Entamoeba histolytica: In Silico and In Vitro Oligomerization of EhHSTF5 Enhances Its Binding to the HSE of the EhPgp5 Gene Promoter.

Throughout its lifecycle, Entamoeba histolytica encounters a variety of stressful conditions. This parasite possesses Heat Shock Response Elements (HSEs) which are crucial for regulating the expression of various genes, aiding in its adaptation and survival. These HSEs are regulated by Heat Shock Transcription Factors (EhHSTFs). Our research has identified seven such factors in the parasite, designated as EhHSTF1 through to EhHSTF7. Significantly, under heat shock conditions and in the presence of the antiamoebic compound emetine, EhHSTF5, EhHSTF6, and EhHSTF7 show overexpression, highlighting their essential role in gene response to these stressors. Currently, only EhHSTF7 has been confirmed to recognize the HSE as a promoter of the EhPgp5 gene (HSE_EhPgp5), leaving the binding potential of the other EhHSTFs to HSEs yet to be explored. Consequently, our study aimed to examine, both in vitro and in silico, the oligomerization, and binding capabilities of the recombinant EhHSTF5 protein (rEhHSTF5) to HSE_EhPgp5. The in vitro results indicate that the oligomerization of rEhHSTF5 is concentration-dependent, with its dimeric conformation showing a higher affinity for HSE_EhPgp5 than its monomeric state. In silico analysis suggests that the alpha 3 α-helix (α3-helix) of the DNA-binding domain (DBD5) of EhHSTF5 is crucial in binding to the major groove of HSE, primarily through hydrogen bonding and salt-bridge interactions. In summary, our results highlight the importance of oligomerization in enhancing the affinity of rEhHSTF5 for HSE_EhPgp5 and demonstrate its ability to specifically recognize structural motifs within HSE_EhPgp5. These insights significantly contribute to our understanding of one of the potential molecular mechanisms employed by this parasite to efficiently respond to various stressors, thereby enabling successful adaptation and survival within its host environment.

Development of nucleic acid lateral flow immunoassay for molecular detection of Entamoeba moshkovskii and Entamoeba dispar in stool samples.

Entamoeba moshkovskii, recently known as a possible pathogenic amoeba, and the non-pathogenic Entamoeba dispar are morphologically indistinguishable by microscopy. Although PCR was used for differential diagnosis, gel electrophoresis is labor-intensive, time-consuming, and exposed to hazardous elements. In this study, nucleic acid lateral flow immunoassay (NALFIA) was developed to detect E. moshkovskii and E. dispar by post-PCR amplicon analysis. E. moshkovskii primers were labeled with digoxigenin and biotin whereas primers of E. dispar were lebeled with FITC and digoxigenin. The gold nanoparticles were labeled with antibodies corresponding to particular labeling. Based on the established assay, NALFIA could detect as low as 975 fg of E. moshkovskii target DNA (982 parasites or 196 parasites/microliter), and 487.5 fg of E. dispar target DNA (444 parasites or 89 parasites/microliter) without cross-reactivity to other tested intestinal organisms. After testing 91 stool samples, NALFIA was able to detect seven E. moshkovskii (87.5% sensitivity and 100% specificity) and eight E. dispar samples (66.7% sensitivity and 100% specificity) compared to real-time PCR. Interestingly, it detected three mixed infections as real-time PCR. Therefore, it can be a rapid, safe, and effective method for the detection of the emerging pathogens E. moshkovskii and E. dispar in stool samples.

Modified trichrome stain for faster and improved detection of intestinal protozoan parasites.

Permanent stains such as trichrome have better sensitivity but are time-consuming and the fixative includes toxic mercuric chloride. Thus, a newer modification was tested and found to be a superior, faster and safer staining technique for intestinal parasitic detection. Our study lasted 9 months and a single stool sample was collected from each enrolled patient. We evaluated classical trichrome (T1 - using Schaudinn fixative) with newer modifications, which involved different fixatives with mordant combinations (T2 - acetic acid + hydrated aluminium sulphate, T3 - citric acid + copper sulphate hydrate). Conventional PCR targeting Entamoeba histolytica, Giardia lamblia and Cryptosporidium spp. was taken as the reference. Out of 175 stool samples, 25.1% protozoa were identified by wet mount, 24% by each T1 and T2, 25.7% by T3. Statistically, T3 and T2 had higher sensitivity as compared to T1 and wet mount when PCR was used as reference.

