Purification properties and specificity of cathepsin D from Cyprinus carpio

Peptidomic Analysis of a Disintegrated Surimi Gel from Deep-Sea Bonefish Pterothrissus gissu

Surimi gel is a commonly found gelled product in Japan. Disintegration of the surimi gel is mainly caused by proteolytic degradation of the myosin heavy chain (MHC) under an inappropriate heating process. Many studies have reported the decrease in MHC in the disintegrated surimi gel but the mechanistic details of this degradation remain unclear. This study employed peptidomic analysis of disintegrated surimi gels from deep-sea bonefish Pterothrissus gissu to reveal the MHC cleavage causing gel disintegration. More peptides derived from an MHC rod were found in the disintegrated P. gissu surimi gels than in the integrated gel. Most MHC peptides were derived from the Src homology 3 domain or near the skip residues. The results of the terminome analysis suggest that the catalytic type of the proteases is responsible for light meromyosin cleavage activated at ∼35 °C. These results showed the temperature-dependent cleavage of the MHC rod, causing disintegration of the P. gissu surimi gel.

Cloning, characterisation, and expression analysis of the cathepsin D gene from rock bream (Oplegnathus fasciatus)

Cathepsins are lysosomal cysteine proteases belonging to the papain family, members of which play important roles in normal metabolism for the maintenance of cellular homeostasis. Rock bream (Oplegnathus fasciatus) cathepsin D (RbCTSD) cDNAs were identified by expressed sequence tag analysis of a lipopolysaccharide-stimulated rock bream liver cDNA library. The full-length RbCTSD cDNA (1644 bp) contained an open reading frame of 1191 bp encoding 396 amino acids. Alignment analysis revealed that the active sites and N-glycosylation sites of the deduced protein were well conserved. Phylogenetic analysis revealed that RbCTSD is most closely related to the Mi-iuy croaker (Miichthys miiuy) cathepsin D. RbCTSD was ubiquitously expressed in all the examined tissues, predominantly in muscle and kidneys. RbCTSD mRNA expression was also examined in several tissues under conditions of bacterial and viral challenge. All examined tissues of fish infected with Edwardsiella tarda (E. tarda), Streptococcus iniae (S. iniae), and red sea bream iridovirus (RSIV) showed significant increases in RbCTSD expression compared with the control. In the kidney and spleen, RbCTSD mRNA expression was markedly upregulated following infection with all tested pathogens. These findings indicate that RbCTSD plays an important role in the innate immune response of rock bream. Furthermore, these results provide important information for the identification of other cathepsin D genes in various fish species.

Molecular cloning, characterization and expression of cathepsin D from grass carp (Ctenopharyngodon idella)

Cathepsin D is a lysosomal aspartic proteinase which participates in various degradation functions within the cell. In this current study, we cloned and characterized the complete cDNA of grass carp cathepsin D through 5'- and 3'-RACE. The cathepsin D contained a 56 bp 5' terminal untranslated region (5'-UTR), a 1197 bp open reading frame encoding 398 amino acids, and a 394 bp 3'-UTR. Grass carp cathepsin D shared high similarity with those from other species, and showed the highest amino acid identity of 91% to Danio rerio. Unlike many other organisms, the grass carp cathepsin D contains only one N-glycosylation site closest to the N-terminal. Real-time quantitative RT-PCR demonstrated that Cathepsin D expressed in all twelve tissues (bladder, brain, liver, heart, gill, muscle, fin, eye, intestines, spleen, gonad and head kidney). The relative expression levels of Cathepsin D in gonad and liver were 26.58 and 24.95 times as much as those in fin, respectively. The expression level of Cathepsin D in muscle approximately 16-fold higher, in intestines and spleen were 12-fold higher. The cathepsin D expression showed an upward trend during embryonic development. After challenged with Aeromonas hydrophil, the expression of grass carp cathepsin D gene showed significant changes in the four test tissues (liver, head kidney, spleen and intestines). The fact that the bacterial infection can obviously improve the cathepsin D expression in immune-related organs, may suggest that cathepsin D plays an important role in the innate immune response of grass carp.

