Intramolecular cyclization of the antimicrobial peptide Polybia‐MPI with triazole stapling: influence on stability and bioactivity

• Published in: Journal of peptide science 2017-11, Vol.23 (11), p.824-832
• Main Authors: Liu, Beijun, Zhang, Wei, Gou, Sanhu, Huang, Haifeng, Yao, Jia, Yang, Zhibin, Liu, Hui, Zhong, Chao, Liu, Beiyin, Ni, Jingman, Wang, Rui
• Format: Article
• Language: English
• Subjects: Alcohols; Alkynes; Amino Acid Sequence; Analogs; Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - pharmacology; Antibiotics; Antiinfectives and antibacterials; Antimicrobial activity; Antimicrobial agents; Antimicrobial Cationic Peptides - chemistry; Antimicrobial Cationic Peptides - pharmacology; Antimicrobial peptides; Bacteria; Biological activity; Cationic antimicrobial peptides; Chemical synthesis; Circular dichroism; click chemistry; Conformation; Cyclization; Cycloaddition; Dichroism; Drug Stability; Electron microscopy; Hemolysis; Infectious diseases; intramolecular cyclization; Iodides; mechanism of action; Microbial Sensitivity Tests; Peptides; Propidium iodide; Protein Stability; Protein structure; Protein Structure, Secondary; Proteolysis; Scanning electron microscopy; Secondary structure; Sodium; Sodium dodecyl sulfate; Sodium lauryl sulfate; stability; Triazoles - chemistry; Triazoles - pharmacology; Trypsin; Wasp Venoms - chemistry; Wasp Venoms - pharmacology
• ISSN: 1075-2617; 1099-1387
• DOI: 10.1002/psc.3031

Cationic antimicrobial peptides have attracted increasing attention as a novel class of antibiotics to treat infectious diseases caused by pathogenic bacteria. However, susceptibility to protease is a shortcoming in their development. Cyclization is one approach to increase the proteolytic resistance of peptides. Therefore, to improve the proteolytic resistance of Polybia‐MPI, we have synthesized the MPI cyclic analogs C‐MPI‐1 (i‐to‐i+4) and C‐MPI‐2 (i‐to‐i+6) by copper(I)‐catalyzed azide–alkyne cycloaddition. Compared with MPI, C‐MPI‐1 displayed sustained antimicrobial activity and had enhanced anti‐trypsin resistance, while C‐MPI‐2 displayed no antimicrobial activity. The relationship between peptide structure and bioactivity was further investigated by probing the secondary structure of the peptides by circular dichroism. This showed that C‐MPI‐1 adopted an α‐helical structure in aqueous solution and, interestingly, had increased α‐helical conformation in 30 mM sodium dodecyl sulfate and 50% trifluoroethyl alcohol compared with MPI. C‐MPI‐2 that was not α‐helical in structure, suggesting that the propensity for α‐helix conformation may play an important role in cyclic peptide design. In addition, scanning electron microscopy, propidium iodide uptake, and membrane permeabilization assays indicated that MPI and the optimized analog C‐MPI‐1 had membrane‐active action modes, indicating that the peptides would not be susceptible to conventional resistance mechanisms. Our study provides additional insight into the influence of intramolecular cyclization at various positions on peptide structure and biological activity. In conclusion, the design and synthesis of cyclic analogs via click chemistry offer a new strategy for the development of stable antimicrobial agents. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd. The MPI cyclic analogs C‐MPI‐1 (i‐ to ‐i+4) and C‐MPI‐2 (i‐ to ‐i+6) were synthesized by copper(I)‐catalyzed azide‐alkyne cycloaddition. Cyclic analogs have different bioactivity, and especially, C‐MPI‐1 has enhanced anti‐trypsin resistance compared with the parent peptide MPI. The mechanism of action and the secondary structure of all peptides were further investigated.