Cathepsin L1 is a member of the Peptidase C1 (
cathepsin)
MEROPS family, which plays an important role in diverse processes including normal lysosome mediated protein turnover, antigen and proprotein processing, and apoptosis. Its substrates include
collagen and
elastin, as well as
alpha-1 protease inhibitor, a major controlling element of
neutrophil elastase activity. The encoded protein has been implicated in several pathologic processes, including
myofibril necrosis in myopathies and in
myocardial ischemia, and in the
renal tubular response to
proteinuria. This protein, which is a member of the peptidase C1 family, is a dimer composed of
disulfide-linked heavy and light chains, both produced from a single protein precursor. At least two transcript variants encoding the same protein have been found for this gene.
Hydroxychloroquine inhibits the action of cathepsin L in endolysosomes, but because cathepsin L cleavage is minor compared to TMPRSS2 cleavage, hydroxychloroquine does little to inhibit SARS-CoV-2 infection. Cathepsin L and other cysteine cathepsins tend to be secreted by
macrophages and other tissue-invading immune cells when causing pathological inflammation. ==Interactions==