MS analysis of rheumatoid arthritic synovial tissue identifies specific citrullination sites on fibrinogen.
OBJECTIVE
Citrullination is a post-translational modification of arginine residues to citrulline catalyzed by peptidyl arginine deiminases. Induced expression of citrullinated proteins are frequently detected in various inflammatory states including arthritis; however, direct detection of citrullination in arthritic samples has not been successfully performed in the past.


METHODS
Citrullination of human fibrinogen, a candidate autoantigen in arthritis, was studied. Accurate identification of citrullinated fibrinogen peptides from rheumatoid arthritis synovial tissue specimens was performed using accurate mass and retention time analysis.


RESULTS
A peptide with the sequence ESSSHHPGIAEFPSRGK corresponding to amino acids 559-575 of fibrinogen α-chain was identified to be citrullinated with an occupancy rate between 1.4 and 2.5%. Citrullination of the peptide KREEAPSLRPAPPPISGGGYRARPAK corresponding to amino acids 52-77 of the fibrinogen β-chain was identified with an occupancy rate of 1.2%.


CONCLUSIONS
We report a proof of principle study for the identification of citrullinated proteins and within them, identification of citrullination sites and quantification of their occupancies in synovial tissue from rheumatoid arthritis patients using high-resolution MS. Detailed studies on which molecules are citrullinated in arthritis can provide information about their role in immune regulation and serve as novel biomarkers and potentially even as therapeutic targets.
Department of Medicine, Unit of Rheumatology/Karolinska Biomics Center, Karolinska University Hospital, Karolinska Institute, Stockholm, Sweden.
Monika
M
Hermansson
Konstantin
K
Artemenko
Elena
E
Ossipova
Hanna
H
Eriksson
Johan
J
Lengqvist
Dimitrios
D
Makrygiannakis
Anca I
AI
Catrina
Anthony P
AP
Nicholas
Lars
L
Klareskog
Mikhail
M
Savitski
Roman A
RA
Zubarev
Per-Johan
PJ
Jakobsson
D000368:Aged; D000595:Amino Acid Sequence; D001172:Arthritis, Rheumatoid / Q000378:metabolism*; D002956:Citrulline / Q000378:metabolism*; D005260:Female; D005340:Fibrinogen / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011499:Protein Processing, Post-Translational; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D013583:Synovial Membrane / Q000378:metabolism*
D002956:Citrulline; D005340:Fibrinogen