Human napsin A: expression, immunochemical detection, and tissue localization

A novel aspartic proteinase, called napsin, has recently been found in human and mouse. Due to high similarity with cathepsin D a structural model of human napsin A could be built. Based on this model a potential epitope SFYLNRDPEEPDGGE has been identified, which was used to immunize rabbits. The resulting antibody was employed in monitoring the expression of recombinant human napsin A in HEK293 cell line. Western blot analysis confirmed the specificity of the antibody and showed that human napsin A is expressed as a single chain protein with the molecular weight of approximately 38 kDa. Immunohistochemical studies revealed high expression levels of napsin A in human kidney and lung but low expression in spleen.