Amino acid sequence of rat liver cathepsin L

Association between Lysosomal Dysfunction and Obesity-Related Pathology: A Key Knowledge to Prevent Metabolic Syndrome

Obesity causes various health problems, such as type 2 diabetes, non-alcoholic fatty liver disease, and cardio- and cerebrovascular diseases. Metabolic organs, particularly white adipose tissue (WAT) and liver, are deeply involved in obesity. WAT contains many adipocytes with energy storage capacity and secretes adipokines depending on the obesity state, while liver plays pivotal roles in glucose and lipid metabolism. This review outlines and underscores the relationship between obesity and lysosomal functions, including lysosome biogenesis, maturation and activity of lysosomal proteases in WAT and liver. It has been revealed that obesity-induced abnormalities of lysosomal proteases contribute to inflammation and cellular senescence in adipocytes. Previous reports have demonstrated obesity-induced ectopic lipid accumulation in liver is associated with abnormality of lysosomal proteases as well as other lysosomal enzymes. These studies demonstrate that lysosomal dysfunction in WAT and liver underlies part of the obesity-related pathology, raising the possibility that strategies to modulate lysosomal function may be effective in preventing or treating the metabolic syndrome.

The Potential Role of the Proteases Cathepsin D and Cathepsin L in the Progression and Metastasis of Epithelial Ovarian Cancer

Epithelial ovarian cancer (EOC) is the leading cause of death from gynecologic malignancies and has a poor prognosis due to relatively unspecific early symptoms, and thus often advanced stage, metastasized cancer at presentation. Metastasis of EOC occurs primarily through the transcoelomic route whereby exfoliated tumor cells disseminate within the abdominal cavity, particularly to the omentum. Primary and metastatic tumor growth requires a pool of proangiogenic factors in the microenvironment which propagate new vasculature in the growing cancer. Recent evidence suggests that proangiogenic factors other than the widely known, potent angiogenic factor vascular endothelial growth factor may mediate growth and metastasis of ovarian cancer. In this review we examine the role of some of these alternative factors, specifically cathepsin D and cathepsin L.

Nobuhiko Katunuma: an outstanding scientist in the field of proteolysis and warm-hearted 'Kendo Fighter' biochemist

Professor Nobuhiko Katunuma is well known for his outstanding contribution to the understanding of proteolysis in general and cysteine proteinases and their inhibitors in mammals. In fact, he is a world pioneer in the field. In 1963, he started his highly successful scientific career as a Professor at the Institute for Enzyme Research, the University of Tokushima. During the initial 30 years of his career, he was interested in vitamin B6 metabolism and discovered the acceleration of turnover rates of pyridoxal enzyme in apoprotein formation. After this period, his interest expanded to lysosomal cystein proteinases and their endogenous inhibitors. After determining the crystal structure of human cathepsin B, he generated a series of chemically synthesized specific inhibitors of cathepsins. These inhibitors are currently used throughout the world and some of them have been applied therapeutically in various diseases. During his career and even at present, Professor Katunuma has been studying Biochemistry in Medicine and also practicing to become a 'Kendo sword fencing Fighter'.

Posttranslational processing and modification of cathepsins and cystatins

Cathepsins are an essential protease family in all living cells. The cathepsins play an essential roles such as protein catabolism and protein synthesis. To targeting to various organella and to regulate their activity, the post translational-processing and modification play an important role Cathepsins are translated in polysome as the pre-pro-mature forms. The pre-peptide is removed cotranslationally and then translocated to Golgi-apparatus and the pro-part is removed and the mature-part is glycosylated, and the mature-part is targeted into the lysosome mediated by mannose-6-phosphate signal and the mature-part is bound with their coenzymes. The degradation of the mature-part is started by the limited proteolysis of the ordered nicked bonds to make hydrophobic peptides. The peptides are incorporated into phagosome or proteasome after ubiquitinated and are degrade into amino-acids. Cystatins are endogenous inhibitors of cathepsins. Cystatin α which is only located in skin is phosphorylated at the near C-terminus by protein kinase-C, and the phosphorylate-cystatin α is incorporated into cornified envelope and conjugated with filaggrin-fiber by transglutaminase to form the linker-fiber of skin. The cystatin α is modified by glutathione or make their dimmer, and they are inactive. Those modifications are regulated by the redox-potential by the glutathione.

