title: Multiple phosphorylation of human SS-B/LA autoantigen and its effect on poly(U) and autoantibody binding.
abstract: The metabolic turnover rates and the effect of in vitro phosphorylation on poly(U) and autoantibody binding of human SS-B/La ribonucleoprotein, an autoantigen expressed in various autoimmune disorders, were studied. The determination of the metabolic turnover rates of SS-B/La protein, SS-B/La protein phosphorylation and RNA binding yielded values of 12.1 h, 3.6 h and 3.7 h, respectively, indicating a possible functional correlation of RNA-binding and phosphorylation. This assumption was confirmed by studies of in vitro phosphorylation using purified SS-B/La protein and purified casein kinase type II as a model system. A high degree of phosphorylation of the SS-B/La protein (molecular mass 49 kDa) substantially diminished its binding capacity for poly[3H]U. However, binding of human autoantibodies against SS-B/La antigen increases 2-fold with increased SS-B/La phosphorylation. Complete phosphorylation in vitro led to partial molecular transformation, yielding an antigenically cross-reacting component with an apparent molecular mass of 51 kDa which could not be detected during in vivo phosphorylation.
mesh_terms: D001323:Autoantibodies; D001324:Autoantigens; D001327:Autoimmune Diseases / Q000276:immunology / Q000378:metabolism; D047388:Casein Kinases; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D010766:Phosphorylation; D011072:Poly U / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D012261:Ribonucleoproteins; D000097585:SS-B Antigen
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D047388:Casein Kinases; D011072:Poly U; D011494:Protein Kinases; D012313:RNA; D012261:Ribonucleoproteins; D000097585:SS-B Antigen