Cysteine protease. May have an important role in corneal physiology. The recombinant enzyme hydrolyzes proteins (serum albumin, collagen) and synthetic substrates (Z-Phe-Arg-NHMec > Z-Leu-Arg-NHMec > Z-Val-Arg-NHMec). Inhibited by CST6. Predominantly expressed in the thymus and testis. Also expressed in corneal epithelium, and to a lesser extent in conjunctival epithelium and skin. Belongs to the peptidase C1 family.