Molecular cloning and functional characterisation of a cathepsin L-like proteinase from the fish kinetoplastid parasite Trypanosoma carassii

Comparative analysis of two cathepsin L genes in Asiatic hard clam (Meretrix meretrix): Similar in sequence features, different in expression profiles

Cathepsin L is widely found in eukaryotes and prokaryotes, and it plays important roles in innate immunity. In the present study, we cloned two cathepsin L genes (designated as MmCTSL1 and MmCTSL2, respectively) from Asiatic hard clam (Meretrix meretrix). The complete sequence of MmCTSL1 cDNA contained a 5' untranslated region (UTR) of 31 bp, a 3' UTR of 228 bp with a poly (A) tail, and an open reading frame (ORF) of 1005 bp encoding 334 amino acids with predicted molecular weight of 37.5 kDa and theoretical isoelectric point of 5.27, and contained a signal peptide (from M1 to A16), a protease inhibitor I29 family domain (from W27 to F87), and a papain family cysteine protease domain (from L118 to T333). The complete sequence of MmCTSL2 cDNA contained a 5' UTR of 50 bp, a 3' UTR of 162 bp with a poly (A) tail, and an ORF of 996 bp encoding a polypeptide of 331 amino acids with predicted molecular weight of 36.8 kDa and theoretical isoelectric point of 7.07. It contained a signal peptide (from M1 to A16), a protease inhibitor I29 family domain (from W30 to F89), and a papain family cysteine protease domain (from L115 to T330). Real-time quantitative PCR analysis demonstrated that MmCTSL1 and MmCTSL2 were widely expressed in all the tested tissues, including adductor muscle, foot, gill, hemocytes, hepatopancreas and mantle, with the highest mRNA expression level in hepatopancreas and hemocytes, respectively. After Vibrio splendidus challenge, the mRNA expression levels of MmCTSL1 and MmCTSL2 in hemocytes and hepatopancreas were both significantly up-regulated with different expression profiles. In hemocytes, the expression levels of MmCTSL1 and MmCTSL2 reached their respective peaks (3.4-fold and 13.0-fold compared with the control, respectively) at 12 h after bacterial challenge, and MmCTSL2 responds earlier than MmCTSL1. In hepatopancreas, the expression levels of MmCTSL1 and MmCTSL2 reached their respective peaks at 6 h (9.0-fold compared with the control) and 24 h (2.8-fold compared with the control) after bacterial challenge, meaning that MmCTSL1 responds earlier than MmCTSL2. At the same time, whether in hepatopancreas or hemocytes, MmCTSL1 persist for a while after the bacterial challenge peak, while MmCTSL2 would quickly return to the initial level after the bacterial challenge peak. These results indicate that cathepsin L may be involved in the immune process of hard clam against V. splendidus with different potential roles.

A role of cathepsin L gene in innate immune response of crayfish (Procambarus clarkii)

Cathepsin L is one of the crucial enzyme superfamilies and involved in the immune responses. In the present study, cathepsin L gene from the red crayfish Procambarus clarkii, named PcCTSL, was cloned and characterized. The cDNA fragment of PcCTSL was 1026 bp in length, which encoded a putative protein of 341 amino acid residues with a molecular weight of 37.884 kDa. The theoretical isoelectric point was 5.218. The prepro-cathepsin L was comprised of a typical signal peptide (Met₁-Ala₁₈), a prodomain proregion peptide (Trp₂₉-Phe₈₉) and a mature peptide (Leu₁₂₄-Leu₃₄₀). Homology analysis indicated that PcCTSL exhibited 53.2%-87.1% identity to other selected species. The recombinant protein of PcCTSL was successfully expressed in Escherichia coli and rabbit anti-PcCTSL polyclonal antibodies were prepared. Real-time quantitative reverse transcription-PCR (qPCR) analysis revealed that the PcCTSL was expressed in all examined tissues, while the greatest mRNA level was observed in hepatopancreas. The expression of PcCTSL mRNA was clearly up regulated in hepatopancreas after challenge by lipopolysaccharide (LPS) and polyriboinosinic polyribocytidylic acid (Poly I:C). RNA interference of PcCTSL affected the gene expression of members of the Toll pathway. Our results suggest that the PcCTSL may play an important role to defend P. clarkii against the pathogens infection.

