Abstract
Glutaredoxins (GRXs), important components of the intracellular thiol redox system, are involved in multiple cellular processes. In a previous study, we identified five GRXs in the apicomplexan parasite, Neospora caninum. In the present study, we confirmed that the GRXs S14 and C5 are located in the apicoplast, which suggests unique functions for these proteins. Although single-gene deficiency did not affect the growth of parasites, a double knockout (Δgrx S14Δgrx C5) significantly reduced their reproductive capacity. However, there were no significant changes in redox indices (GSH/GSSG ratio, reactive oxygen species and hydroxyl radical levels) in double-knockout parasites, indicating that grx S14 and grx C5 are not essential for maintaining the redox balance in parasite cells. Key amino acid mutations confirmed that the Cys203 of grx S14 and Cys253/256 of grx C5 are important for parasite growth. Based on comparative proteomics, 79 proteins were significantly downregulated in double-knockout parasites, including proteins mainly involved in the electron transport chain, the tricarboxylic acid cycle and protein translation. Collectively, GRX S14 and GRX C5 coordinate the growth of parasites. However, considering their special localization, the unique functions of GRX S14 and GRX C5 need to be further studied.
Highlights
Neospora caninum is an obligate, intracellular, apicomplexan parasite that is found worldwide
We found that GRX C5 has a typical CXXC motif and is a dithiol GRX; GRX S14 has a typical CXXS motif and is a monothiol GRX (Figure 1a)
Sequence alignment shows that GRX C5 and GRX S14 has the highest homology with Toxoplasma gondii GRX C5 and GRX S14, respectively (Figure 1a,b)
Summary
Neospora caninum is an obligate, intracellular, apicomplexan parasite that is found worldwide. This parasite causes spontaneous abortion in cattle and neural system dysfunction in dogs and results in major economic losses in the breeding industry [1,2,3]. N. caninum is exposed to various oxidative stresses, and the parasites develop complex redox networks to maintain redox balance in different stages [4]. Glutaredoxins (GRXs) are ubiquitous oxidoreductases that maintain a cellular redox balance with the thioredoxin family and catalyse thiol-disulphide exchange reactions by utilizing glutathione (GSH) [5]. The number and localization of GRXs differ by species. GRXs are involved in DNA/RNA synthesis, Fe–S cluster assembly, cell signal transduction, apoptosis and cell proliferation [5,6]
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