Entamoeba dispar: cloning and characterization of peroxiredoxin genes

Peroxiredoxins in parasites

SIGNIFICANCE

Parasite survival and virulence relies on effective defenses against reactive oxygen and nitrogen species produced by the host immune system. Peroxiredoxins (Prxs) are ubiquitous enzymes now thought to be central to such defenses and, as such, have potential value as drug targets and vaccine antigens.

RECENT ADVANCES

Plasmodial and kinetoplastid Prx systems are the most extensively studied, yet remain inadequately understood. For many other parasites our knowledge is even less well developed. Through parasite genome sequencing efforts, however, the key players are being discovered and characterized. Here we describe what is known about the biochemistry, regulation, and cell biology of Prxs in parasitic protozoa, helminths, and fungi. At least one Prx is found in each parasite with a sequenced genome, and a notable theme is the common patterns of expression, localization, and functionality among sequence-similar Prxs in related species.

CRITICAL ISSUES

The nomenclature of Prxs from parasites is in a state of disarray, causing confusion and making comparative inferences difficult. Here we introduce a systematic Prx naming convention that is consistent between organisms and informative about structural and evolutionary relationships.

FUTURE DIRECTIONS

The new nomenclature should stimulate the crossfertilization of ideas among parasitologists and with the broader redox research community. The diverse parasite developmental stages and host environments present complex systems in which to explore the variety of roles played by Prxs, with a view toward parlaying what is learned into novel therapies and vaccines that are urgently needed.

Immunological role of thiol-dependent peroxiredoxin gene in Macrobrachium rosenbergii

In this study, we have reported a full length of peroxiredoxin (designated MrPrdx) gene, identified from the transcriptome of freshwater prawn Macrobrachium rosenbergii. The complete gene sequence of the MrPrdx is 940 base pairs in length, and encodes 186 amino acids. MrPrdx contains a long thioredoxin domain in the amino acid sequence between 34 and 186. The gene expressions of MrPrdx in healthy and the infectious hypodermal and hematopoietic necrosis virus (IHHNV) challenged M. rosenbergii were examined using quantitative real time polymerase chain reaction. MrPrdx is highly expressed in all the other tissues of M. rosenbergii considered for analysis and the highest in gills. The expression is strongly up-regulated in gills after IHHNV infection. To understand MrPrdx functional properties, the recombinant MrPrdx protein was expressed in Escherichia coli BL21 (DE3) and purified. A peroxidise activity assay was conducted using recombinant MrPrdx protein at different concentrations. This peroxidises activity showed that the recombinant MrPrdx is a thiol-dependant protein. Additionally, this result showed that recombinant MrPrdx protein, as a secretory protein can remove H₂O₂ and protect DNA damage. This finding leads a possible way to propose the recombinant MrPrdx protein as an effective medicine for reactive oxygen species (ROS) related diseases.

An unusual surface peroxiredoxin protects invasive Entamoeba histolytica from oxidant attack

Peroxiredoxins are an important class of antioxidant enzymes found from Archaea to humans, which reduce and thereby detoxify peroxides and peroxynitrites. The major thiol-containing surface antigen of the invasive ameba, Entamoeba histolytica, is a peroxiredoxin and is likely to be important during the transition from the anaerobic environment of the large intestine to human tissues. The closely related species, Entamoeba dispar, is incapable of invasion and more sensitive to hydrogen peroxide, yet also has a peroxiredoxin. We cloned and expressed the two active recombinant enzymes and found that their activity was similar by a fluorometric stopped-flow assay, giving a Km of <10 microM for hydrogen peroxide. Three monoclonal antibodies produced to recombinant E. histolytica peroxiredoxin cross-reacted with Entamoeba dispar.E. histolytica contains as much as 50 times more peroxiredoxin than E. dispar as demonstrated by a sensitive capture ELISA. In addition, the peroxiredoxin is present largely on the outer surface of the cell, in contrast to E. dispar. This unusual peroxiredoxin localizes to the site of parasite-host cell contact where it can effectively counteract oxidants generated by host cells, thus facilitating invasion.

Molecular characterization of peroxiredoxin from Entamoeba moshkovskii and a comparison with Entamoeba histolytica

