Dimerization and lysine substitution of melittin have differing effects on bacteria
Tamara Matthyssen1, Wenyi Li1,2, James A Holden3
1ACTV Research Group, Melbourne Dental School, Division of Basic and Clinical Oral Sciences, Royal Dental Hospital and The Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Melbourne, VIC, Australia.
Introduction:
Melittin is a potent antimicrobial peptide from bee venom that is effective against both Gram-positive and Gram-negative bacteria. However, it is extremely toxic to mammalian cells and, as yet, has no clinical use. Modifications to its amino acid sequence, cyclization, truncation, and dimerization have been attempted in order to reduce its toxicity whilst maintaining its antimicrobial activity.
Methods:
In this study, we targeted the three lysine residues present in melittin and substituted them with lysine homologs containing shorter side chains (ornithine, Orn, diaminobutyric acid, Dab, and diaminopropanoic acid, Dap) and made both parallel and antiparallel melittin dimers to observe how lysine substitution and dimerization affects its activity and toxicity. The antibacterial activity of melittin and its analogs was tested against S. aureus (Gram-positive bacteria) and E. coli (Gram-negative bacteria), and cytotoxicity was tested against the mammalian cell lines HEK293 and H4IIE.
Results:
Overall, dimerization and lysine substitution exhibited improved antimicrobial activity toward E. coli and limited improvement toward S. aureus. However, mammalian cell toxicity was only marginally reduced compared to native melittin. Interestingly, the parallel dimer was found to be marginally more active than the antiparallel dimer, indicating orientation maybe important for activity, although both dimers were less effective than the native and Lys-analog peptides toward S. aureus. Of the Lys substitutions, Dab and Dap improved melittin's activity toward E. coli.
Discussion:
Dimerization and Lys substitution of melittin improved the antimicrobial activity toward Gram-negative bacteria but did not significantly improve its activity toward Gram-positive bacteria. Some analogs also displayed reduced toxicity toward HEK293 and H4IIE cells but overall remained toxic at bactericidal concentrations. Our data indicates that although highly antibacterial, melittin's toxicity is the major drawback in its potential use.
Insights
Melittin analogs with modified lysine residues and dimerization showed improved activity against Gram-negative bacteria but not Gram-positive bacteria. While some analogs had reduced toxicity, melittin
Area of Science:
- Biochemistry
- Microbiology
- Toxicology
Background:
- Melittin, a bee venom peptide, possesses potent antimicrobial properties.
- High mammalian cell toxicity limits melittin's clinical applications.
- Previous studies explored modifications like cyclization and truncation to reduce melittin's toxicity.
Purpose of the Study:
- To investigate the effects of lysine substitution and dimerization on melittin's antimicrobial activity and toxicity.
- To assess the impact of specific lysine substitutions (ornithine, diaminobutyric acid, diaminopropanoic acid) and dimer orientation (parallel, antiparallel) on melittin's efficacy.
Main Methods:
- Synthesized melittin analogs with lysine substitutions at key positions.
- Created parallel and antiparallel melittin dimers.
- Evaluated antibacterial activity against *S. aureus* and *E. coli*.
- Assessed cytotoxicity against HEK293 and H4IIE mammalian cell lines.
Main Results:
- Dimerization and lysine substitution enhanced activity against *E. coli* but showed limited improvement against *S. aureus*.
- Mammalian cell toxicity was only marginally reduced in modified analogs compared to native melittin.
- Diaminobutyric acid and diaminopropanoic acid substitutions improved activity against *E. coli*.
Conclusions:
- Melittin modifications can enhance activity against Gram-negative bacteria but not significantly against Gram-positive bacteria.
- Toxicity remains a significant barrier to clinical use, even with reduced toxicity in some analogs.
- Further research is needed to overcome melittin's inherent toxicity for therapeutic development.
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