Immunoreactivity between a monoclonal lupus autoantibody and the arginine/aspartic acid repeats within the U1-snRNP 70K autoantigen is conformationally restricted

Abstract

Immunoreactivity of the arginine/aspartic acid (RD) repeats of the 70K protein of U1 small nuclear ribonucleoprotein (snRNP) was determined to be conformationally dependent. The monoclonal autoantibody 2.73, isolated from a lupus-prone MRL/n mouse model, is reactive with the RD repeat regions of U1 snRNP 70K protein. Immunochemical analysis of the antigenic determinants with use of chemically synthesized peptides characterized the 2.73 epitope as the RD repeat [Pelsue, S., et al. (1993) Autoimmunity, 15, 231-236] Analysis by circular dichroism (CD) and nuclear magnetic resonance spectroscopy indicates conformational preferences in the immunoreactive peptides. Computer analyses of CD spectra obtained on the RD-containing peptides predict beta-turns and beta-sheet to be the preferred conformations of the RD repeats. This structure was also predicted by the Chou-Fasman algorithm. The RD repeat is believed to be a conserved structural motif; however, the biological function is still unclear. Immunological and biochemical analysis of autoimmune antibodies and their respective antigenic determinants has helped to characterize the possible mechanisms that lead to autoimmune diseases. This is the first report of a conformationally dependent, linear epitope of an autoantibody.

Conformational Analysis in a Multidimensional Energy Landscape: Study of an Arginylglutamate Repeat

“…It is clear that the peptide displays a high conformational diversity, adopting some β-like and helix-like structures, as well as other less canonical conformations. The predominance of β-like structures at pH 7 is in agreement with experimental results from circular dichroism studies of arginylaspartic acid repeats …”

“…With this in mind, we chose a peptide made of five arginylglutamic acid (RE) repeats, which will be referred to as RE5. There are several proteins containing repetitive motifs that alternate between basic and acidic residues in consecutive positions, some of which contain RE repeats. − The biological function of the RE repeats is not known, but experimental data indicates that it may be related to protein−protein interaction. − This peptide is essentially nonprotonable at pH 7 but highly protonable at both acidic and basic pH, thus being an interesting model to compare the performance of the method in both the nonprotonable and protonable cases. In the present work, we decided to study the neutral and acidic pH, performing the sampling of conformations using both standard MD and constant-pH MD simulations …”

Polar zippers: Their role in human disease

“…Most sera from systemic lupus erythematosis patients who react against the ribonucleoprotein recognize the RD epitope, which appears to dominate the immune reaction. One human and all mouse monoclonal antibodies specific against snRNP U1 70K react with the RD repeat (Pelsue & Agris, 1994a). The significance of the repeat for human systemic lupus erythematosis makes it tantalizing that so little is known about its structure and function.…”

IK: A novel cell mitosis regulator that contributes to carcinogenesis

“…13 In addition, some studies showed that RED repeats, which are mainly located in the nuclear proteins, are also well-known autoantigens in systemic lupus erythematosus (SLE). 14 In addition, autoantibodies from the serum of patients with SLE preferentially recognized beta-sheet structures in the repeats. 8 This further confirmed that the RED domain had a propensity to form stable beta-sheet structures.…”