Major Increase in Endopeptidase Activity of Human Cathepsin B upon Removal of Occluding Loop Contacts (original) (raw)

Biochemical characterization of human cathepsin X revealed that the enzyme is an exopeptidase, acting as carboxymonopeptidase or carboxydipeptidase

European Journal of Biochemistry, 2000

Cathepsin X, purified to homogeneity from human liver, is a single chain glycoprotein with a molecular mass of < 33 kDa and pI 5.1±5.3. Cathepsin X was inhibited by stefin A, cystatin C and chicken cystatin (K i 1.7±15.0 nm), but poorly or not at all by stefin B (K i . 250 nm) and l-kininogen, respectively. The enzyme was also inhibited by two specific synthetic cathepsin B inhibitors, CA-074 and GFG-semicarbazone. Cathepsin X was similar to cathepsin B and found to be a carboxypeptidase with preference for a positively charged Arg in P1 position. Contrary to the preference of cathepsin B, cathepsin X normally acts as a carboxymonopeptidase. However, the preference for Arg in the P1 position is so strong that cathepsin X cleaves substrates with Arg in antepenultimate position, acting also as a carboxydipeptidase. A large hydrophobic residue such as Trp is preferred in the P1 H position, although the enzyme cleaved all P1 H residues investigated (Trp, Phe, Ala, Arg, Pro). Cathepsin X also cleaved substrates with amide-blocked C-terminal carboxyl group with rates similar to those of the unblocked substrates. In contrast, no endopeptidase activity of cathepsin X could be detected on a series of o-aminobenzoic acid-peptidyl-N-[2,-dinitrophenyl]ethylenediamine substrates. Furthermore, the standard cysteine protease methylcoumarine amide substrates (k cat /K m < 5.0 Â 10 3 m 21´s21 ) were degraded < 25-fold less efficiently than the carboxypeptidase substrates (k cat /K m < 120.0 Â 10 3 m 21´s21 ).

Biochemical characterization of human cathepsin X revealed that the enzyme is an exopeptidase, acting as carboxymonopeptidase or carboxydipeptidase: Human cathepsin X

European Journal of Biochemistry, 2003

Cathepsin X, purified to homogeneity from human liver, is a single chain glycoprotein with a molecular mass of < 33 kDa and pI 5.1±5.3. Cathepsin X was inhibited by stefin A, cystatin C and chicken cystatin (K i 1.7±15.0 nm), but poorly or not at all by stefin B (K i . 250 nm) and l-kininogen, respectively. The enzyme was also inhibited by two specific synthetic cathepsin B inhibitors, CA-074 and GFG-semicarbazone. Cathepsin X was similar to cathepsin B and found to be a carboxypeptidase with preference for a positively charged Arg in P1 position. Contrary to the preference of cathepsin B, cathepsin X normally acts as a carboxymonopeptidase. However, the preference for Arg in the P1 position is so strong that cathepsin X cleaves substrates with Arg in antepenultimate position, acting also as a carboxydipeptidase. A large hydrophobic residue such as Trp is preferred in the P1 H position, although the enzyme cleaved all P1 H residues investigated (Trp, Phe, Ala, Arg, Pro). Cathepsin X also cleaved substrates with amide-blocked C-terminal carboxyl group with rates similar to those of the unblocked substrates. In contrast, no endopeptidase activity of cathepsin X could be detected on a series of o-aminobenzoic acid-peptidyl-N-[2,-dinitrophenyl]ethylenediamine substrates. Furthermore, the standard cysteine protease methylcoumarine amide substrates (k cat /K m < 5.0 Â 10 3 m 21´s21 ) were degraded < 25-fold less efficiently than the carboxypeptidase substrates (k cat /K m < 120.0 Â 10 3 m 21´s21 ).

Cathepsins X and B Can Be Differentiated through Their Respective Mono- and Dipeptidyl Carboxypeptidase Activities †

