Structure–activity relationship of an antimicrobial peptide, Phylloseptin-PHa: balance of hydrophobicity and charge determines the selectivity of bioactivities

Abstract

Background

Antimicrobial peptides (AMPs) from the skin secretions of amphibians are now considered as a potential alternative to conventional antibiotics. Phylloseptins are a family of AMPs identified in the skin secretions of Phyllomedusinae tree frogs which exhibit highly conserved structural characteristics. This study examines the structure–activity relationship of the newly discovered phylloseptin, Phylloseptin-PHa (PSPHa) from Pithecopus hypochondrialis.

Materials and methods

PSPHa and modified analogs were produced by solid phase synthesis and purified by reverse-phase HPLC. Rationally designed modified analogs incorporating changes in significant physicochemical parameters such as hydrophobicity, hydrophobic moment and net charge were investigated to determine their influence on secondary structure, antimicrobial activity, membrane permeabilization and cytotoxicity.

Results

Overall, we found that when rationally designing AMPs by altering their primary structure it is important to keep a balance between hydrophobicity and charge.

Conclusion

This study provides new insights which will help in the future development of AMPs as alternatives to conventional antibiotics for the treatment of Staphylococcus aureus and methicillin-resistant S. aureus infections.

Keywords:

• phylloseptin
• antimicrobial activity
• hydrophobicity
• charge
• membrane selectivity

Supplementary materials

Figure S1 The antimicrobial activity of each peptide against the selected microorganisms from 512 to 1 µM.

Notes: The growth control was presented as bacteria culture without peptides. The vehicle control was employed a final concentration of 1% (v/v) DMSO. The sterilize control employed fresh MHB. The positive controls were applied as 5 mg/L vancomycin for Gram-positive bacteria, 5 mg/L gentamicin for Gram-negative bacteria and 5 mg/L amphotericin B for C. albicans. Bars show the mean and the error bars show the standard error from five independent experiments.
Abbreviations: DMSO, dimethyl sulfoxide; MHB, Mueller Hinton Broth; MRSA, methicillin-resistant S. aureus; PSPHa, Phylloseptin-PHa.

Figure S2 The hemolytic activity of each peptide on horse erythrocytes from 512 to 1 µM.

Notes: 1% TritonX-100 and PBS were employed as positive control and negative control, respectively. Bars show the mean and the error bars show the standard error from five independent experiments.
Abbreviation: PSPHa, Phylloseptin-PHa.

Figure S3 The HC₅₀ of each peptide on horse erythrocytes.

Notes: Bars show the mean and the error bars show the standard error from five independent experiments. P-value was calculated using unpaired t-test, indicating significance ***P<0.001.
Abbreviations: HC₅₀, half maximal hemolysis concentration; PSPHa, Phylloseptin-PHa.

Figure S4 The MTT assays of each peptide against the selected cancer cell lines.

Notes: The cell viability of growth control (cell growth without peptides) was applied as 100% cell viability. Bars show the mean and the error bars show the standard error from five independent experiments.
Abbreviation: PSPHa, Phylloseptin-PHa.

Acknowledgments

This work was supported by grants from the National Nature Science Foundation of China (No 81703572 to QD and No 81702611 to HW).

Author contributions

All authors contributed to data analysis, drafting and revising the article, gave final approval of the version to be published, and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.