Amino acid sequence of porcine spleen cathepsin D.

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Abstract
The amino acid sequence of porcine spleen cathepsin D H chain was determined, and, hence, the complete structure of this enzyme is not known. The sequence of H chain was constructed by aligning the structures of peptides generated by cyanogen bromide, trypsin and endoproteinase Lys C cleavages. The structure of the L chain was previously published. The cathepsin D molecule contains 339 amino acid residues in 2 polypeptide chains: a 97-residue L chain and a 242-residue H chain, with a combined MW of 36,779 (without carbohydrate). There are 2 carbohydrate units linked to asparagine residues 70 and 192. The disulfide bond arrangement in cathepsin D is probably similar to that of pepsin, because the positions of 6 half-cystine residues are conserved. The active site aspartyl residues, corresponding to aspartic acid-32 and -215 of pepsin, are located at residues 33 and 224 in the cathepsin D molecule. The amino acid sequence around these aspartyl residues is strongly conserved. Cathepsin D shows a strong homology with other acid proteases. When the sequence of cathepsin D, renin and pepsin are aligned, 32.7% of the residues are identical. The homology is observed throughout the length of the molecules, indicating that 3-dimensional structures of all 3 molecules are similar.