title: A novel arsenate reductase from the arsenic hyperaccumulating fern Pteris vittata.
abstract: Pteris vittata sporophytes hyperaccumulate arsenic to 1% to 2% of their dry weight. Like the sporophyte, the gametophyte was found to reduce arsenate [As(V)] to arsenite [As(III)] and store arsenic as free As(III). Here, we report the isolation of an arsenate reductase gene (PvACR2) from gametophytes that can suppress the arsenate sensitivity and arsenic hyperaccumulation phenotypes of yeast (Saccharomyces cerevisiae) lacking the arsenate reductase gene ScACR2. Recombinant PvACR2 protein has in vitro arsenate reductase activity similar to ScACR2. While PvACR2 and ScACR2 have sequence similarities to the CDC25 protein tyrosine phosphatases, they lack phosphatase activity. In contrast, Arath;CDC25, an Arabidopsis (Arabidopsis thaliana) homolog of PvACR2 was found to have both arsenate reductase and phosphatase activities. To our knowledge, PvACR2 is the first reported plant arsenate reductase that lacks phosphatase activity. CDC25 protein tyrosine phosphatases and arsenate reductases have a conserved HCX5R motif that defines the active site. PvACR2 is unique in that the arginine of this motif, previously shown to be essential for phosphatase and reductase activity, is replaced with a serine. Steady-state levels of PvACR2 expression in gametophytes were found to be similar in the absence and presence of arsenate, while total arsenate reductase activity in P. vittata gametophytes was found to be constitutive and unaffected by arsenate, consistent with other known metal hyperaccumulation mechanisms in plants. The unusual active site of PvACR2 and the arsenate reductase activities of cell-free extracts correlate with the ability of P. vittata to hyperaccumulate arsenite, suggesting that PvACR2 may play an important role in this process.
authors.affiliation: Department of Botany and Plant Pathology , Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Danielle R
authors.initials: DR
authors.lastname: Ellis
authors.forename: Luke
authors.initials: L
authors.lastname: Gumaelius
authors.forename: Emily
authors.initials: E
authors.lastname: Indriolo
authors.forename: Ingrid J
authors.initials: IJ
authors.lastname: Pickering
authors.forename: Jo Ann
authors.initials: JA
authors.lastname: Banks
authors.forename: David E
authors.initials: DE
authors.lastname: Salt
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D053502:Arsenate Reductases; D001149:Arsenates / Q000378:metabolism; D001151:Arsenic / Q000378:metabolism*; D053501:Arsenite Transporting ATPases; D003001:Cloning, Molecular; D017353:Gene Deletion; D005816:Genetic Complementation Test; D016623:Ion Pumps / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D032495:Pteris / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D020687:cdc25 Phosphatases / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D001149:Arsenates; D016623:Ion Pumps; D009097:Multienzyme Complexes; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; C506971:ARR2 protein, S cerevisiae; D053502:Arsenate Reductases; D020687:cdc25 Phosphatases; D053501:Arsenite Transporting ATPases; D001151:Arsenic; C025657:arsenic acid