Nucleotide sequences of immunoglobulin heavy and light chain V-regions from a monoclonal autoantibody specific for a unique set of small nuclear ribonucleoprotein complexes

Structure-function correlates of autoantibodies to nucleic acids. Lessons from immunochemical, genetic and structural studies

Nucleic acid binding autoantibodies are the hallmark of the human autoimmune disease, systemic lupus erythematosus (SLE) and are also prevalent in mouse models of this disease. The immunologic stimuli for the production of these antibodies as well as their pathogenic mechanisms are not well understood. However, extensive immunochemical and genetic studies, together with initial crystallographic analysis and computer modeling, have suggested several structure-function correlates which will form the basis for future research. The anti-DNA and anti-RNA autoantibodies comprise a continuous spectrum of specificities in which a delicate balance exists between the binding to the sugar-phosphate backbone and the interactions with the heterocyclic bases of the nucleic acid. Prominent in these interactions are the products of specific V-region immunoglobulin genes, some of which appear to be uniquely suitable for nucleic acid binding. Other structural elements encoded by D minigenes, N sequences and somatic mutations, help to increase the affinity of the binding interaction, and may also increase the repertoire of nucleic acid binding antibodies by combining with a relatively large number of additional V-gene products. Initial crystallographic analyses of anti-DNA antibodies indicate some fundamental differences in the structure and shape of ssDNA and dsDNA antibody combining sites. However, they also suggest a considerable degree of flexibility of both antibody and antigen, which is induced by their binding interaction.

Molecular and structural analysis of nuclear localizing anti-DNA lupus antibodies

To determine the structure of three nuclear localizing lupus anti-DNA immunoglobulins (Igs) and to search for clues to mechanisms of cellular and/or nuclear access, their H- and L-chain variable region sequences were determined and subjected to three-dimensional modeling. Although the results indicate heterogeneity in their primary structures, the H chains are encoded by 3 members of the J558 VH gene family with a common tertiary conformation that is not shared by a J558-encoded nonnuclear localizing anti-DNA control Ig. Furthermore, at least two of the Igs share a conformational motif in the H-chain CDR3, and all three Igs contain multiple positively charged amino acids in their CDRs, resembling nuclear localization signals that direct protein nuclear import. Notably, each VH and VK gene is also found recurrently among previously described autoantibodies. Molecular analysis further indicates that both germline-encoded and significantly mutated V genes can generate nuclear localizing anti-DNA Ig.