Biochemistry, 2001

Several new cysteine proteases of the papain family have been discovered in the past few years. To help in the assignment of physiological roles and in the design of specific inhibitors, a clear picture of the specificities of these enzymes is needed. One of these novel enzymes, cathepsin X, displays a unique specificity, cleaving single amino acid residues at the C-terminus of substrates very efficiently. In this study, the carboxypeptidase activities and substrate specificity of cathepsins X and B have been investigated in detail and compared. Using quenched fluorogenic substrates and HPLC measurements, it was shown that cathepsin X preferentially cleaves substrates through a monopeptidyl carboxypeptidase pathway, while cathepsin B displays a preference for the dipeptidyl pathway. The preference for one or the other pathway is about the same for both enzymes, i.e., approximately 2 orders of magnitude, a result supported by molecular modeling of enzyme-substrate complexes. Cleavage of a C-terminal dipeptide of a substrate by cathepsin X can become more important under conditions that preclude efficient monopeptidyl carboxypeptidase activity, e.g., nonoptimal interactions in subsites S(2)-S(1). These results confirm that cathepsin X is designed to function as a monopeptidyl carboxypeptidase. Contrary to a recent report [Klemencic, I., et al. (2000) Eur. J. Biochem. 267, 5404-5412], it is shown that cathepsins X and B do not share similar activity profiles, and that reagents are available to clearly distinguish the two enzymes. In particular, CA074 was found to inactivate cathepsin B at least 34000-fold more efficiently than cathepsin X. The insights obtained from this and previous studies have been used to produce an inhibitor designed to exploit the unique structural features responsible for the carboxypeptidase activity of cathepsin X. Although of moderate potency, this E-64 derivative is the first reported example of a cathepsin X-specific inhibitor.

Crystal structure of porcine cathepsin H determined at 2.1 å resolution: location of the mini-chain C-terminal carboxyl group defines cathepsin H aminopeptidase function

Structure, 1998

Background: Cathepsin H is a lysosomal cysteine protease, involved in intracellular protein degradation. It is the only known mono-aminopeptidase in the papain-like family and is reported to be involved in tumor metastasis. The cathepsin H structure was determined in order to investigate the structural basis for its aminopeptidase activity and thus to provide the basis for structure-based design of synthetic inhibitors. Results: The crystal structure of native porcine cathepsin H was determined at 2.1 Å resolution. The structure has the typical papain-family fold. The so-called mini-chain, the octapeptide EPQNCSAT, is attached via a disulfide bond to the body of the enzyme and bound in a narrowed active-site cleft, in the substratebinding direction. The mini-chain fills the region that in related enzymes comprises the non-primed substrate-binding sites from S2 backwards. Conclusions: The crystal structure of cathepsin H reveals that the mini-chain has a definitive role in substrate recognition and that carbohydrate residues attached to the body of the enzyme are involved in positioning the mini-chain in the active-site cleft. Modeling of a substrate into the active-site cleft suggests that the negatively charged carboxyl group of the C terminus of the mini-chain acts as an anchor for the positively charged N-terminal amino group of a substrate. The observed displacements of the residues within the active-site cleft from their equivalent positions in the papain-like endopeptidases suggest that they form the structural basis for the positioning of both the mini-chain and the substrate, resulting in exopeptidase activity.

Carboxy-monopeptidase substrate specificity of human cathepsin X

Biochemical and Biophysical Research Communications, 2005

Cathepsin X is a papain-like cysteine protease with restricted positional specificity, acting primarily as a carboxy-monopeptidase. We mapped the specificities at the S2, S1, and S1&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; subsites of human cathepsin X by systematically and independently substituting the P2, P1, and P1&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; positions of the carboxy-monopeptidase substrate Abz-FRF(4NO(2)) with natural amino acids. Human cathepsin X has broad S2, S1, and S1&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; specificities within two orders of magnitude in k(cat)/K(M), excluding proline that is not tolerated at these subsites. Glycine is not favored in S2, but is among the preferred residues in S1 and S1&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;, which highlights S2 as the affinity-determinant subsite. The presence of peculiar residues at several binding site positions (Asp76, His234, Asn75, and Glu72) does not translate into a markedly different sequence specificity profile relative to other human cathepsins. These findings suggest that a specific function of human cathepsin X is unlikely to result from sequence specificity, but rather from a combination of its unique positional specificity and the co-localization of enzyme and substrate in a specific cellular environment.

Expression and characterization of cathepsin P

Biochemical Journal, 2004

The mouse genome contains a family of clan C1A proteases that appear to be restricted to rodents within Eutherian (placental) mammals. mRNA analysis has shown that these genes are expressed exclusively in placenta. Sequence analysis predicts that the expressed proteins will be functional and consequently it was proposed that this family of proteases may have evolved to perform subspecialized functions of the closely related protease, cathepsin L, that is expressed in placental tissues of all mammalian species. In the present study, it was shown that cathepsin P can be expressed in Pichia pastoris as an inactive zymogen that can be activated with proteinase K, chymotrypsin or pancreatic elastase at neutral pH. Unlike other mammalian cathepsins, cathepsin P could also be autoactivated at neutral pH, but not at acidic pH. The activated enzyme was capable of hydrolysing peptidyl substrates and the protein substrates azocasein and transferrin, with optimal activity at pH 6.5-7.5. Little activity could be detected at pH 5.0 and below. Salts such as Na 2 SO 4 and hyaluronate stimulated the activity of the protease against peptidyl substrates. The properties of cathepsin P appear to be quite distinct from those of cathepsin L, indicating that the duplication that gave rise to cathepsin P has probably not yielded an enzyme that provides a subfunction of cathepsin L in rodents. It seems probable that cathepsin P has evolved to perform a function that is performed by an evolutionarily unrelated protease in other mammalian species.

