Melittin peptides exhibit different activity on different cells and model membranes

Area of Science:

• Biochemistry
• Molecular Biology
• Peptide Chemistry

Background:

• Melittin (MLT) is a potent lytic peptide active against diverse cell types.
• Understanding the structural contributions of proline and cysteine to MLT's activity is crucial.

Purpose of the Study:

• To investigate the roles of proline and cysteine's thiol group in melittin's cytolytic and antimicrobial activities.
• To compare the activities of monomeric and dimeric MLT analogs.

Main Methods:

• Solid-phase peptide synthesis to create native MLT and cysteine-containing analogs.
• Assays to evaluate antimicrobial activity, cytotoxicity, hemolysis, and lytic activity against model membranes.
• Circular dichroism spectroscopy to determine peptide secondary structure in various conditions.

Main Results:

• Proline is indispensable for MLT's antimicrobial and cytotoxic properties; its absence markedly reduces membrane lysis and hemolysis.
• MLT dimers exhibited reduced lytic activity against model membranes but enhanced hemolytic activity compared to monomers.
• Peptide structure varied: native MLT and monomer were unstructured in buffer, dimer adopted helical structure; all peptides increased helical content with vesicles.
• Lytic activity did not correlate with secondary structure or helical propensity.

Conclusions:

• The proline residue is critical for the antimicrobial and cytotoxic functions of melittin.
• Melittin's lytic activity is independent of its secondary structure, particularly helical conformation.
• Structural modifications, like dimerization, can alter specific activities (hemolysis vs. membrane lysis).