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Abstract: Sulfurtransferases (Str) comprise a group of enzymes widely distributed in archaea, eubacteria, and eukaryota which catalyse the transfer of a sulfur atom from suitable sulfur donors to nucleophilic sulfur acceptors. Neither the in vivo sulfur donors nor the acceptors of Str could be clearly identified in any of the organisms investigated so far. In Arabidopsis thaliana 20 Str proteins have been identified and grouped according to sequence homology. To investigate their respective in vivo function, Arabidopsis plants were grown in sterile hydroponic cultures at different sulfate (50, 500, and 1500μM) and phosphate (0.1 and 1mM) concentrations, and in medium supplemented with 1mM thiosulfate. Northern blot analysis revealed the differential expression of the Str investigated. Thiosulfate Str activity was significantly increased at low sulfate concentrations in the medium. The Str mRNA levels were highly dependent on the developmental stage of the Arabidopsis plants. The expression of most Str analysed increased with progressing plant age in parallel with increasing 3-mercaptopyruvate and thiosulfate Str activities. The Str investigated were differentially expressed in a light/dark cycle whereas Str enzyme activities were not affected by the light conditions. The results indicate that each Str is regulated in a different way and plays an individual specific role in the plant metabolism. [Copyright &y& Elsevier]

Sulfurtransferases/rhodaneses (Str) are enzymes widely distributed in archaea, prokaryota and eukaryota, and catalyze the transfer of sulfur from a donor molecule to a thiophilic acceptor substrate. In this reaction, Str cycles between the sulfur-free and the sulfur-substituted form. Two-domain Str consist of two globular domains of nearly identical size and conformation connected by a short linker sequence, which is elongated in plant two-domain Str proteins compared to Str in other organisms. The two-domain Arabidopsis thaliana Str1 protein (At1g79230) was expressed in Escherichia coli as a mature protein, as a variant without the elongated linker sequence, and as AtStr1C332S and AtStr1C339V. The persulfuration state of the purified recombinant proteins was investigated in the presence and absence of sulfur donors by fluorescence spectroscopy. The secondary structure was analyzed by circular dichroism (CD) in the far-UV range, while overall changes in tertiary structure were determined by CD in the near-UV range. Finally, protein stability was analyzed by tryptic digestion. The elongated linker sequence is essential for correct conformation and stability, and thereby affects the catalytic activity of AtStr1. Replacement of the catalytic cysteine residue C332 leads to higher rigidity of the molecule, whereas replacement of C339 does not lead to any conformational changes, providing evidence of the direct involvement of C339 in catalysis. [ABSTRACT FROM AUTHOR]