Cathepsin V (also known as Cathepsin L2 and U) is a cysteine protease of the papain family (1). It is expressed as a proenzyme in lysosomes, which can be autocatalytically converted to the mature form at pH 4.0 (2). Cathepsin V shows high amino acid identity with Cathepsin L (77% for the proenzymes and 80% for the mature enzymes) (3). However, Cathepsin V is specifically expressed in the thymus, testis, and corneal epithelium whereas Cathepsin L is expressed throughout the body.
