Schematic diagram of the PR3 molecule. The light and dark gray bars represent the amino-terminal signal peptide and activation dipeptide, respectively. The mature enzyme is represented by the white bar, and the carboxy-terminal peptide extension is represented by the black bar. The cysteine residues forming the four disulfide bonds (horizontal black lines) are shown as circled residues. The asparagine residues at positions 102 and 147 represent two potential glycosylation sites. The histidine-44, aspartic acid-91, and serine-176 residues make up the active site. The single-letter code for amino acid residues is used. Amino acids are numbered consecutively starting with the first residue of the mature enzyme [20*]. The diagram is not drawn to scale.