Biology subjects

De Koning, H. P.

Publications and source records attributed to De Koning, H. P..

5 recordsLinked to original sources

bioRxiv2026

Screening of purine nucleoside analogues against intracellular Toxoplasma gondii.

Toxoplasmosis remains a world-wide public health concern, especially for the immunocompromised. Although this population segment is increasing due to therapeutic interventions, organ transplants and infections including HIV, treatment relies almost exclusively on sulfadoxine and pyrimethamine, antifolates developed against malaria but with only moderate efficacy against acute toxoplasmosis and no effect on the chronic stage. Here we explore whether 7-substituted analogues of 7-deazaadenosine (tubercidin) that have shown remarkable efficacy against other protozoan pathogens, might also show anti-toxoplasmic activity. Tubercidin and a series of eleven 7-substituted analogues including 2-deoxy and 3-deoxyribofuranoses was tested against intracellular Toxoplasma gondii tachyzoites. The test compounds yielded EC50 values between 0.012 and 1.72 {micro}M, well below those of the control drug sulfadiazine (11.9 {micro}M) and the previously identified purine analogue adenosine arabinoside (Ara-A; 11.4 {micro}M). The tubercidin analogues displayed at most moderate toxicity to HFF cells, with the most efficacious compound, 7-(3,4-di-Cl-phenyl)-3-deoxytubercidin (FH8513) reaching a selectivity index of >2500. These nucleosides are most likely taken up by T. gondii through one of the four Equilibrative Nucleoside Transporters (ENTs) encoded by the parasites. However, deletion of TgENT2 and/or TgENT3 had no effect on the EC50 values, and deletion of TgAT1 actually sensitised the tachyzoites to most of the tubercidin analogues. We propose that these nucleosides are internalised through the TgENT1 uridine transporter and that the sensitisation in {Delta}TgAT1 cells is the result of reduced uptake of adenosine that competes with the tubercidin analogues for metabolic enzymes such as adenosine kinase.

microbiology↗

bioRxiv2025

Insights from aquaporin structures into drug-resistant sleeping sickness

Trypanosoma brucei is the causal agent of African trypanosomiasis in humans and animals, the latter resulting in significant negative economic impacts in afflicted areas of the world. Resistance has arisen to the trypanocidal drugs pentamidine and melarsoprol through mutations in the aquaglyceroporin TbAQP2 that prevent their uptake. Here we use cryogenic electron microscopy to determine the structure of TbAQP2 from Trypanosoma brucei, bound to either the substrate glycerol or to the sleeping sickness drugs, pentamidine or melarsoprol. The drugs bind within the AQP2 channel at a site completely overlapping that of glycerol. Mutations leading to a drug-resistant phenotype were found in the channel lining. Molecular dynamics simulations showed the channel can be traversed by pentamidine, with a low energy binding site at the centre of the channel, flanked by regions of high energy association at the extracellular and intracellular ends. Drug-resistant TbAQP2 mutants are still predicted to bind pentamidine, but the much weaker binding in the centre of the channel observed in the MD simulations would be insufficient to compensate for the high energy processes of ingress and egress, hence impairing transport at pharmacologically relevant concentrations. The structures of drug-bound TbAQP2 represent a novel paradigm for drug-transporter interactions that could provide new mechanisms for targeting drugs into pathogens and human cells.

molecular biology↗

bioRxiv2023

Pyrimidine salvage in Toxoplasma gondii as a target for new treatment

Toxoplasmosis is a common protozoan infection that can have severe outcomes in the immunocompromised and during pregnancy, but treatment options are limited. Recently, nucleotide metabolism has received much attention as a target for new antiprotozoal agents and here we focus on pyrimidine salvage by Toxoplasma gondii as a drug target. Whereas uptake of [3H]-cytidine and particularly [3H]-thymidine was at most marginal, [3H]-uracil and [3H]-uridine were readily taken up. Kinetic analysis of uridine uptake was consistent with a single transporter with a Km of 3.3 {+/-} 0.8 {micro}M, which was inhibited by uracil with high affinity (Ki = 1.15 {+/-} 0.07 {micro}M) but not by thymidine or 5-methyluridine, showing that the 5-Me group is incompatible with uptake by T. gondii. Conversely, [3H]-uracil transport displayed a Km of 2.05 {+/-} 0.40 {micro}M, not significantly different from the uracil Ki on uridine transport, and was inhibited by uridine with a Ki 2.44 {+/-} 0.59 {micro}M, also not significantly different from the experimental uridine Km. The reciprocal, complete inhibition, displaying Hill slopes of approximately [~]1, strongly suggest that uridine and uracil share a single transporter with similarly high affinity for both, and we designate it uridine/uracil transporter 1 (TgUUT1). While TgUUT1 excludes 5-methyl substitutions, the smaller 5F substitution was tolerated as 5F-uracil inhibited uptake of [3H]-uracil with a Ki of 6.80 {+/-} 2.12 {micro}M (P > 0.05 compared to uracil Km). Indeed, we found that 5F-Uridine, 5F-uracil and 5F,2-deoxyuridine were all potent antimetabolites against T. gondii with EC50 values well below that of the current first line treatment, sulfadiazine. In vivo evaluation also showed that 5F-uracil and 5F,2-deoxyuridine were similarly effective as sulfadiazine against acute toxoplasmosis. Our preliminary conclusion is that TgUUT1 mediates potential new anti-toxoplasmosis drugs with activity superior to the current treatment.