Peroxiredoxin of the pathogenic parasite, Entamoeba histolytica, is thought to be involved in protection from oxidative attack by host phagocytic cells and endogenously generated hydrogen peroxide. In this study, we cloned peroxiredoxin genes from the nonpathogenic ameba, Entamoeba moshkovskii, and characterized the peroxiredoxin protein. The open reading frame of three cloned cDNAs was demonstrated to encode a polypeptide of 218 or 217 amino acids. Identity of the amino acid sequence of peroxiredoxins between E. moshkovskii and E. histolytica was considerably high (77-81%), but the N-terminus portion of E. moshkovskii peroxiredoxin was shorter than that of E. histolytica. A recombinant peroxiredoxin of E. moshkovskii expressed in Escherichia coli exhibited hydrogen peroxidase activity. Its K(m) and V(max) values of 35 microM and 0.07 micromol/min/mg protein were approximately 1 and 1.5 times greater than E. histolytica peroxiredoxin, respectively. In addition, the protective effect of E. moshkovskii peroxiredoxin against oxidative-nicking of supercoiled plasmid DNA was shown to be greater than that of E. histolytica peroxiredoxin. Confocal laser scanning microscopy, using polyclonal antibody against the recombinant E. moshkovskii peroxiredoxin, demonstrated that this protein was localized in the nucleus and cytoplasm of trophozoites, supporting its function as a protectant against DNA damage. Southern blot and real-time reverse transcription PCR analyses of the E. moshkovskii peroxiredoxin gene demonstrated that it was a multi-copy gene and its expression was comparable to that of E. histolytica. These results suggest that the antioxidant peroxiredoxin is important for protection against endogenously generated hydrogen peroxide in the nonpathogenic ameba.

Entamoeba histolytica: cDNAs cloned as 30kDa collagen-binding proteins (CBP) belong to an antioxidant molecule family. Protection of hamsters from amoebic liver abscess by immunization with recombinant CBP

A cDNA expression library of Entamoeba histolytica was screened with antiserum to native amoebic collagen binding proteins (CBPs), and two clones C13 and C7 which partially encode for the 30 kDa CBP were obtained. The sequenced clones were 90% homologous. C7 had a 69 bp deletion at the 5' end that is present in C13 and encodes for a Glu-Cys-Lys rich region and a four amino acids repeat (Glu-Lys-Glu-Cys). Purified fusion proteins from these cDNA clones were able to bind native type I collagen gels in a pH, calcium, ionic strength, and temperature dependent way. The binding of pgtC13 to collagen gel was time and temperature stable, while pgtC7 binding was not, suggesting that the deleted region in C7 is important for the binding. The clones reported here partially encode a 30 kDa CBP that also belong to an antioxidant molecule family. We demonstrated that the fusion protein pgtC13 is immunogenic and partially protective as a subunit vaccine in the hamster model of amoebic liver abscess.

Detection and genotyping of Entamoeba histolytica, Entamoeba dispar, Giardia lamblia, and Cryptosporidium parvum by oligonucleotide microarray

Entamoeba histolytica, Giardia lamblia, and Cryptosporidium parvum are the most frequently identified protozoan parasites causing waterborne disease outbreaks. The morbidity and mortality associated with these intestinal parasitic infections warrant the development of rapid and accurate detection and genotyping methods to aid public health efforts aimed at preventing and controlling outbreaks. In this study, we describe the development of an oligonucleotide microarray capable of detecting and discriminating between E. histolytica, Entamoeba dispar, G. lamblia assemblages A and B, and C. parvum types 1 and 2 in a single assay. Unique hybridization patterns for each selected protozoan were generated by amplifying six to eight diagnostic sequences/organism by multiplex PCR; fluorescent labeling of the amplicons via primer extension; and subsequent hybridization to a set of genus-, species-, and subtype-specific covalently immobilized oligonucleotide probes. The profile-based specificity of this methodology not only permitted for the unequivocal identification of the six targeted species and subtypes, but also demonstrated its potential in identifying related species such as Cryptosporidium meleagridis and Cryptosporidium muris. In addition, sensitivity assays demonstrated lower detection limits of five trophozoites of G. lamblia. Taken together, the specificity and sensitivity of the microarray-based approach suggest that this methodology may provide a promising tool to detect and genotype protozoa from clinical and environmental samples.

Serodiagnosis of amoebiasis using a recombinant protein fragment of the 29 kDa surface antigen of Entamoeba histolytica

To develop an improved serodiagnostic test for amoebiasis, we performed a detailed analysis of the immunodominant epitopes of the 29 kDa surface antigen and evaluated its sensitivity and specificity. Enzyme-linked immunosorbent assay (ELISA) based on the fragment containing the immunodominant epitope was evaluated further and compared with full-length recombinant 29 kDa protein. Specificity and sensitivity of the two ELISAs were assessed using 55 human sera of parasitic protozoa infection cases (25 amoebiasis, 20 giardiasis and 10 toxoplasmosis sera) and 10 healthy control sera. The immunodominant epitope of the 29 kDa antigen is localised only in the N-terminus 14-54 amino acid residues. The sensitivities of the two ELISAs were very high, 92 and 96%, respectively. The specificity of the fragment was 100%, whereas the specificity of the full-length 29 kDa protein was 86.6%. These results indicate that the fragment containing the immunodominant epitope of the 29 kDa protein can be used to accurately serodiagnose amoebiasis without cross-reactivity from other parasites.

Recent developments in amoebiasis research

Invasive amoebiasis, the infection of humans by Entamoeba histolytica associated with dysentery and liver abscess, is still a major cause of morbidity and mortality in developing countries. This review attempts to reduce the gap between the overwhelming amount of information coming recently from laboratory research and the sparse contributions resulting from clinical and epidemiological investigations of the second parasitic cause of death resulting from a protozoan parasite.