Heterogeneous nuclear ribonucleoproteins C1/C2 identified as autoantigens by biochemical and mass spectrometric methods

The antigenic specificity of an unusual antinuclear antibody pattern in thr ee patient sera was identified after separating HeLa-cell nuclear extracts by two-dimensional (2D) gel electrophoresis and localizing the antigens by immunoblotting with patient serum. Protein spots were excised from the 2D g el and their contents were analyzed by matrix-assisted laser desorption-ion ization (MALDI) or nanoelectrospray ionization time-of-flight (TOF) tandem mass spectrometry (MS) after in-gel digestion with trypsin. A database sear ch identified the proteins as the C1 and C2 heterogeneous nuclear ribonucle oproteins. The clinical spectrum of patients with these autoantibodies incl udes arthritis, psoriasis, myositis, and scleroderma. None of 59 patients w ith rheumatoid arthritis, 19 with polymyositis, 33 with scleroderma, and 10 with psoriatic arthritis had similar antibodies. High-resolution protein-s eparation methods and mass-spectrometric peptide mapping in combination wit h database searches are powerful tools in the identification of novel autoa ntigen specificities.