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Protein Science (2003), 12:760-767.
Copyright © 2003 The Protein Society

Unexpected similarity in regulation between an archaeal inositol monophosphatase/fructose bisphosphatase and chloroplast fructose bisphosphatase

Kimberly A. Stieglitz1, Barbara A. Seaton2, James F. Head2, Boguslaw Stec3 and Mary F. Roberts1

1 Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467, USA
2 Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118, USA
3 Department of Chemistry, University of Texas, El Paso, Texas 79968, USA

Reprint requests to: Mary Roberts, Department of Chemistry, Boston College, Chestnut Hill, MA 02467, USA; e-mail: mary.roberts{at}bc.edu; fax: (617) 552-2705.

Hyperthermophilic archaea have an unusual phosphatase that exhibits activity toward both inositol-1-phosphate and fructose-1,6-bisphosphate, activities carried out by separate gene products in eukaryotes and bacteria. The structures of phosphatases from Archaeoglobus fulgidus (AF2372) and Methanococcus jannaschii (MJ0109), both anaerobic organisms, resemble the dimeric unit of the tetrameric pig kidney fructose bisphosphatase (FBPase). A striking feature of AF2372, but not of MJ0109, is that the sulfhydryl groups of two cysteines, Cys150 and Cys186, are in close proximity (4 Å). A similar arrangement of cysteines has been observed in chloroplast FBPases that are regulated by disulfide formation controlled by redox signaling pathways (ferredoxin/thioredoxin). This mode of regulation has not been detected in any other FBPase enzymes. Biochemical assays show that the AF2372 phosphatase activity can be abolished by incubation with O2. Full activity is restored by incubation with thiol-containing compounds. Neither the C150S variant of AF2372 nor the equivalent phosphatase from M. jannaschii loses activity with oxidation. Oxidation experiments using Escherichia coli thioredoxin, in analogy with the chloroplast FBPase system, indicate an unexpected mode of regulation for AF2372, a key phosphatase in this anaerobic sulfate reducer.

Keywords: Inositol monophosphatase; fructose bisphosphatase; disulfide formation; archaea; thioredoxin


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