Cathepsin L plays an important role in the lysosomal degradation of L-lactate dehydrogenase

A cystatin alpha-sensitive cysteine proteinase that plays an important role in the lysosomal inactivation and degradation of L-lactate dehydrogenase (LDH) was purified by column chromatography from an ammonium sulfate precipitate of lysosome extract prepared from rat livers. It was eluted with marked delay from cathepsins B and H in a Sephacryl S-200 column by its specific interaction with the gel, and then effectively separated from cathepsins B and H and other proteins. It was eluted with 0.5 M NaCl after washing with 0.2 M NaCl in a CM-Sephadex column, indicating that it showed the same elution behavior as cathepsin L from the CM-Sephadex column. It had activity to hydrolyze z-Phe-Arg-NH-Mec, a synthetic substrate for cysteine proteinases, including cathepsins B and L. The N-terminal sequences of the final preparation of LDH-inactivating enzyme were identical with those of rat cathepsin L. Inactivation and degradation of LDH by the final preparation were observed and effectively inhibited by a low level of cystatin alpha as well as a general cysteine proteinase inhibitor, leupeptin or (L-3-trans-carboxyoxirane-2-carbonyl)-L-leucine (3-methylbutyl)amide (E-64-c). From these results, it is concluded that cathepsin L plays a critical role in the lysosomal degradation of native LDH.

Characterization and expression of AmphiCL encoding cathepsin l proteinase from amphioxus Branchiostoma belcheri tsingtauense

An amphioxus complementary DNA, AmphiCL, encoding cathepsin L proteinase was isolated from the gut cDNA library of Branchiostoma belcheri tsingtauense. It is 1480 bp long, and its longest open reading frame codes for a precursor protein, which consists of 327 amino acid residues including a signal peptide (preregion), a propeptide, and a mature proteinase. Northern blot showed that AmphiCL was expressed in the gill, testis, hepatic cecum, and hind-gut with a molecular size of about 1480 bp. AmphiCL was also expressed at low level in the muscle, notochord, and ovary as revealed by the more sensitive reverse transcriptase polymerase chain reaction techniques. Semiquantitative RT-PCR also showed that although AmphiCL expression in the gut was significantly downregulated by feeding Arthrospira platensis powder, a protein-rich food, its expression in the same tissue was upregulated by exposure to lipopolysaccharide, an integral component of the outer membrane of gram-negative bacteria. This suggests that although the involvement of AmphiCL in food digestion remains to be confirmed, AmphiCL may play a role in inflammatory reaction in amphioxus.

Molecular characterization of cathepsin L from hepatopancreas of the carp Cyprinus carpio

Purified cathepsin L from carp, Cyprinus carpio, consists of a 28 kDa single-chain form that is different from the 24 and 5 kDa mammalian two-chain form. We cloned cathepsin L from carp hepatopancreas. The sequence consisted of a 1490 bp cDNA and a 1014 bp open reading frame, encoding a deduced protein of 337 amino acids that is likely processed to an active enzyme (single-chain form) with 222 amino acids. Its similarity to other types of vertebrate cathepsin L is less than 69%. Mammalian cathepsin L is further processed to a two-chain form, but possibly this is not the case with carp cathepsin L: the P1 site where cleavage occurred in the two-chain form of mammalian cathepsin L contains a serine, while carp cathepsin L processes a valine. Therefore, carp cathepsin L may have a different mechanism of action from mammalian cathepsin L.