Mucosal expression signatures of two Cathepsin L in channel catfish (Ictalurus punctatus) following bacterial challenge

The mucosal surfaces of fish are the first line of host defense against various pathogens. The mucosal immune responses are the most critical events to prevent pathogen attachment and invasion. Cathepsins are a group of peptidases that involved in different levels of immune responses, but the knowledge of the roles of Cathepsin in mucosal immune responses against bacterial infection are still lacking. Therefore, in the present study we characterized the Cathepsin L gene family in channel catfish, and profiled their expression levels after challenging with two different Gram-negative bacterial pathogens. Here, two Cathepsin L genes were identified from channel catfish and were designated CTSL1a and CTSL.1. Comparing to other fish species, the catfish CTSL genes are highly conserved in their structural features. Phylogenetic analysis was conducted to confirm the identification of CTSL genes. Expression analysis revealed that the CTSL genes were ubiquitously expressed in all tested tissues. Following infection, the CTSL genes were significantly induced at most timepoints in mucosal tissues. But the expression patterns varied depending on both pathogen and tissue types, suggesting that CTSL genes may exert disparate functions or exhibit distinct tissue-selective roles in mucosal immune responses. Our findings here, clearly revealed the key roles of CTSL in catfish mucosal immunity; however, further studies are needed to expand functional characterization and examine whether CTSL may also play additional physiological roles in catfish mucosal tissues.

Molecular cloning and characterization of cathepsin L from freshwater mussel, Cristaria plicata

Cathepsin L is one of the crucial enzyme superfamilies and involved in the immune responses. The Cathepsin L cDNA and genome of Cristaria plicata（CpCL） was cloned from the hemocytes using degenerate primers by the rapid amplification of cDNA ends (RACE) PCR. The genomic DNA was 9353 bp long and had a total of six introns and seven exons. The full-length cDNA of CpCL was 1144 bp, the cDNA contained a 5' untranslated region (UTR) of 34 nucleotides, the 3' UTR of 108 bp with a canonical polyadenylation signal sequence AATAAA and a polyA tail, and an open reading frame (ORF) of 1002 bp, encoding 333 amino acid residues with 37.65 kDa predicted molecular weight. The theoretical isoelectric point was 8.61. The prepro-cathepsin L was consisted of a typical signal peptide (Met1-Gly20), a pro-region peptide (Leu21-Glu116) and a mature peptide (Tyr117-Val333). Many members of the papain family possessed of a proline residue at position 2 in the mature enzymem, this was also observed in CpCL. The preproprotein included an oxyanion hole (Gln 135), the active center formed by Cys141, His280 and Asn 300, the potential N-glycosylation site (Asn38, Asn 113 and Asn 272) and the conserved GCXGG motifs, which was characteristic of cathepsin, the conserved ERWNIN and GNFD motifs, which were characteristic for cathepsin L. Homology analysis revealed that the CpCL shared 49-87% identity to other known cathepsin L sequences. The phylogenetic tree showed that the CpCL clustered with the invertebrate cathepsin L cysteine proteases, and was closely related to the cathepsin L of Hyriopsis cumingii. The expression of CpCL mRNA was detected in hepatopancreas, hemocytes, mantle, gills and adductor muscle, and the higher expression level was in hepatopancreas. After A. hydrophila stimulation, the expression of the CpCL mRNA was up-regulated in hemocytes and hepatopancreas, and the expression level was significantly lower in gill than one after PBS challenge group.

