Abstract
Sulfurtransferases (Strs) and thioredoxins (Trxs) are members of large protein families. Trxs are disulfide reductases and play an important role in redox-related cellular processes. They interact with a broad range of proteins. Strs catalyze the transfer of a sulfur atom from a suitable sulfur donor to nucleophilic sulfur acceptors in vitro, but the physiological roles of these enzymes are not well defined. Several studies in different organisms demonstrate protein–protein interactions of Strs with members of the Trx family. We are interested in investigating the specificity of the interaction between Str and Trx isoforms. In order to use the bimolecular fluorescence complementation (BiFC), several Str and Trx sequences from Arabidopsis thaliana were cloned into the pUC-SPYNE and pUC-SPYCE split-YFP vectors, respectively. Each couple of plasmids containing the sequences for the putative interaction partners were transformed into Arabidopsis protoplasts and screened using a confocal laser scanning microscope. Compartment- and partner-specific interactions could be observed in transformed protoplasts. Replacement of cysteine residues in the redox-active site of Trxs abolished the interaction signal. Therefore, the redox site is not only involved in the redox reaction but also responsible for the interaction with partner proteins. Biochemical assays support a specific interaction among Strs and certain Trxs. Based on the results obtained, the interaction of Strs and Trxs indicates a role of Strs in the maintenance of the cellular redox homeostasis.
Highlights
Rhodanese activity, the transfer of a reduced sulfur from thiosulfate to cyanide, was found in many organisms
The protein family of Strs in Arabidopsis thaliana consists of 20 proteins containing one or two rhodanese domains, and they are located in different cellular compartments [31]
Sulfurtransferase interacts with thioredoxin as demonstrated by bimolecular fluorescence studies
Summary
The transfer of a reduced sulfur from thiosulfate to cyanide, was found in many organisms. The main physiological function of these rhodanese/sulfurtransferase (Str) proteins was described to be cyanide detoxification [43]. This high abundance of Str sequences makes the sole function as cyanide detoxification enzymes questionable. The protein family of Strs in Arabidopsis thaliana consists of 20 proteins containing one or two rhodanese domains, and they are located in different cellular compartments [31]. All together more than 40 Trxs and Trx-like proteins were identified in Arabidopsis containing a five amino acid redox site with two cysteine residues (WCXXC) and being located in the different compartments of the cell.
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