Novel designed VmCT1 analogs with increased antimicrobial activity

Antimicrobial peptides are biologically active molecules produced by a wide range of organisms as an essential component of the innate immune response. They have recently attracted great interest, since they have antimicrobial activity against a broad spectrum of microorganisms. VmCT1 is a cationic peptide from the venom of Vaejovis mexicanus smithi scorpions, which presents antibacterial activity and tends to helical structures. Its analogs were synthesized, characterized and the conformational studies were performed by circular dichroism. The peptides were designed to verify if the single and double substitutions proposed at the hydrophilic and hydrophobic portions of the amphipathic structure would alter antimicrobial activity against Gram-negative and Gram-positive bacteria, yeast and filamentous fungus, besides the hemolytic activity in human erythrocytes. Total charge of the peptides were modified from +2 to +3 by the introduction of a Lysine residue in the hydrophilic face of the amphiphilic helical structure leading to enhanced antimicrobial activity. [K]¹¹-VmCT1-NH₂ presented the lower MIC value against the microorganisms (from 0.39 to 6.25 μmol L^-1), however it showed higher hemolytic activity. The other Lysine-substituted analogs presented also lower MIC values ranging from 0.39 to 25 μmol L^-1 for the microorganisms assessed. The circular dichroism spectra analyses suggest that the Lysine-substituted analogs tend to adopt helical structures in trifluoroethanol solution and vesicles (f_H: 0.43-1), however they were coiled in water. Alanine substitution by a Glutamic acid residue in the hydrophilic face promotes the increase of polar angle in [E]⁴-VmCT1-NH₂ analog, which was important to led lower hemolytic activity (MHC value = 25 μmol L^-1). [W]⁹-VmCT1-NH₂ and [E]⁴[W]⁹-VmCT1-NH₂ were designed to favors hydrophobic interactions by the introduction of Tryptophan residue. [W]⁹-VmCT1-NH₂ presented MIC values lower or similar than the model molecule in the most of microorganisms tested. These results provided information about the structure-activity relationship and showed the influence of physicochemical parameters on antimicrobial and hemolytic activity.