Cloning and expression of the dihydroorotate dehydrogenase from Toxoplasma gondii

Cloning and Characterization of Yak DHODH Gene and Its Functional Studies in a Bisphenol S-Induced Ferroptosis Model of Fetal Fibroblasts

Dihydroorotate dehydrogenase (DHODH) is a rate-limiting enzyme of de novo biosynthesis of pyrimidine. Although the involvement of DHODH in resisting ferroptosis has been successively reported in recent years, which greatly advanced the understanding of the mechanism of programmed cell death (PCD), the genetic sequence of the yak DHODH gene and its roles in ferroptosis are still unknown. For this purpose, we firstly cloned the coding region sequence of DHODH (1188 bp) from yak liver and conducted a characterization analysis of its predictive protein that consists of 395 amino acids. We found that the coding region of the yak DHODH gene presented high conservation among species. Second, the expression profile of the DHODH gene in various yak tissues was investigated using RT-qPCR. The results demonstrated that DHODH was widely expressed in different yak tissues, with particularly high levels in the spleen, heart, and liver. Third, to investigate the involvement of DHODH in regulating ferroptosis in cells, yak skin fibroblasts (YSFs) were isolated from fetuses. And then, bisphenol S (BPS) was used to induce the in vitro ferroptosis model of YSFs. We observed that BPS decreased the cell viability (CCK8) and membrane potential (JC-1) of YSFs in a dose-dependent manner and induced oxidative stress by elevating reactive oxygen species (ROS). Simultaneously, it was evident that BPS effectively augmented the indicators associated with ferroptosis (MDA and BODIPY staining) and reduced GSH levels. Importantly, the co-administration of Ferrostatin-1 (Fer), a potent inhibitor of ferroptosis, significantly alleviated the aforementioned markers, thereby confirming the successful induction of ferroptosis in YSFs by BPS. Finally, overexpression plasmids and siRNAs of the yak DHODH gene were designed and transfected respectively into BPS-cultured YSFs to modulate DHODH expression. The findings revealed that DHODH overexpression alleviated the occurrence of BPS-induced ferroptosis, while interference of DHODH intensified the ferroptosis process in YSFs. In summary, we successfully cloned the coding region of the yak DHODH gene, demonstrating its remarkable conservation across species. Moreover, using BPS-induced ferroptosis in YSFs as the model, the study confirmed the role of the DHODH gene in resisting ferroptosis in yaks. These results offer valuable theoretical foundations for future investigations into the functionality of the yak DHODH gene and the underlying mechanisms of ferroptosis in this species.

Pyrimidine metabolism in schistosomes: A comparison with other parasites and the search for potential chemotherapeutic targets

Schistosomes are responsible for the parasitic disease schistosomiasis, an acute and chronic parasitic ailment that affects >240 million people in 70 countries worldwide. It is the second most devastating parasitic disease after malaria. At least 200,000 deaths per year are associated with the disease. In the absence of the availability of vaccines, chemotherapy is the main stay for combating schistosomiasis. The antischistosomal arsenal is currently limited to a single drug, Praziquantel, which is quite effective with a single-day treatment and virtually no host-toxicity. Recently, however, the question of reduced activity of Praziquantel has been raised. Therefore, the search for alternative antischistosomal drugs merits the study of new approaches of chemotherapy. The rational design of a drug is usually based on biochemical and physiological differences between pathogens and host. Pyrimidine metabolism is an excellent target for such studies. Schistosomes, unlike most of the host tissues, require a very active pyrimidine metabolism for the synthesis of DNA and RNA. This is essential for the production of the enormous numbers of eggs deposited daily by the parasite to which the granulomas response precipitates the pathogenesis of schistosomiasis. Furthermore, there are sufficient differences between corresponding enzymes of pyrimidine metabolism from the host and the parasite that can be exploited to design specific inhibitors or "subversive substrates" for the parasitic enzymes. Specificities of pyrimidine transport also diverge significantly between parasites and their mammalian host. This review deals with studies on pyrimidine metabolism in schistosomes and highlights the unique characteristic of this metabolism that could constitute excellent potential targets for the design of safe and effective antischistosomal drugs. In addition, pyrimidine metabolism in schistosomes is compared with that in other parasites where studies on pyrimidine metabolism have been more elaborate, in the hope of providing leads on how to identify likely chemotherapeutic targets which have not been looked at in schistosomes.

Babesia bovis dihydroorotate dehydrogenase (BboDHODH) is a novel molecular target of drug for bovine babesiosis

The emergence of drug resistance and adverse side effects of current bovine babesiosis treatment suggest that the search of new drug targets and development of safer and effective compounds are required. This study focuses on dihydroorotate dehydrogenase (DHODH), the fourth enzyme of pyrimidine biosynthesis pathway as a potential drug target for bovine babesiosis. Recombinant Babesia bovis DHODH protein (rBboDHODH) was produced in Escherichia coli and used for characterization and measurement of enzymatic activity. Furthermore, the effects of DHODH inhibitors were evaluated in vitro. The recombinant B. bovis DHODH histidine fusion protein (rBboDHODH) had 42.4-kDa molecular weight and exhibited a specific activity of 475.7 ± 245 Unit/mg, a K_m = 276.2 µM for L-dihydroorotate and a K_m= 94.41 µM for decylubiquinone. A 44-kDa band of native BboDHODH was detected by Western blot analysis and found in parasites mitochondria using a confocal microscope. Among DHODH inhibitors, atovaquone (ATV) and leflunomide (LFN) significantly inhibited the activity of rBboDHODH as well as the growth of B. bovis in vitro. The half maximal inhibitory concentration (IC₅₀) of ATV and LFN was 2.38 ± 0.53 nM and 52.41 ± 11.47 µM, respectively. These results suggest that BboDHODH might be a novel target for development of new drug for treatment of B. bovis infection.