Identification and expressional analysis of two cathepsins from half-smooth tongue sole (Cynoglossus semilaevis)

Cathepsins are a family of lysosomal proteases that play an important role in protein degradation, antigen presentation, apoptosis, and inflammation. Cathepsins are divided into three groups, i.e., cysteine protease, serine protease, and aspartic protease. Cathepsin D and cathepsin L, which are aspartic protease and cysteine protease respectively, have been identified in a number of teleosts; however, the immunological relevance of fish cathepsins is largely unknown. In this study, we cloned and analyzed the expression profiles of a cathepsin D (CsCatD) and a cathepsin L (CsCatL) homologs from half-smooth tongue sole (Cynoglossus semilaevis). CsCatD is composed of 396 amino acid residues and shares 67.6-88.4% overall sequence identities with fish and human cathepsin D. Structurally CsCatD possesses an aspartic endopeptidase domain, which contains two conserved aspartic acid residues that form the catalytic site. CsCatL is 336 residues in length and shares 64.7-90.2% overall sequence identities with fish and human cathepsin L. CsCatL has an N-terminal cathepsin propeptide inhibitor domain followed by a Papain family cysteine protease domain, the latter containing four conserved catalytic residues: Gln-133, Cys-139, His-279, and Asn-303. Recombinant CsCatL purified from Escherichia coli exhibited apparent protease activity. Quantitative real time RT-PCR analysis detected constitutive expression of CsCatD and CsCatL in multiple tissues, with the lowest level found in heart and the highest level found in liver. Experimental challenge of tongue sole with the bacterial pathogen Vibrio anguillarum and megalocytivirus caused significant inductions of both CsCatD and CsCatL expression in kidney and spleen in time-dependent manners. Immunization of the fish with a subunit vaccine also enhanced CsCatD and CsCatL expression in the first week post-vaccination. These results suggest involvement of CsCatD and CsCatL in host immune reactions to bacterial and viral infections and in the process of antigen-induced immune response.

Cathepsin D from the hepatopancreas of the cuttlefish (Sepia officinalis): purification and characterization

Cathepsin D from the hepatopancreas of cuttlefish ( Sepia officinalis ) was purified to homogeneity by precipitation with ammonium sulfate (30-60%, w/v), Sephadex G-100 gel filtration, Mono-S cation-exchange chromatography, Sephadex G-75 gel filtration, and Mono-S FPLC with a 54-fold increase in specific activity and 17% recovery. The molecular weight of the purified cathepsin D was estimated to be 37.5 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). On the basis of the native-PAGE and hemoglobin zymography, the purified protease appeared as a single band. The optimum pH and temperature for the cathepsin D activity were pH 3.0 and 50 °C, respectively, using hemoglobin as a substrate. The purified enzyme was completely inhibited by pepstatin A; however, no inhibition was observed with phenylmethylsulfonyl fluoride and ethylenediaminetetraacetic acid. Moreover, the activity was strongly inhibited by SDS and molybdate and enhanced by ATP. The purified cathepsin D was activated by Mg(2+), Ni(2+), Zn(2+), Cu(2+), Cd(2+), Sr(2+), and Co(2+) ions, whereas it was not affected by Na(+), K(+), and Ca(2+) ions. The N-terminal amino acid sequence of the first 13 amino acids of the purified cathepsin D was APTPEPLSNYMDA. S. officinalis cathepsin D, which showed high homology with cathepsin D from marine vertebrates and invertebrates, had a Pro residue at position 6 and a Ser residue at position 8, where Thr and Lys are common in all marine vertebrates cathepsins D. S. officinalis cathepsin D showed high efficiency for the hydrolysis of myofibrillar proteins extracted from cuttlefish muscle.

An acidic protease from the grass carp intestine (Ctenopharyngodon idellus)

The acidic Protease was extracted from the intestine of the grass carp (Ctenopharyngodon idellus) by 0.1 M sodium phosphate buffer, pH 7.0 at 4 degrees C after neat intestine was defatted with acetone, and partially purified by ammonium sulfate precipitation, gel filtration chromatography and ionic exchange chromatography. SDS-PAGE electrophoresis showed that the enzyme was homogeneous with a relative molecular mass of 28,500. Substrate-PAGE at pH7.0 showed that the purified acidic protease has only an active component. Specificity and inhibiting assays showed that it should be a cathepsin D. The optimal pH and optimal temperature of the enzyme were pH2.5 and 37 degrees C, respectively. It retained only 20% of its initial activity after incubating at 50 degrees C for 30 min. The enzyme lost 81% of its activity after incubation with pepstatin A at room temperature, but was not inhibited by soybean trypsin inhibitor or phenylmethylsulfonyl fluoride (PMSF). Its V(max) and K(m) values were determined to be 3.57 mg/mL and 0.75 min(-1), respectively.