Revisiting the isolation and characterisation of Entamoeba histolytica lipopeptidophosphoglycan.

The parasite Entamoeba histolytica is the cause of amoebic dysentery and liver abscess in humans. On the protozoan cell surface, a variety of glycosylated molecules are involved in the interaction with the environment, such as attachment to the colonic mucus. One of these molecules is the lipopeptidophosphoglycan (LPPG), a complex surface component with antigenic properties. Its structure is only partly known, it is a glycosylphosphatidylinositol (GPI)-linked glycoprotein with a large amount of O-glycosylation. To date, the sequence of a core protein has not been identified. In this study, we further investigated this complex surface molecule aided by the availability of the monoclonal antibody EH5, which had been raised in our laboratory. We studied the extraction of LPPG in various solvent mixtures and discovered that 2-butanol saturated water was simple and superior to other solvents used in the past. The isolated LPPG was subjected to treatment with several proteases and the Ser/Thr specific cleavage agent scandium (III) trifluoromethanesulfonate (scandium triflate). The products were probed with antibody EH5 and the blots showed that the LPPG preparation was largely resistant to standard proteases, but could be cleaved by the scandium compound. These observations could point to the existence of a Ser- or Thr-rich core protein structure.

Genome-Wide Classification of Myb Domain-Containing Protein Families in Entamoeba invadens.

Entamoeba histolytica, the causative agent of amebiasis, is the third leading cause of death among parasitic diseases globally. Its life cycle includes encystation, which has been mostly studied in Entamoeba invadens, responsible for reptilian amebiasis. However, the molecular mechanisms underlying this process are not fully understood. Therefore, we focused on the identification and characterization of Myb proteins, which regulate the expression of encystation-related genes in various protozoan parasites. Through bioinformatic analysis, we identified 48 genes in E. invadens encoding MYB-domain-containing proteins. These were classified into single-repeat 1R (20), 2R-MYB proteins (27), and one 4R-MYB protein. The in-silico analysis suggests that these proteins are multifunctional, participating in transcriptional regulation, chromatin remodeling, telomere maintenance, and splicing. Transcriptomic data analysis revealed expression signatures of eimyb genes, suggesting a potential orchestration in the regulation of early and late encystation-excystation genes. Furthermore, we identified probable target genes associated with reproduction, the meiotic cell cycle, ubiquitin-dependent protein catabolism, and endosomal transport. In conclusion, our findings suggest that E. invadens Myb proteins regulate stage-specific proteins and a wide array of cellular processes. This study provides a foundation for further exploration of the molecular mechanisms governing encystation and unveils potential targets for therapeutic intervention in amebiasis.

Identification and Characterization of Entamoeba histolytica Choline Kinase.

