Membranolytic selectivity of cystine-stabilized cyclic protegrins

Area of Science:

• Biochemistry
• Molecular Biology
• Medicinal Chemistry

Background:

• Antimicrobial peptides (AMPs) are crucial in innate immunity.
• Protegrin-1 (PG-1) is a broad-spectrum AMP with potential therapeutic applications.
• Modulating AMP structure can optimize activity and reduce toxicity.

Purpose of the Study:

• To investigate the correlation between conformational rigidity and membranolytic selectivity of antimicrobial activity and cytotoxicity.
• To design and synthesize cyclic analogs of protegrin-1 (PG-1) with varying degrees of conformational constraint.

Main Methods:

• Synthesis of six cyclic protegrin analogs with end-to-end peptide bonds and 0-3 disulfide constraints.
• Antimicrobial assays against 10 diverse organisms (bacteria, fungi, HIV-1) under varying salt conditions.
• Hemolytic assays against human cells.
• Circular dichroism spectroscopy to assess secondary structures.

Main Results:

• Cyclic protegrins exhibited broad antimicrobial activity with distinct profiles against Gram-positive and Gram-negative bacteria.
• The most constrained analog, cyclic tricystine protegrin (ccPG 3), showed a 10-fold decrease in hemolytic activity and 6-30 fold improvement in membranolytic selectivity.
• Analogs with fewer disulfide bonds ([DeltaSS]cPG 8, [DeltaCys6,15]cPG 5) had activity and cytotoxicity similar to PG-1.
• Cyclic protegrins with 1-3 cystine bonds displayed beta-strand structures in solution.

Conclusions:

• Cyclic structures are effective in designing antimicrobial peptides.
• Increased conformational rigidity in protegrins can enhance membranolytic selectivity, dissociating antimicrobial effects from hemolytic activity.
• This suggests a strategy for developing safer and more effective antimicrobial peptide therapeutics.