Mutations or duplications in MECP2 cause Rett and Rett-like syndromes, neurodevelopmental disorders characterized by mental retardation, motor dysfunction, and autistic behaviors. MeCP2 is expressed in many mammalian tissues and functions as a global repressor of transcription; however, the molecular mechanisms by which MeCP2 dysfunction leads to the neural-specific phenotypes of RTT remain poorly understood. Here, we show that neuronal activity and subsequent calcium influx trigger the de novo phosphorylation of MeCP2 at serine 421 (S421) by a CaMKII-dependent mechanism. MeCP2 S421 phosphorylation is induced selectively in the brain in response to physiological stimuli. Significantly, we find that S421 phosphorylation controls the ability of MeCP2 to regulate dendritic patterning, spine morphogenesis, and the activity-dependent induction of Bdnf transcription. These findings suggest that, by triggering MeCP2 phosphorylation, neuronal activity regulates a program of gene expression that mediates nervous system maturation and that disruption of this process in individuals with mutations in MeCP2 may underlie the neural-specific pathology of RTT.

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Polyhistidine tags were added to the carboxyl termini of the two homologous subunits of yeast NAD ؉ -specific isocitrate dehydrogenase (IDH). The tag in either the IDH1 or IDH2 subunit permits one-step affinity purification from yeast cellular extracts of catalytically active and allosterically responsive holoenzyme. This expression system was used to investigate subunit-specific contributions of residues with putative functions in adenine nucleotide binding. The primary effect of simultaneous replacement of the adjacent Asp-279 and Ile-280 residues in IDH1 with alanines is a dramatic loss of activation by AMP. In contrast, alanine replacement of the homologous Asp-286 and Ile-287 residues in IDH2 does not alter the allosteric response to AMP, but produces a 160-fold reduction in V max due to a 70-fold increase in the S 0.5 value for NAD ؉ . These results suggest that the targeted aspartate/isoleucine residues may contribute to regulator binding in IDH1 and to cofactor binding in IDH2, i.e. that these homologous residues are located in regions that have evolved for binding the adenine nucleotide components of different ligands. In other mutant enzymes, an alanine replacement of Asp-191 in IDH1 eliminates measurable catalytic activity, and a similar substitution of the homologous Asp-197 in IDH2 produces pleiotropic catalytic effects. A model is presented for the primary function of IDH2 in catalysis and of IDH1 in regulation, with crucial roles for these single aspartate residues in the communication and functional interdependence of the two subunits.The oxidative decarboxylation reaction catalyzed by mitochondrial NAD ϩ -specific isocitrate dehydrogenase (IDH) 1 is believed to be a rate-limiting step in the tricarboxylic acid cycle. The enzyme isolated from Saccharomyces cerevisiae has been described as responsive to energy charge due to allosteric activation by AMP and inhibition by ATP and NADH (1). Mammalian enzymes exhibit similar regulatory properties, but utilize ADP as a positive regulator (2).The catalytically active form of IDH from yeast is an octamer composed of two subunits in a 1:1 ratio (3, 4). Independent nuclear genes encoding the IDH1 and IDH2 subunits have been cloned, and gene disruption studies show that both subunits are essential for catalytic activity (5, 6). Disruption of either or both of the IDH1 and IDH2 genes results in an inability to grow with acetate as a carbon source, a phenotype shared with several other tricarboxylic acid cycle mutants in yeast (7,8).The deduced amino acid sequences and amino-terminal sequence analyses indicate that the mature IDH1 and IDH2 polypeptides contain 349 and 354 amino acid residues, respectively, and share 42% residue identity. The yeast polypeptides share ϳ32% sequence identity with Escherichia coli NADP ϩ -specific isocitrate dehydrogenase (9), a homodimeric enzyme analyzed in several crystallographic studies (10 -12).Equilibrium binding and kinetic analyses (13, 14) conducted with purified yeast IDH led to the characterization of four binding sit...

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