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

• Published in: Scientific reports Vol. 10; no. 1; p. 2376
• Main Authors: Al-Adwani, Salma, Wallin, Cecilia, Balhuizen, Melanie D., Veldhuizen, Edwin J. A., Coorens, Maarten, Landreh, Michael, Végvári, Ákos, Smith, Margaretha E., Qvarfordt, Ingemar, Lindén, Anders, Gräslund, Astrid, Agerberth, Birgitta, Bergman, Peter
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 11-02-2020; Nature Publishing Group
• Subjects: 631/250; 631/326; 631/57; Alveoli; Anti-Bacterial Agents - analysis; Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - pharmacology; Antibacterial activity; Antimicrobial peptides; Arginine; Bronchoalveolar Lavage Fluid - chemistry; Bronchus; Calorimetry; Cathelicidins - analysis; Cathelicidins - chemistry; Cathelicidins - pharmacology; Cells, Cultured; Circular dichroism; Citrulline; Citrulline - analogs & derivatives; Clinical Medicine; E coli; Erythrocytes; Erythrocytes - drug effects; Escherichia coli - drug effects; Farmakologi och toxikologi; High temperature; Humanities and Social Sciences; Humans; Klinisk medicin; Lipopolysaccharides; Medicin och hälsovetenskap; Medicinska och farmaceutiska grundvetenskaper; Mikrobiologi inom det medicinska området; multidisciplinary; Peptides; Protein Conformation, alpha-Helical; Protein Stability; Proteomics; Science; Science (multidisciplinary); Spectrometry; Synthetic peptides; Titration; Transmission electron microscopy
• ISSN: 2045-2322; 2045-2322
• 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.