Immunity against selected piscine flagellates

This discussion is on immune response to Amyloodinium ocellatum, Cryptobia salmositica, Trypanoplasma borreli and Trypanosoma carassii. Piscidin and histone-like proteins enhance innate resistance to Amyloodinium. Fish that are naturally resistant to Cryptobia and Trypanoplasma can be bred. Cryptobia resistance in charr is controlled by a dominant Mendelian locus and protection is via the Alternative Pathway of Complement Activation. Studies on Cryptobia-tolerant charr may lead to production of transgenic Cryptobia-tolerant salmon. Innate response to T. borreli is associated with NO in macrophages. Transferrin regulates resistance and carp have been bred for transferrin genotypes. Recovered fish are protected from homologous challenge, and complement fixing antibodies are crucial in protection. Studies on antigens in T. carassii may lead to a vaccine. There are two vaccines against cryptobiosis; a single dose of the attenuated vaccine protects salmonids. On challenge fish inoculated with the metalloprotease-DNA vaccine do not have the disease and they recover faster.

Expression and characterization of cathepsin L-like cysteine protease from Philasterides dicentrarchi

Philasterides dicentrarchi is a causative agent of scuticociliatosis in olive flounder Paralichthys olivaceus, aquaculture in Korea. In this study, a cDNA encoding a cathepsin L-like cysteine protease (PdCtL) of P. dicentrarchi (synonym Miamiensis avidus) was identified. To express the PdCtL recombinant protein in a heterologous system, 10 codons were redesigned to conform to the standard eukaryotic genetic code using polymerase chain reaction (PCR)-based site-directed mutagenesis. The recombinant P. dicentrarchi procathepsin L (proPdCtL) was expressed at high levels in E. coli Rosetta (DE3) pLysS with a pPET21a vector, and successfully refolded, purified, and activated into a functional and enzymatically active form. The optimal pH for protease activity was 5. Similar to other cysteine proteases, enzyme activity was inhibited by E64 and leupeptin. Immunogenicity of recombinant PdCtL was assessed by enzyme-linked immunosorbent assay, western blot, and specific anti-recombinant PdCtL antibodies were detected. Our results suggest that the biochemical characteristics of the recombinant ciliate proPdCtL protein are similar to those of the cathepsin L-like cysteine protease, that the PCR-based site-direct mutated ciliate gene was successfully expressed in a biochemically active form, and that the recombinant PdCtL acted as a specific epitope in olive flounder.

Macrobrachium rosenbergii cathepsin L: molecular characterization and gene expression in response to viral and bacterial infections

Cathepsin L (MrCathL) was identified from a constructed cDNA library of freshwater prawn Macrobrachium rosenbergii. MrCathL full-length cDNA is 1161 base pairs (bp) with an ORF of 1026bp which encodes a polypeptide of 342 amino acid (aa) long. The eukaryotic cysteine proteases, histidine and asparagine active site residues were identified in the aa sequence of MrCathL at 143-154, 286-296 and 304-323, respectively. The pair wise clustalW analysis of MrCathL showed the highest similarity (97%) with the homologous cathepsin L from Macrobrachium nipponense and the lowest similarity (70%) from human. Phylogenetic analysis revealed two distinct clusters of the invertebrates and vertebrates cathepsin L in the phylogenetic tree. MrCathL and cathepsin L from M. nipponense were clustered together, formed a sister group to cathepsin L of Penaeus monodon, and finally clustered to Lepeophtheirus salmonis. High level of (P<0.05) MrCathL gene expression was noticed in haemocyte and lowest in eyestalk. Furthermore, the MrCathL gene expression in M. rosenbergii was up-regulated in haemocyte by virus [M. rosenbergii nodovirus (MrNV) and white spot syndrome baculovirus (WSBV)] and bacteria (Vibrio harveyi and Aeromonas hydrophila). The recombinant MrCathL exhibited a wide range of activity in various pH between 3 and 10 and highest at pH 7.5. Cysteine proteinase (stefin A, stefin B and antipain) showed significant influence (100%) on recombinant MrCathL enzyme activity. The relative activity and residual activity of recombinant MrCathL against various metal ions or salts and detergent tested at different concentrations. These results indicated that the metal ions, salts and detergent had an influence on the proteinase activity of recombinant MrCathL. Conclusively, the results of this study imply that MrCathL has high pH stability and is fascinating object for further research on the function of cathepsin L in prawn innate immune system.