Biochemical and molecular characterization of the pyrimidine biosynthetic enzyme dihydroorotate dehydrogenase from Toxoplasma gondii

The pyrimidine biosynthesis pathway in the protozoan pathogen Toxoplasma gondii is essential for parasite growth during infection. To investigate the properties of dihydroorotate dehydrogenase (TgDHOD), the fourth enzyme in the T. gondii pyrimidine pathway, we expressed and purified recombinant TgDHOD. TgDHOD exhibited a specific activity of 84U/mg, a k(cat) of 89s(-1), a K(m)=60μM for l-dihydroorotate, and a K(m)=29μM for decylubiquinone (Q(D)). Quinones lacking or having short isoprenoid side chains yielded lower k(cat)s than Q(D). As expected, fumarate was a poor electron acceptor for this family 2 DHOD. The IC(50)s determined for A77-1726, the active derivative of the human DHOD inhibitor leflunomide, and related compounds MD249 and MD209 were, 91μM, 96μM, and 60μM, respectively. The enzyme was not significantly affected by brequinar or TTFA, known inhibitors of human DHOD, or by atovaquone. DSM190, a known inhibitor of Plasmodium falciparum DHOD, was a poor inhibitor of TgDHOD. TgDHOD exhibits a lengthy 157-residue N-terminal extension, consistent with a potential organellar targeting signal. We constructed C-terminally c-myc tagged TgDHODs to examine subcellular localization of TgDHOD in transgenic parasites expressing the tagged protein. Using both exogenous and endogenous expression strategies, anti-myc fluorescence signal colocalized with antibodies against the mitochondrial marker ATPase. These findings demonstrate that TgDHOD is associated with the parasite's mitochondrion, revealing this organelle as the site of orotate production in T. gondii. The TgDHOD gene appears to be essential because while gene tagging was successful at the TgDHOD gene locus, attempts to delete the TgDHOD gene were not successful in the KU80 background. Collectively, our study suggests that TgDHOD is an excellent target for the development of anti-Toxoplasma drugs.

The OsDHODH1 gene is involved in salt and drought tolerance in rice

In the present paper, we identified and cloned OsDHODH1 encoding a putative cytosolic dihydroorotate dehydrogenase (DHODH) in rice. Expression analysis indicated that OsDHODH1 is upregulated by salt, drought and exogenous abscisic acid (ABA), but not by cold. By prokaryotic expression, we determined the enzymatic activity of OsDHODH1 and found that overproduction of OsDHODH1 significantly improved the tolerance of Escherichia coli cells to salt and osmotic stresses. Overexpression of the OsDHODH1 gene in rice increased the DHODH activity and enhanced plant tolerance to salt and drought stresses as compared with wild type and OsDHODH1-antisense transgenic plants. Our findings reveal, for the first time, that cytosolic dihydroorotate dehydrogenase is involved in plant stress response and that OsDHODH1 could be used in engineering crop plants with enhanced tolerance to salt and drought.

Targeting purine and pyrimidine metabolism in human apicomplexan parasites

Synthesis de novo, acquisition by salvage and interconversion of purines and pyrimidines represent the fundamental requirements for their eventual assembly into nucleic acids as nucleotides and the deployment of their derivatives in other biochemical pathways. A small number of drugs targeted to nucleotide metabolism, by virtue of their effect on folate biosynthesis and recycling, have been successfully used against apicomplexan parasites such as Plasmodium and Toxoplasma for many years, although resistance is now a major problem in the prevention and treatment of malaria. Many targets not involving folate metabolism have also been explored at the experimental level. However, the unravelling of the genome sequences of these eukaryotic unicellular organisms, together with increasingly sophisticated molecular analyses, opens up possibilities of introducing new drugs that could interfere with these processes. This review examines the status of established drugs of this type and the potential for further exploiting the vulnerability of apicomplexan human pathogens to inhibition of this key area of metabolism.

Two different dihydroorotate dehydrogenases from yeast Saccharomyces kluyveri

Genes for two structurally and functionally different dihydroorotate dehydrogenases (DHODHs, EC 1.3.99.11), catalyzing the fourth step of pyrimidine biosynthesis, have been previously found in yeast Saccharomyces kluyveri. One is closely related to the Schizosaccharomyces pombe mitochondrial family 2 enzymes, which use quinones as direct and oxygen as the final electron acceptor. The other one resembles the Saccharomyces cerevisiae cytosolic family 1A fumarate-utilizing DHODH. The DHODHs from S. kluyveri, Sch. pombe and S. cerevisiae, were expressed in Escherichia coli and compared for their biochemical properties and interaction with inhibitors. Benzoates as pyrimidine ring analogs were shown to be selective inhibitors of cytosolic DHODs. This unique property of Saccharomyces DHODHs could appoint DHODH as a species-specific target for novel anti-fungal therapeutics.