Human proteoglycan testican-1 inhibits the lysosomal cysteine protease cathepsin L.
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.[1]References
- Human proteoglycan testican-1 inhibits the lysosomal cysteine protease cathepsin L. Bocock, J.P., Edgell, C.J., Marr, H.S., Erickson, A.H. Eur. J. Biochem. (2003) [Pubmed]
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