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Biological Chemistry

Editor-in-Chief: Brüne, Bernhard

Editorial Board Member: Buchner, Johannes / Ludwig, Stephan / Sies, Helmut / Turk, Boris / Wittinghofer, Alfred

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A Persulfurated Cysteine Promotes Active Site Reactivity in Azotobacter vinelandii Rhodanese

Domenico Bordo / Fabio Forlani / Andrea Spallarossa / Rita Colnaghi / Aristodemo Carpen / Martino Bolognesi / Silvia Pagani

Citation Information: Biological Chemistry. Volume 382, Issue 8, Pages 1245–1252, ISSN (Print) 1431-6730, DOI: 10.1515/BC.2001.155, June 2005

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Active site reactivity and specificity of RhdA, a thiosulfate:cyanide sulfurtransferase (rhodanese) from Azotobacter vinelandii, have been investigated through ligand binding, sitedirected mutagenesis, and Xray crystallographic techniques, in a combined approach. In native RhdA the active site Cys230 is found persulfurated; fluorescence and sulfurtransferase activity measurements show that phosphate anions interact with Cys230 persulfide sulfur atom and modulate activity. Crystallographic analyses confirm that phosphate and hypophosphite anions react with native RhdA, removing the persulfide sulfur atom from the active site pocket. Considering that RhdA and the catalytic subunit of Cdc25 phosphatases share a common threedimensional fold as well as active site Cys (catalytic) and Arg residues, two RhdA mutants carrying a single amino acid insertion at the active site loop were designed and their phosphatase activity tested. The crystallographic and functional results reported here show that specific sulfurtransferase or phosphatase activities are strictly related to precise tailoring of the catalytic loop structure in RhdA and Cdc25 phosphatase, respectively.

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