Difference between revisions of "Phosphatase Subfamily Acr2"

Revision as of 18:58, 29 April 2016

Phosphatase Classification: Fold CC3: Superfamily CC3: Family CDC25: Subfamily Acr2

Acr2, phosphatase or arsenate reductase?

Acr2 is found in fungi, plants and protists, but not in animals. It is close to CDC25 in both sequence and structure. Yeast has both CDC25 and Acr2 orthologs (MIH1 and ARR2, respectively). They are regarded as tyrosine phosphatases involved in cell cycle and arsenate reductase, respectively. However, in plants, Acr2 is the only gene close to CDC25, and it is controversial whether it functions as both phosphatase and arsenate reductase in vivo, and if not, what its major function is (see below). It is not very surprising that Acr2s can complement the arsenate-sensitive phenotype of arsenate reductase deletion strain of E. coli or of Saccharomyces cerevisiae, since even human CDC25B and CDC25C has been shown to have arsenate reductase activity in vitro [1].

A brief review of arsentate reductase

Prokaryotes and eukaryotes use arsenate reductases from distinct folds. E. coli uses ArsC, which has a CC3 fold like the LMWPTP and SSU72 protein phosphatases. Eukaryotes, particularly fungi, plants and protists, may use ACR2 which has a CC3 fold, like the same fold as CDC25 [2]. Knockout of ACR2 does not affect arsenic redox status in Arabidopsis thaliana or Saccharomyces cerevisiae, which implies the existence of other arsenate reductase(s) in plants and yeast [3].

Saccharomyces cerevisiae

Overexpressed yeast ARR2 in E. coli showed arsenate reductase activity and complemented the arsenate-sensitive phenotype of an ArsC deletion [2, 4, 5]. The Cx5R motif is required for its arsenate reductase activity [6]. Arr2 is a fast evolving protein with no confident orthologs outside of closely-related species. S. cerevisiae has a gene named YCH1 similar to ARR2 in sequence. S. cerevisiae has a CDC25 MIH1.

Arabidopsis thaliana

Acr2 was initially characterized as a phosphatase, given that: i) protein structure solved by NMR [7], ii) recombinant expression in E. coli showed tyrosine phosphatase activity towards an artificial substrate [8], and iii) overexpression in fission yeast accelerated mitosis [9]. However, its overexpression or knockout has no obvious cell cycle phenotype [10].

Arabidopsis thaliana Acr2 has been suggested to play a role in arsenate reduction [11, 12, 13]. However, knocking out ACR2 does not affect arsenic redox status in Arabidopsis thaliana [3]. Another CC2 fold protein, HAC1/AT2G21045 was recently shown to be the dominant arsenate reductase in A. thaliana [14].

Oryza sativa (rice)

Rice has two Acr2s, which can complement the arsenate-sensitive phenotype of an ArsC deletion in E. coli at different levels [15] and have both arsenate reductase and phosphatase activity, both of which required the Cx5R cysteine [15].

Pteris vittata (fern)

Pteris vittata has a single ACR2 (PvACR2). It product protein can suppress the arsenate sensitivity and arsenic hyperaccumulation phenotypes of yeast (Saccharomyces cerevisiae) lacking the arsenate reductase gene ACR2 [13, 16]. Interestingly, PvACR2 has replaced arginine with serine at the catalytic motif Cx5R, previously shown to be essential for phosphatase and reductase activity. While Acr2s in Arabidopsis thaliana and rice show both arsenate reductase and phosphatase activities, PvACR2 only shows arsenate reductase activity [16].

Chlamydomonas reinhardtii (green alga)

Chlamydomonas reinhardtii has two Acr2s. One of them complements the arsenate-sensitive phenotype of an ArsC deletion in E. coli [17].

Leishmania major

Leishmania major Acr2 was able to complement the arsenate-sensitive phenotype of an arsC deletion strain of E. coli or an ACR2 deletion strain of Saccharomyces cerevisiae [18].

Reference

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