Indolicidin

Indolicidin is a unique tryptophan-rich antimicrobial peptide isolated from cytoplasmic granules of bovine neutrophils. Its remarkably high tryptophan content (39%) distinguishes it from other antimicrobial peptides and confers distinctive membrane-interaction properties through the indole side chains.

The 13-amino acid peptide adopts extended and turn conformations rather than the alpha-helical or beta-sheet structures typical of other antimicrobial peptides. Despite this unusual structure, indolicidin demonstrates broad-spectrum activity against gram-positive and gram-negative bacteria, fungi, protozoa, and enveloped viruses.

Indolicidin's mechanism involves membrane perturbation through tryptophan-mediated insertion into the lipid bilayer, but also includes intracellular targeting of DNA synthesis. This dual mechanism - membrane disruption plus DNA binding - may contribute to its activity and reduced susceptibility to resistance development.

The peptide has served as a template for developing optimized antimicrobial analogs with improved activity, reduced hemolytic toxicity, or enhanced selectivity. Its unique properties make indolicidin a valuable model for understanding how tryptophan-rich sequences interact with membranes and contribute to antimicrobial mechanisms.