RESUMO
The parasite Schistosoma mansoni possess all pathways for pyrimidine biosynthesis, whereby deaminases play an essential role in the thymidylate cycle, a crucial step to controlling the ratio between cytidine and uridine nucleotides. In this study, we heterologously expressed and purified the deoxycytidylate (dCMP) deaminase from S. mansoni to obtain structural, biochemical and kinetic information. Small-angle X-ray scattering of this enzyme showed that it is organized as a hexamer in solution. Isothermal titration calorimetry was used to determine the kinetic constants for dCMP-dUMP conversion and the role of dCTP and dTTP in enzymatic regulation. We evaluated the metals involved in activating the enzyme and show for the first time the dependence of correct folding on the interaction of two metals. This study provides information that may be useful for understanding the regulatory mechanisms involved in the metabolic pathways of S. mansoni. Thus, improving our understanding of the function of these essential pathways for parasite metabolism and showing for the first time the hitherto unknown deaminase function in this parasite.
Assuntos
DCMP Desaminase/química , Nucleotídeos de Desoxicitosina/química , Nucleotídeos de Desoxiuracil/química , Magnésio/química , Proteínas de Protozoários/química , Schistosoma mansoni/enzimologia , Zinco/química , Sequência de Aminoácidos , Animais , Sítios de Ligação , Cátions Bivalentes , Cristalografia por Raios X , DCMP Desaminase/genética , DCMP Desaminase/metabolismo , Nucleotídeos de Desoxicitosina/metabolismo , Nucleotídeos de Desoxiuracil/metabolismo , Expressão Gênica , Cinética , Magnésio/metabolismo , Modelos Moleculares , Ligação Proteica , Conformação Proteica em alfa-Hélice , Conformação Proteica em Folha beta , Domínios e Motivos de Interação entre Proteínas , Multimerização Proteica , Proteínas de Protozoários/genética , Proteínas de Protozoários/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Schistosoma mansoni/química , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Especificidade por Substrato , Zinco/metabolismoRESUMO
In adult schistosomes, the enzyme adenosine kinase (AK) is responsible for the incorporation of some adenosine analogues, such as 2-fluoroadenosine and tubercidin, into the nucleotide pool, but not others. In the present study, the structures of four complexes of Schistosoma mansoni AK bound to adenosine and adenosine analogues are reported which shed light on this observation. Two differences in the adenosine-binding site in comparison with the human counterpart (I38Q and T36A) are responsible for their differential specificities towards adenosine analogues, in which the Schistosoma enzyme does not tolerate bulky substituents at the N7 base position. This aids in explaining experimental data which were reported in the literature more than two decades ago. Furthermore, there appears to be considerable plasticity within the substrate-binding sites that affects the side-chain conformation of Ile38 and causes a previously unobserved flexibility within the loop comprising residues 286-299. These results reveal that the latter can be sterically occluded in the absence of ATP. Overall, these results contribute to the body of knowledge concerning the enzymes of the purine salvage pathway in this important human parasite.
Assuntos
Adenosina Quinase/química , Adenosina/química , Schistosoma mansoni/enzimologia , Adenosina/análogos & derivados , Adenosina/metabolismo , Adenosina Quinase/genética , Adenosina Quinase/metabolismo , Animais , Cristalização , Cristalografia por Raios X , Humanos , Schistosoma mansoni/genética , Schistosoma mansoni/metabolismo , Alinhamento de Sequência , Especificidade por Substrato/genéticaRESUMO
Schistosomiasis is one of the most important human helminthiases worldwide. Praziquantel is the current treatment, and no vaccine is available until the present. Thus, the presented study aimed to evaluate the immunization effects with recombinant Schistosoma mansoni enzymes: Adenosine Kinase (AK) and Hypoxanthine-Guanine Phosphoribosyltransferase (HGPRT), as well as a MIX of the two enzymes. Female Balb/c mice were immunized in three doses, and 15 days after the last immunization, animals were infected with S. mansoni. Our results showed that the group MIX presented a reduction in the eggs in feces by 30.74% and 29%, respectively, in the adult worms. The groups AK, HGPRT and MIX could produce IgG1 antibodies, and the groups AK and MIX produced IgE antibodies anti-enzymes and anti-S. mansoni total proteins. The groups AK, HGPRT and MIX induced a reduction in the eosinophils in the peritoneal cavity. Besides, the group AK showed a decrease in the number of hepatic granulomas (41.81%) and the eggs present in the liver (42.30%). Therefore, it suggests that immunization with these enzymes can contribute to schistosomiasis control, as well as help to modulate experimental infection inducing a reduction of physiopathology in the disease.