PURPOSE: Entamoeba histolytica is one of the death-causing parasites in the world. Study on its lipid composition revealed that it is predominated by phosphatidylcholine and phosphatidylethanolamine. Further study revealed that its phosphorylated metabolites might be produced by the Kennedy pathway. Here, we would like to report on the characterizations of enzymes from this pathway that would provide information for the design of novel inhibitors against these enzymes in future. METHODOLOGY: E. histolytica HM-1:IMSS genomic DNA was isolated and two putative choline/ethanolamine kinase genes (EhCK1 and EhCK2) were cloned and expressed from Escherichia coli BL21 strain. Enzymatic characterizations were further carried out on the purified enzymes. RESULTS: EhCK1 and EhCK2 were identified from E. histolytica genome. The deduced amino acid sequences were more identical to its homologues in human (35-48%) than other organisms. The proteins were clustered as ethanolamine kinase in the constructed phylogeny tree. Sequence analysis showed that they possessed all the conserved motifs in choline kinase family: ATP-binding loop, Brenner's phosphotransferase motif, and choline kinase motif. Here, the open reading frames were cloned, expressed, and purified to apparent homogeneity. EhCK1 showed activity with choline but not ethanolamine. The biochemical characterization showed that it had a Vmax of 1.9 ± 0.1 µmol/min/mg. Its Km for choline and ATP was 203 ± 26 µM and 3.1 ± 0.4 mM, respectively. In contrast, EhCK2 enzymatic activity was only detected when Mn2+ was used as the co-factor instead of Mg2+ like other choline/ethanolamine kinases. Highly sensitive and specific antibody against EhCK1 was developed and used to confirm the endogenous EhCK1 expression using immunoblotting. CONCLUSIONS: With the understanding of EhC/EK importance in phospholipid metabolism and their unique characteristic, EhC/EK could be a potential target for future anti-amoebiasis study.

Peristomal cutaneous amebiasis causing rapidly progressive necrotic wound of a left lower quadrant end colostomy.

Cutaneous amebiasis is a rare clinical entity caused by the invasive protozoan parasite Entamoeba histolytica that can be readily diagnosed with skin biopsy if suspected. It presents as a rapidly progressive and destructive ulceration with necrosis. A man in his 40s with metastatic rectal cancer who underwent palliative abdominal perineal resection with end colostomy in his left lower quadrant and on systemic chemotherapy developed progressive breakdown of his peristomal skin unresponsive to antibiotics that was then diagnosed to be cutaneous amebiasis. It is important to be aware of cutaneous amebiasis and include it in the differential diagnosis when peristomal wounds do not respond to treatment.

Multi-locus sequence analysis reveals phylogenetically segregated Entamoeba histolytica population.

Amoebiasis, caused by the enteric parasite, Entamoeba histolytica, is one of the major food- and water-borne parasitic diseases in developing countries with improper sanitation and poor hygiene. Infection with E. histolytica has diverse disease outcomes, which are determined by the genetic diversity of the infecting strains. Comparative genetic analysis of infecting E. histolytica strains associated with differential disease outcomes from different geographical regions of the world is important to identify the specific genetic patterns of the pathogen that trigger certain disease outcomes of Amoebiasis. The strategy is able to elucidate the genealogical relation and population structure of infecting E. histolytica strains from different geographical regions. In the present study, we have performed a comparative genetic analysis of circulating E. histolytica strains identified from different parts of the world, including our study region, based on five tRNA-linked short tandem repeat (STR) loci (i.e., D-A, NK2, R-R, STGA-D and A-L) and evaluated their potential associations with differential disease outcomes of Amoebiasis. A number of regional-specific, emerging haplotypes of E. histolytica, significantly associated with specific disease outcomes have been identified. Haplotypes, which have a significant positive association with asymptomatic and amoebic liver abscess outcomes, showed a significant negative association with diarrheal outcome, or vice versa. Comparative multi-locus analysis revealed that E. histolytica isolates from our study region are phylogenetically segregated from the isolates of other geographical regions. This study provides a crucial overview of the population structure and emerging pattern of the enteric parasite, E. histolytica.

Screening and Structural Characterization of Heat Shock Response Elements (HSEs) in Entamoeba histolytica Promoters.

Entamoeba histolytica (E. histolytica) exhibits a remarkable capacity to respond to thermal shock stress through a sophisticated genetic regulation mechanism. This process is carried out via Heat Shock Response Elements (HSEs), which are recognized by Heat Shock Transcription Factors (EhHSTFs), enabling fine and precise control of gene expression. Our study focused on screening for HSEs in the promoters of the E. histolytica genome, specifically analyzing six HSEs, including Ehpgp5, EhrabB1, EhrabB4, EhrabB5, Ehmlbp, and Ehhsp100. We discovered 2578 HSEs, with 1412 in promoters of hypothetical genes and 1166 in coding genes. We observed that a single promoter could contain anywhere from one to five HSEs. Gene ontology analysis revealed the presence of HSEs in essential genes for the amoeba, including cysteine proteinases, ribosomal genes, Myb family DNA-binding proteins, and Rab GTPases, among others. Complementarily, our molecular docking analyses indicate that these HSEs are potentially recognized by EhHSTF5, EhHSTF6, and EhHSTF7 factors in their trimeric conformation. These findings suggest that E. histolytica has the capability to regulate a wide range of critical genes via HSE-EhHSTFs, not only for thermal stress response but also for vital functions of the parasite. This is the first comprehensive study of HSEs in the genome of E. histolytica, significantly contributing to the understanding of its genetic regulation and highlighting the complexity and precision of this mechanism in the parasite's survival.

