Antimicrobial activity of rabbit CAP18-derived peptides

Area of Science:

• Biochemistry
• Microbiology
• Immunology

Background:

• Cationic antimicrobial protein of 18 kDa (CAP18) is found in rabbit granulocytes.
• The C-terminal 37 amino acids (CAP18(106-142)) form the lipopolysaccharide-binding domain.
• CAP18(106-142) exhibits broad antimicrobial activity.

Purpose of the Study:

• To investigate the antimicrobial activity of synthetic CAP18(106-142).
• To determine the structure-activity relationship of CAP18(106-142) fragments.
• To assess the activity of CAP18(106-142) in serum.

Main Methods:

• Synthesis of CAP18(106-142) and its fragments.
• Antimicrobial activity assays against Gram-positive and Gram-negative bacteria.
• Determination of 50% inhibitory concentrations (IC50).
• Activity assessment in the presence of serum.

Main Results:

• Synthetic CAP18(106-142) showed broad-spectrum activity against bacteria like Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa.
• IC50 values ranged from 20-100 nM for Gram-negative and 130-200 nM for Gram-positive bacteria.
• A 32-amino acid peptide derived from CAP18(106-142) retained high activity, while other fragments were inactive.
• CAP18(106-142) remained active in serum, unlike other granulocyte-derived antimicrobial peptides.

Conclusions:

• The lipopolysaccharide-binding domain of CAP18, specifically CAP18(106-142), possesses potent antimicrobial properties.
• Antimicrobial activity is dependent on the specific peptide structure.
• CAP18(106-142) is active in serum and may hold therapeutic potential for bacterial sepsis.