Inhibition of cathepsin B by its propeptide: Use of overlapping peptides to identify a critical segment

FEBS Letters, 1996

Ten overlapping 15-mer peptides (peptidyl amides) spanning the proregion of rat cathepsin B (residues lp-60p) were constructed to identify minimal segments having inhibitory activity towards the mature enzyme, that could be used to develop a new generation of peptide-derived inhibitors specifically targeting the active site of the corresponding proteinase. Three synthetic peptides, containing the pentapeptide Leu-Cys-Gly-Thr-Val (residues 41p-45p) in their sequence, inhibited cathepsin B with Ki values in the micromolar range. Alkylation of the thiol group of Cys-42p of peptide PB8 (36p-50p) resulted in its rapid proteolytic degradation, suggesting that this residue is essential for inhibition. The inhibition constant was slightly improved (Kt = 2 ltM) using a longer peptide (26p-50p) which was completely resistant to cleavage even after a prolonged incubation. Alkylation of its cysteinyl residue also resulted in rapid cleavage of the peptide chain. Peptides derived from the rat cathepsin B prosequence also inhibited human cathepsin B with similar Kl values. Unlike rat cathepsin B, which cleaves peptide PB8 at the G47p-G48p bond after prolonged incubation, the human enzyme cleaved both PB8 and PBll at the Lys-40p-Leu-41p bond, in agreement with the different kinetic properties of these two proteinases. New probes with improved specificity for cysteine proteinases may therefore be designed based on the sequences of their propeptides.

Cystatin inhibition of cathepsin B requires dislocation of the proteinase occluding loop. Demonstration by release of loop anchoring through mutation of His110

FEBS Letters, 2000

Cystatins A and C were both shown to inhibit cathepsin B by a two-step mechanism, involving an initial weak interaction followed by a conformational change. Disruption of the major salt bridge anchoring the occluding loop of cathepsin B to the main body of the enzyme by mutation of His110 to Ala converted the binding to an apparent one-step reaction. The second step of cystatin binding to cathepsin B must therefore be due to the inhibitor having to alter the conformation of the enzyme by displacing the occluding loop to allow a tight complex to be formed. Cystatin A was appreciably less effective in displacing the loop than cystatin C, resulting in a considerably lower overall inhibition rate constant. ß Abbreviations: C29A-cathepsin B, cathepsin B variant in which Cys29 is replaced by Ala; DTT, dithiothreitol; H110A/C29A-cathepsin B, C29A-cathepsin B variant in which His110 is replaced by Ala; K d , overall dissociation equilibrium constant; K i , inhibition constant; k obs , observed pseudo-¢rst-order rate constant; k off , overall dissociation rate constant; k on , overall association rate constant; SDSP AGE, sodium dodecyl sulphate^polyacrylamide gel electrophoresis FEBS 24429 FEBS Letters 487 (2000) 156^160

Specificity of human cathepsin G

Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology, 1998

A series of tetrapeptide p-nitroanilide substrates of the general formula: suc-Ala-Ala-Pro-Aaa-p-nitroanilide was used to map the S 1 binding pocket of human cathepsin G. Based on the k cat /K m parameter, the following order of preference was found: Lys = Phe s Arg = Leu s Met s Nle = Nva s Ala s Asp. Thus, the enzyme exhibits clear dual and equal trypsin-and chymotrypsin-like specificities. Particularly deleterious were L-branched side chains of Ile and Val. The P 1 substrate preferences found for cathepsin G are distinctly different from many other serine proteinases, including fiddler crab collagenase and chymotrypsin. The k cat /K m values obtained for P 1 Lys, Phe, Arg and Leu substrates correlate well with those determined for analogous P 1 mutants of basic pancreatic trypsin inhibitor (BPTI) obtained through recombinant techniques. To characterise the subsite specificity of the enzyme, a series of Cucurbita maxima trypsin inhibitor I (CMTI I) mutants were used comprising P 2^P3 P and P 12 P positions. All the mutants obtained were inhibitors of cathepsin G with association constants in the range: 10 5^1 0 9 M 31 . Some of the mutations destabilised complex formation. In particular, Met 8 CArg substitution at P 3 P, which increased association constant for chymotrypsin 46-fold, led to a 7-fold decrease of binding with cathepsin G. In addition, mutation of Ile 6 at position P 1 P either to Val or Asp was deleterious for cathepsin G. In two cases (Ala 18 CGly (P 12 P) and Pro 4 CThr (P 2 )), about a 10-fold increase in association constants was observed. ß 1998 Elsevier Science B.V. All rights reserved.