RESUMO
Schistosomiasis is a parasitic infection caused by trematode worms (also called blood flukes) of the genus Schistosoma sp., which affects over 230 million people worldwide, causing 200,000 deaths annually. There is no vaccine or new drugs available, which represents a worrying aspect, since there is loss of sensitivity of the parasite to the medication recommended by the World Health Organization, Praziquantel. The present study evaluated the effects of the recombinant enzymes of S. mansoni Hypoxanthine-Guanine Phosphoribosyltransferase (HGPRT), Purine Nucleoside Phosphorylase (PNP) and the MIX of both enzymes in the immunotherapy of schistosomiasis in murine model. These enzymes are part of the purine salvage pathway, the only metabolic pathway present in the parasite for this purpose, being essential for the synthesis of DNA and RNA. Female mice of Swiss and BALB/c strains were infected with cercariae and treated, intraperitoneally, with three doses of 100 µg of enzymes. After the immunotherapy, the eggs and adult worms were counted in the feces; the number of eosinophils from the fluid in the peritoneal cavity and peripheral blood was observed; and the quantification of the cytokine IL-4 and the production of antibodies IgE was analyzed. The evaluation of the number of granulomas and collagen deposition via histological slides of the liver was performed. The results demonstrate that immunotherapy with the enzyme HGPRT seems to stimulate the production of IL-4 and promoted a significant reduction of granulomas in the liver in treated animals. The treatment with the enzyme PNP and the MIX was able to reduce the number of worms in the liver and in the mesenteric vessels of the intestine, to reduce the number of eggs in the feces and to negatively modulate the number of eosinophils. Therefore, immunotherapy with the recombinant enzymes of S. mansoni HGPRT and PNP might contribute to the control and reduction of the pathophysiological aspects of schistosomiasis, helping to decrease the morbidity associated with the infection in murine model.
RESUMO
Schistosomiasis, caused by Schistosoma mansoni trematode worm, affects more than 1.5 million people in Brazil. The current treatment consists in the administration of Praziquantel, the only medicine used for treatment for more than 40 years. Some of the limitations of this drug consist in its inactivity against schistosomula and parasite eggs, the appearance of resistant strains and non-prevention against reinfection. Thus, the objective of this study was to evaluate the effect of immunization with recombinant functional enzymes of the purine salvage pathway of S. mansoni, Nucleoside Diphosphate Kinase (NDPK) and Adenylosuccinate Lyase (ADSL), to evaluate the host immune response, as well as the parasite load after vaccination. For this, Balb/c mice were divided into 5 groups: control (uninfected and untreated), non-immunized/infected, NDPK infected, ADSL infected, and NDPK + ADSL infected. Immunized groups received three enzyme dosages, with a 15-day interval between each dose, and after 15 days of the last application the animals were infected with 80 cercariae of S. mansoni. On the 47th day after the infection, fecal eggs were counted and, on the 48th day after the infection, the evaluation of leukocyte response, parasite load, antibody production, cytokines quantification, and histopathological analysis were performed. The results showed that immunizations with NDPK, ADSL or NDPK + ADSL promoted a discreet reduction in eosinophil counts in lavage of peritoneal cavity. All immunized animals showed increased production and secretion of IgG1, IgG2a, and IgE antibodies. Increased production of IL-4 was observed in the group immunized with the combination of both enzymes (NDPK + ADSL). In addition, in all immunized groups there were reductions in egg counts in the liver and intestine, such as reductions in liver granulomas. Thus, we suggest that immunizations with these enzymes could contribute to the reduction of schistosomiasis transmission, besides being important in immunopathogenesis control of the disease.