Cloning and characterization of a cathepsin L-like cysteine protease from Taenia pisiformis

Rabbit cysticercosis, caused by the larval stage of Taenia pisiformis, is a serious parasitic disease of rabbits. It was reported that some cysteine peptidases have potential roles in the pathogenesis of various parasitic infections. To investigate the biochemical characteristics and roles in the pathogenesis/host-invasion of cysteine peptidases, a cDNA sequence encoding for a cathepsin L-like cysteine protease (TpCP) was cloned and identified from the T. pisiformis metacestodes. This sequence was 1220 bp in its length, which included a 1017 bp open reading frame encoding a 339 amino acid peptide. Multiple sequence alignments revealed a 28.9-88.5% similarity with cathepsin L-like cysteine proteases from other helminth parasites and mammals. The recombinant TpCP expressed in Escherichia coli did not show the proteolytic activity by zymography gel assay. However, the TpCP expressed in Pichia pastoris had typical biochemical activities that could hydrolyze rabbit immunoglobulin G, bovine serum albumin and fibronectin. Substrate studies indicated pronounced cleavage of Z-Phe-Arg-AMC. This activity was sensitive to cysteine protease inhibitor E-64 and immunohistochemistry results also indicated that TpCP was distributed as an intense positive reaction in the bladder wall. Our results gave us insights into future studies of TpCP's roles in the infection.

The protease degrading sperm histones post-fertilization in sea urchin eggs is a nuclear cathepsin L that is further required for embryo development

Proteolysis of sperm histones in the sea urchin male pronucleus is the consequence of the activation at fertilization of a maternal cysteine protease. We previously showed that this protein is required for male chromatin remodelling and for cell-cycle progression in the newly formed embryos. This enzyme is present in the nucleus of unfertilized eggs and is rapidly recruited to the male pronucleus after insemination. Interestingly, this cysteine-protease remains co-localized with chromatin during S phase of the first cell cycle, migrates to the mitotic spindle in M-phase and is re-located to the nuclei of daughter cells after cytokinesis. Here we identified the protease encoding cDNA and found a high sequence identity to cathepsin proteases of various organisms. A phylogenetical analysis clearly demonstrates that this sperm histone protease (SpHp) belongs to the cathepsin L sub-type. After an initial phase of ubiquitous expression throughout cleavage stages, SpHp gene transcripts become restricted to endomesodermic territories during the blastula stage. The transcripts are localized in the invaginating endoderm during gastrulation and a gut specific pattern continues through the prism and early pluteus stages. In addition, a concomitant expression of SpHp transcripts is detected in cells of the skeletogenic lineage and in accordance a pharmacological disruption of SpHp activity prevents growth of skeletal rods. These results further document the role of this nuclear cathepsin L during development.

Repertoire, genealogy and genomic organization of cruzipain and homologous genes in Trypanosoma cruzi, T. cruzi-like and other trypanosome species

