title: The crystal structure of human procathepsin K.
abstract: Cathepsin K is a cysteine protease present in human osteoclasts that plays an important role in bone resorption. Cathepsin K is synthesized as an inactive proenzyme and activated under conditions of low pH. Autoproteolytic processing of the N-terminal 99 amino acid propeptide produces the active, mature form of cathepsin K. It is presumed that the activation of procathepsin K in vivo occurs in the bone resorption pit, which has a low-pH environment. We have determined the structure of human procathepsin K at 2.8 A resolution. The structure of the mature enzyme domain within procathepsin K is virtually identical to that of mature cathepsin K. The fold of the propeptide of procathepsin K is similar to that observed in procathepsins B and L despite differences in length and sequence. A portion of the propeptide occupies the active site cleft of cathepsin K. Hydrophobic interactions, salt bridges, and hydrogen-bonding interactions are observed in the structure of the propeptide and between the propeptide and the mature enzyme of procathepsin K. These interactions suggest an explanation for the stability of the proenzyme. The structure of procathepsin K contributes to an understanding of the molecular basis of inhibition by the propeptide portion of the molecule and activation of this important member of the cysteine protease family.
authors.affiliation: Department of Structural Biology, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: LaLonde
authors.forename: B
authors.initials: B
authors.lastname: Zhao
authors.forename: C A
authors.initials: CA
authors.lastname: Janson
authors.forename: K J
authors.initials: KJ
authors.lastname: D'Alessio
authors.forename: M S
authors.initials: MS
authors.lastname: McQueney
authors.forename: M J
authors.initials: MJ
authors.lastname: Orsini
authors.forename: C M
authors.initials: CM
authors.lastname: Debouck
authors.forename: W W
authors.initials: WW
authors.lastname: Smith
mesh_terms: D001665:Binding Sites; D002401:Cathepsin B / Q000737:chemistry; D056657:Cathepsin K; D056668:Cathepsin L; D002403:Cathepsins / Q000037:antagonists & inhibitors / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry; D004792:Enzyme Precursors / Q000737:chemistry*; D006801:Humans; D006868:Hydrolysis; D046911:Macromolecular Substances; D010446:Peptide Fragments / Q000737:chemistry; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals / Q000737:chemistry; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
chemical_list: D004791:Enzyme Inhibitors; D004792:Enzyme Precursors; D046911:Macromolecular Substances; D010446:Peptide Fragments; D021382:Protein Sorting Signals; D002403:Cathepsins; C057832:procathepsin B; C063905:procathepsin L; D002401:Cathepsin B; D056668:Cathepsin L; C534130:CTSK protein, human; D056657:Cathepsin K