Biosynthetic processing of cathepsins and lysosomal degradation are abolished in asparaginyl endopeptidase-deficient mice

Asparaginyl endopeptidase (AEP)/legumain, an asparagine-specific cysteine proteinase in animals, is an ortholog of plant vacuolar processing enzyme (VPE), which processes the exposed asparagine residues of various vacuolar proteins. In search for its physiological role in mammals, here we generated and characterized AEP-deficient mice. Although their body weights were significantly reduced, they were normally born and fertile. In the wild-type kidney where the expression of AEP was exceedingly high among various organs, the localization of AEP was mainly found in the lamp-2-positive late endosomes in the apical region of the proximal tubule cells. In these cells of AEP-deficient mice, the lamp-2-positive membrane structures were found to be greatly enlarged. These aberrant lysosomes, merged with the late endosomes, accumulated electron-dense and membranous materials. Furthermore, the processing of the lysosomal proteases, cathepsins B, H, and L, from the single-chain forms into the two-chain forms was completely defected in the deficient mice. Thus, the AEP deficiency caused the accumulation of macromolecules in the lysosomes, highlighting a pivotal role of AEP in the endosomal/lysosomal degradation system.

Splenic cathepsin L is maturated from the proform by interferon-gamma after immunization with exogenous antigens

The processing of foreign protein antigens into peptides requires the participation of various endo/lysosomal proteases in antigen-presenting cells (APCs). In this study, a proenzyme of cathepsin L, procathepsin L, was found to be present in the spleens of naive mice, as demonstrated by immunoblotting. Interestingly, the maturation of cathepsin L from procathepsin L was strongly induced when the host BALB/c mice were immunized with ovalbumin or soluble leishmanial antigen, despite the fact that mouse albumin, a kind of self-antigen, did not have such a potential. Furthermore, foreign antigens, but not self-antigens, could increase the activity of cathepsin L, probably being mediated by interferon-gamma, as demonstrated by in vivo and in vitro experiments. As cathepsin L matured, the efficiency of antigen processing was increased in APCs. These results suggest that endo/lysosomal cathepsin L plays an important role in the immune regulation via antigen processing even in peripheral lymphoid tissues as well as in the thymus.

Structure-based development of pyridoxal propionate derivatives as specific inhibitors of cathepsin K in vitro and in vivo

We found that pyridoxal phosphate shows considerable inhibition of cathepsins. CLIK-071, in which the phosphate ester of position 3 of pyridoxal phosphate was replaced by propionate, strongly inhibited cathepsin B. Three new types of synthetic pyridoxal propionate derivatives showing specific inhibition of cathepsin K were developed. New synthetic pyridoxal propionate derivatives, -162, -163, and -164, in which the methyl arm of position 6 of CLIK-071 was additionally modified, strongly inhibited cathepsin K and cathepsin S weakly, but other cathepsins were not inhibited. CLIK-166, in which the position 4 aldehyde of CLIK-071 is replaced by a vinyl radical and position 5 is additionally modified, showed cathepsin K-specific inhibition at 10(-5) M. Pit formation due to bone collagen degradation by cathepsin K of rat osteoclasts was specifically suppressed by administration of CLIK-164, but not by inhibitors of cathepsin L or B.

Structure based development of novel specific inhibitors for cathepsin L and cathepsin S in vitro and in vivo

Specific inhibitors for cathepsin L and cathepsin S have been developed with the help of computer-graphic modeling based on the stereo-structure. The common fragment, N-(L-trans-carbamoyloxyrane-2-carbonyl)-phenylalanine-dimethyla mide, is required for specific inhibition of cathepsin L. Seven novel inhibitors of the cathepsin L inhibitor Katunuma (CLIK) specifically inhibited cathepsin L at a concentration of 10(-7) M in vitro, while almost no inhibition of cathepsins B, C, S and K was observed. Four of the CLIKs are stable, and showed highly selective inhibition for hepatic cathepsin L in vivo. One of the CLIK inhibitors contains an aldehyde group, and specifically inhibits cathepsin S at 10(-7) M in vitro.