Assuntos
Adenilossuccinato Liase/imunologia , Antígenos de Helmintos/imunologia , Núcleosídeo-Difosfato Quinase/imunologia , Schistosoma mansoni/enzimologia , Schistosoma mansoni/imunologia , Esquistossomose mansoni/imunologia , Esquistossomose mansoni/parasitologia , Animais , Antígenos de Helmintos/administração & dosagem , Biomarcadores , Citocinas/sangue , Eosinófilos , Feminino , Imunização , Esquemas de Imunização , Contagem de Leucócitos , Fígado/metabolismo , Fígado/parasitologia , Fígado/patologia , Camundongos , Carga Parasitária , Proteínas Recombinantes/administração & dosagem , Proteínas Recombinantes/imunologia , Esquistossomose mansoni/patologia , Esquistossomose mansoni/prevenção & controleRESUMO
Schistosoma mansoni, the parasite responsible for schistosomiasis, lacks the "de novo" purine biosynthetic pathway and depends entirely on the purine salvage pathway for the supply of purines. Numerous reports of praziquantel resistance have been described, as well as stimulated efforts to develop new drugs against schistosomiasis. Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) is a key enzyme of the purine salvage pathway. Here, we describe a crystallographic structure of the S. mansoni HPGRT-1 (SmHGPRT), complexed with IMP at a resolution of 2.8 Ǻ. Four substitutions were identified in the region of the active site between SmHGPRT-1 and human HGPRT. We also present data from RNA-Seq and WISH, suggesting that some isoforms of HGPRT might be involved in the process related to sexual maturation and reproduction in worms; furthermore, its enzymatic assays show that the isoform SmHGPRT-3 does not present the same catalytic efficiency as other isoforms. Finally, although other studies have previously suggested this enzyme as a potential antischistosomal chemotherapy target, the kinetics parameters reveal the impossibility to use SmHGPRT as an efficient chemotherapeutic target.
Assuntos
Proteínas de Helminto/química , Proteínas de Helminto/genética , Hipoxantina Fosforribosiltransferase/química , Hipoxantina Fosforribosiltransferase/genética , Isoenzimas/química , Isoenzimas/genética , Schistosoma mansoni/enzimologia , Sequência de Aminoácidos , Animais , Domínio Catalítico , Proteínas de Helminto/metabolismo , Hipoxantina Fosforribosiltransferase/metabolismo , Isoenzimas/metabolismo , Cinética , Dados de Sequência Molecular , Reprodução , Schistosoma mansoni/química , Schistosoma mansoni/genética , Schistosoma mansoni/fisiologia , Alinhamento de SequênciaRESUMO
Nucleoside diphosphate kinases (NDPKs) are crucial to keep the high triphosphate nucleotide levels in the biological process. The enzymatic mechanism has been extensively described; however, the structural characteristics and kinetic parameters have never been fully determined. In Schistosoma mansoni, NDPK (SmNDPK) is directly involved in the pyrimidine and purine salvage pathways, being essential for nucleotide metabolism. The SmNDPK enzymatic activity is the highest of the known purine metabolisms when compared to the mammalian NDPKs, suggesting the importance of this enzyme in the worm metabolism. Here, we report the recombinant expression of SmNDPK that resulted in 1.7 and 1.9 Å apo-form structure in different space-groups, as well as the 2.1 Å SmNDPK.ADP complex. The binding and kinetic assays reveal the ATP-dependence for enzyme activation. Moreover, in situ hybridization showed that SmNDPK transcripts are found in reproductive organs and in the esophagus gland of adult worms, which can be intrinsically related with the oviposition and digestive processes. These results will help us fully understand the crucial participation of this enzyme in Schistosoma mansoni and its importance for the pathology of the disease.
