The crystal and molecular structures of a cathepsin K:chondroitin sulfate complex |
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Authors: | Li Zhenqiang Kienetz Martin Cherney Maia M James Michael N G Brömme Dieter |
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Institution: | 1 Mount Sinai School of Medicine, Department of Human Genetics, New York, NY 10029, USA 2 University of British Columbia, Faculty of Dentistry, Vancouver, Canada V6T 1Z3 3 Group in Protein Structure and Function, Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7 |
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Abstract: | Cathepsin K is the major collagenolytic enzyme produced by bone-resorbing osteoclasts. We showed earlier that the unique triple-helical collagen-degrading activity of cathepsin K depends on the formation of complexes with bone-or cartilage-resident glycosaminoglycans, such as chondroitin 4-sulfate (C4-S). Here, we describe the crystal structure of a 1:n complex of cathepsin K:C4-S inhibited by E64 at a resolution of 1.8 Å. The overall structure reveals an unusual “beads-on-a-string”-like organization. Multiple cathepsin K molecules bind specifically to a single cosine curve-shaped strand of C4-S with each cathepsin K molecule interacting with three disaccharide residues of C4-S. One of the more important sets of interactions comes from a single turn of helix close to the N terminus of the proteinase containing a basic amino acid triplet (Arg8-Lys9-Lys10) that forms multiple hydrogen bonds either to the caboxylate or to the 4-sulfate groups of C4-S. Altogether, the binding sites with C4-S are located in the R-domain of cathepsin K and are distant from its active site. This explains why the general proteolytic activity of cathepsin K is not affected by the binding of chondroitin sulfate. Biochemical analyses of cathepsin K and C4-S mixtures support the presence of a 1:n complex in solution; a dissociation constant, Kd, of about 10 nM was determined for the interaction between cathepsin K and C4-S. |
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Keywords: | HS heparin sulfate C4-S chondroitin 4-sulfate ASG 2&prime -deoxy-2&prime d-galactose-4-sulfate" target="_blank">-acetamido-β-d-galactose-4-sulfate GCU d-glucuronic acid" target="_blank">β-d-glucuronic acid E-64 L-3-carboxy-trans-2 3-epoxypropionyl-leucylamido-(4-guanidino)butane Z carbobenzoxy MCA 7-amino-4-methylcoumarin DCG-04 biotin and tyrosine-modified E-64 derivative |
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