Cathepsin L1 Protein, Human (HEK293)

Cathepsin L1 Protein, a thiol protease, emerges as a crucial player in the comprehensive degradation of proteins within lysosomes, impacting various cellular functions such as general protein turnover, antigen processing, and bone remodeling. Its involvement extends to the solubilization of cross-linked TG/thyroglobulin, facilitating the release of thyroid hormone thyroxine (T4) through limited proteolysis in the thyroid follicle lumen. Furthermore, Cathepsin L1 catalyzes the processing of prohormone proenkephalin into the active enkephalin peptide neurotransmitter within neuroendocrine chromaffin cells' secretory vesicles. In the thymus, it regulates CD4(+) T cell positive selection by generating MHCII-bound peptide ligands and mediates invariant chain processing in cortical thymic epithelial cells. Operating as a major elastin-degrading enzyme at neutral pH, Cathepsin L1 accumulates in the extracellular space of antigen-presenting cells, modulating the degradation of the extracellular matrix during inflammation. Additionally, its secreted form contributes to endostatin generation from COL18A1. Beyond its enzymatic roles, Cathepsin L1 is indispensable for cardiac morphology and function, as well as hair follicle morphogenesis, cycling, and epidermal differentiation. Moreover, it plays a vital role in maximizing steroidogenesis stimulated by TIMP1. In the context of microbial infection, especially in cells lacking TMPRSS2 expression, Cathepsin L1 facilitates the entry of human coronaviruses, such as SARS-CoV and SARS-CoV-2, through a slow acid-activated route by proteolysis of coronavirus spike (S) glycoproteins in lysosomes. This activity underscores its significance in host cell infection by these viruses.