In Vitro Analysis of the Interaction between Atovaquone and Proguanil against Liver Stage Malaria Parasites.

The interaction between atovaquone and proguanil has never been studied against liver stage malaria, which is the main target of this drug combination when used for chemoprevention. Using human hepatocytes lacking cytochrome P450 activity, and thus avoiding proguanil metabolizing into potent cycloguanil, we show in vitro that the atovaquone-proguanil combination synergistically inhibits the growth of rodent Plasmodium yoelii parasites. These results provide a pharmacological basis for the high efficacy of atovaquone-proguanil used as malaria chemoprevention.

Deletion of Crry and DAF on murine platelets stimulates thrombopoiesis and increases factor H-dependent resistance of peripheral platelets to complement attack.

Complement receptor 1-related gene/protein y (Crry) and decay-accelerating factor (DAF) are two murine membrane C3 complement regulators with overlapping functions. Crry deletion is embryonically lethal whereas DAF-deficient mice are generally healthy. Crry(-/-)DAF(-/-) mice were viable on a C3(-/-) background, but platelets from such mice were rapidly destroyed when transfused into C3-sufficient mice. In this study, we used the cre-lox system to delete platelet Crry in DAF(-/-) mice and studied Crry/DAF-deficient platelet development in vivo. Rather than displaying thrombocytopenia, Pf4-Cre(+)-Crry(flox/flox) mice had normal platelet counts and their peripheral platelets were resistant to complement attack. However, chimera mice generated with Pf4-Cre(+)-Crry(flox/flox) bone marrows showed platelets from C3(-/-) but not C3(+/+) recipients to be sensitive to complement activation, suggesting that circulating platelets in Pf4-Cre(+)-Crry(flox/flox) mice were naturally selected in a complement-sufficient environment. Notably, Pf4-Cre(+)-Crry(flox/flox) mouse platelets became complement susceptible when factor H function was blocked. Examination of Pf4-Cre(+)-Crry(flox/flox) mouse bone marrows revealed exceedingly active thrombopoiesis. Thus, under in vivo conditions, Crry/DAF deficiency on platelets led to abnormal platelet turnover, but peripheral platelet count was compensated for by increased thrombopoiesis. Selective survival of Crry/DAF-deficient platelets aided by factor H protection and compensatory thrombopoiesis demonstrates the cooperation between membrane and fluid phase complement inhibitors and the body's ability to adaptively respond to complement regulator deficiencies.

Enlightening the molecular basis of trypanothione specificity in trypanosomatids: mutagenesis of Leishmania infantum glyoxalase II.

Leishmania infantum glyoxalase II shows absolute specificity towards its trypanothione thioester substrate. In the previous work, we performed a comparative analysis of glyoxalase II structures determined by X-ray crystallography which revealed that Tyr291 and Cys294, absent in the human homologue, are essential for substrate binding. To validate this trypanothione specificity hypothesis we produced a mutant L. infantum GLO2 enzyme by replacing Tyr291 and Cys294 by arginine and lysine, respectively. This new enzyme is capable to use the glutathione thioester substrate, with kinetic parameters similar to the ones from the human enzyme. Substrate specificity is likely to be mediated by spermidine moiety binding, providing a primer for understanding the molecular basis of trypanothione specificity.

Cloning, expression, purification, crystallization and preliminary X-ray diffraction analysis of glyoxalase I from Leishmania infantum.

Glyoxalase I (GLO1) is the first of the two glyoxalase-pathway enzymes. It catalyzes the formation of S-D-lactoyltrypanothione from the non-enzymatically formed hemithioacetal of methylglyoxal and reduced trypanothione. In order to understand its substrate binding and catalytic mechanism, GLO1 from Leishmania infantum was cloned, overexpressed in Escherichia coli, purified and crystallized. Two crystal forms were obtained: a cube-shaped form and a rod-shaped form. While the cube-shaped form did not diffract X-rays at all, the rod-shaped form exhibited diffraction to about 2.0 A resolution. The crystals belonged to space group P2(1)2(1)2, with unit-cell parameters a = 130.03, b = 148.51, c = 50.63 A and three dimers of the enzyme per asymmetric unit.

Catalysis and structural properties of Leishmania infantum glyoxalase II: trypanothione specificity and phylogeny.

The glyoxalase pathway catalyzes the formation of d-lactate from methylglyoxal, a toxic byproduct of glycolysis. In trypanosomatids, trypanothione replaces glutathione in this pathway, making it a potential drug target, since its selective inhibition might increase methylglyoxal concentration in the parasites. Two glyoxalase II structures were solved. One with a bound spermidine molecule (1.8 A) and the other with d-lactate at the active site (1.9 A). The second structure was obtained by crystal soaking with the enzyme substrate (S)-d-lactoyltrypanothione. The overall structure of Leishmania infantum glyoxalase II is very similar to its human counterpart, with important differences at the substrate binding site. The crystal structure of L. infantum glyoxalase II is the first structure of this enzyme from trypanosomatids. The differential specificity of glyoxalase II toward glutathione and trypanothione moieties was revealed by differential substrate binding. Evolutionary analysis shows that trypanosomatid glyoxalases II diverged early from eukaryotic enzymes, being unrelated to prokaryotic proteins.

Purification, crystallization and preliminary X-ray diffraction analysis of the glyoxalase II from Leishmania infantum.

In trypanosomatids, trypanothione replaces glutathione in all glutathione-dependent processes. Of the two enzymes involved in the glyoxalase pathway, glyoxalase I and glyoxalase II, the latter shows absolute specificity towards trypanothione thioester, making this enzyme an excellent model to understand the molecular basis of trypanothione binding. Cloned glyoxalase II from Leishmania infantum was overexpressed in Escherichia coli, purified and crystallized. Crystals belong to space group C222(1) (unit-cell parameters a = 65.6, b = 88.3, c = 85.2 angstroms) and diffract beyond 2.15 angstroms using synchrotron radiation. The structure was solved by molecular replacement using the human glyoxalase II structure as a search model. These results, together with future detailed kinetic characterization using lactoyltrypanothione, should shed light on the evolutionary selection of trypanothione instead of glutathione by trypanosomatids.