Assuntos
Proteínas de Helminto/química , Proteínas de Helminto/metabolismo , Núcleosídeo-Difosfato Quinase/química , Núcleosídeo-Difosfato Quinase/metabolismo , Schistosoma mansoni/enzimologia , Esquistossomose mansoni/parasitologia , Difosfato de Adenosina/química , Difosfato de Adenosina/metabolismo , Trifosfato de Adenosina/química , Trifosfato de Adenosina/metabolismo , Sequência de Aminoácidos , Animais , Domínio Catalítico , Esôfago/química , Esôfago/enzimologia , Feminino , Trato Gastrointestinal/química , Trato Gastrointestinal/enzimologia , Proteínas de Helminto/genética , Humanos , Cinética , Masculino , Modelos Moleculares , Núcleosídeo-Difosfato Quinase/genética , Schistosoma mansoni/genética , Schistosoma mansoni/metabolismo , Alinhamento de SequênciaRESUMO
Purine nucleoside phosphorylases (PNPs) play an important role in the blood fluke parasite Schistosoma mansoni as a key enzyme of the purine salvage pathway. Here we present the structural and kinetic characterization of a new PNP isoform from S. mansoni, SmPNP2. Thermofluorescence screening of different ligands suggested cytidine and cytosine are potential ligands. The binding of cytosine and cytidine were confirmed by isothermal titration calorimetry, with a KD of 27 µM for cytosine, and a KM of 76.3 µM for cytidine. SmPNP2 also displays catalytic activity against inosine and adenosine, making it the first described PNP with robust catalytic activity towards both pyrimidines and purines. Crystal structures of SmPNP2 with different ligands were obtained and comparison of these structures with the previously described S. mansoni PNP (SmPNP1) provided clues for the unique capacity of SmPNP2 to bind pyrimidines. When compared with the structure of SmPNP1, substitutions in the vicinity of SmPNP2 active site alter the architecture of the nucleoside base binding site thus permitting an alternative binding mode for nucleosides, with a 180° rotation from the canonical binding mode. The remarkable plasticity of this binding site enhances our understanding of the correlation between structure and nucleotide selectivity, thus suggesting new ways to analyse PNP activity.
Assuntos
Nucleosídeos/metabolismo , Purina-Núcleosídeo Fosforilase/química , Purina-Núcleosídeo Fosforilase/metabolismo , Schistosoma mansoni/enzimologia , Schistosoma mansoni/genética , Adenosina/metabolismo , Animais , Sítios de Ligação , Domínio Catalítico , Cristalografia por Raios X , Citidina/metabolismo , Citosina/metabolismo , Proteínas de Helminto/química , Proteínas de Helminto/metabolismo , Inosina/metabolismo , Cinética , Modelos Moleculares , Mutação , Conformação Proteica , Isoformas de Proteínas/química , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Purina-Núcleosídeo Fosforilase/genética , Schistosoma mansoni/química , Especificidade por SubstratoRESUMO
BACKGROUND: Schistosoma mansoni is the etiological agent of schistosomiasis, a debilitating treatment neglected tropical disease that affects approximately 218 million people worldwide. Despite its importance, the treatment of schistosomiasis relies on a single drug, praziquantel. Some reports on the resistance of S. mansoni to this drug have stimulated efforts to develop new drugs to treat this disease. S. mansoni possesses all the same pyrimidine pathways (de novo, salvage and thymidylate cycles) as those of its host. The opposite scenario is true for purine metabolism, in which only the salvage pathway is present. These pathways have previously been proposed as potential drug targets. RESULTS: Using modern molecular biology techniques, large-scale study of these pathways has become possible; 24 genes have been studied, and several protein structures and kinetic parameters have been determined. Unique characteristics of schistosomal enzymes have been obtained, which show that this organism possesses two isoforms of uridine phosphorylase (UP), which share 92% of identity. However, only one isoform has a canonical function, whereas the second isoform is expressed through all life stages and does not have a known function. In addition, the methylthioadenosine phosphorylase (MTAP) is one of the enzymes responsible for the previously described adenosine phosphorylase activity, thus representing one main difference between S. mansoni and its host. The study of adenine phosphoribosyltransferase has revealed possible differential expression of the APRT gene in females. This result is consistent with those obtained for the experimental treatment of schistosomiasis in monkeys with the adenosine analog tubercidin, which eliminates the disease mainly in females. CONCLUSION: These important conclusions may aid in the development of new alternative drugs to treat schistosomiasis.
