Abstract
Conserved clusters of genes encoding DsrE and TusA homologs occur in many archaeal and bacterial sulfur oxidizers. TusA has a well documented function as a sulfurtransferase in tRNA modification and molybdenum cofactor biosynthesis in Escherichia coli, and DsrE is an active site subunit of the DsrEFH complex that is essential for sulfur trafficking in the phototrophic sulfur-oxidizing Allochromatium vinosum. In the acidothermophilic sulfur (S(0))- and tetrathionate (S4O6(2-))-oxidizing Metallosphaera cuprina Ar-4, a dsrE3A-dsrE2B-tusA arrangement is situated immediately between genes encoding dihydrolipoamide dehydrogenase and a heterodisulfide reductase-like complex. In this study, the biochemical features and sulfur transferring abilities of the DsrE2B, DsrE3A, and TusA proteins were investigated. DsrE3A and TusA proved to react with tetrathionate but not with NaSH, glutathione persulfide, polysulfide, thiosulfate, or sulfite. The products were identified as protein-Cys-S-thiosulfonates. DsrE3A was also able to cleave the thiosulfate group from TusA-Cys(18)-S-thiosulfonate. DsrE2B did not react with any of the sulfur compounds tested. DsrE3A and TusA interacted physically with each other and formed a heterocomplex. The cysteine residue (Cys(18)) of TusA is crucial for this interaction. The single cysteine mutants DsrE3A-C(93)S and DsrE3A-C(101)S retained the ability to transfer the thiosulfonate group to TusA. TusA-C(18)S neither reacted with tetrathionate nor was it loaded with thiosulfate with DsrE3A-Cys-S-thiosulfonate as the donor. The transfer of thiosulfate, mediated by a DsrE-like protein and TusA, is unprecedented not only in M. cuprina but also in other sulfur-oxidizing prokaryotes. The results of this study provide new knowledge on oxidative microbial sulfur metabolism.
Highlights
The dsrE3A-dsrE2B-tusA cluster from Metallosphaera cuprina encodes putative sulfur-trafficking proteins and is flanked by genes encoding a heterodisulfide reductase-like complex and dihydrolipoamide dehydrogenase
TusA has a well documented function as a sulfurtransferase in tRNA modification and molybdenum cofactor biosynthesis in Escherichia coli, and DsrE is an active site subunit of the DsrEFH complex that is essential for sulfur trafficking in the phototrophic sulfur-oxidizing Allochromatium vinosum
Occurrence, Genetic Environment, and Grouping of Archaeal DsrE Proteins—The genome of M. cuprina encodes four different DsrE-like proteins: Mcup_0681, Mcup_0682, Mcup_1706, and Mcup_1724. All of these proteins contain cysteine residues corresponding to the active cysteine residue of DsrE from A. vinosum (Fig. 2A), which had been demonstrated experimentally [23]
Summary
The dsrE3A-dsrE2B-tusA cluster from Metallosphaera cuprina encodes putative sulfur-trafficking proteins and is flanked by genes encoding a heterodisulfide reductase-like complex and dihydrolipoamide dehydrogenase. Results: DsrE3A and TusA react with tetrathionate, yielding protein Cys-S-thiosulfonates, triggering irreversible thiosulfate transfer from DsrE3A to TusA. In the acidothermophilic sulfur (S0)- and tetrathionate (S4O62؊)-oxidizing Metallosphaera cuprina Ar-4, a dsrE3A-dsrE2B-tusA arrangement is situated immediately between genes encoding dihydrolipoamide dehydrogenase and a heterodisulfide reductase-like complex. DsrE3A was able to cleave the thiosulfate group from TusA-Cys18-S-thiosulfonate. The single cysteine mutants DsrE3A-C93S and DsrE3A-C101S retained the ability to transfer the thiosulfonate group to TusA. TusA-C18S neither reacted with tetrathionate nor was it loaded with thiosulfate with DsrE3A-Cys-S-thiosulfonate as the donor. The transfer of thiosulfate, mediated by a DsrE-like protein and TusA, is unprecedented in M. cuprina and in other sulfur-oxidizing prokaryotes. The results of this study provide new knowledge on oxidative microbial sulfur metabolism
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