Autoantibodies as Diagnostic Markers and Mediator of Joint Inflammation in Arthritis

Figure 1

Schematic overview of the posttranslational modifications citrullination, carbamylation, and acetylation. The process of citrullination modifies an arginine (R) present in the amino acid sequence of a protein into citrulline, whereas the process of carbamylation modifies a lysine (K) into homocitrulline. Citrullinated and carbamylated proteins are recognized by anticitrullinated protein antibodies and anticarbamylated protein antibodies, respectively. The process of citrullination is mediated by peptidyl arginine deiminase (PAD) enzymes, whereas the process of carbamylation is a chemical reaction driven by cyanate. Acetylation is catalyzed by acetyl transferases. Ac-CoA: acetyl-CoA; H₂O₂: hydrogen peroxide; MPO: myeloperoxidase [6–8].

(a) Citrullination

(b) Carbamylation

(c) Acetylation