Cathepsin A

Cathepsin A/lyososomal carboxypeptidase A is a member of the serine carboxypeptidase family. Cathepsin A is a multifunctional enzyme that expresses deaminidase and esterase activities at neutral pH and carboxypeptidase activity at acidic pH. Also known as protective protein, its association with βgalactosidase (βgal) and neuraminidase is essential for βgal stability and neuraminidase activation in the lysosomes. Inherited deficiency of Cathepsin A causes the lysosomal storage disorder galactosialidosis, characterized by a combined secondary deficiency of βgal and neuraminidase. Cathepsin A is capable of hydrolyzing a variety of bioactive peptide hormones including tachykinins, indicating that extralysosomal Cathepsin A plays a role in regulation of functions of these molecules. Cathepsin A is synthesized as a singlechain precursor and processed into heavy (32 kDa) and light (20 kDa) chains, which are linked by disulfide bonds.