Amoebic colitis and liver abscess: A rare case of autochthonous invasive infection due to Entamoeba histolytica.

We report an unusual and confirmed case of invasive amebiasis in a non-endemic area where the source of infection remains unknown. During her admission, the patient developed amebic colitis and extraintestinal liver abscess with a favorable outcome following the antiparasitic therapy.

Antigiardial and antiamebic activities of fexinidazole and its metabolites: new drug leads for giardiasis and amebiasis.

The intestinal parasites Giardia lamblia and Entamoeba histolytica are major causes of morbidity and mortality associated with diarrheal diseases. Metronidazole is the most common drug used to treat giardiasis and amebiasis. Despite its efficacy, treatment failures in giardiasis occur in up to 5%-40% of cases. Potential resistance of E. histolytica to metronidazole is an increasing concern. Therefore, it is critical to search for more effective drugs to treat giardiasis and amebiasis. We identified antigiardial and antiamebic activities of the rediscovered nitroimidazole compound, fexinidazole, and its sulfone and sulfoxide metabolites. Fexinidazole is equally active against E. histolytica and G. lamblia trophozoites, and both metabolites were 3- to 18-fold more active than the parent drug. Fexinidazole and its metabolites were also active against a metronidazole-resistant strain of G. lamblia. G. lamblia and E. histolytica cell extracts exhibited decreased residual nitroreductase activity when metabolites were used as substrates, indicating nitroreductase may be central to the mechanism of action of fexinidazole. In a cell invasion model, fexinidazole and its metabolites significantly reduced the invasiveness of E. histolytica trophozoites through basement membrane matrix. A q.d. oral dose of fexinidazole and its metabolites at 10 mg/kg for 3 days reduced G. lamblia infection significantly in mice compared to control. The newly discovered antigiardial and antiamebic activities of fexinidazole, combined with its FDA-approval and inclusion in the WHO Model List of Essential Medicines for the treatment of human African trypanosomiasis, offer decreased risk and a shortened development timeline toward clinical use of fexinidazole for treatment of giardiasis or amebiasis.

Evaluation of a rapid immunochromatographic test for the diagnosis of intestinal protozoan infections among patients attending a rural outreach outpatient department in Northern India.

Despite great efforts, intestinal protozoan infections remain a significant healthcare concern worldwide. Although many point-of-care (POC) tests are increasingly being used, microscopic examination of stool specimens remains the mainstay for their diagnosis, especially in resource-limited settings. We assessed the utility of rapid POC tests based on immunochromatography among patients from rural Northern India. A total of 78 patients were enrolled in the study. Out of nine specimens that tested positive for Giardia duodenalis on microscopy, an immunochromatographic test (ICT) could detect only five (55.55%). Entamoeba histolytica/dispar was demonstrated in two specimens on microscopy, both of which were missed by ICT. Its overall sensitivity, specificity, and positive and negative predictive value were 50%, 98.5%, 83.3%, and 93%, respectively. Its performance was considered unsatisfactory. Although ICT-based tests provide a relatively rapid and less labor-intensive alternative, they should be used to supplement and not replace stool microscopy.

Links between cholesteryl sulfate-dependent and -independent processes in the morphological and physiological changes of Entamoeba encystation.

