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Glutaredoxin Function for the Carboxyl-Terminal Domain of the Plant-Type 5-adenylylsulfate Reductase

Julie-Ann Bick, Fredrik Aslund, Yichang Chen and Thomas Leustek
Proceedings of the National Academy of Sciences of the United States of America
Vol. 95, No. 14 (Jul. 7, 1998), pp. 8404-8409
Stable URL: http://www.jstor.org/stable/45761
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Glutaredoxin Function for the Carboxyl-Terminal Domain of the Plant-Type 5′-adenylylsulfate Reductase
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Abstract

5′-Adenylylsulfate (APS) reductase (EC 1.8.99.-) catalyzes the reduction of activated sulfate to sulfite in plants. The evidence presented here shows that a domain of the enzyme is a glutathione (GSH)-dependent reductase that functions similarly to the redox cofactor glutaredoxin. The APR1 cDNA encoding APS reductase from Arabidopsis thaliana is able to complement the cysteine auxotrophy of an Escherichia coli cysH [3′-phosphoadenosine-5′-phosphosulfate (PAPS) reductase] mutant, only if the E. coli strain produces glutathione. The purified recombinant enzyme (APR1p) can use GSH efficiently as a hydrogen donor in vitro, showing a Km[GSH] of ≈ 0.6 mM. Gene dissection was used to express separately the regions of APR1p from amino acids 73-327 (the R domain), homologous with microbial PAPS reductase, and from amino acids 328-465 (the C domain), homologous with thioredoxin. The R and C domains alone are inactive in APS reduction, but the activity is partially restored by mixing the two domains. The C domain shows a number of activities that are typical of E. coli glutaredoxin rather than thioredoxin. Both the C domain and APR1p are highly active in GSH-dependent reduction of hydroxyethyldisulfide, cystine, and dehydroascorbate, showing a Km[GSH] in these assays of ≈ 1 mM. The R domain does not show these activities. The C domain is active in GSH-dependent reduction of insulin disulfides and ribonucleotide reductase, whereas APR1p and R domain are inactive. The C domain can substitute for glutaredoxin in vivo as demonstrated by complementation of an E. coli mutant, underscoring the functional similarity between the two enzymes.

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