Molecular cloning of a novel mouse aspartic protease-like protein that is expressed abundantly in the kidney

By use of the signal sequence trap method, we isolated a cDNA encoding a novel aspartic protease-like protein from the mouse kidney, and termed it 'kidney-derived aspartic protease-like protein (KAP).' The protein, a 419-amino-acid polypeptide with a 16-amino-acid signal sequence, had 47% identity with mouse cathepsin D, and its overall structure was closely related to known aspartic proteases, Northern blot analysis revealed that KAP mRNA is expressed at the highest level in the kidney, at a moderate level in the lung, and at low levels in the spleen and adipose tissue, In situ hybridization analysis demonstrated that the mRNA is expressed abundantly in the proximal straight tubule and slightly, but significantly, in the proximal convoluted tubule in the kidney, This intra-renal distribution differs distinctly from those of previously reported proteases such as cathepsins B, D, and H.