Study of the functional share of lysosomal cathepsins by the development of specific inhibitors

To analyze the functional share of individual cathepsins, we developed powerful and specific inhibitors for individual cathepsins using computer graphics of substrate binding pockets based on X-ray crystallography. These new inhibitors were named CLIK group. Epoxy succinate peptide derivatives, CLIK-066, 088, 112, 121, 148, 181, 185 and 187, are typical specific inhibitors for cathepsin L. Aldehyde derivatives CLIK-060 and CLIK-164 showed specific inhibition against cathepsin S and cathepsin K, respectively. We found that pyridoxal phosphate (PLP), a coenzyme form of vitamin B6, inhibits all cathepsins and also new artificially synthesized pyridoxal derivatives, CLIK-071 and -072, in which the phosphate esters of PLP were replaced by propionic acid, exhibited strong inhibition for cathepsins. Furthermore, CLIK-071 was easy to incorporate into cells and showed powerful inhibition for intracellular cathepsins. Using these selective inhibitors, the allotment of individual cathepsin functions in cells has been studied as follows. Cathepsin L and/or K participate in bone resorption based on bone type-1 collagen degradation and the L-type protease inhibitors suppressed the bone resorption. Cathepsins B and S participate in antigen presentations based on antigen processing and invariant chain degradation, respectively. Also cathepsin L participates in cell apoptosis mediated by caspase III activation.

Acidic pH as a physiological regulator of human cathepsin L activity

Human cysteine protease cathepsin L was inactivated at acid pH by a first-order process. The inactivation rate decreased with increasing concentrations of a small synthetic substrate, suggesting that substrates stabilize the active conformation. The substrate-independent inactivation rate constant increased with organic solvent content of the buffer, consistent with internal hydrophobic interactions, disrupted by the organic solvent, also stabilizing the enzyme. Circular dichroism showed that the inactivation is accompanied by large structural changes, a decrease in alpha-helix content being especially pronounced. The high activation energy of the reaction at pH 3.0 (200 kJ.mol-1) supported such a major conformational change occurring. The acid inactivation of cathepsin L was irreversible, consistent with the propeptide being needed for proper folding of the enzyme. Aspartic protease cathepsin D was shown to cleave denatured, but not active cathepsin L, suggesting a potential mechanism for in-vivo regulation and turnover of cathepsin L inside lysosomes.

Multiple processing of procathepsin L to cathepsin L in vivo

Three amino-terminal-specific peptidic antibodies against cathepsin L were generated. These antibodies recognize in vitro processing products of procathepsin L in time-course-dependent fashion. Immunoblot analyses with these antibodies followed by immunoprecipitation with anti-cathepsin L antibody showed that the amino terminal amino acid sequences of intracellular cathepsin L are heterogeneous: the single chain form of cathepsin L starts with either EPLML, LKIPK or IPKSV, and the heavy chain of the two chain form with IPKSV. Percoll density gradient and fluorescence immunohistochemistry suggested that these three species of cathepsin L localize in the lysosomes where procathepsin L processing occurs.

Cloning and expression of cathepsin L-like proteinases in the hepatopancreas of the shrimp Penaeus vannamei during the intermolt cycle

