Abstract
Heat stress induces misfolding and aggregation of proteins unless they are guarded by chaperone systems. Here, we examined the function of the glutaredoxin GRXS17, a member of thiol reductase families in the model plant Arabidopsis (Arabidopsis thaliana). GRXS17 is a nucleocytosolic monothiol glutaredoxin consisting of an N-terminal thioredoxin domain and three CGFS active-site motif-containing GRX domains that coordinate three iron-sulfur (Fe-S) clusters in a glutathione-dependent manner. As an Fe-S cluster-charged holoenzyme, GRXS17 is likely involved in the maturation of cytosolic and nuclear Fe-S proteins. In addition to its role in cluster biogenesis, GRXS17 presented both foldase and redox-dependent holdase activities. Oxidative stress in combination with heat stress induced loss of its Fe-S clusters followed by subsequent formation of disulfide bonds between conserved active-site cysteines in the corresponding thioredoxin domains. This oxidation led to a shift of GRXS17 to a high-molecular-weight complex and thus activated its holdase activity in vitro. Moreover, GRXS17 was specifically involved in plant tolerance to moderate high temperature and protected root meristematic cells from heat-induced cell death. Finally, GRXS17 interacted with a different set of proteins upon heat stress, possibly protecting them from heat injuries. Therefore, we propose that the Fe-S cluster enzyme GRXS17 is an essential guard that protects proteins against moderate heat stress, likely through a redox-dependent chaperone activity. We reveal the mechanism of an Fe-S cluster-dependent activity shift that converts the holoenzyme GRXS17 into a holdase, thereby preventing damage caused by heat stress.
Highlights
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We reveal the mechanism of an Fe-S cluster-dependent activity shift that converts the holoenzyme glutaredoxin S17 (GRXS17) into a holdase, thereby preventing damage caused by heat stress
We showed that the presence of the Fe-S cluster prevents the oligomerization of GRXS17
Summary
General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Oxidative stress in combination with heat stress induced loss of its Fe-S clusters followed by subsequent formation of disulfide bonds between conserved active-site cysteines in the corresponding thioredoxin domains This oxidation led to a shift of GRXS17 to a highmolecular-weight complex and activated its holdase activity in vitro. We propose that the Fe-S cluster enzyme GRXS17 is an essential guard that protects proteins against moderate heat stress, likely through a redox-dependent chaperone activity. GRX from class I exhibit oxidoreductase activities, controlling thiol redox homeostasis of many proteins, mostly through glutathionylation/deglutathionylation activities This activity generally depends on glutathione (GSH) as a reductant and relies on an active site harboring at least one Cys (Meyer et al, 2012). Class II GRX is coordinated by a conserved monocysteinic active site (CGFS) and a GSH molecule, a feature largely conserved within eukaryotic organisms (Lillig et al, 2005; Wingert et al, 2005; Rouhier et al, 2007; Bandyopadhyay et al, 2008; Couturier et al, 2011; Riondet et al, 2012; Berndt and Lillig, 2017)
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