Scheme of HNE. Exon boundaries of the neutrophil elastase sequence, including the amino-terminal signal, the propeptide, and the carboxy-terminal tail. ▧, predicted, hypothetical transmembrane domains¹² ; ▪ hypothetical tyrosine-based sorting signal; □, locations of 3 residues forming the catalytic site (His-41, Asp-88, Ser-173); □ locations of the Asn that are N-glycosylated (Asn-95, Asn-144); ▪ mutations analyzed in the present study and causing SCN; and • mutations causing SCN or CyN.