RESUMO
The parasite Schistosoma mansoni possesses all pathways for pyrimidine biosynthesis, in which dihydrofolate reductase (DHFR), thymidylate cycle participants, is essential for nucleotide metabolism to obtain energy and structural nucleic acids. Thus, DHFRs have been widely suggested as therapeutic targets for the treatment of infectious diseases. In this study, we expressed recombinant SmDHFR in a heterologous manner to obtain structural, biochemical and kinetic information. X-ray diffraction of recombinant SmDHFR at 1.95Å resolution showed that the structure exhibited the canonical DHFR fold. Isothermal titration calorimetry was used to determine the kinetic constants for NADP+ and dihydrofolate. Moreover, inhibition assays were performed using the commercial folate analogs methotrexate and aminopterin; these analogs are recognized as folate competitors and are used as chemotherapeutic agents in cancer and autoimmune diseases. This study provides information that may prove useful for the future discovery of novel drugs and for understanding these metabolic steps from this pathway of S. mansoni, thus aiding in our understanding of the function of these essential pathways for parasite metabolism.
Assuntos
Schistosoma mansoni/enzimologia , Tetra-Hidrofolato Desidrogenase/química , Tetra-Hidrofolato Desidrogenase/metabolismo , Animais , Antagonistas do Ácido Fólico/farmacologia , Humanos , Cinética , Metotrexato/farmacologia , Proteínas Recombinantes , Difração de Raios XRESUMO
Schistosoma mansoni depends upon the purine salvage pathway to obtain purine nucleotides; therefore, enzymes from this pathway are essential for parasite survival. Here, we focused on the adenine phosphoribosyltransferase (APRT) enzyme, which catalyzes the condensation reaction between adenine and PRPP (5-phosphoribosylpyrophosphate) to produce AMP and PPi. Kinetic experiments using the heterologously expressed protein of one APRT isoform from S. mansoni indicate that it is catalytically active, and whole-mount in situ hybridization studies indicate that the transcripts of this protein are concentrated in the posterior region of the ovary and vitellaria of female adult worms. Moreover, a phylogenetic analysis has shown that APRT exists in multiple copies originating from gene duplications at the base of the Schistosoma genus. Other enzymes from the purine and pyrimidine salvage pathways have also been found to present multiple copies in schistosomes, suggesting that evolutionary pressure to diversify these genes' families may be related to a specialized role in parasite reproduction.
