Identification and functional analysis of peroxiredoxin isoforms in Euglena gracilis

Abstract

Euglena gracilis lacks catalase and contains ascorbate peroxidase (APX) which is localized exclusively in the cytosol. Other enzymes that scavenge reactive oxygen species (ROS) in Euglena have not yet been identified; therefore, ROS metabolism, especially in organelles, remains unclear in Euglena. The full-length cDNAs of four Euglena peroxiredoxins (EgPrxs) were isolated in this study. EgPrx1 and -4 were predicted to be localized in the cytosol, and EgPrx2 and -3 in plastids and mitochondria, respectively. The catalytic efficiencies of recombinant EgPrxs were similar to those of plant thiol-peroxidases, but were markedly lower than those of APX from Euglena. However, transcript levels of EgPrx1, -2, and -3 were markedly higher than those of APX. The growth rate of Euglena cells, in which the expression of EgPrx1 and -4 was suppressed by gene silencing, was markedly reduced under normal conditions, indicating physiological significance of Prx proteins.

The Mitochondrion of Euglena gracilis

“…Alternative respiratory pathways are likely involved in cellular responses to oxidative stress (Castro-Guerrero et al 2004, since E. gracilis lacks catalase, but contains ascorbate peroxidase (APX), which localizes exclusively to the cytosol (Shigeoka et al 2002). Other enzymes involved in detoxification of reactive oxygen species (ROS) have not been found yet, thus little is known about ROS metabolism in Euglena (Tamaki et al 2014). Euglena was shown to contain 2-CysPrxs in the mitochondria (Castro and Tomás 2008).…”

“…Euglena was shown to contain 2-CysPrxs in the mitochondria (Castro and Tomás 2008). Tamaki et al (2014) examined four peroxiredoxins (Prx), two localized in the cytosol and the others in the plastids and the mitochondria, respectively. All could reduce both H 2 O 2 and alkyl hydroperoxide and might contribute to ROS metabolism -also in mitochondria Under aerobic conditions (shown in the upper part in red) either pyruvate from the glycolytic pathway enters the mitochondrion or malate or lactate via the lactate shuttle enter the mitochondrion, where they are converted to pyruvate.…”

“…Electrons are transferred via a branched respiratory chain to oxygen as the terminal electron acceptor generating the proton gradient for ATP synthesis. A ATPase, AOX alternative oxidase, C cytochrome c, CI to CIV respiratory complexes I to IV, FRD fumarate reductase, IMM inner mitochondrial membrane, LDH lactate dehydrogenase, OMM outer mitochondrial membrane, RQ rhodoquinone (Tamaki et al 2014). But H 2 O 2 can also diffuse from the mitochondria into the cytosol, where it is then detoxified by APX (Ishikawa et al 1993).…”

Biochemistry and Physiology of Reactive Oxygen Species in Euglena

“…4.4. However, Euglena cell lines in which EgPrx2 and NTRC gene expression were individually silenced did not show any critical cell damages by oxidative stress under illumination suggesting that the thiol-redox system is not a decisive factor for ROS metabolism in Euglena chloroplasts (Tamaki et al 2014(Tamaki et al , 2015. As described in Sect.…”

“…Euglena lacks APX isoenzymes in its chloroplasts raising the significant question of how Euglena metabolizes H 2 O 2 generated in these organelles. Tamaki et al (2014) reported that Euglena possesses peroxiredoxin (EgPrx2), also called thioredoxin peroxidase, in chloroplasts as well as NADPH-dependent thioredoxin reductase (type NTRC) indicating that a thiol-redox system functions to metabolize ROS in chloroplasts replacing the AsA-GSH cycle (Fig. 4.2).…”