Assuntos
Fosfoproteínas Fosfatases/química , Fosfoproteínas Fosfatases/metabolismo , Animais , Sítios de Ligação , Linhagem Celular , Análise Mutacional de DNA/métodos , Eletroforese em Gel de Poliacrilamida/métodos , Mamíferos , Mutagênese Sítio-Dirigida , Fosfoproteínas Fosfatases/genética , Fosfoproteínas Fosfatases/isolamento & purificação , Proteína Fosfatase 2 , Subunidades Proteicas/química , Subunidades Proteicas/genética , Subunidades Proteicas/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Sequências Reguladoras de Ácido Nucleico , Especificidade por Substrato , Moldes Genéticos , TransfecçãoRESUMO
Protein phosphatase 2A (PP2A) is an essential intracellular serine/threonine phosphatase containing a catalytic subunit that possesses the potential to dephosphorylate promiscuously tyrosine-phosphorylated substrates in vitro. How PP2A acquires its intracellular specificity and activity for serine/threonine-phosphorylated substrates is unknown. Here we report a novel and phylogenetically conserved mechanism to generate active phospho-serine/threonine-specific PP2A in vivo. Phosphotyrosyl phosphatase activator (PTPA), a protein of so far unknown intracellular function, is required for the biogenesis of active and specific PP2A. Deletion of the yeast PTPA homologs generated a PP2A catalytic subunit with a conformation different from the wild-type enzyme, as indicated by its altered substrate specificity, reduced protein stability, and metal dependence. Complementation and RNA-interference experiments showed that PTPA fulfills an essential function conserved from yeast to man.