Fine epitope mapping of the human SS-B/La protein. Identification of a distinct autoepitope homologous to a viral gag polyprotein.
To analyze the autoepitopes on the SS-B/La protein, a cDNA covering the entire region coding the protein was isolated from a human cDNA library. The cDNA was subcloned into an expression plasmid vector, pEX, to express its protein product as a fusion protein with cro-beta-galactosidase in Escherichia coli. A recombinant pEX plasmid expressing three-fourths of the protein (amino acid 112-408) was also constructed. The antigenicities of these recombinant proteins were confirmed with a patient's serum. Their various deletion mutants were produced with exonuclease III treatment from the 3' ends of the cDNAs without changing the proper translational frame. Immunoblot analysis and enzyme-linked immunosorbent assay were used to evaluate the reactivities of the recombinant proteins with patients' sera to determine the autoepitopes. A narrow segment (amino acid 88-101) and the region where several epitopes were located (amino acid 283-338) on the SS-B/La protein were universally recognized by all the sera with anti-SS-B/La antibodies examined. An additional epitope region (amino acid 179-220) was recognized by some patients' sera. Computer analysis revealed that the most distinct autoepitope, amino acid 88-101, had a striking homology to a retroviral gag polyprotein. These findings indicate that exogenous or endogenous retroviruses may play a role in initiation of the anti-SS-B/La autoimmunity.
Kohsaka
H
H
Department of Medicine and Physical Therapy, Faculty of Medicine, University of Tokyo, Japan.
Yamamoto
K
K
Fujii
H
H
Miura
H
H
Miyasaka
N
N
Nishioka
K
K
Miyamoto
T
T
D000595:Amino Acid Sequence; D001323:Autoantibodies / Q000302:isolation & purification; D001324:Autoantigens / Q000235:genetics* / Q000276:immunology; D001483:Base Sequence; D002846:Chromatography, Affinity; D002872:Chromosome Deletion; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D000939:Epitopes / Q000032:analysis / Q000235:genetics*; D015723:Gene Library; D015683:Gene Products, gag / Q000235:genetics*; D006801:Humans; D015151:Immunoblotting; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids; D012261:Ribonucleoproteins; D012689:Sequence Homology, Nucleic Acid; D012859:Sjogren's Syndrome / Q000097:blood / Q000235:genetics / Q000276:immunology; D000097585:SS-B Antigen
D001323:Autoantibodies; D001324:Autoantigens; D004247:DNA; D000939:Epitopes; D015683:Gene Products, gag; D012261:Ribonucleoproteins; D000097585:SS-B Antigen