title: Repetitive P68-autoantigen specific epitopes recognized by human anti-(U1) small nuclear ribonucleoprotein autoantibodies.
abstract: The major target of anti-(U1)snRNP autoantibodies, a serological marker of patients with mixed connective tissue disease and related rheumatic disorders, is a 68 kDa protein (p68) associated with (U1)RNA-containing small nuclear ribonucleoprotein particles. With recombinant p68 fusion proteins, multiple autoepitopes have been identified, and one of these has been mapped to the pentamer sequence ERKRR, which is located within antigenic domain A in the amino-terminal half of p68. The lysine residue (K) of this epitope can be replaced by isoleucine without loss of autoantibody binding. Here we have investigated whether other variants of this epitope are present on the p68 autoantigen and if these are recognized by anti-p68 autoantibodies. We identified four related motifs in the carboxy-terminal half of the p68-protein, and three of these (all containing glutamic acid instead of lysine (ERERR] mapped to the previously characterized autoantigenic domains C and D. Immunoreaction of anti-ERKRR autoantibodies, affinity-purified from domain A with recombinant fusion proteins containing either domain C or domain D of p68, revealed that anti-ERKRR autoantibodies cross-react with the ERERR-motifs. This finding, which was confirmed by competitive inhibition-ELISA with solid-phase coupled domain A-, C- and D-fusion proteins and ERKRR-containing synthetic peptides as competitors, suggests that a subset of patient autoantibodies is directed against repetitive structures on a single snRNP component.
authors.affiliation: Max-Planck-Institut für Biochemie, Martinsried, Germany.
authors.forename: H J
authors.initials: HJ
authors.lastname: Netter
authors.forename: H
authors.initials: H
authors.lastname: Will
authors.forename: C
authors.initials: C
authors.lastname: Szostecki
authors.forename: H H
authors.initials: HH
authors.lastname: Guldner
mesh_terms: D000595:Amino Acid Sequence; D000974:Antibodies, Antinuclear / Q000276:immunology*; D015153:Blotting, Western; D003240:Connective Tissue Diseases / Q000276:immunology*; D003429:Cross Reactions / Q000276:immunology; D053487:DEAD-box RNA Helicases; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000276:immunology; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000276:immunology*; D009842:Oligopeptides / Q000037:antagonists & inhibitors / Q000276:immunology; D011494:Protein Kinases; D020365:RNA Helicases; D011993:Recombinant Fusion Proteins; D012261:Ribonucleoproteins / Q000276:immunology*; D017411:Ribonucleoproteins, Small Nuclear
chemical_list: D000974:Antibodies, Antinuclear; D000939:Epitopes; D009687:Nuclear Proteins; D009842:Oligopeptides; D011993:Recombinant Fusion Proteins; D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear; D011494:Protein Kinases; C506749:Ddx5 protein, human; D053487:DEAD-box RNA Helicases; D020365:RNA Helicases