Cathepsin B

Cathepsin B (from human liver) [9047-22-7] Mr 27,500 [EC 3.4.22.1]. Purified by affinity chromatography on the semicarbazone of Gly-Phe-glycinal-linked to Sepharose 4B, with elution by 2,2 -dipyridyl disulfide [Rich el al. Biochem J 235 731 1986 Methods Enzymol 80 551 1981]. 

More recently, miraziridine A (113) was isolated from a marine sponge related to Theonella mirabilis and shown to inhibit the cysteine protease cathepsin B. It has been shown that the aziridine ring plays a key role in this biological activity and gives rise to irreversible inhibition of cathepsins B and L, presumably through... 

For many serine and cysteine peptidases catalysis first involves formation of a complex known as an acyl intermediate. An essential residue is required to stabilize this intermediate by helping to form the oxyanion hole. In cathepsin B a glutamine performs this role and sometimes a catalytic tetrad (Gin, Cys, His, Asn) is referred too. In chymotrypsin, a glycine is essential for stabilizing the oxyanion hole. 

Gener ally, a family of peptidases contains either exopeptidases or endopeptidases, but there are exceptions. Family Cl contains not only endopeptidases such as cathepsin L, but also the aminopeptidase bleomycin hydrolase. Some members of this family can act as exopeptidases as well as endopeptidases. For example, cathepsin B also acts as a peptidyl-dipeptidase, and... 

Cysteinyl proteases Cathepsins (B, H, K, M, S, T) Proline endopeptidase Interleukin-converting enzyme Apopain (CPP-32)... 

The N-terminal sequence of one peptide from the 35 kDa zone of H-gal-GP showed some homology to cathepsin B-like cysteine proteases. Molecular cloning has also identified a thrombospondin homologue associated with the diffusely staining region between zones A and B, a galectin associated with zone D (Newlands et al., 1999) and a low molecular weight (approximately 13 kDa) cysteine protease inhibitor, cystatin. 

Fig. 13.4. Comparison of the predicted three-dimensional structure of an H. contortus gut-derived cysteine protease (HMCP1) with that of human cathepsin B.

A novel class of cathepsin B inhibitors has been developed with a 1,2,4-thiadiazole heterocycle as the thiol-trapping pharmacophore. The most potent inhibitor is compound 128 <2003BML5529>. 

Necrosis is a dramatic and very rapid form of cell death in which essentially every compartment of the cell disintegrates. Necrosis is characterized by marked dysregulation of ion homeostasis resulting in cell swelling, dilation of mitochondria and the ER and the formation of vacuoles in the cytoplasm [33], Proteases play important roles in the degradation of cells during necrosis. In contrast to apoptosis, where caspases are the key death proteases, calpains and lysosomal proteases (cathepsins B and D, in particular) are major players in necrosis. Caspases may be activated in response to mitochondrial damage and... 

Cathepsin K (Cat K) is a member of the CA1 family of lysosomal cysteine proteases. This family is comprised of 11 human members (cathepsins B, C, F, H, K, L, O, S, V, W, Z) which share a common papain-like structural fold and a conserved active site Cys-Asn-His triad of residues [1-3]. These enzymes are synthesized as pre-pro-enzymes and are converted from the catalytically inactive zymogen into the active form in acidic lysosomal environment. In some cases, cathepsins are also secreted in the active form from cells. The sequence identity of... 

Screening of over 66,000 compounds from the MLSMR by scientists at the PCMD for inhibitors of Cathepsin B resulted in the identification and characterization of an alternate substrate, SID 16952359 [29]. This study also describes issues relating to the nucleophilicity of dithiothreitol (DTT) and cysteine, reductants frequently used in HTS protocols, and the potential for reactivity with electrophilic sites of probe molecules. 

Figure 7. Two examples of irreversible inactivators that are not suicide substrates a) TPCK, a classic" affinity label of the serine protease chymotrypsin, b) ZFK-CH2-mesitoate, a quiescent" affinity label of the cysteine protease cathepsin B, and c) the kinetic scheme for both forms of affinity label-inactivation.

Degradation of these natural barriers by invading cancer cells is believed to be brought about by the release of a number of different proteases from the invading tumor. The proteases implicated in degradation of the extracellular matrix include the urokinase form of plasminogen activator (uPA), cathepsin B (CB), cathepsin D (CD), and various metalloproteases. These proteases appear to act in a cascade manner (Fig. 2) (S2). A brief description of the main proteases involved in metastasis now follows. 

It is generally believed that proteases enhance cancer spread primarily by catalyzing degradation of the extracellular matrix. Since multiple substrates are encountered in this matrix, a number of different proteases are likely to be required to complete the metastatic process. Multiple proteases may also be required to activate different inactive precursor forms. Thus, in vitro, plasmin (D7), cathepsin B (D7), and a trypsin-like protease (K12) can all activate pro-uPA, while plasmin, which results from the action of uPA on plasminogen, can activate certain metalloproteases (M4). As mentioned earlier, completion of the metastatic process may require a cascade of different proteases operating, as shown in Fig. 2. 

E2. Eekhout, Y., and Vaes, G., Further studies on the activation of procollagenase, the latest precursor of bone collagenase Effects of lysosomal cathepsin B. plasmin and kallikrein and spontaneous activation. Biochem. J. 36, 1555-1563 (1977). 

K2. Keren, Z., and LeGrue, S. J., Identification of cell surface cathepsin B-like activity on murine melanomas and fibrosarcomas Modulation by butanol extraction. Cancer Res. 48, 1416-1421 (1988). 

KIO. Kobayashi, H., Schmitt, M., Goretzki, L., Chuchowolski, N., Calvete, J., Karamer, M., Gunzler, W. A., Janicke, F., and Graeff, H., Cathepsin B efficiently activates the soluble and the tumor cell receptor-bound form of the proenzyme urokinase-type plasminogen activator (pro-uPA). J. Biol. Chem. 266, 5147-5152 (1991). 

K. V., and Sloane, B. F., Cathepsin B to cysteine proteinase inhibitor balance in metastatic cell subpopulations isolated from murine tumors. Cancer Res. 50, 6278-6284 (1990). 

One of the general principles of the Nomenclature Committee is that enzymes should be classified and named according to the reaction they catalyze. However, the overlapping specificities of and great similarities in the action of different peptidases render naming solely on the basis of function impossible [10]. For example, some enzymes can act as both endo- and exopeptidases. Thus, cathepsin H (EC 3.4.22.16) is not only an endopeptidase but also acts as an aminopeptidase (EC 3.4.11), and cathepsin B (EC 3.4.22.1) acts as an endopeptidase as well as a peptidyl-dipeptidase (EC 3.4.15). The actual classification of peptidases is, therefore, a compromise based not only on the reaction catalyzed but also on the chemical nature of the catalytic site, on physiological function, and on historical priority. 

G. M. Dubowchik, R. A. Firestone, Cathepsin B-Sensitive Dipeptide Prodrugs. 1. A Model Study of Structural Requirements for Efficient Release of Doxorubicin , Bioorg. Med. Chem. Lett. 1998, 8, 3341-3346. 

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