Assuntos
Adenina Fosforribosiltransferase/análise , Ovário/enzimologia , Schistosoma mansoni/enzimologia , Adenina Fosforribosiltransferase/genética , Monofosfato de Adenosina/metabolismo , Estruturas Animais/enzimologia , Animais , Evolução Molecular , Feminino , Duplicação Gênica , Fosfatos/metabolismo , Filogenia , Schistosoma mansoni/genéticaRESUMO
Schistosoma mansoni is the parasite responsible for schistosomiasis, a disease that affects about 218 million people worldwide. Currently, both direct treatment and disease control initiatives rely on chemotherapy using a single drug, praziquantel. Concerns over the possibility of resistance developing to praziquantel, have stimulated efforts to develop new drugs for the treatment of schistosomiasis. Schistosomes do not have the de novo purine biosynthetic pathway, and instead depend entirely on the purine salvage pathway to supply its need for purines. The purine salvage pathway has been reported as a potential target for developing new drugs against schistosomiasis. Adenylosuccinate lyase (SmADSL) is an enzyme in this pathway, which cleaves adenylosuccinate (ADS) into adenosine 5'-monophosphate (AMP) and fumarate. SmADSL kinetic characterization was performed by isothermal titration calorimetry (ITC) using both ADS and SAICAR as substrates. Structures of SmADSL in Apo form and in complex with AMP were elucidated by x-ray crystallography revealing a highly conserved tetrameric structure required for their function since the active sites are formed from residues of three different subunits. The active sites are also highly conserved between species and it is difficult to identify a potent species-specific inhibitor for the development of new therapeutic agents. In contrast, several mutagenesis studies have demonstrated the importance of dimeric interface residues in the stability of the quaternary structure of the enzyme. The lower conservation of these residues between SmADSL and human ADSL could be used to lead the development of anti-schistosomiasis drugs based on disruption of subunit interfaces. These structures and kinetics data add another layer of information to Schistosoma mansoni purine salvage pathway.
Assuntos
Adenilossuccinato Liase/química , Adenilossuccinato Liase/metabolismo , Schistosoma mansoni/enzimologia , Monofosfato de Adenosina/metabolismo , Adenilossuccinato Liase/genética , Animais , Domínio Catalítico , Sequência Conservada , Cristalografia por Raios X , Fumaratos/metabolismo , Cinética , Modelos Moleculares , Ligação Proteica , Conformação Proteica , Multimerização Proteica , Estabilidade ProteicaRESUMO
Reports of Schistosoma mansoni strains resistant to praziquantel, the only therapeutic strategy available for the treatment of schistosomiasis, have motivated the scientific community towards the search for new possible therapies. Biochemical characterization of the parasite's metabolism is an essential component for the rational development of new therapeutic alternatives. One of the so far uncharacterized enzymes is uridine phosphorylase (UP) (EC 2.4.2.3), for which the parasite genome presents two isoforms (SmUPa and SmUPb) that share 92% sequence identity. In this paper, we present crystal structures for SmUPa and SmUPb in their free states as well as bound to different ligands. This we have complemented by enzyme kinetic characterization and phylogenetic analyses. Both enzymes present an overall fold and active site structure similar to other known UPs. The kinetic analyses showed conclusively that SmUPa is a regular uridine phosphorylase but by contrast SmUPb presented no detectable activity. This is particularly noteworthy given the high level of sequence identity between the two isoforms and is probably the result of the significant differences observed for SmUPb in the vicinity of the active site itself, suggesting that it is not a UP at all. On the other hand, it was not possible to identify an alternative function for SmUPb, although our phylogenetic analyses and expression data suggest that SmUPb is still functional and plays a role in parasite metabolism. The unusual UPb isoform may open up new opportunities for understanding unique features of S. mansoni metabolism.
Assuntos
Proteínas de Helminto/química , Schistosoma mansoni/enzimologia , Uridina Fosforilase/química , Animais , Cristalografia por Raios X , Isoenzimas , Domínios ProteicosRESUMO
The human parasite Schistosoma mansoni is totally dependent on the purine salvage pathway in order to supply large quantities of purine precursors for its energy and DNA biosynthetic needs. Adenylate kinase (ADK) is responsible for the conversion of AMP (produced by the adenosine kinase reaction) into ADP, which is subsequently converted into ATP by nucleoside diphosphate kinase (NDPK). ADK and NDPK are the most active enzymes of the pathway, probably reflecting an evolutionary adaptation due to the intense use of the branch in which they participate. However, notwithstanding their importance very little information has been accumulated found regarding these enzymes. In this work two adenylate kinases from S. mansoni were cloned and heterologously expressed in Escherichia coli. The purified products were utilized in activity assays, and displayed kinetic parameters similar to the corresponding human orthologous proteins. The cytosolic S. mansoni ADK was crystallized and its structure solved allowing us to detect a difference in the nucleotide binding site when compared with the human ortholog.