Molecular Parasitology

Previous Research Results

Our laboratory focuses on Leishmania, the agents of human and canine Leishmaniasis in many regions of the world, Portugal included. Leishmaniasis is a serious, often fatal, condition for which no satisfactory therapy exists. We have been studying aspects of the thiol metabolism of Leishmania, namely the processes used by these parasites to eliminate peroxides. Initiated with the identification and the characterization of several Leishmania antioxidant enzymes, our work has recently led to two important findings. One of these refers to the discovery that redox metabolism in the mitochondrion of Leishmania and other trypanosomatids is not dependent on the activity of a class of trypanosomatid-specific oxidoreductases named as tryparedoxins. Our most recent significant contribution relates to another Leishmania mitochondrial enzyme, the peroxiredoxin LimTXNPx which we identified as a factor essential for the parasites to thrive in their mammalian hosts. Noticeably, the in vivo crucial function of LimTXNPX could not be explained by its well characterized peroxidase activity. Rather, our observations suggested this mitochondrial peroxiredoxin to function as a chaperone, an activity that may allow the parasite to sustain the change of temperature as it passes from the insect to the mammalian host.

IMAGE: This immunofluorescence micrograph shows one wild type Leishmania infantum contaminating a culture of parasites knockout for a mitochondrial peroxiredoxin. Analysis of these mutants revealed that this protein is crucial for parasite pathogenicity (Castro et al. 2011, PLoS Pathogens, 7:e1002325, 2011

Future Research

Our research on thiol metabolism has 3 immediate aims:

1. To characterize the chaperone activity of LimTXNPx at the biochemical level and confirm its in vivo significance.
2. LimTXNPx is essential for Leishmania survival in the mammalian hosts but is redundant in the insect stage, the promastigote. Our objective is to investigate if Leishmania promastigotes devoid of LimTXNPx can be used as a basis for a life attenuated vaccine.
3. Leishmania thiol metabolism is interesting for drug development because it depends on trypanothione and not, as their hosts, on glutathione. This suggests that it can be used as a target for new anti-Leishmania therapeutics. Presently, we are genetically and chemically validating the enzymes involved in the synthesis of trypanothione in Leishmania infantum.

We have now initiated a second area of research, metal acquisition in intracellular Leishmania. A detailed knowledge of the parasite metal transport machinery and of the modifications in metal metabolism occurring in infected cells will not only increase our understanding of the infective process itself, but may provide also an opportunity for therapeutic intervention. Our aims are:

1. To identify and characterize components of metal uptake systems in Leishmania infantum.
2. To investigate the changes taking place in iron metabolism proteins and in iron traffic in L. infantum-infected macrophages.

Selected References:

Castro H, Teixeira F, Romao S, Santos M, Cruz T, Flórido M, Appelberg R, Oliveira P, Ferreira-da-Silva F, Tomás AM. Leishmania mitochondrial peroxiredoxin plays a crucial peroxidase-unrelated role during infection. Insight into its novel chaperone activity. PLoS Pathogens. 7:e1002325, 2011.

Castro H, Romao S, Carvalho S, Teixeira F, Sousa C, Tomás AM. Mitochondrial redox metabolism in trypanosomatids is independent of tryparedoxin activity. PLoS One, 5:e12607, 2010.

Carvalho S, Cruz T, Santarém N, Castro H, Costa V, Tomás AM. Heme as a source of iron to Leishmania infantum amastigotes. Acta Trop, 109:131-135, 2009.

Castro H, Tomás AM. Peroxidases of trypanosomatids. Antioxid Redox Signal 10:1593-1606, 2008.

Castro H, Sousa C, Novais M, Santos M, Budde H, Cordeiro-da-Silva A, Flohé L, Tomás AM. Two linked genes of Leishmania infantum encode tryparedoxins localized to cytosol and mitochondrion. Mol Biochem Parasitol 136:137-147, 2004.

Castro H, Sousa C, Santos M, Cordeiro-da-Silva A, Flohé L, Tomás AM. Complementary antioxidant defence by cytoplasmic and mitochondrial peroxiredoxins in Leishmania infantum. Free Radical Bio Med, 33:1552-1562, 2002.