Multiple Functions of the Eya Phosphotyrosine Phosphatase

Abstract

Eyes absent (Eya), a protein conserved from plants to humans and best characterized as a transcriptional coactivator, is also the prototype for a novel class of eukaryotic aspartyl protein tyrosine phosphatases. This minireview discusses recent breakthroughs in elucidating the substrates and cellular events regulated by Eya's tyrosine phosphatase function and highlights some of the complexities, new questions, and surprises that have emerged from efforts to understand how Eya's unusual multifunctionality influences developmental regulation and signaling.

FIG 1

Functional domains of Eya family proteins. Shown is a diagram, not drawn precisely to scale, comparing the Drosophila Eya, human Eya1, and Arabidopsis Eya proteins. The conserved Eya domain (ED) is depicted in blue, with dark bars marking motifs 1, 2, and 3 that define the HAD phosphotyrosine phosphatase (pY-P) domain; key catalytic residues are noted below. The aspartic acid in motif 1 is the most commonly mutated to generate “phosphatase-dead” Eya. The transactivation domain (TAD) is denoted by the pink N-terminal region in the fly and human proteins, with the embedded sequences implicated in phosphothreonine phosphatase (pT-P) activity in yellow. The pT-P motif overlaps a tyrosine-rich loosely conserved motif called Eya domain 2 (ED2). Gray areas denote stretches of protein sequence of unknown function with no conservation across species.

FIG 2

(A) Conservation of the HAD tyrosine phosphatase in Eya proteins from plants to humans. Shown is an alignment of three noncontiguous stretches of ED sequence, with motifs 1 to 3 that define the HAD family in blue and key catalytic residues in boldface. Intervening sequences have been removed, as indicated by dashed lines. The nucleophilic aspartic acid residue in motif 1 is underlined in those Eya proteins where in vitro phosphatase has been measured and shown to be abrogated by mutation of that residue. Residues in red highlight the sequence divergence of Drosophila and Caenorhabditis relative to all other species. Multisequence alignments were performed with the Cobalt Constraint-based multiple protein alignment tool using the following protein sequences: NP_001275503.1, CAA71310.1, CAA71311.1, CAA76636.1, NP_001083888.1, AAI54188.1, CAG09098.1, EEN65685.1, XP_011666140.1, AHA91757.1, CAD89531.1, CAB05707.2, CAP36181.1, AAN10587.1, EDW63329.1, EDW76186.1, XP_011290277.1, XP_314837.3, EHJ75518.1, CCX34986.1, EFA07446.1, XP_008208098.1, XP_006562598.1, AEC09093.1, ACG36155.1, and NP_001056580.1. Hs, Homo sapiens; Xl, Xenopus laevis; Dr, Danio rerio; Tn, Tetraodon nigroviridis; Bf, Branchiostoma floridae; Sp, Strongylocentrotus purpuratus; Es, Euprymna scolopes; Dj, Dugesia japonica; Ce, Caenorhabditis elegans; Cb, Caenorhabditis briggsae; Dm, Drosophila melanogaster; Dv, Drosophila virilis; Dw, Drosophila willisoni; Md, Musca domestica; Ag, Anopheles gambiae; Dp, Danaus plexippus; Bg, Blatella germanica; Tc, Tribolium castaneum; Nv, Nasonia vitripennis; Am, Apis mellifera; At, Arabidopsis thaliana; Zm, Zea mays; Os, Oryza sativa. (B) Pairwise comparisons of ED sequences of human Eya1 to -4 and Drosophila Eya highlight the high degree of conservation between paralogs and across species. Percentages of amino acid identities and similarities were calculated using LALIGN and are shown above and below the diagonal white line, respectively. Percentile bins are colored from dark to light in descending order. Focusing on percentage of identity, the ED of Eya3 appears to be the most divergent of the four paralogs, although the high degree of similarity across all four paralogs suggests the amino acid differences may have limited impact on function. A more extensive discussion of similarities and differences among the Eya paralogs can be found in the article by Tadjuidje and Hegde (34).

FIG 3

Summary of Eya's phosphotyrosine and phosphothreonine phosphatase (pY-P and pT-P) functions in both nucleus and cytoplasm. Both phosphatase activities operate in in both compartments, although major gaps remain in substrate identification, as indicated by question marks. Phosphorylated residues are shown only on Eya substrates; other phospho-based regulation is not depicted. See the text and references for details (17, 20, 38, 64, 66, 92).