Calcium and magnesium ions modulate the oligomeric state and function of mitochondrial 2-Cys peroxiredoxins in Leishmania parasites

Overoxidation and Oligomerization of Trypanosoma cruzi Cytosolic and Mitochondrial Peroxiredoxins

Peroxiredoxins (Prxs) have been shown to be important enzymes for trypanosomatids, counteracting oxidative stress and promoting cell infection and intracellular survival. In this work, we investigate the in vitro sensitivity to overoxidation and the overoxidation dynamics of Trypanosoma cruzi Prxs in parasites in culture and in the infection context. We showed that recombinant m-TXNPx, in contrast to what was observed for c-TXNPx, exists as low molecular mass forms in the overoxidized state. We observed that T. cruzi Prxs were overoxidized in epimastigotes treated with oxidants, and a significant proportion of the overoxidized forms were still present at least 24 h after treatment suggesting that these forms are not actively reversed. In in vitro infection experiments, we observed that Prxs are overoxidized in amastigotes residing in infected macrophages, demonstrating that inactivation of at least part of the Prxs by overoxidation occurs in a physiological context. We have shown that m-TXNPx has a redox-state-dependent chaperone activity. This function may be related to the increased thermotolerance observed in m-TXNPx-overexpressing parasites. This study suggests that despite the similarity between protozoan and mammalian Prxs, T. cruzi Prxs have different oligomerization dynamics and sensitivities to overoxidation, which may have implications for their function in the parasite life cycle and infection process.

Manipulating polydispersity of lens β-crystallins using divalent cations demonstrates evidence of calcium regulation

Crystallins comprise the protein-rich tissue of the eye lens. Of the three most common vertebrate subtypes, β-crystallins exhibit the widest degree of polydispersity due to their complex multimerization properties in situ. While polydispersity enables precise packing densities across the concentration gradient of the lens for vision, it is unclear why there is such a high degree of structural complexity within the β-crystallin subtype and what the role of this feature is in the lens. To investigate this, we first characterized β-crystallin polydispersity and then established a method to dynamically disrupt it in a process that is dependent on isoform composition and the presence of divalent cationic salts (CaCl2 or MgCl2). We used size-exclusion chromatography together with dynamic light scattering and mass spectrometry to show how high concentrations of divalent cations dissociate β-crystallin oligomers, reduce polydispersity, and shift the overall protein surface charge-properties that can be reversed when salts are removed. While the direct, physiological relevance of these divalent cations in the lens is still under investigation, our results support that specific isoforms of β-crystallin modulate polydispersity through multiple chemical equilibria and that this native state is disrupted by cation binding. This dynamic process may be essential to facilitating the molecular packing and optical function of the lens.

Trypanosoma cruzi Mitochondrial Peroxiredoxin Promotes Infectivity in Macrophages and Attenuates Nifurtimox Toxicity

Trypanosoma cruzi is the causative agent of Chagas disease which is currently treated by nifurtimox (NFX) and benznidazole (BZ). Nevertheless, the mechanism of action of NFX is not completely established. Herein, we show the protective effects of T. cruzi mitochondrial peroxiredoxin (MPX) in macrophage infections and in response to NFX toxicity. After a 3-day treatment of epimastigotes with NFX, MPX content increased (2.5-fold) with respect to control, and interestingly, an MPX-overexpressing strain was more resistant to the drug. The generation of mitochondrial reactive species and the redox status of the low molecular weight thiols of the parasite were not affected by NFX treatment indicating the absence of oxidative stress in this condition. Since MPX was shown to be protective and overexpressed in drug-challenged parasites, non-classical peroxiredoxin activity was studied. We found that recombinant MPX exhibits holdase activity independently of its redox state and that its overexpression was also observed in temperature-challenged parasites. Moreover, increased holdase activity (2-fold) together with an augmented protease activity (proteasome-related) and an enhancement in ubiquitinylated proteins was found in NFX-treated parasites. These results suggest a protective role of MPX holdase activity toward NFX toxicity. Trypanosoma cruzi has a complex life cycle, part of which involves the invasion of mammalian cells, where parasite replication inside the host occurs. In the early stages of the infection, macrophages recognize and engulf T. cruzi with the generation of reactive oxygen and nitrogen species toward the internalized parasite. Parasites overexpressing MPX produced higher macrophage infection yield compared with wild-type parasites. The relevance of peroxidase vs. holdase activity of MPX during macrophage infections was assessed using conoidin A (CA), a covalent, cell-permeable inhibitor of peroxiredoxin peroxidase activity. Covalent adducts of MPX were detected in CA-treated parasites, which proves its action in vivo. The pretreatment of parasites with CA led to a reduced infection index in macrophages revealing that the peroxidase activity of peroxiredoxin is crucial during this infection process. Our results confirm the importance of peroxidase activity during macrophage infection and provide insights for the relevance of MPX holdase activity in NFX resistance.

Single molecule mass photometry reveals the dynamic oligomerization of human and plant peroxiredoxins

Protein oligomerization is central to biological function and regulation, yet its experimental quantification and measurement of dynamic transitions in solution remain challenging. Here, we show that single molecule mass photometry quantifies affinity and polydispersity of heterogeneous protein complexes in solution. We demonstrate these capabilities by studying the functionally relevant oligomeric equilibria of 2-cysteine peroxiredoxins (2CPs). Comparison of the polydispersity of plant and human 2CPs as a function of concentration and redox state revealed features conserved among all 2CPs. In addition, we also find species-specific differences in oligomeric transitions, the occurrence of intermediates and the formation of high molecular weight complexes, which are associated with chaperone activity or act as a storage pool for more efficient dimers outlining the functional differentiation of human 2CPs. Our results point to a diversified functionality of oligomerization for 2CPs and illustrate the power of mass photometry for characterizing heterogeneous oligomeric protein distributions in near native conditions.