Trypanosoma cruzi, the agent of Chagas disease, is a complex of genetically diverse isolates highly phylogenetically related to T. cruzi-like species, Trypanosoma cruzi marinkellei and Trypanosoma dionisii, all sharing morphology of blood and culture forms and development within cells. However, they differ in hosts, vectors and pathogenicity: T. cruzi is a human pathogen infective to virtually all mammals whilst the other two species are non-pathogenic and bat restricted. Previous studies suggest that variations in expression levels and genetic diversity of cruzipain, the major isoform of cathepsin L-like (CATL) enzymes of T. cruzi, correlate with levels of cellular invasion, differentiation, virulence and pathogenicity of distinct strains. In this study, we compared 80 sequences of genes encoding cruzipain from 25 T. cruzi isolates representative of all discrete typing units (DTUs TcI-TcVI) and the new genotype Tcbat and 10 sequences of homologous genes from other species. The catalytic domain repertoires diverged according to DTUs and trypanosome species. Relatively homogeneous sequences are found within and among isolates of the same DTU except TcV and TcVI, which displayed sequences unique or identical to those of TcII and TcIII, supporting their origin from the hybridization between these two DTUs. In network genealogies, sequences from T. cruzi clustered tightly together and closer to T. c. marinkellei than to T. dionisii and largely differed from homologues of T. rangeli and T. b. brucei. Here, analysis of isolates representative of the overall biological and genetic diversity of T. cruzi and closest T. cruzi-like species evidenced DTU- and species-specific polymorphisms corroborating phylogenetic relationships inferred with other genes. Comparison of both phylogenetically close and distant trypanosomes is valuable to understand host-parasite interactions, virulence and pathogenicity. Our findings corroborate cruzipain as valuable target for drugs, vaccine, diagnostic and genotyping approaches.

Immune evasion strategies of trypanosomes: a review

Trypanosomes are digenetic protozoans that infect domestic and wild animals, as well as humans. They cause important medical and veterinary diseases, making them a major public health concern. There are many species of trypanosomes that infect virtually all vertebrate taxa. They typically cycle between insect or leech vectors and vertebrate hosts, and they undergo biochemical and morphological changes in the process. Trypanosomes have received much attention in the last 4 decades because of the diseases they cause and their remarkable armamentarium of immune evasion mechanisms. The completed genome sequences of trypanosomes have revealed an extensive array of molecules that contribute to various immune evasion mechanisms. The different species interact uniquely with their vertebrate hosts with a wide range of evasion strategies and some of the most fascinating immune evasion mechanisms, including antigenic variation that was first described in the trypanosomes. This review focuses on the variety of strategies that these parasites have evolved to evade or modulate immunity of endothermic and ectothermic vertebrates.

Cysteine proteases as potential antigens in antiparasitic DNA vaccines

Cysteine proteases in parasites are potent inducers of vertebrate host immune responses and may under certain circumstances take part in the pathogen's immune evasion strategies. These capacities place these parasite molecules as interesting candidate antigens in antiparasitic vaccines for use in vertebrates. Parasite cysteine proteases are able to skew the Th1/Th2 profile in mammals towards a response which allows sustainable parasite burdens in the host. DNA vaccines are also able to skew the Th1/Th2 profile by different administration techniques and the use of cysteine proteases in these genetic immunizations open perspectives for manipulation of the host immune response towards higher protection.

Cysteine proteases of Trypanosoma (Megatrypanum) theileri: cathepsin L-like gene sequences as targets for phylogenetic analysis, genotyping diagnosis

Although Trypanosomatheileri and allied trypanosomes are the most widespread trypanosomes in bovids little is known about proteolytic enzymes in these species. We have characterized genes encoding for cathepsin L-like (CATL) cysteine proteases from isolates of cattle, water buffalo and deer that largely diverged from homologues of other trypanosome species. Analysis of 78 CATL catalytic domain sequences from 22 T. theileri trypanosomes disclosed 6 genotypes tightly clustered together into the T. theileri clade. The CATL genes in these trypanosomes are organized in tandem arrays of approximately 1.7kb located in 2 chromosomal bands of 600-720kb. A diagnostic PCR assay targeting CATL sequences detected T. theileri of all genotypes from cattle, buffaloes and cervids and also from tabanid vectors. Expression of T. theileri cysteine proteases was demonstrated by proteolytic activity in gelatin gels and hydrolysis of Z-Phe-Arg-AMC substrate. Results from this work agree with previous data using ribosomal and spliced leader genes demonstrating that CATL gene sequences are useful for diagnosis, population genotyping and evolutionary studies of T. theileri trypanosomes.

