A soluble inorganic pyrophosphatase from the cattle tick Rhipicephalus microplus capable of hydrolysing polyphosphates.

Polyphosphates have been found in all cell types examined to date and play diverse roles depending on the cell type. In eukaryotic organisms, polyphosphates have been investigated mainly in mammalian cells, and only a few studies have addressed arthropods. Pyrophosphatases have been shown to regulate polyphosphate metabolism. However, these studies were restricted to trypanosomatids. Here we focus on the tick Rhipicephalus microplus, a haematophagous ectoparasite that is highly harmful to cattle. We produced a recombinant R. microplus pyrophosphatase (rRmPPase) with the aim of investigating its kinetic parameters using polyphosphates as substrate. Molecular docking assays of RmPPase with polyphosphates were also carried out. The kinetic and Hill coefficient parameters indicated that rRmPPase has a greater affinity, higher catalytic efficiency and increased cooperativity for sodium phosphate glass type 15 (polyP15 ) than for sodium tripolyphosphate (polyP3 ). Through molecular docking, we found that polyP3 binds close to the Mg2+ atoms in the catalytic region of the protein, participating in their coordination network, whereas polyP15 interactions involve negatively charged phosphate groups and basic amino acid residues, such as Lys56, Arg58 and Lys193; polyP15 has a more favourable theoretical binding affinity than polyP3 , thus supporting the kinetic data. This study shows, for the first time in arthropods, a pyrophosphatase with polyphosphatase activity, suggesting its participation in polyphosphate metabolism.

Design, synthesis and activity against Trypanosoma cruzi of azaheterocyclic analogs of megazol.

This study describes the design, synthesis and trypanocidal evaluation of new azaheterocyclic derivatives (4-8). These compounds were designed as megazol (1) analogs based on bioisosterism tools and were synthesized to investigate the possible pharmacophoric contribution of the 1,2,4-triazole nucleus, the position of the heterocyclic nucleus and presence of the nitro group, to the activity against the bloodstream trypomastigote forms of Trypanosoma cruzi. The most potent compound was 6, a nitro derivative obtained by substitution of a thiadiazole by a triazole ring and by moving the nitro group from C-5 position, as in 1, to the C-4 position. Finally, we have used semi-empirical theoretical calculations to discuss the correlation of some stereo electronic properties with biological activity in an attempt to understand the possible mechanism of action of the designed series of compounds.