Relevance of peroxiredoxins in pathogenic microorganisms

The oxidative and nitrosative responses generated by animals and plants are important defenses against infection and establishment of pathogenic microorganisms such as bacteria, fungi, and protozoa. Among distinct oxidant species, hydroperoxides are a group of chemically diverse compounds that comprise small hydrophilic molecules, such as hydrogen peroxide and peroxynitrite, and bulky hydrophobic species, such as organic hydroperoxides. Peroxiredoxins (Prx) are ubiquitous enzymes that use a highly reactive cysteine residue to decompose hydroperoxides and can also perform other functions, like molecular chaperone and phospholipase activities, contributing to microbial protection against the host defenses. Prx are present in distinct cell compartments and, in some cases, they can be secreted to the extracellular environment. Despite their high abundance, Prx expression can be further increased in response to oxidative stress promoted by host defense systems, by treatment with hydroperoxides or by antibiotics. In consequence, some isoforms have been described as virulence factors, highlighting their importance in pathogenesis. Prx are very diverse and are classified into six different classes (Prx1-AhpC, BCP-PrxQ, Tpx, Prx5, Prx6, and AhpE) based on structural and biochemical features. Some groups are absent in hosts, while others present structural peculiarities that differentiate them from the host's isoforms. In this context, the intrinsic characteristics of these enzymes may aid the development of new drugs to combat pathogenic microorganisms. Additionally, since some isoforms are also found in the extracellular environment, Prx emerge as attractive targets for the production of diagnostic tests and vaccines. KEY POINTS: • Peroxiredoxins are front-line defenses against host oxidative and nitrosative stress. • Functional and structural peculiarities differ pathogen and host enzymes. • Peroxiredoxins are potential targets to microbicidal drugs.

Effects of Serine or Threonine in the Active Site of Typical 2-Cys Prx on Hyperoxidation Susceptibility and on Chaperone Activity

Typical 2-Cys peroxiredoxins (2-Cys Prx) are ubiquitous Cys-based peroxidases, which are stable as decamers in the reduced state, and may dissociate into dimers upon disulfide bond formation. A peroxidatic Cys (CP) takes part of a catalytic triad, together with a Thr/Ser and an Arg. Previously, we described that the presence of Ser (instead of Thr) in the active site stabilizes yeast 2-Cys Prx as decamers. Here, we compared the hyperoxidation susceptibilities of yeast 2-Cys Prx. Notably, 2-Cys Prx containing Ser (named here Ser-Prx) were more resistant to hyperoxidation than enzymes containing Thr (Thr-Prx). In silico analysis revealed that Thr-Prx are more frequent in all domains of life, while Ser-Prx are more abundant in bacteria. As yeast 2-Cys Prx, bacterial Ser-Prx are more stable as decamers than Thr-Prx. However, bacterial Ser-Prx were only slightly more resistant to hyperoxidation than Thr-Prx. Furthermore, in all cases, organic hydroperoxide inhibited more the peroxidase activities of 2-Cys Prx than hydrogen peroxide. Moreover, bacterial Ser-Prx displayed increased thermal resistance and chaperone activity, which may be related with its enhanced stability as decamers compared to Thr-Prx. Therefore, the single substitution of Thr by Ser in the catalytic triad results in profound biochemical and structural differences in 2-Cys Prx.

Thiol-based switching mechanisms of stress-sensing chaperones

Thiol-based redox switches evolved as efficient post-translational regulatory mechanisms that enable individual proteins to rapidly respond to sudden environmental changes. While some protein functions need to be switched off to save resources and avoid potentially error-prone processes, protective functions become essential and need to be switched on. In this review, we focus on thiol-based activation mechanisms of stress-sensing chaperones. Upon stress exposure, these chaperones convert into high affinity binding platforms for unfolding proteins and protect cells against the accumulation of potentially toxic protein aggregates. Their chaperone activity is independent of ATP, a feature that becomes especially important under oxidative stress conditions, where cellular ATP levels drop and canonical ATP-dependent chaperones no longer operate. Vice versa, reductive inactivation and substrate release require the restoration of ATP levels, which ensures refolding of client proteins by ATP-dependent foldases. We will give an overview over the different strategies that cells evolved to rapidly increase the pool of ATP-independent chaperones upon oxidative stress and provide mechanistic insights into how stress conditions are used to convert abundant cellular proteins into ATP-independent holding chaperones.

A defined medium for Leishmania culture allows definition of essential amino acids

Axenic culture of Leishmania is generally performed in rich, serum-supplemented media which sustain robust growth over multiple passages. The use of such undefined media, however, obscures proteomic analyses and confounds the study of metabolism. We have established a simple, defined culture medium that supports the sustained growth of promastigotes over multiple passages and which yields parasites that have similar infectivity to macrophages to parasites grown in a conventional semi-defined medium. We have exploited this medium to investigate the amino acid requirements of promastigotes in culture and have found that phenylalanine, tryptophan, arginine, leucine, lysine and valine are essential for viability in culture. Most of the 20 proteogenic amino acids promote growth of Leishmania promastigotes, with the exception of alanine, asparagine, and glycine. This defined medium will be useful for further studies of promastigote substrate requirements, and will facilitate future proteomic and metabolomic analyses.