4oem | pdb_00004oem
Crystal structure of Cathepsin C in complex with dipeptide substrates
Structural highlights
Disease[CATC_HUMAN] Defects in CTSC are a cause of Papillon-Lefevre syndrome (PLS) [MIM:245000]; also known as keratosis palmoplantaris with periodontopathia. PLS is an autosomal recessive disorder characterized by palmoplantar keratosis and severe periodontitis affecting deciduous and permanent dentitions and resulting in premature tooth loss. The palmoplantar keratotic phenotype vary from mild psoriasiform scaly skin to overt hyperkeratosis. Keratosis also affects other sites such as elbows and knees.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] Defects in CTSC are a cause of Haim-Munk syndrome (HMS) [MIM:245010]; also known as keratosis palmoplantaris with periodontopathia and onychogryposis or Cochin Jewish disorder. HMS is an autosomal recessive disorder characterized by palmoplantar keratosis, onychogryphosis and periodontitis. Additional features are pes planus, arachnodactyly, and acroosteolysis.[13] Defects in CTSC are a cause of aggressive periodontititis type 1 (AP1) [MIM:170650]; also known as juvenile periodontitis (JPD) and prepubertal periodontitis (PPP). AP1 is characterized by severe and protracted gingival infections, leading to tooth loss. AP1 inheritance is autosomal dominant.[14] [15] Function[CATC_HUMAN] Thiol protease. Has dipeptidylpeptidase activity. Active against a broad range of dipeptide substrates composed of both polar and hydrophobic amino acids. Proline cannot occupy the P1 position and arginine cannot occupy the P2 position of the substrate. Can act as both an exopeptidase and endopeptidase. Activates serine proteases such as elastase, cathepsin G and granzymes A and B. Can also activate neuraminidase and factor XIII.[16] Publication Abstract from PubMedWe examined the cathepsin C-catalyzed hydrolysis of dipeptide substrates of the form Yaa-Xaa-AMC, using steady-state and pre-steady-state kinetic methods. The substrates group into three kinetic profiles based upon the broad range observed for k(cat)/K(a) and k(cat) values, pre-steady-state time courses, and solvent kinetic isotope effects (sKIEs). The dipeptide substrate Gly-Arg-AMC displayed large values for k(cat)/K(a) (1.6 +/- 0.09 muM(-1) s(-1)) and k(cat) (255 +/- 6 s(-1)), an inverse sKIE on k(cat)/K(a) ((D)(k(cat)/K(a)) = 0.6 +/- 0.15), a modest, normal sKIE on k(cat) ((D)k(cat) = 1.6 +/- 0.2), and immeasurable pre-steady-state kinetics, indicating an extremely fast pre-steady-state rate (>400 s(-1)). (Errors on fitted values are omitted in the text for clarity but may be found in Table 2.) These results conformed to a kinetic model where the acylation (k(ac)) and deacylation (k(dac)) half-reactions are very fast and similar in value. The second substrate type, Gly-Tyr-AMC and Ser-Tyr-AMC, the latter the subject of a comprehensive kinetic study (Schneck et al. (2008) Biochemistry 47, 8697-8710), were found to be less active substrates compared to Gly-Arg-AMC, with respective k(cat)/K(a) values of 0.49 +/- 0.07 muM(-1 )s(-1) and 5.3 +/- 0.5 muM(-1 )s(-1), and k(cat) values of 28 +/- 1 s(-1) and 25 +/- 0.5 s(-1). Solvent kinetic isotope effects for Ser-Tyr-AMC were found to be inverse for k(cat)/K(a) ((D)(k(cat)/K(a)) = 0.74 +/- 0.05) and normal for k(cat) ((D)k(cat) = 2.3 +/- 0.1) but unlike Gly-Arg-AMC, pre-steady-state kinetics of Gly-Tyr-AMC and Ser-Tyr-AMC were measurable and characterized by a single-exponential burst, with fast transient rates (490 s(-1) and 390 s(-1), respectively), from which it was determined that k(ac) >> k(dac) approximately k(cat). The third substrate type, Gly-Ile-AMC, gave very low values of k(cat)/K(a) (0.0015 +/- 0.0001 muM(-1) s(-1)) and k(cat) (0.33 +/- 0.02 s(-1)), no sKIEs, ((D)(k(cat)/K(a)) = 1.05 +/- 0.5 and (D)k(cat) = 1.06 +/- 0.4), and pre-steady-state kinetics exhibited a discernible, but negligible, transient phase. For this third class of substrate, kinetic modeling was consistent with a mechanism in which k(dac) > k(ac) approximately k(cat), and for which an isotope-insensitive step in the acylation half-reaction is the slowest. The combined results of these studies suggested that the identity of the amino acid at the P(1) position of the substrate is the main determinant of catalysis. On the basis of these kinetic data, together with crystallographic studies of substrate analogues and molecular dynamics analysis with models of acyl-enzyme intermediates, we present a catalytic model derived from the relative rates of the acylation vs deacylation half-reactions of cathepsin C. The chemical steps of catalysis are proposed to be dependent upon the conformational freedom of the amino acid substituents for optimal alignment for thiolation (acylation) or hydrolysis (deacylation). These studies suggest ideas for inhibitor design for papain-family cysteine proteases and strategies to progress drug discovery for other classes of disease-relevant cysteine proteases. The amino-acid substituents of dipeptide substrates of cathepsin C can determine the rate-limiting steps of catalysis.,Rubach JK, Cui G, Schneck JL, Taylor AN, Zhao B, Smallwood A, Nevins N, Wisnoski D, Thrall SH, Meek TD Biochemistry. 2012 Sep 25;51(38):7551-68. doi: 10.1021/bi300719b. Epub 2012 Sep, 13. PMID:22928782[17] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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