Cysteine protease activities have been characterized with benzyloxycarbonyl-lysine p-nitrophenyl ester as a synthetic substrate and E64 as a specific inhibitor in the hepatopancreas of the shrimp Penaeus vannamei. An optimum pH of 5.1 has been measured. To characterize these cysteine proteases, a hepatopancreas cDNA library was screened by hybridization to a Norway lobster cysteine protease cDNA fragment. Two cDNAs encoding P. vannamei cysteine protease precursors have been cloned and sequenced. The encoded polypeptides have 326 and 322 amino acid residues, respectively, each consisting of partial signal sequences (15 and 10 residues), a pro-region (93 and 94 residues), and a mature enzyme polypeptide (218 residues). Cys25, His159 and Asn175 form the catalytic triad in the putative active site of the mature enzymes. Compared with invertebrate cysteine proteases (Homarus and Fasciola), each of the two shrimp enzymes shows 70 and 52% amino acid sequence identity, respectively; 63% identity is shown with rat cathepsin L. Northern hybridization analysis showed the same size for the different cysteine protease transcripts in hepatopancreas tissue (approximately 1.1 kb). During intermolt cycles, variations in cysteine protease activity were correlated with the variations in the levels of specific mRNA.

Rat brain contains high levels of mannose-6-phosphorylated glycoproteins including lysosomal enzymes and palmitoyl-protein thioesterase, an enzyme implicated in infantile neuronal lipofuscinosis

Mannose 6-phosphate (Man-6-P) is a posttranslational carbohydrate modification typical of newly synthesized acid hydrolases that signals targeting from the Golgi apparatus to the lysosome via Man-6-P receptors (MPRs). Using iodinated cation independent MPR as a probe in a Western blot assay, we surveyed levels of Man-6-P glycoproteins in a number of different rat tissues. Considerable variation was observed with respect to total amounts and types of Man-6-P glycoproteins in the different tissues. Brain contained 2-8-fold more Man-6-P glycoproteins than other tissues, with relative abundance being brain >> testis approximately heart > lung approximately kidney approximately ovary approximately spleen > skeletal muscle approximately liver approximately serum. Analysis of 16 different lysosomal enzyme activities revealed that brain contains lower activities than other tissues which suggested that decreased removal of Man-6-P results in increased levels of Man-6-P glycoproteins. This was directly demonstrated by comparing activities of phosphorylated lysosomal enzymes, purified by immobilized MPR affinity chromatography, with total activities. The phosphorylated forms accounted for a considerable proportion of the MPR-targeted activities measured in brain (on average, 36.2%) but very little in lung, kidney, and liver (on average, 5.5, 2.3, and 0. 7%, respectively). Man-6-P glycoproteins were also isolated from rat brain by MPR affinity chromatography on a preparative scale. Of the 18 bands resolvable by SDS-polyacrylamide gel electrophoresis, seven bands were NH2-terminally sequenced and identified as the known lysosomal enzymes cathepsin L, cathepsin A, cathepsin D, alpha-galactosidase A, arylsulfatase A, and alpha-iduronidase. One of the major Man-6-P glycoproteins was identified as palmitoyl protein thioesterase, which was not previously thought to be lysosomal. This finding raises important questions about the cellular location and function of palmitoyl protein thioesterase, mutations in which result in the neurodegenerative disorder, infantile neuronal ceroid lipofuscinosis.

Multi-step processing of procathepsin L in vitro

The proteolytic processes involved in the conversion of procathepsin L to cathepsin L on a negatively charged surface, dextran sulfate, were studied. Upon incubation for 30 min at 37 degrees C, pH 5.5 with dextran-sulfate and dithiothreitol, purified procathepsin L showed maximal activation and, correspondingly, the complete conversion to the 30 kDa, single chain mature form of enzyme was observed. In contrast, incubation under the same conditions on ice rather than at 37 degrees C for 30 or 60 min resulted in partial proteolysis to produce a 31 kDa form without a significant increase in activity. Amino terminal amino acid sequence analyses showed that the 30 kDa form obtained by incubation at 37 degrees C corresponds to the purified form of mature cathepsin L with a 2 amino acid extension at the amino terminal, and that the 31 kDa form generated by incubation on ice possesses a 6 amino acid amino terminal extension, suggesting that the activation and processing of procathepsin L are different processes, and that 4 amino acid residues (Glu-Pro-Leu-Met) at the carboxyterminal in the propeptide function to prevent the activation of processed cathepsin L.

