title: Quantification of citrullination by means of skewed isotope distribution pattern.
abstract: Citrullination is a post-translational modification of arginine, resulting in a loss of positive charge and a 1 Da mass increase. Research on citrullinated proteins is crucial in rheumatoid arthritis, an autoimmune disease characterized by the presence of antibodies against citrullinated proteins. However, little is known about the location or quantity of deiminated arginine residues in these proteins. Since citrullination gives rise to a mass gain of only 1 Da, the isotope pattern of the citrullinated and the noncitrullinated version of a peptide will overlap. However, the difference between the theoretical, or noncitrullinated, and the measured isotope pattern can be used to quantify the amount of citrullination. We developed a method to quantify citrullinated peptides by means of their skewed isotopic distribution pattern. The method was first optimized with synthetic peptides, after both direct infusion and RP-HPLC separation on an ESi-QqTOF mass spectrometer. Additionally, we analyzed synovial fluid samples from rheumatoid arthritis patients and were able to quantify citrullinated peptides originating from citrullinated fibrinogen, a well-known antigen.
authors.affiliation: Laboratory for Pharmaceutical Biotechnology, Ghent University, Ghent, Belgium.
authors.forename: Marlies
authors.initials: M
authors.lastname: De Ceuleneer
authors.forename: Katleen
authors.initials: K
authors.lastname: Van Steendam
authors.forename: Maarten
authors.initials: M
authors.lastname: Dhaenens
authors.forename: Dirk
authors.initials: D
authors.lastname: Elewaut
authors.forename: Dieter
authors.initials: D
authors.lastname: Deforce
mesh_terms: D000595:Amino Acid Sequence; D015153:Blotting, Western; D002851:Chromatography, High Pressure Liquid; D002956:Citrulline / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D007554:Isotopes / Q000378:metabolism*; D008969:Molecular Sequence Data; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D007554:Isotopes; D011506:Proteins; D002956:Citrulline