Leishmania Mitochondrial Peroxiredoxin Plays a Crucial Peroxidase-Unrelated Role during Infection: Insight into Its Novel Chaperone Activity

Abstract

Two-cysteine peroxiredoxins are ubiquitous peroxidases that play various functions in cells. In Leishmania and related trypanosomatids, which lack catalase and selenium-glutathione peroxidases, the discovery of this family of enzymes provided the molecular basis for peroxide removal in these organisms. In this report the functional relevance of one of such enzymes, the mitochondrial 2-Cys peroxiredoxin (mTXNPx), was investigated along the Leishmania infantum life cycle. mTXNPx null mutants (mtxnpx−) produced by a gene replacement strategy, while indistinguishable from wild type promastigotes, were found unable to thrive in a murine model of infection. Unexpectedly, however, the avirulent phenotype of mtxnpx− was not due to lack of the peroxidase activity of mTXNPx as these behaved like controls when exposed to oxidants added exogenously or generated by macrophages during phagocytosis ex vivo. In line with this, mtxnpx− were also avirulent when inoculated into murine hosts unable to mount an effective oxidative phagocyte response (B6.p47phox−/− and B6.RAG2−/− IFN-γ−/− mice). Definitive conclusion that the peroxidase activity of mTXNPx is not required for parasite survival in mice was obtained by showing that a peroxidase-inactive version of this protein was competent in rescuing the non-infective phenotype of mtxnpx−. A novel function is thus proposed for mTXNPx, that of a molecular chaperone, which may explain the impaired infectivity of the null mutants. This premise is based on the observation that the enzyme is able to suppress the thermal aggregation of citrate synthase in vitro. Also, mtxnpx− were more sensitive than controls to a temperature shift from 25°C to 37°C, a phenotype reminiscent of organisms lacking specific chaperone genes. Collectively, the findings reported here change the paradigm which regards all trypanosomatid 2-Cys peroxiredoxins as peroxide-eliminating devices. Moreover, they demonstrate, for the first time, that these 2-Cys peroxiredoxins can be determinant for pathogenicity independently of their peroxidase activity.

Mitochondrial peroxiredoxin functions as crucial chaperone reservoir in Leishmania infantum

“…This shift in temperature is similar to the shift parasites encounter upon transitioning from the insect to the mammalian host. Consistent with this result, we found that mTXNPx-deficient amastigotes (i.e., the mammalian form) are unable to survive within their mammalian host (13). These phenotypes could not be attributed to the peroxidase function of mTXNPx, because an L. infantum line expressing a peroxidase-inactive mutant variant of mTXNPx lacking Cp (mTXNPxC81S) was fully capable of surviving the temperature shift to 37°C and infecting mice (13).…”

“…We showed that mTXNPxdeficient promastigotes (i.e., the insect form) are significantly more sensitive to a temperature shift from 25°C to 37°C than promastigotes harboring functional mTXNPx (13). This shift in temperature is similar to the shift parasites encounter upon transitioning from the insect to the mammalian host.…”

“…Leishmania infantum, an intracellular protozoan parasite with a digenetic life cycle (i.e., it shuttles between two hosts, insects and mammals), encodes several 2-Cys-Prxs (10)(11)(12), one of which is the mitochondrial homolog called mitochondrial tryparedoxin-peroxidase mTXNPx (13). We showed that mTXNPxdeficient promastigotes (i.e., the insect form) are significantly more sensitive to a temperature shift from 25°C to 37°C than promastigotes harboring functional mTXNPx (13).…”

Novel Heteroaryl Selenocyanates and Diselenides as Potent Antileishmanial Agents

“…The choice of the chemical form for the selenium derivatives can modulate the level of this element on the basis of several metabolic routes (16). The mechanism of action for selenium is unknown, though some enzymatic pathways, such as mitochondrial peroxiredoxins (17), selenophosphate synthetases (18), or ascorbate peroxidases (19), could be implicated. On the other hand, the incorporation of selenium into novel nanomaterials has demonstrated effectiveness in the treatment of leishmaniasis (20).…”

How pH Modulates the Dimer-Decamer Interconversion of 2-Cys Peroxiredoxins from the Prx1 Subfamily

“…Up-regulation of this protein has been associated with protection against apoptosis-like death (26) and resistance to miltefosine (27), a drug whose activity is linked to apoptosis and disturbance of lipiddependent cell signaling pathways (28). Moreover, Leishmania Prx1m confers thermotolerance to the parasite and displays in vitro chaperone activity, which seems to be crucial for virulence (29). In this work, we solved the crystal structure of LbPrx1m at basic and acidic conditions, providing, for the first time to our knowledge, structural data of a Prx1 subfamily member in both dimeric and decameric states induced by pH variations.…”