Its spatial structure in detergent micelles was determined by 1 H nuclear magnetic resonance (NMR) and refined by Monte Carlo simulations in an implicit water-octanol slab. The Ltcl molecule was found to form a straight uninterrupted amphiphilic helix comprising 8-23 residues. A dye-leakage fluorescent assay and 31 P NMR spectroscopy established that the peptide does not induce the release of fluorescent marker nor deteriorate the bilayer structure of the membranes. The voltage-clamp technique showed that Ltcl 1 induces the current fluctuations through planar membranes when the sign of the applied potential coincides with the one across the bacterial inner membrane. This implies that Ltcl acts on the membranes via a specific mechanism, which is different from the carpet mode demonstrated by another latarcin, Ltc2a, featuring a helix-hinge-helix structure with a hydrophobicity gradient along the peptide chain. In contrast, the hydrophobic surface of the Ltcl helix is narrow-shaped and extends with no gradient along the axis. We have also disclosed a number of peptides, structurally homologous to Ltcl and exhibiting similar membrane activity. This indicates that the hydrophobic pattern of the Ltcl helix and related antimicrobial peptides specifies their activity mechanism. The latter assumes the formation of variable-sized lesions, which depend upon the potential across the membrane.