Indolicidin – Antimicrobial Peptides – AMP

Indolicidin is a natural cationic cathelicidin family anti-microbial peptide (AMP) with a very wide killing spectrum which includes: Gram-positive and Gram-negative bacteria, fungi, protozoa and HIV. It is also an immune system modulator and an inhibitor of aminoglycoside antibiotic-resistance enzymes. Indolicidin contains 5 tryptophan residues (39% of peptide content)- the highest tryptophan proportion ever seen in a peptide or protein. When indolicidin interacts with biological membranes it assumes a wedge- shaped conformation, with the hydrophobic tryptophan residues in the trough of the wedge, and positively charged regions flanking them at each end. If fully extended, indolicidin is able to span both lipid bilayers despite only consisting of 13 amino acid residues. This is possible because indolicidin adopts an approximate poly-l-proline type II helix conformation, which is characterized by very high helical pitches. The exact mode of action of indolicidin is still unknown. At bactericidal concentrations the peptide appears to translocate through the membrane into the cytosol where it may bind to nucleic acids, whereas at higher concentrations it is membranolytic.