title: The crystal and molecular structures of a cathepsin K:chondroitin sulfate complex.
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 A. 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, K(d), of about 10 nM was determined for the interaction between cathepsin K and C4-S.
authors.affiliation: Mount Sinai School of Medicine, Department of Human Genetics, New York, NY 10029, USA.
authors.forename: Zhenqiang
authors.initials: Z
authors.lastname: Li
authors.forename: Martin
authors.initials: M
authors.lastname: Kienetz
authors.forename: Maia M
authors.initials: MM
authors.lastname: Cherney
authors.forename: Michael N G
authors.initials: MN
authors.lastname: James
authors.forename: Dieter
authors.initials: D
authors.lastname: Brömme
mesh_terms: D001665:Binding Sites; D001862:Bone Resorption / Q000201:enzymology; D002118:Calcium / Q000378:metabolism; D002236:Carbohydrate Conformation; D056657:Cathepsin K; D002403:Cathepsins / Q000737:chemistry* / Q000378:metabolism; D002809:Chondroitin Sulfates / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D006801:Humans; D046911:Macromolecular Substances / Q000737:chemistry; D008958:Models, Molecular; D010010:Osteoclasts / Q000201:enzymology; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence
chemical_list: D046911:Macromolecular Substances; D002809:Chondroitin Sulfates; D002403:Cathepsins; C534130:CTSK protein, human; D056657:Cathepsin K; D002118:Calcium