Cathepsin D from Atlantic cod (Gadus morhua L.) liver. Isolation and comparative studies

The isolated cathepsin D-like enzyme from Atlantic cod (Gadus morhua L.) liver was shown to be a monomer with a molecular mass of approximately 40 kDa. It was inhibited by Pepstatin A and had an optimum for degradation of haemoglobin at pH 3.0. The purified enzyme had lower temperature stability than bovine cathepsin D. Antibodies raised against the purified enzyme and against two C-terminal peptides of cod cathepsin D recognized a 40 kDa protein in immunoblotting of the samples from the purification process. Both antisera showed cross reactivity with a similar sized protein in liver from cod, saithe (Pollachius virens L.), Atlantic herring (Clupea harengus L.) and Atlantic salmon (Salmo salar L.). A protein of same size was detected in wolffish (Anarhichas lupus L.) liver with the antibody directed against the purified enzyme. This antibody also recognized the native enzyme and detected the presence of cathepsin D in muscle of cod, saithe, herring and salmon. These antibodies may be useful in understanding the mechanisms of post mortem muscle degradation in fish by comparing immunohistochemical localization and enzyme activity, in particular in cod with different rate of muscle degradation. They may also be used for comparing muscle degradation in different fish species.

Identification and characterization of proteases involved in specific proteolysis of vitellogenin and yolk proteins in salmonids

A pepstatin A-sensitive enzyme involved in yolk formation was purified from the masu salmon (Oncorhynchus masou) ovary using in vitro generation of yolk proteins from purified vitellogenin to assay enzymatic activity. Purification of the enzyme involved precipitation of ovarian extracts by water and ammonium sulfate followed by five steps of column chromatography. After SDS-PAGE and Western blotting, the purified enzyme appeared as a single approximately 42 kDa band that was immunoreactive to anti-human cathepsin D. The course of proteolytic cleavage of the three major yolk proteins (lipovitellin, beta'-component, and phosvitin) in fertilized masu salmon and Sakhalin taimen (Hucho perryi) eggs and embryos was visualized by SDS-PAGE and Western blotting using specific antisera. Major yolk protein bands appeared in positions corresponding to 92 kDa, 68 kDa, and 22 kDa (lipovitellin-derived peptides), as well as 17 kDa (beta'-component). During embryo development, the 92 kDa and 22 kDa bands gradually decreased in intensity, becoming undetectable in alevins. The 68 kDa band and a minor 24 kDa band became more intense after the eyed stage. Two additional peptides, corresponding to 40 and 28 kDa, newly appeared in alevins. During embryonic growth, the beta'-component band (17 kDa) persisted and phosvitin appeared to be progressively dephosphorylated. In vitro analysis of lipovitellin proteolysis indicated that the enzyme involved is a Pefabloc SC-sensitive serine protease. These results demonstrate, for the first time, that a cathepsin D-like protease and serine proteases play key roles in yolk formation and degradation, respectively, in salmonid fishes.

Purification and characterization of cathepsin D from herring muscle (Clupea harengus)

Cathepsin D was purified and concentrated 469-fold from a homogenate of Clupea harengus muscle. The purified enzyme is a monomer with a molecular weight of 38000-39000. It is inhibited by pepstatin and has optimal activity at pH 2.5 with hemoglobin as the substrate. The isoelectric point is at pH 6.8. Glycosidase treatment and binding to Concanavalin A indicated that the enzyme contains one N-linked carbohydrate moiety of the high-mannose type per molecule. The first 21 amino acid residues of the N-terminal showed high similarity to cathepsin D from antarctic icefish liver (Chionodraco hamatus) and trout ovary (Oncorhynchus mykiss). Digestion of the beta-chain of oxidized insulin resulted in preferential cleavage at Leu(15)-Tyr(16), (47%), Tyr(16)-Leu(17) (34%) and Ala(14)-Leu(15) (18%). Incubation with myofibrils from herring muscle at pH 4.23 showed that the enzyme mainly degraded myosin, actin and tropomyosin.