Immunological significances of invariant chain from the aspect of its structural homology with the cystatin family

The primary structure of p31 of invariant chain (Ii-chain) shows about 50% homology with those of the cystatin family which are endogenous cysteine protease inhibitors. The binding domains between Ii-chain and HLA-DR-7 were estimated from the structural homology between cystatin and Ii-chain and also between cathepsins and DR-7, respectively. The QL64-71 and GS76-88 of Ii-chain were estimated to be the binding domains with GG45-51 and VS57-63 of HLA-DR7, respectively. The purified human Ii-chain from spleen is capable of forming four molecular forms from monomer to tetramer by redox-potential dependent disulfide bond formation. The Ii-chain inhibits cathepsin L and H competitively as a dimer and the K(i) value for cathepsin L was 4.1 x 10(-8) M, but cathepsin B was not inhibited at all. The Ii-chain showed mainly a dimer (60 kDa) under the assay condition of cathepsins with cysteine and was not degraded by these cathepsins. The Ii-chain may play an important role in the regulation of antigenic peptide presentation to MHC class II.

Mechanism and regulation of antigen processing by cathepsin B

Cellular and humoral immune responses to vaccines of hepatitis B and rabies as antigens were suppressed by specific inhibitors of cathepsin B, anti-cathepsin B antibody and the specific substrate of cathepsin B. The antigenic peptides of these vaccines are processed by cathepsin B and the fragments are capable of binding with the desetope of MHC class II, beta-chain, because one of the active sites of cathepsin B (14, 15) VN217-222 shares high homology with a part of the desetope, VN57-62, of MHC class II, beta-chain. Rechallenge of the synthesized antigenic peptides of these vaccine molecules shows a strong proliferative response to the splenocyte primed by these vaccines. However, the response to these antigenic peptides was not inhibited by cathepsin B inhibitors. These findings suggest that cathepsin B inhibitors do not inhibit any other processes of immune responses than the proteolytic processing of antigens. Some investigators reported recently that the Ii-chain is degraded by purified cathepsin B in vitro (23-25). However, we showed that the suppression of these immune responses by cathepsin B inhibitors is not due to the inhibition of invariant chain degradation. We found that the invariant chain shares about 40% homology with the cystatin family which are the endogenous inhibitors of cysteine proteases (23, 24). Therefore, the Ii-chain is one of the members of the cystatin superfamily and may participate in the regulation of presentation of antigenic peptides and also antigen processing by cathepsin B.

Purification of a cathepsin L-like proteinase secreted by adult Fasciola hepatica

A cysteine proteinase released in vitro by Fasciola hepatica was purified to homogeneity by Sephacryl S-200 gel filtration chromatography followed by QAE-Sephadex chromatography. The purified enzyme resolves as a single band with an apparent molecular size of 27 kDa on reducing SDS-polyacrylamide gel electrophoresis; however, under non-reducing conditions it migrates as multiple bands, each with enzymatic activity, in the apparent molecular size range 60-90 kDa. The sequence of the first 20 N-terminal amino acids of the enzyme shows considerable homology with cathepsin L-like proteinases. Immunolocalisation studies revealed that the cathepsin L-like proteinase is concentrated within vesicles in the gut epithelial cells of liver fluke.

Participation of cathepsin B in processing of antigen presentation to MHC class II

Cellular and humoral immune responses to vaccines of hepatitis B type and rabies were inhibited by specific inhibitors of cathepsin B, specific synthetic substrates of cathepsin B and anti-cathepsin B antibody. Therefore the lysosomal cathepsin B of antigen presenting cells plays an essential role in processing of these antigens for presentation to MHC class II. One of the active sites of cathepsin B, VN217-222 shares highly homologous sequences with a part of the desetope, a binding domain of antigenic peptides, VN57-62 of MHC class II, beta-chain. This evidence suggests that the peptides processed by the substrate specificity of cathepsin B exhibit a common affinity to bind with the desetope of MHC class II, beta-chain.

