Protein redox regulation in the thylakoid lumen: The importance of disulfide bonds for violaxanthin de‐epoxidase

Abstract

a b s t r a c tWhen exposed to saturating light conditions photosynthetic eukaryotes activate the xanthophyll cycle where the carotenoid violaxanthin is converted into zeaxanthin by the enzyme violaxanthin de-epoxidase (VDE). VDE protein sequence includes 13 cysteine residues, 12 of which are strongly conserved in both land plants and algae. Site directed mutagenesis of Arabidopsis thaliana VDE showed that all these 12 conserved cysteines have a major role in protein function and their mutation leads to a strong reduction of activity. VDE is also shown to be active in its completely oxidized form presenting six disulfide bonds. Redox titration showed that VDE activity is sensitive to variation in redox potential, suggesting the possibility that dithiol/disulfide exchange reactions may represent a mechanism for VDE regulation.

The Path to Thioredoxin and Redox Regulation in Chloroplasts

“…The results suggested a previously unrecognized paradigm for redox regulation opposite to that in the stroma-i.e., enzyme activation (conversion of SH to S-S) by light through the onset of an oxidative environment coupled to O 2 evolution. The FKBP13 results have been extended in a recent study to violaxanthin de-epoxidase, another resident of the lumen (129). This and related research (82,89) opens the door to a largely unexplored field encompassing enzymes such as those engaged in photosystem II supercomplex formation.…”

An algal enzyme required for biosynthesis of the most abundant marine carotenoids

“…4G), although PtVDL1 contains six of the eight cysteine residues conserved in PtVDE (17). These results point to a constitutive activity of PtVDL1 modulated only by pH, whereas VDE activity is controlled on multiple levels, among them a pHdependent affinity for its co factor ascorbate (39) and the redox state in the thylakoid lumen (36,37).…”

Lipid Dependence of Xanthophyll Cycling in Higher Plants and Algae

“…With regard to the dimerization it has been proposed that the C-terminus of the VDE plays a role in the interaction of the VDE monomers (Hallin et al, 2016) and that four specific amino acid residues are important for the pH-dependent activation (Fufezan et al, 2012). In addition, it has been suggested that the conserved cysteine residues and the disulfide bridges formed by the cysteines are sensitive to redox changes of the thylakoid membrane induced by the photosynthetic electron transport (Hallin et al, 2015;Simionato et al, 2015). Changes of the thylakoid redox potential may play a role in the regulation and activation of the VDE via dithiol/disulfide exchange reactions.…”