microbiology↗

bioRxiv2023

Novel kinetoplastid-specific cAMP binding proteins identified by RNAi screening for cAMP resistance in T. brucei

Cyclic AMP signalling in trypanosomes differs from most eukaryotes due to absence of known cAMP effectors and cAMP independence of PKA. We have previously identified four genes from a genome-wide RNAi screen for resistance to the cAMP phosphodiesterase (PDE) inhibitor NPD-001. The genes were named cAMP Response Protein (CARP) 1 through 4. Here, we report an additional six CARP candidate genes from the original sample, after deep sequencing of the RNA interference target pool retrieved after NPD-001 selection (RIT-seq). The resistance phenotypes were confirmed by targeted RNAi knockdown and highest level of resistance to NPD-001, approximately 17-fold, was seen for knockdown of CARP7 (Tb927.7.4510). CARP1 and CARP11 contain predicted cyclic AMP binding domains and bind cAMP as evidenced by capture and competition on immobilised cAMP. CARP orthologues are strongly enriched in kinetoplastid species, and CARP3 and CARP11 are unique to Trypanosoma. Localization data and/or domain architecture of all CARPs predict association with the T. brucei flagellum. This suggests a crucial role of cAMP in flagellar function, in line with the cell division phenotype caused by high cAMP and the known role of the flagellum for cytokinesis. The CARP collection is a resource for discovery of unusual cAMP pathways and flagellar biology. ImportanceTrypanosomes are major pathogens of humans and livestock. In addition they have been invaluable as a model system to investigate new biological systems, and not just of protozoa. Equally, they are known to have a lot of unique biology and biochemistry. One example of this is signal transduction by cyclic nucleotides. Some elements, including phosphodiesterases and the catalytic domains of its dozens of adenylate cyclase isoforms, are highly conserved, while the absence of G-proteins, a cAMP-responsive protein kinase A and other known effector types suggests a unique cAMP-dependent pathway, which as yet is mostly uncharacterised. Here, we identify a set of ten Trypanosoma brucei proteins, all localised to its flagellum, that appear to be involved in the production of cAMP, or in mediating its cellular effects. These cAMP Response Proteins (CARPs) were mostly unique to trypanosomes, suggesting a completely novel pathway. Two of the CARPs were shown to bind cAMP and were found to possess structurally conserved cyclic nucleotide binding domains.

microbiology↗

bioRxiv2020

Positively selected modifications in the pore of TbAQP2 allow pentamidine to enter Trypanosoma brucei

Mutations in the Trypanosoma brucei aquaporin AQP2 are associated with resistance to pentamidine and melarsoprol. We show that TbAQP2 but not TbAQP3 was positively selected for increased pore size from a common ancestor aquaporin. We demonstrate that TbAQP2s unique architecture permits pentamidine permeation through its central pore and show how specific mutations in highly conserved motifs affect drug permeation. Introduction of key TbAQP2 amino acids into TbAQP3 renders the latter permeable to pentamidine. Molecular dynamics demonstrates that permeation by dicationic pentamidine is energetically favourable in TbAQP2, driven by the membrane potential, although aquaporins are normally strictly impermeable for ionic species. We also identify the structural determinants that make pentamidine a permeant but exclude most other diamidine drugs. Our results have wide-ranging implications for optimising antitrypanosomal drugs and averting cross-resistance. Moreover, these new insights in aquaporin permeation may allow the pharmacological exploitation of other members of this ubiquitous gene family.

biochemistry↗