Procathepsin L-specific antibodies that recognize procathepsin L but not cathepsin L

Procathepsin L was purified to apparent homogeneity from the culture medium of v-Ha-ras transformed NIH3T3 (Ras-NIH) cells in three steps; anion-exchange chromatography, gel filtration, and re-gel filtration. SDS-PAGE analyses revealed that the purified samples contained only the precursor form, procathepsin L, but not the mature enzyme, cathepsin L. Antibodies against purified procathepsin L were raised. These recognized both rat cathepsin L and the purified procathepsin L. To isolate procathepsin L-specific antibodies that did not recognize cathepsin L, sequential affinity chromatography procedures were carried out. Immunoblot analyses showed that the procathepsin L-specific antibodies recognized only procathepsin L, but not cathepsin L.

Purification and characterization of cathepsin J from rat liver

Cathepsin J has been partially purified [Liao, J. C. R. & Lenney, J. F. (1984) Biochem. Biophys. Res. Commun. 124, 909-916], but its detailed properties are still unknown. In this study, we have purified cathepsin J completely and characterized it. It was purified to homogeneity from the mitochondrial-lysosomal fraction of rat liver by acid treatment, followed by ammonium sulfate precipitation (20-65%), and chromatographies on S-Sepharose, ConA-Sepharose, Affi-gel 501, HPLC DEAE-5PW and HPLC TSK G3000SW. Cathepsin J was found to be a lysosomal high-molecular-mass cysteine protease of about 160 kDa consisted of two different subunits. One subunit (alpha subunit) was a glycoprotein with a molecular mass of 19-24 kDa which was reduced to 19 kDa by treatment with endoglycosidase F. It has the amino acid sequence LPESWDWRNVR at its N-terminus, which was very similar to those at the N-termini of rat cathepsins B, H and L. The other subunit (beta subunit) was a glycoprotein with a molecular mass of 17 kDa, which was reduced to 14 kDa by treatment with endoglycosidase F. It had DTPANETYPDLLG at its N-terminus, which had no similarity with the N-terminal sequences of other cathepsins. Cathepsin J showed strong affinity for synthetic substrates such as N-benzyloxycarbonyl-phenylalanyl-arginine 4-methyl-coumaryl-7-amide and glycyl-arginine beta-naphthylamide. It was activated by thiol reagents and chloride ion and was inhibited by cysteine protease inhibitors. However, its initial inhibition constant Ki(initial) by N-(L-3-trans-carboxyoxirane-2-carbonyl)-L-leucine-3- methylbutylamide (E-64-c) was 1800 nM, which was 100-500 times those of cathepsins B and L. Many properties of cathepsin J were similar to those of cathepsin C (dipeptidylaminopeptidase I) reported as a lysosomal cysteine protease with dipeptidyl-aminopeptidase activity [McDonald, J. K., Reilly, T. J. & Ellis, S. (1964) Biochem. Biophys. Res. Commun. 16, 135-140]. Furthermore, antiserum against rat liver cathepsin C reacted with rat liver cathepsin J. These findings suggested that cathepsin J is identical with cathepsin C.

Gene structure and 5'-upstream sequence of rat cathepsin L

The structure of rat cathepsin L gene has been determined. The gene spans 8.5 kilobase pairs comprising 8 exons, and has an intron located near the active site cysteine residue. The gene structure does not correspond well to the functional units of the proteinase. These characteristics are found to be in common with the cysteine proteinase gene family. In the 5'-upstream region, one CAAT-box and four SP-1 binding sites, together with two AP-2 binding sites and CRE, but no typical TATA-box are found. Further, SP-1 and AP-2 binding sites and an octamer motif are also found in the 1st intron, suggesting a complex regulatory mechanism for the expression of the cathepsin L gene.