The protozoan parasite Entamoeba histolytica causes amoebiasis, a global public health problem. Amoebiasis is solely transmitted by cysts that are produced from proliferative trophozoites by encystation in the large intestine of humans. During encystation, various metabolites, pathways, and cascades sequentially orchestrate the morphological and physiological changes required to produce cysts. Cholesteryl sulfate (CS) has recently been revealed to be among the key molecules that control the morphological and physiological changes of encystation by exerting pleiotropic effects. CS promotes the rounding of encysting Entamoeba cells and maintains this spherical morphology as encysting cells are surrounded by the cyst wall, a prerequisite for resistance against environmental stresses. CS is also involved in the development of membrane impermeability, another prerequisite for resistance. The initiation of cyst wall formation is, however, CS-independent. Here, we overview CS-dependent and -independent processes during encystation and discuss their functional linkage. We also discuss a potential transcriptional cascade that controls the processes necessary to produce dormant Entamoeba cysts.

Short tandem repeat (STR) based sequence typing of Entamoeba histolytica identifies STGA-D locus as a genetic marker, associated with disease outcomes.

Amoebiasis, caused by the enteric parasite Entamoeba histolytica has differential disease outcomes. The association of parasite genotypes with outcomes of amoebic infection is still a paradox and requires to be explored. The genetic information of infecting strains from endemic settings of different geographical regions is essential to evaluate the relation. Comparative genetics of E. histolytica clinical isolates from different disease outcomes have been explored based on two tRNA-linked STR loci (STGA-D and A-L). All of the repeat patterns in the A-L locus were newly identified and unique to Indian isolates. The majority of newly identified repeat patterns in STGA-D locus have outcome-specific distributions, predicting the emergence of disease-specific mutations in this target locus. Statistical analysis further reinforces this observation, as identified repeat patterns only from STGA-D but not A-L locus were significantly associated with disease outcomes. Phylogenetic analysis indicates independent segregation and divergence of tRNA-linked STR arrays for each STR locus.

Involvement of NOX2-derived ROS in human hepatoma HepG2 cell death induced by Entamoeba histolytica.

Entamoeba histolytica is an enteric tissue-invasive protozoan parasite causing amoebic colitis and liver abscesses in humans. Amoebic contact with host cells activates intracellular signaling pathways that lead to host cell death via generation of caspase-3, calpain, Ca2+ elevation, and reactive oxygen species (ROS). We previously reported that various NADPH oxidases (NOXs) are responsible for ROS-dependent death of various host cells induced by amoeba. In the present study, we investigated the specific NOX isoform involved in ROS-dependent death of hepatocytes induced by amoebas. Co-incubation of hepatoma HepG2 cells with live amoebic trophozoites resulted in remarkably increased DNA fragmentation compared to cells incubated with medium alone. HepG2 cells that adhered to amoebic trophozoites showed strong dichlorodihydrofluorescein diacetate (DCF-DA) fluorescence, suggesting intracellular ROS accumulation within host cells stimulated by amoebic trophozoites. Pretreatment of HepG2 cells with the general NOX inhibitor DPI or NOX2-specific inhibitor GSK 2795039 reduced Entamoeba-induced ROS generation. Similarly, Entamoeba-induced LDH release from HepG2 cells was effectively inhibited by pretreatment with DPI or GSK 2795039. In NOX2-silenced HepG2 cells, Entamoeba-induced LDH release was also significantly inhibited compared with controls. Taken together, the results support an important role of NOX2-derived ROS in hepatocyte death induced by E. histolytica.

Genes differentially expressed between pathogenic and non-pathogenic Entamoeba histolytica clones influence pathogenicity-associated phenotypes by multiple mechanisms.

