A hydrophobic patch on proteinase 3, the target of autoantibodies in Wegener's granulomatosis, mediates membrane binding via NB1 receptors

Abstract

Proteinase 3 (PR3), the target antigen of antineutrophil cytoplasmic antibodies which are found in patients with Wegener's granulomatosis, is a neutrophil serine protease localized within cytoplasmic granules. A small fraction of it is translocated to the plasma membrane of neutrophils after cytokine priming. Recently, the human neutrophil antigen NB1 was identified as a specific neutrophil cell surface receptor of PR3. We hypothesized that the unique hydrophobic cluster of PR3 that is not present in other PR3 homologs accounts for its binding to the NB1 receptor expressed on the cellular surface of NB1 expressing cells. Instead of generating and testing various artificial human PR3 mutants, we cloned and expressed the very closely related gibbon (Hylobates pileatus) PR3 homolog which did not bind to the human NB1 receptor. Moreover, a human‐gibbon hybrid constructed from the N‐ and C‐terminal half of the human and gibbon PR3, respectively, did also not interact with human NB1. The C‐terminal half of gibbon PR3 differs only by 9 residues from human PR3, among which four closely spaced hydrophobic residues are substituted in a non conservative manner (Phe166Leu, Trp218Arg, Gly219Ala, Leu223His). The NB1 bound PR3 was active and was rapidly cleared from the surface by alpha‐1‐protease inhibitor (a1‐PI).Deutsche Forschungsgemeinschaft (SFB 571)