Genes of cathepsin L-like proteases in Trypanosoma rangeli isolates: markers for diagnosis, genotyping and phylogenetic relationships

We have sequenced genes encoding cathepsin L-like (CatL-like) cysteine proteases from isolates of Trypanosoma rangeli from humans, wild mammals and Rhodnius species of Central and South America. Phylogenetic trees of sequences encoding mature CatL-like enzymes of T. rangeli and homologous genes from other trypanosomes, Leishmania spp. and bodonids positioned sequences of T. rangeli (rangelipain) closest to T. cruzi (cruzipain). Phylogenetic tree of kinetoplastids based on sequences of CatL-like was totally congruent with those derived from SSU rRNA and gGAPDH genes. Analysis of sequences from the CatL-like catalytic domains of 17 isolates representative of the overall phylogenetic diversity and geographical range of T. rangeli supported all the lineages (A-D) previously defined using ribosomal and spliced leader genes. Comparison of the proteolytic activities of T. rangeli isolates revealed heterogeneous banding profiles of cysteine proteases in gelatin gels, with differences even among isolates of the same lineage. CatL-like sequences proved to be excellent targets for diagnosis and genotyping of T. rangeli by PCR. Data from CatL-like encoding genes agreed with results from previous studies of kDNA markers, and ribosomal and spliced leader genes, thereby corroborating clonal evolution, independent transmission cycles and the divergence of T. rangeli lineages associated with sympatric species of Rhodnius.

Cathepsin L-like genes of Trypanosoma vivax from Africa and South America--characterization, relationships and diagnostic implications

We characterized sequences from genes encoding cathepsin L-like (CatL-like) cysteine proteases from African and South American isolates of Trypanosoma vivax and T. vivax-like organisms, and evaluated their suitability as genetic markers for population structure analysis and diagnosis. Phylogenetic analysis of sequences corresponding to CatL-like catalytic domains revealed substantial polymorphism, and clades of sequences (TviCatL1-9) were separated by large genetic distances. TviCatL1-4 sequences were from cattle isolates from West Africa (Nigeria and Burkina Faso) and South America (Brazil and Venezuela), which belonged to the same T. vivax genotype. T. vivax-like genotypes from East Africa showed divergent sequences, including TviCatL5-7 for isolates from Mozambique and TviCatL8-9 for an isolate from Kenya. Phylogenetic analysis of CatL-like gene data supported the relationships among trypanosome species reflected in the phylogenies based on the analysis of small subunit (SSU) of ribosomal RNA gene sequence data. The discovery of different CatL-like sequences for each genotype, defined previously by ribosomal DNA data, indicate that these sequences provide useful targets for epidemiological and population genetic studies. Regions in CatL-like sequences shared by all T. vivax genotypes but not by other trypanosomes allowed the establishment of a specific and sensitive diagnostic PCR for epidemiological studies in South America and Africa.

cDNA expression library screening and identification of two novel antigens: ubiquitin and receptor for activated C kinase (RACK) homologue, of the fish parasite Trypanosoma carassii

Trypanosoma carassii is a kinetoplastid parasite infecting cyprinid fish with a high prevalence in nature. Antibodies have been shown to play a protective role in the immune response against this parasite in common carp, Cyprinus carpio. To identify immunogenic and putative protective T. carassii antigens we constructed a lambdaTriplEx2 expression library of the parasite and screened this with pooled carp immune serum collected 6 weeks post-infection. Screening of the library not only revealed ribosomal proteins but identified ubiquitin and a homologue of the receptor for activated C kinase (RACK) as immunogenic proteins. Equivalents of all these proteins have been identified as immunogenic in expression library screenings of other Trypanosomatida, suggesting an evolutionary conservation of their immunogenicity. The possibility that ubiquitin and/or the homologue of RACK could represent protective antigens and be targets for the design of novel therapies is discussed.