Recently, two genes involved in amoebic liver abscess formation in a mouse model were identified by their differential expression of non-pathogenic (A1np) and pathogenic (B2p) clones of the Entamoeba histolytica isolate HM:1-IMSS. While overexpression of a gene encoding the metallopeptidase EhMP8-2 reduces the virulence of the pathogenic clone B2p, overexpression of the gene ehi_127670 (ehhp127), encoding a hypothetical protein, increases the virulence of the non-pathogenic clone A1np, while silencing this gene in the pathogenic B2p reduces virulence. To understand the role of both molecules in determining the pathogenicity of E. histolytica, silencing, and overexpression transfectants were characterized in detail. Silencing of ehmp8-2, of the homologous gene ehmp8-1, or both in non-pathogenic A1np trophozoites significantly altered the transcript levels of 347, 216, and 58 genes, respectively. This strong change in the expression profiles caused by the silencing of ehmp8-1 and ehmp8-2 implies that these peptidases regulate the expression of numerous genes. Consequently, numerous phenotypic characteristics, including cytopathic, hemolytic, and cysteine peptidase activity, were altered in response to their silencing. Silencing of ehhp127 in pathogenic B2p trophozoites did not affect the expression of other genes, whereas its overexpression in non-pathogenic A1np trophozoites results in an altered expression of approximately 140 genes. EhHP127 is important for trophozoite motility, as its silencing reduces, while its overexpression enhances movement activity. Interestingly, the specific silencing of ehhp127 also significantly affects cytopathic, cysteine peptidase, and hemolytic activities. All three molecules characterized in this study, namely EhMP8-1, EhMP8-2, and EhHP127, are present in amoeba vesicles. The results show that ehmp8-2 and ehhp127 are not only differentially expressed between pathogenic and non-pathogenic amoebae, but that they also significantly affect amoeba pathogenicity-associated phenotypes by completely different mechanisms. This observation suggests that the regulation of amoeba pathogenicity is achieved by a complex network of molecular mechanisms rather than by single factors.

Fumagillin inhibits growth of the enteric protozoan parasite Entamoeba histolytica by covalently binding to and selectively inhibiting methionine aminopeptidase 2.

Amebiasis is an important cause of morbidity and mortality worldwide, and caused by infection with the protozoan parasite Entamoeba histolytica. Metronidazole is currently the first-line drug despite adverse effects and concerns on the emergence of drug resistance. Fumagillin, a fungal metabolite from Aspergillus fumigatus, and its structurally related natural and synthetic compounds have been previously explored as potential anti-angiogenesis inhibitors for cancers, anti-microbial, and anti-obese compounds. Although fumagillin was used for human amebiasis in clinical trials in 1950s, the mode of action of fumagillin remains elusive until now. In this report, we showed that fumagillin covalently binds to methionine aminopeptidase 2 (MetAP2) and non-covalently but abundantly binds to patatin family phospholipase A (PLA). Susceptibility against fumagillin of the amebic strains in which expression of E. histolytica MetAP2 (EhMetAP2) gene was silenced increased compared to control strain. Conversely, overexpression of EhMetAP2 mutants that harbors amino acid substitutions responsible for resistance to ovalicin, a fumagillin analog, in human MetAP2, also resulted in decrease in fumagillin susceptibility. In contrast, neither gene silencing nor overexpression of E. histolytica PLA (EhPLA) affected fumagillin susceptibility. These data suggest that EhPLA is not essential and not the target of fumagillin for its amebicidal activity. Taken together, our data have demonstrated that EhMetAP2 is the primary target for amebicidal activity of fumagillin, and EhMetAP2 represents a rational explorable target for the development of alternative therapeutic agents against amebiasis.

Digestive exophagy of biofilms by intestinal amoeba and its impact on stress tolerance and cytotoxicity.

