A unique insertion of low complexity amino acid sequence underlies protein-protein interaction in human malaria parasite orotate phosphoribosyltransferase and orotidine 5'-monophosphate decarboxylase

Culex pipiens pallens cuticular protein CPLCG5 participates in pyrethroid resistance by forming a rigid matrix

Background

Chemical insecticides have hugely reduced the prevalence of vector-borne diseases around the world, but resistance threatens their continued effectiveness. Despite its importance, cuticle resistance is an under-studied area, and exploring the detailed molecular basis of resistance is critical for implementing suitable resistance management strategies.

Methods

We performed western blotting of cuticular protein CPLCG5 in deltamethrin-susceptible (DS) and laboratory-produced deltamethrin-resistant (DR) strains of Culex pipiens pallens. Immunofluorescence assays using a polyclonal antibody to locate cuticular CPLCG5 in mosquitoes. EM immunohistochemical analysis of the femur segment was used to compare the cuticle in control and CPLCG5-deficient siRNA experimental groups.

Results

The gene CPLCG5 encodes a cuticle protein that plays an important role in pyrethroid resistance. Based on a prior study, we found that expression of CPLCG5 was higher in the resistant (DR) strain than the susceptible (DS) strain. CPLCG5 transcripts were abundant in white pupae and 1-day-old adults, but expression was dramatically decreased in 3-day-old adults, then remained stable thereafter. Western blotting revealed that the CPLCG5 protein was ~2.2-fold higher in the legs of the DR strain than the DS strain. Immunofluorescence assays revealed CPLCG5 expression in the head, thorax, abdomen, wing, and leg, and expression most abundant in the leg and wing. EM immunohistochemical analysis suggested that the exocuticle thickness of the femur was significantly thinner in the CPLCG5-deficient siCPLCG5 strain (0.717 ± 0.110 μm) than the siNC strain (0.946 ± 0.126 μm). Depletion of CPLCG5 by RNA interference resulted in unorganised laminae and a thinner cuticle.

Conclusions

The results suggest CPLCG5 participates in pyrethroid resistance by forming a rigid matrix and increasing the thickness of the cuticle.

Electronic supplementary material

The online version of this article (doi: 10.1186/s13071-017-2567-9) contains supplementary material, which is available to authorized users.

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.

Bifunctional activity of fused Plasmodium falciparum orotate phosphoribosyltransferase and orotidine 5'-monophosphate decarboxylase

Fusion of the last two enzymes in the pyrimidine biosynthetic pathway in the inversed order by having a COOH-terminal orotate phosphoribosyltransferase (OPRT) and an NH₂-terminal orotidine 5'-monophosphate decarboxylase (OMPDC), as OMPDC-OPRT, are described in many organisms. Here, we produced gene fusions of Plasmodium falciparum OMPDC-OPRT and expressed the bifunctional protein in Escherichia coli. The enzyme was purified to homogeneity using affinity and anion-exchange chromatography, exhibited enzymatic activities and functioned as a dimer. The activities, although unstable, were stabilized by its substrate and product during purification and long-term storage. Furthermore, the enzyme expressed a perfect catalytic efficiency (k_cat/K_m). The k_cat was selectively enhanced up to three orders of magnitude, while the K_m was not much affected and remained at low μM levels when compared to the monofunctional enzymes. The fusion of the two enzymes, creating a "super-enzyme" with perfect catalytic power and more flexibility, reflects cryptic relationship of enzymatic reactivities and metabolic functions on molecular evolution.

Insights into the pyrimidine biosynthetic pathway of human malaria parasite Plasmodium falciparum as chemotherapeutic target

Malaria is a major cause of morbidity and mortality in humans. Artemisinins remain as the first-line treatment for Plasmodium falciparum (P. falciparum) malaria although drug resistance has already emerged and spread in Southeast Asia. Thus, to fight this disease, there is an urgent need to develop new antimalarial drugs for malaria chemotherapy. Unlike human host cells, P. falciparum cannot salvage preformed pyrimidine bases or nucleosides from the extracellular environment and relies solely on nucleotides synthesized through the de novo biosynthetic pathway. This review presents significant progress on understanding the de novo pyrimidine pathway and the functional enzymes in the human parasite P. falciparum. Current knowledge in genomics and metabolomics are described, particularly focusing on the parasite purine and pyrimidine nucleotide metabolism. These include gene annotation, characterization and molecular mechanism of the enzymes that are different from the human host pathway. Recent elucidation of the three-dimensional crystal structures and the catalytic reactions of three enzymes: dihydroorotate dehydrogenase, orotate phosphoribosyltransferase, and orotidine 5'-monophosphate decarboxylase, as well as their inhibitors are reviewed in the context of their therapeutic potential against malaria.