RESUMO
The Arabidopsis thaliana homologue of the Eyes Absent genes (AtEYA) encodes a protein corresponding to the C-terminal conserved domain of the animal Eyes Absent proteins. We show here that AtEYA is a tyrosine-specific phosphatase that hydrolyzes its substrates in a metal-dependent reaction analogous to the phosphoserine phosphatases of the haloacid dehalogenase (HAD) family. The animal Eyes Absent proteins are a novel family of dual-function enzymes: they are transcription factors as well as phosphatases. They also represent a new mechanistic class of tyrosine phosphatases (PTPs) that do not have the Cys-containing signature motif. In contrast, AtEYA is only a tyrosine phosphatase and has no transactivation domain. Using the reaction mechanism of other HAD family enzymes as a model, we have conducted mutational analyses on AtEYA to query the roles of conserved residues. This analysis confirms the importance of the putative nucleophile, the general acid, and the metal-binding residues. Additionally, an inhibitory profile that is diagnostic of this new class of protein tyrosine phosphatases is described. The results of these studies on AtEYA reveal that while the animal and plant Eyes Absent proteins catalyze the same dephosphorylation reaction, the details of their specificity and active site environment, as well as their biological roles, are distinct.
Assuntos
Proteínas de Arabidopsis/química , Arabidopsis/enzimologia , Ácido Aspártico/química , Proteínas Tirosina Fosfatases/química , Animais , Proteínas de Arabidopsis/antagonistas & inibidores , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Sítios de Ligação/genética , Catálise , Análise Mutacional de DNA , Proteínas de Drosophila/química , Inibidores Enzimáticos/química , Proteínas do Olho/química , Concentração de Íons de Hidrogênio , Metais Pesados/química , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Peptídeos/química , Peptídeos/metabolismo , Fosforilação , Fosfotirosina/química , Fosfotirosina/metabolismo , Proteínas Tirosina Fosfatases/antagonistas & inibidores , Proteínas Tirosina Fosfatases/genética , Proteínas Tirosina Fosfatases/metabolismo , Homologia Estrutural de Proteína , Especificidade por Substrato/genética , Compostos de Tungstênio/química , Vanadatos/químicaRESUMO
The CD44 transmembrane glycoprotein family has been implicated in cell-cell adhesion and cell signaling in response to components of the extracellular matrix but its role in the nervous system is not understood. CD44 proteins are elevated in Schwann cells and oligodendrocytes following nervous system insults, in inflammatory demyelinating lesions, and in tumors. Here, we tested the hypothesis that elevated CD44 expression influences Schwann cell and oligodendrocyte functions by generating transgenic mice that express CD44 under the control of the 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNPase) promoter. These mice failed to develop peripheral nerve or CNS tumors. However, they did develop severe tremors that were associated with CNS dysmyelination and progressive demyelination. Loss of CNS myelin was not due to alterations in early oligodendrocyte precursor differentiation, proliferation, or survival. Myelination in the PNS appeared normal. In no instance was there any evidence of an inflammatory response that could account for the loss of CNS myelin. These findings suggest that CNPase-CD44 mice are a novel model for noninflammatory progressive demyelinating disease and support a potential role for CD44 proteins expressed by glial cells in promoting demyelination.