The human protozoan parasite Entamoeba histolytica is responsible for amebiasis, a disease endemic to developing countries. E. histolytica trophozoites colonize the large intestine, primarily feeding on bacteria. However, in the gastrointestinal tract, bacterial cells form aggregates or structured communities called biofilms too large for phagocytosis. Remarkably, trophozoites are still able to invade and degrade established biofilms, utilizing a mechanism that mimics digestive exophagy. Digestive exophagy refers to the secretion of digestive enzymes that promote the digestion of objects too large for direct phagocytosis by phagocytes. E. histolytica cysteine proteinases (CPs) play a crucial role in the degradation process of Bacillus subtilis biofilm. These proteinases target TasA, a major component of the B. subtilis biofilm matrix, also contributing to the adhesion of the parasite to the biofilm. In addition, they are also involved in the degradation of biofilms formed by Gram-negative and Gram-positive enteric pathogens. Furthermore, biofilms also play an important role in protecting trophozoites against oxidative stress. This specific mechanism suggests that the amoeba has adapted to prey on biofilms, potentially serving as an untapped reservoir for novel therapeutic approaches to treat biofilms. Consistently, products derived from the amoeba have been shown to restore antibiotic sensitivity to biofilm cells. In addition, our findings reveal that probiotic biofilms can act as a protective shield for mammalian cells, hindering the progression of the parasite towards them.

On the occurrence of a glutaredoxin-like small protein in the anaerobic protozoan parasite Entamoeba histolytica.

BACKGROUND: Entamoeba histolytica, an intestinal parasitic protozoan that usually lives and multiplies within the human gut, is the causative agent of amoebiasis. To date, de novo glutathione biosynthesis and its associated enzymes have not been identified in the parasite. Cysteine has been proposed to be the main intracellular thiol. METHODS: Using bioinformatics tools to search for glutaredoxin homologs in the E. histolytica genome database, we identified a coding sequence for a putative Grx-like small protein (EhGLSP) in the E. histolytica HM-1:IMSS genome. We produced the recombinant protein and performed its biochemical characterization. RESULTS: Through in vitro experiments, we observed that recombinant EhGLSP could bind GSH and L-Cys as ligands. However, the protein exhibited very low GSH-dependent disulfide reductase activity. Interestingly, via UV-Vis spectroscopy and chemical analysis, we detected that recombinant EhGLSP (freshly purified from Escherichia coli cells by IMAC) was isolated together with a redox-labile [FeS] bio-inorganic complex, suggesting that this protein could have some function linked to the metabolism of this cofactor. Western blotting showed that EhGLSP protein levels were modulated in E. histolytica cells exposed to exogenous oxidative species and metronidazole, suggesting that this protein cooperates with the antioxidant mechanisms of this parasite. CONCLUSIONS AND GENERAL SIGNIFICANCE: Our findings support the existence of a new metabolic actor in this pathogen. To the best of our knowledge, this is the first report on this protein class in E. histolytica.

Glycerol biosynthetic pathway plays an essential role in proliferation and antioxidative defense in the human enteric protozoan parasite Entamoeba histolytica.

Amebiasis is caused by the protozoan parasite Entamoeba histolytica. Treatment options other than metronidazole and its derivatives are few, and their low efficacy against asymptomatic cyst carriers, and experimental evidence of resistance in vitro justify the discovery/repurposing campaign for new drugs against amebiasis. Global metabolic responses to oxidative stress and cysteine deprivation by E. histolytica revealed glycerol metabolism may represent a rational target for drug development. In this study using 14C-labelled glucose, only 11% of the total glucose taken up by E. histolytica trophozoites is incorporated to lipids. To better understand the role of glycerol metabolism in this parasite, we focused on characterizing two important enzymes, glycerol kinase (GK) and glycerol 3-phosphate dehydrogenase (G3PDH). Recombinant GK was biochemically characterized in detail, while G3PDH was not due to failure of protein expression and purification. GK revealed novel characteristics and unprecedented kinetic properties in reverse reaction. Gene silencing revealed that GK is essential for optimum growth, whereas G3PDH is not. Gene silencing of G3PDH caused upregulated GK expression, while that of GK resulted in upregulation of antioxidant enzymes as shown by RNA-seq analysis. Although the precise molecular link between GK and the upregulation of antioxidant enzymes was not demonstrated, the observed increase in antioxidant enzyme expression upon GK gene silencing suggests a potential connection between GK and the cellular response to oxidative stress. Together, these results provide the first direct evidence of the biological importance and coordinated regulation of the glycerol metabolic pathways for proliferation and antioxidative defense in E. histolytica, justifying the exploitation of these enzymes as future drug targets.