Cathepsin L1 (CTSL1)

Cathepsin L1 is a lysosomal cysteine protease primarily responsible for intracellular protein degradation and turnover, functioning as part of the Peptidase C1 (cathepsin) family. It is involved in critical processes such as antigen presentation, apoptosis, cell cycle progression (by processing transcription factors), and extracellular matrix breakdown, contributing to tissue remodeling and immunological responses. Cathepsin L1 also plays distinctive roles in pathological conditions like cancer, inflammation, and viral infection, and is secreted by immune cells in inflammatory states. It is a dimer of disulfide-linked chains, formed after cleavage from a precursor protein, and exhibits highly conserved active-site architecture essential for catalytic activity. Elevated levels and activity are associated with several disease states, and inhibitors have been explored as possible therapeutics, though safety and specificity remain notable therapeutic challenges.

Other names

Cathepsin LCTSLCathepsin L-typeProcathepsin LPeptidase C1

Inhibitors block the active site cysteine, preventing proteolysis. Lysosomal alkalization (by agents such as hydroxychloroquine) reduces cathepsin L activation.