Studies on citrullinated LL-37: detection in human airways, antibacterial effects and biophysical properties

Sci Rep. 2020 Feb 11;10(1):2376. doi: 10.1038/s41598-020-59071-7.


Arginine residues of the antimicrobial peptide LL-37 can be citrullinated by peptidyl arginine deiminases, which reduce the positive charge of the peptide. Notably, citrullinated LL-37 has not yet been detected in human samples. In addition, functional and biophysical properties of citrullinated LL-37 are not fully explored. The aim of this study was to detect citrullinated LL-37 in human bronchoalveolar lavage (BAL) fluid and to determine antibacterial and biophysical properties of citrullinated LL-37. BAL fluid was obtained from healthy human volunteers after intra-bronchial exposure to lipopolysaccharide. Synthetic peptides were used for bacterial killing assays, transmission electron microscopy, isothermal titration calorimetry, mass-spectrometry and circular dichroism. Using targeted proteomics, we were able to detect both native and citrullinated LL-37 in BAL fluid. The citrullinated peptide did not kill Escherichia coli nor lysed human red blood cells. Both peptides had similar α-helical secondary structures but citrullinated LL-37 was more stable at higher temperatures, as shown by circular dichroism. In conclusion, citrullinated LL-37 is present in the human airways and citrullination impaired bacterial killing, indicating that a net positive charge is important for antibacterial and membrane lysing effects. It is possible that citrullination serves as a homeostatic regulator of AMP-function by alteration of key functions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / analysis
  • Anti-Bacterial Agents / chemistry
  • Anti-Bacterial Agents / pharmacology*
  • Antimicrobial Cationic Peptides
  • Bronchoalveolar Lavage Fluid / chemistry
  • Cathelicidins / analysis
  • Cathelicidins / chemistry
  • Cathelicidins / pharmacology*
  • Cells, Cultured
  • Citrulline / analogs & derivatives
  • Erythrocytes / drug effects
  • Escherichia coli / drug effects
  • Humans
  • Protein Conformation, alpha-Helical
  • Protein Stability


  • Anti-Bacterial Agents
  • Antimicrobial Cationic Peptides
  • Cathelicidins
  • Citrulline