Alternative titles; symbols
HGNC Approved Gene Symbol: NAPSA
Cytogenetic location: 19q13.33 Genomic coordinates (GRCh38) : 19:50,358,477-50,365,639 (from NCBI)
Aspartic proteinases belong to the class of endopeptidases. They contain 2 homologous domains, each of which contains a structural feature known as the psi loop. By EST database searching for sequences homologous to the aspartic proteinase cathepsin E (116890), Tatnell et al. (1998) cloned a novel aspartic proteinase, which they called napsin A (NAPA). The NAPA cDNA encodes a deduced 420-amino acid polypeptide consisting of 4 regions: 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 protein contains 3 predicted disulfide bonds and 3 potential N-linked oligosaccharide attachment sites. It also contains an RGD motif, a recognition motif for integrin binding, in the C terminus, immediately before a 4-amino acid insert that is unique among aspartic proteinases. Human napsin A shares 72.6% amino acid identity with the mouse homolog. Northern blot analysis detected expression of a 1.6-kb transcript predominantly in lung and at lower levels in kidney, spleen, and leukocytes. Immunohistochemical studies by Schauer-Vukasinovic et al. (1999) revealed high expression of napsin A in kidney and lung but low expression in spleen.
Chuman et al. (1999) cloned NAPA from an adenocarcinoma. They detected expression of NAPA in type II alveolar cells of the lung. They noted that since NAPA is expressed in greater than 90% of primary lung adenocarcinomas but not in other malignancies, it is a potential marker for this form of carcinoma.
Tatnell et al. (1998) isolated a related gene, which they called napsin B, that shares 86% amino acid identity with NAPA. Unlike NAPA, napsin B is only expressed in spleen. Because napsin B cDNA lacks an in-frame stop codon and contains a polymorphism at the Hydrophobic-Hydrophobic-gly region that will render the enzyme inactive, the authors suggested that it is a transcribed pseudogene.
Chuman, Y., Bergman, A.-C., Ueno, T., Saito, S., Sakaguchi, K., Alaiya, A. A., Franzen, B., Bergman, T., Arnott, D., Auer, G., Appella, E., Jornvall, H., Linder, S. Napsin A, a member of the aspartic protease family is abundantly expressed in normal lung and kidney tissue and is expressed in lung adenocarcinomas. FEBS Lett. 462: 129-134, 1999. [PubMed: 10580105] [Full Text: https://doi.org/10.1016/s0014-5793(99)01493-3]
Schauer-Vukasinovic, V., Bur, D., Kling, D., Gruninger, F., Giller, T. Human napsin A: expression, immunochemical detection, and tissue localization. FEBS Lett. 462: 135-139, 1999. [PubMed: 10580106] [Full Text: https://doi.org/10.1016/s0014-5793(99)01458-1]
Tatnell, P. J., Powell, D. J., Hill, J., Smith, T. S., Tew, D. G., Kay, J. Napsins: new human aspartic proteinases. Distinction between two closely related genes. FEBS Lett. 441: 43-48, 1998. [PubMed: 9877162] [Full Text: https://doi.org/10.1016/s0014-5793(98)01522-1]