Epitopes, structural domains, and asymmetry of amino acid residues in SS-B/La nuclear protein.
SS-B/La is a conserved cellular phosphoprotein of 46 to 48 KD that is the target antigen of autoantibodies in sera of patients with Sjogren's syndrome and systemic lupus erythematosus. SS-B/La is also known to be associated with certain small cellular and viral RNA, including adenovirus VAI and VAII RNA. Two relatively protease-resistant domains (X and Y) were defined in SS-B from HeLa cells by using human autoantibodies as reagents. Domain X, a methionine-containing nonphosphorylated 28 KD polypeptide, was found to be resistant to partial digestion with six different proteases. Similar domains were also found in calf and rabbit SS-B. Domain Y, a 23 KD polypeptide, was detected after limited digestion with S. aureus V8 and trypsin. This domain contained little if any methionine, but all the detectable phosphorylated amino acids. Among 16 anti-SS-B sera tested by immunoblotting, 11 (69%) were reactive with both domains, three (19%) only with domain X, and two (13%) only with domain Y. These results showed that there are at least two distinct antigenic epitopes on the 46 to 48 KD SS-B/La protein, each located on a separate structural domain. The asymmetric distribution of methionine and phosphorylated amino acid residues in SS-B/La show striking similarity to the two reported domains of the adenovirus 72 KD DNA-binding protein, and raises questions concerning functional similarities that await investigation.
E K
EK
Chan
A M
AM
Francoeur
E M
EM
Tan
D000941:Antigens / Q000276:immunology*; D001324:Autoantigens / Q000276:immunology*; D002467:Cell Nucleus / Q000276:immunology; D000939:Epitopes; D006367:HeLa Cells; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D008970:Molecular Weight; D010446:Peptide Fragments / Q000276:immunology; D010447:Peptide Hydrolases; D010750:Phosphoproteins / Q000276:immunology*; D011487:Protein Conformation; D012261:Ribonucleoproteins / Q000276:immunology; D000097585:SS-B Antigen
D000941:Antigens; D001324:Autoantigens; D000939:Epitopes; D010446:Peptide Fragments; D010447:Peptide Hydrolases; D010750:Phosphoproteins; D012261:Ribonucleoproteins; D000097585:SS-B Antigen