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Cathepsin X binds to cell surface heparan sulfate proteoglycans
Fábio D Nascimento1, Claudia C A Rizzi, Iseli L Nantes
1Departamento de Bioquímica, Universidade Federal de São Paulo, Escola Paulista de Medicina, São Paulo, Brazil.
Archives of Biochemistry and Biophysics
|March 31, 2005
Summary
Heparan sulfate proteoglycans regulate cathepsin X activity and cellular uptake. This interaction influences enzyme function and cell trafficking, highlighting a key mechanism for controlling cathepsin X activity.
Area of Science:
- Biochemistry
- Cell Biology
- Enzymology
Background:
- Glycosaminoglycans regulate papain-like cathepsins' activity, stability, and activation.
- Cathepsin X interaction with heparin was previously suggested.
Purpose of the Study:
- To investigate the specific interaction between cathepsin X and heparan sulfate proteoglycans.
- To determine the functional consequences of this interaction on enzyme activity and cellular uptake.
Main Methods:
- Affinity chromatography using heparin-Sepharose.
- Far UV-circular dichroism spectroscopy.
- Enzyme kinetics assays.
- Flow cytometry and confocal microscopy in CHO cells.
Main Results:
- Cathepsin X specifically binds to heparin and heparan sulfate, but not other glycosaminoglycans.
- Heparin binding induces conformational changes in cathepsin X, increasing its catalytic activity (kcat) and altering enzyme-substrate interaction.
- Cathepsin X binds to cell surface heparan sulfate proteoglycans and is endocytosed by wild-type CHO cells, but not by GAG-deficient cells.
Conclusions:
- Heparan sulfate proteoglycans specifically regulate cathepsin X activity and cellular trafficking.
- This interaction mediates the endocytosis of cathepsin X by cells expressing heparan sulfate proteoglycans.
- Heparan sulfate proteoglycans play a crucial role in controlling the cellular localization and enzymatic function of cathepsin X.