THE CRYSTAL-STRUCTURE OF PR3, A NEUTROPHIL SERINE PROTEINASE ANTIGEN OF WEGENERS GRANULOMATOSIS ANTIBODIES

The crystal structure of PR3, a serine proteinase from the azurophilic granules of human polymorphonuclear neutrophils, has been solved by m olecular replacement using the human leukocyte elastase structure. The PR3 structure has been refined to an R-factor (=Sigma parallel to F-o \-\F-c parallel to/Sigma\F-o\) of 0.201 for all data in the range of 1 0.0 to 2.2 Angstrom resolution. The enzyme was crystallized in space g roup P2(1) with four molecules in the asymmetric unit (V-m congruent t o 2.6 Angstrom/Da). The overall fold consists of two domains of beta-b arrel structures typical of the chymotrypsin family of serine proteina ses. In general, the substrate binding sites, S4 to S3', are more pola r than comparable sites in the related proteinase, human leukocyte ela stase. The experimentally observed preference of PR3 for small aliphat ic residues at the P1 position of a substrate is explained by the Val to Ile substitution at position 190 when compared to the elastase stru cture. The substitution of Ala by Asp at position 213 at the back of S 1 should not affect its specificity greatly, as the Asp side-chain poi nts back into the interior of the protein. The PR3 structure includes a disaccharide unit (N-linked 2-acetamido-2-deoxy-beta-D-glucopyranose and 1,6-linked alpha-L-fucopyranose) covalently attached to Asn159. T he linear antigenic sites of PR3 reported to react with Wegener's gran ulomatosis autoantibodies occur in regions of the three-dimensional st ructure that may implicate the inactive pro-form of the enzyme in the pathogenesis of the disease. (C) 1996 Academic Press Limited