MOLECULAR STRUCTURE OF AUTOANTIGENS

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Anti-Sm antibodies are intrinsically associated with the rheumatic disease systemic lupus erythematosus (SLE). This is a chronic inflammatory disease affecting a significant proportion of the female population in this country. The proposed studies were intended to model the molecular properties that define the Sm polypeptides as autoantibody targets in SLE. This information is a necessary prelude to the development of the next generation of clinical assays. Such assays will be designed to have a breadth and a level of sensitivity that should detect any pathologically significant anti-Sm antibodies present in an individual's serum. In delineating discrete Sm immunoreactive domains, the initial emphasis will be on two of the major Sm antigens, Sm-D (D1) and Sm-B'/(B3). These autoantigens will be characterized as to both continuous and discontinuous epitopes. A new approach is proposed to look at the individual Sm antigens as a whole, using the technique of random PCR mutagenesis to target individual amino acid residues - and ultimately to generate a topographical map of residues which, when changed, result in a loss of antigenicity. In light of preliminary evidence that suggests the preponderance of Sm-D1 epitopes are conformational, structural studies will be implemented to visualize the folded structure. The specific experimental approach (NMR shift correlation spectra studies) was chosen both for its simplicity and for its applicability to the study of antigen-antibody contact sites. All these experiments will generate information to direct the expression of recombinant polypeptides that closely mimic the bona fide antigens. These recombinant proteins will serve as the basis for the development of new, selective assays for the anti-Sm antibodies that are diagnostic/prognostic for SLE. Similar studies will encompass the newly described Sm-D2 and Sm-D3 antigens to extend the profile of the major Sm polypeptides. Finally, the nature of the Sm polypeptides cross- reactivities will be explored with particular attention to the intra- group relationships (within the D family of proteins) and the inter-group relationships (of B versus D). The Sm polypeptides, by virtue of their number and diversity, and their association with a prominent rheumatic disease, provide a unique model system. All of these studies should draw a multi-dimensional composite of this major autoantigen family, which information is basic to any understanding of the etiology of SLE and its attendant autoantibody production.