Indolicidin Targets Duplex DNA: Structural and Mechanistic Insight through a Combination of Spectroscopy and Microscopy

Indolicidin (IR13), a 13‐residue antimicrobial peptide from the cathelicidin family, is known to exhibit a broad spectrum of antimicrobial activity against various microorganisms. This peptide inhibits bacterial DNA synthesis resulting in cell filamentation. However, the precise mechanism remains unclear and requires further investigation. The central PWWP motif of IR13 provides a unique structural element that can wrap around, and thus stabilize, duplex B‐type DNA structures. Replacements of the central Trp‐Trp pair with Ala‐Ala, His‐His, or Phe‐Phe residues in the PxxP motif significantly affects the ability of the peptide to stabilize duplex DNA. Results of microscopy studies in conjunction with spectroscopic data confirm that the DNA duplex is stabilized by IR13, thereby inhibiting DNA replication and transcription. In this study we provide high‐resolution structural information on the interaction between indolicidin and DNA, which will be beneficial for the design of novel therapeutic antibiotics based on peptide scaffolds. That′s a wrap! The PWWP short peptide derived from indolicidin provides a unique structural element that stabilizes the DNA duplex. Substitution of Trp residues in PWWP with Ala, His, or Phe significantly destabilizes the DNA duplex structure, thereby establishing a strong correlation between the surface area of the residues (decreasing order: Ala