Computational simulation of the reactive oxygen species and redox network in the regulation of chloroplast metabolism

Abstract

Cells contain a thiol redox regulatory network to coordinate metabolic and developmental activities with exogenous and endogenous cues. This network controls the redox state and activity of many target proteins. Electrons are fed into the network from metabolism and reach the target proteins via redox transmitters such as thioredoxin (TRX) and NADPHdependent thioredoxin reductases (NTR). Electrons are drained from the network by reactive oxygen species (ROS) through thiol peroxidases, e.g., peroxiredoxins (PRX). Mathematical modeling promises access to quantitative understanding of the network function and was implemented by using published kinetic parameters combined with fitting to known biochemical data. Two networks were assembled, namely the ferredoxin (FDX), FDX-dependent TRX reductase (FTR), TRX, fructose-1,6-bisphosphatase (FBPase) pathway with 2cysteine PRX/ROS as oxidant, and separately the FDX, FDX-dependent NADP reductase (FNR), NADPH, NTRC-pathway for 2-CysPRX reduction. Combining both modules allowed drawing several important conclusions of network performance. The resting H 2 O 2 concentration was estimated to be about 30 nM in the chloroplast stroma. The electron flow to metabolism exceeds that into thiol regulation of FBPase more than 7000-fold under physiological conditions. The electron flow from NTRC to 2-CysPRX is about 5.32-times more efficient than that from TRX-f1 to 2-CysPRX. Under severe stress (30 μM H 2 O 2) the ratio of electron flow to the thiol network relative to metabolism sinks to 1:251 whereas the ratio of eflow from NTRC to 2-CysPRX and TRX-f1 to 2-CysPRX rises up to 1:67. Thus, the simulation provides clues on experimentally inaccessible parameters and describes the functional state of the chloroplast thiol regulatory network.

Single Molecule Mass Photometry Reveals Dynamic Oligomerization of Plant and Human Peroxiredoxins for Functional Conservation and Diversification

“…[8,28] Essentially, this mechanism represents a futile cycle, since oxidized enzymes and TRXs need to be reduced again in order to keep the Calvin-Benson cycle active and was recently simulated by mathematical modeling. [29] Future models should include the presence of pools of differently efficient thiol peroxidases in order to estimate their significance for keeping the futile cycle in check. KM(H2O2)-values of bacterial and plant 2-CysPRX were reported with 1-2 µᴍ.…”

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

“…We find that addition of reduced TRX, leads to an increase in the decamer abundance, a sign of reduction of 2CP ( Figure 2 B). Complementary approaches with intact plants, in vitro biochemistry and mathematical modeling validated this function ( Vaseghi et al., 2018 ; Telman et al., 2020 ; Gerken et al., 2020 ). Future models should include the presence of pools of differently efficient thiol peroxidases in order to estimate their contribution to the regulatory cycle.…”

Thiol Redox Regulation of Plant β-Carbonic Anhydrase

“…Thiol peroxidases function as redox sensors and are important in the thiol-redox regulatory network for oxidation of target protein. Only the balance between reducing and oxidizing input allows for fine-tuned adjustment of the redox state of target proteins like malate dehydrogenase, ribulose-5-phosphate kinase or fructose-1,6-bisphosphatase [17,41], and likely of βCA1. Recent interactome study of 2-CysPRX showed interaction between βCA1 and 2-CysPRXA and affected its activity [42] Activity measurements and mPEG-Mal-labeling during βCA1 extraction from stressed leaves indicate that thiol oxidation of βCA1 occurs (Figures 4 and 5), but not necessarily as an on/off-switch, e.g., between light and darkness, but rather in a more subtle manner in dependence on light intensity.…”