Anti-Sm autoantibodies cross-react with ribosomal protein S10: a common structural unit shared by the small nuclear RNP proteins and the ribosomal protein.
OBJECTIVE
Cross-reactivity of anti-Sm autoantibodies with a certain ribosomal protein has been reported previously. The present study was undertaken to identify the anti-Sm-reactive ribosomal protein, and to characterize the cross-reactive epitope.


METHODS
Two-dimensional gel electrophoresis followed by immunoblotting was used to identify the ribosomal protein (S10) which was reactive with the Y12 anti-Sm monoclonal antibody (MAb). Human anti-Sm antibodies were also tested for cross-reactivity with the Sm-B/B', Sm-D, and isolated S10 proteins by immunoblotting. Epitope analysis was performed by immunoprecipitation of in vitro-translated products of the recombinant S10 and its various mutants.


RESULTS
The Y12 MAb and the affinity-purified human anti-Sm autoantibodies cross-reacted with ribosomal S10 protein. Reactivity of the Y12 MAb with S10 protein was abolished by deletion of 19 amino acids at the carboxyl-terminus of S10, containing the Gly-Arg-Gly sequence motif shared by Sm-B/B' and Sm-D (D1 and D3). Replacements of Arg-158 with Gly and of Arg-158/Arg-160 with Gly/Gly at the carboxyl-terminal 157-Gly-Arg-Gly-Arg-Gly region disrupted the Y12 MAb recognition.


CONCLUSIONS
At least a part of human anti-Sm antibodies and Y12 MAb show cross-reactivity among Sm-B/B', Sm-D, and ribosomal protein S10. The carboxyl-terminal Gly-Arg-Gly region of S10 protein is involved in constructing the cross-reactive epitope. This demonstrates that a common structural feature is shared by the ribosomal protein and the small nuclear RNP proteins.
Hasegawa
H
H
Niigata University School of Medicine, Japan.
Uchiumi
T
T
Sato
T
T
Arakawa
M
M
Kominami
R
R
D000595:Amino Acid Sequence; D000818:Animals; D001323:Autoantibodies / Q000276:immunology*; D001324:Autoantigens / Q000235:genetics / Q000276:immunology*; D003429:Cross Reactions / Q000276:immunology*; D000939:Epitopes / Q000276:immunology; D006801:Humans; D051379:Mice; D008815:Mice, Inbred Strains; D008969:Molecular Sequence Data; D051381:Rats; D017411:Ribonucleoproteins, Small Nuclear / Q000235:genetics / Q000276:immunology*; D012269:Ribosomal Proteins / Q000235:genetics / Q000276:immunology*; D055517:snRNP Core Proteins
D001323:Autoantibodies; D001324:Autoantigens; D000939:Epitopes; D017411:Ribonucleoproteins, Small Nuclear; D012269:Ribosomal Proteins; C526416:Snrpb protein, mouse; C029537:ribosomal protein S10; D055517:snRNP Core Proteins