Napsin A is an aspartic proteinase that belongs to the peptidase A1 family and plays a role in pneumocyte surfactant processing. It is a 420-amino acid polypeptide consisting of a 24-residue signal peptide, a 40-amino acid propart, the mature enzyme of 336 amino acids, and a C-terminal extension of 18 residues. The mature Napsin A protein contains 3 predicted disulfide bonds, 3 potential N-linked oligosaccharide attachment sites, an RGD motif, a recognition motif for integrin binding, in the