title: Human proteoglycan testican-1 inhibits the lysosomal cysteine protease cathepsin L.
abstract: Testican-1, a secreted proteoglycan enriched in brain, has a single thyropin domain that is highly homologous to domains previously shown to inhibit cysteine proteases. We demonstrate that purified recombinant human testican-1 is a strong competitive inhibitor of the lysosomal cysteine protease, cathepsin L, with a Ki of 0.7 nM, but it does not inhibit the structurally related lysosomal cysteine protease cathepsin B. Testican-1 inhibition of cathepsin L is independent of its chondroitin sulfate chains and is effective at both pH 5.5 and 7.2. At neutral pH, testican-1 also stabilizes cathepsin L, slowing pH-induced denaturation and allowing the protease to remain active longer, although the rate of proteolysis is reduced. These data indicate that testican-1 is capable of modulating cathepsin L activity both in intracellular vesicles and in the extracellular milieu.
mesh_terms: D000595:Amino Acid Sequence; D002401:Cathepsin B / Q000037:antagonists & inhibitors; D056668:Cathepsin L; D002403:Cathepsins / Q000037:antagonists & inhibitors*; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D004795:Enzyme Stability / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000201:enzymology*; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D011509:Proteoglycans / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid
chemical_list: D015853:Cysteine Proteinase Inhibitors; D011509:Proteoglycans; D011994:Recombinant Proteins; C504369:SPOCK1 protein, human; D002403:Cathepsins; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; C534281:CTSL protein, human; D056668:Cathepsin L