Plasticity in Plastid Redox Networks: Evolution of Glutathione-Dependent Redox Cascades and Glutathionylation Sites

Abstract

Background: Flexibility of plant metabolism is supported by redox regulation of enzymes via posttranslational modification of cysteine residues, especially in plastids. Here, the redox states of cysteine residues are partly coupled to the thioredoxin system and partly to the glutathione pool for reduction. Moreover, several plastid enzymes involved in reactive oxygen species (ROS) scavenging and damage repair draw electrons from glutathione. In addition, cysteine residues can be post-translationally modified by forming a disulfide with glutathione (S-glutathionylation), which protects thiol groups from further oxidation and can influence protein activity. However, the evolution of the plastid glutathione-dependent redox network in land plants and the conservation of cysteine residues undergoing S-glutathionylation is largely unclear.Results: We analysed the genomes of nine representative model species from streptophyte algae to angiosperms and find that the components of the plastid glutathione-dependent redox network are largely conserved, except for lambda- and the closely related iota-glutathione S-transferases. Screening the literature for target thiols of S-glutathionylation, we find that 151 plastid proteins have been identified as glutathionylation targets, while the exact cysteine residue is only known for 17% (26 proteins), with one or multiple sites per protein, resulting in 37 known S-glutathionylation sites for plastids. However, 38% (14) of the known sites were completely conserved in model species from green algae to flowering plants, with 22% (8) on non-catalytic cysteines. Variable conservation of the remaining sites indicates independent gains and losses of cysteines at the same position during land plant evolution.Conclusions: We conclude that the glutathione dependent redox network in plastids is highly conserved in streptophytes with some variability in scavenging and damage repair enzymes. Our analysis of cysteine conservation suggests that S-glutathionylation in plastids plays an important and yet under-investigated role in redox regulation and stress response.

Thiol-based Oxidative Posttranslational Modifications (OxiPTMs) of Plant Proteins

“…S -glutathionylation appears to play a major role in certain organelles. Accordingly, in an analysis of nine photosynthetic species from streptophyte algae to angiosperms, Müller-Schüssele et al. (2021) have identified 364 proteins susceptible to undergo S -glutathionylation, of which 151 have a plastid location.…”

High robustness of cytosolic glutathione redox potential under combined salt and osmotic stress in barley as revealed by the biosensor Grx1-roGFP2

“…This includes enzymes involved in the scavenging of reactive oxygen species (ROS) or oxidative damage repair, e.g. dehydroascorbate reductase (DHAR) or atypical methionine sulfoxide reductases B (MSRB1) (Foyer & Noctor 2011;Rey & Tarrago 2018;Müller-Schüssele, Bohle, et al 2021). The compartment-specific study of EGSH has been largely driven by the characterization of redox-sensitive GFP2 (Meyer et al 2007;Schwarzländer et al 2008) that contains a GSH-dependent thiol switch on the outer face of the GFP beta-barrel structure.…”

“…This includes enzymes involved in the scavenging of reactive oxygen species (ROS) or oxidative damage repair, e.g. dehydroascorbate reductase (DHAR) or atypical methionine sulfoxide reductases B (MSRB1) (Foyer & Noctor 2011; Rey & Tarrago 2018; Müller-Schüssele, Bohle, et al . 2021).…”

Structural snapshots of nitrosoglutathione binding and reactivity underlying S-nitrosylation of photosynthetic GAPDH

“…The identification of a -SNO consensus motif in target proteins has been sought, but a universal pattern has not been established yet. Besides acting as a trans-nitrosylating agent, GSNO can also induce Sglutathionylation, a redox modification consisting in the formation of a mixed disulfide between a molecule of glutathione and a protein cysteine (14)(15)(16). S-glutathionylation shares with Snitrosylation the ability to regulate protein function and conformation, and it can be induced by alternative mechanisms involving a thiol/disulfide exchange mediated by oxidized glutathione (GSSG) or H2O2-dependent primary oxidation of a cystine thiol to sulfenic acid followed by the spontaneous reaction with reduced glutathione (GSH) (6).…”