Carbamylated LL-37 as a modulator of the immune response

Abstract

Carbamylation (or carbamoylation) of lysine residues and protein N-termini is a ubiquitous, non-enzymatic post-translational modification. Carbamylation at sites of inflammation is due to cyanate formation during the neutrophil oxidative burst and may target lysine residues within the antimicrobial peptide LL-37, which is secreted by activated neutrophils. The bactericidal and immunomodulatory properties of LL-37 depend on its structure and cationic nature, which are conferred by arginine and lysine residues. Therefore, carbamylation may affect the biological functions of LL-37. This may be of great importance in the context of using LL-37 as a target for drug development. The present study examined the kinetics and pattern of LL-37 carbamylation to investigate how this modification affects the bactericidal, cytotoxic, and immunomodulatory function of the peptide. The results indicated that LL-37 undergoes rapid modification in the presence of physiological concentrations of cyanate, yielding a spectrum of diverse carbamylated peptides. Mass spectrometry analyses revealed that the N-terminal amino group of Leu-1 was highly reactive and was modified almost instantly by cyanate to generate the predominant form of the modified peptide, named LL37C1. This was followed by the sequential carbamylation of Lys-8, Lys-12, and Lys-15, to yield LL37C8, and LL37C12,15, respectively. Carbamylation had profound and diverse effects on the structure and biological properties of LL-37. In some cases, anti-inflammatory LL-37 was rapidly converted to pro-inflammatory LL-37. Thus, caution should be exercised when treating patients with severe inflammatory conditions, such as sepsis, with pro-inflammatory LL-37.

Anti-LL37 Antibodies Are Present in Psoriatic Arthritis (PsA) Patients: New Biomarkers in PsA

“…It is reported that LL37 can become a substrate for post-translational modifications such as citrullination and carbamylation ( 20 , 21 ). Of note, carbamylated proteins can be the targets of autoantibodies in PsA ( 9 ).…”

Citrullination Alters the Antiviral and Immunomodulatory Activities of the Human Cathelicidin LL-37 During Rhinovirus Infection

“…Significantly, another posttranslational modification affecting the cationicy of LL-37 has also been reported. Carbamylation results in the non-enzymatic conversion of lysine residues to neutral homocitrulline (65,66) and thus reduces the net positive charge of LL-37. Similarly to citrullinated LL-37, carbamylated LL-37 also displays reduced direct antibacterial activity and reduced ability to modulate LPS-mediated cytokine release (65), confirming the importance of positive charge in the normal function of LL-37.…”

Immunomodulatory effects of anti-microbial peptides

“…In a grand scheme, LL-37 controls the expression of both pro-and anti-inflammatory cytokines during infection. In the presence of physiological concentrations of cyanate, LL-37 undergoes compositional changes yielding a variety of carbamylated peptides [83]. As small structural changes as carbamylation have diverse effects on the biological properties of LL-37, most notably conversion from anti-inflammatory to pro-inflammatory properties.…”