Haem-responsive gene transporter enables mobilization of host haem in ticks.

Ticks, notorious blood-feeders and disease-vectors, have lost a part of their genetic complement encoding haem biosynthetic enzymes and are, therefore, dependent on the acquisition and distribution of host haem. Solute carrier protein SLC48A1, aka haem-responsive gene 1 protein (HRG1), has been implicated in haem transport, regulating the availability of intracellular haem. HRG1 transporter has been identified in both free-living and parasitic organisms ranging from unicellular kinetoplastids, nematodes, up to vertebrates. However, an HRG1 homologue in the arthropod lineage has not yet been identified. We have identified a single HRG1 homologue in the midgut transcriptome of the tick Ixodes ricinus, denoted as IrHRG, and have elucidated its role as a haem transporter. Data from haem biosynthesis-deficient yeast growth assays, systemic RNA interference and the evaluation of gallium protoporphyrin IX-mediated toxicity through tick membrane feeding clearly show that IrHRG is the bona fide tetrapyrrole transporter. We argue that during evolution, ticks profited from retaining a functional hrg1 gene in the genome because its protein product facilitates host haem escort from intracellularly digested haemoglobin, rendering haem bioavailable for a haem-dependent network of enzymes.

Carbohydrate-naphthalene diimide conjugates as potential antiparasitic drugs: Synthesis, evaluation and structure-activity studies.

The neglected tropical diseases Human African Trypanosomiasis and leishmaniasis are caused by infection with trypanosomatid parasites Trypanosoma brucei and Leishmania spp, respectively. The genomes of these organisms contain multiple putative G-quadruplex (G4) forming sequences which have recently been proposed to mediate processes relevant for parasite survival. Therefore, G4 could be considered as potential targets for a novel approach towards the development of antiparasitic drugs. Recently, we have demonstrated that G4 ligands such as carbohydrate naphthalene diimide conjugates (carb-NDIs) possess notable antiparasitic activity. Herein, we have synthesized a new family of carb-NDIs, characterized by significant structural variability, and evaluated their anti-parasitic activity, with special focus on T. brucei. The interaction with relevant G4 sequences was evaluated in vitro through independent biophysical methods (FRET melting assays under competing conditions with double stranded DNA, circular dichroism and fluorescence titrations). Finally, flow cytometry and confocal microscopy experiments demonstrated that the conjugates exhibit excellent uptake into T. brucei parasites, localizing in the nuclei and kinetoplasts. Promising antiparasitic activity and selectivity against control mammalian cells, together with their peculiar mechanism of action, render the carb-NDI conjugates as suitable candidates for the development of an innovative treatment of trypanosomiasis.