1. Department of Pathophysiology, University of Vienna, Austria
2. ^*Clinical Institute for Medical and Chemical Laboratory Diagnostics, University of Vienna, Austria
3. ^†Institute of Chemistry and Structural Biology, Karl-Franzens-University Graz, Austria

Correspondence: Rudolf Valenta, Molecular Immunopathology Group, Department of Pathophysiology, Vienna General Hospital, University of Vienna, Waehringer Guertel 18–20, A-1090 Vienna, Austria. Email: rudolf.valenta@akh-wien.ac.at

Received 26 April 2002; Revised 15 May 2002; Accepted 30 May 2002.

Abstract

The nascent polypeptide-associated complex is required for intracellular translocation of newly synthesized polypeptides in eukaryotic cells. It may also act as a transcriptional coactivator in humans and various eukaryotic organisms and binds to nucleic acids. Recently, we provided evidence that a component of nascent polypeptide-associated complex, -nascent polypeptide-associated complex, represents an IgE-reactive autoantigen for atopic dermatitis patients. By oligonucleotide screening we isolated a complete cDNA coding for a so far unknown -nascent polypeptide-associated complex isoform from a human epithelial cDNA library. Southern blot hybridization experiments provided further evidence that -nascent polypeptide-associated complex is encoded by a gene family. Recombinant -nascent polypeptide-associated complex was expressed in Escherichia coli as a soluble, His-tagged protein, and purified via nickel affinity chromatography. By circular dichroism analysis it is demonstrated that purified recombinant -nascent polypeptide-associated complex represents a folded protein of mixed -helical and -sheet conformation with unusual high thermal stability and remarkable refolding capacity. Complete recombinant -nascent polypeptide-associated complex (215 amino acids) and its 86 amino acid C-terminal fragment specifically bound IgE autoantibodies. Recombinant -nascent polypeptide-associated complex also inhibited IgE binding to natural -nascent polypeptide-associated complex, demonstrating the presence of common IgE epitopes between the recombinant and natural protein. Furthermore, recombinant -nascent polypeptide-associated complex induced specific lymphoproliferative responses in peripheral blood mononuclear cells of a sensitized atopic dermatitis patient. As has been proposed for environmental allergens it is possible that T cell responses to IgE-defined autoantigens may contribute to the chronic skin manifestations in atopic dermatitis.