Phosphoglycerate mutase (PGAM) is an enzyme of intermediary metabolism that converts 3-phosphoglycerate to 2-phosphoglycerate in glycolysis. Here, we discovered PGAM5 that is anchored in the mitochondrial membrane lacks PGAM activity and instead associates with the MAP kinase kinase kinase ASK1 and acts as a specific protein Ser/Thr phosphatase that activates ASK1 by dephosphorylation of inhibitory sites. Mutation of an active site His-105 in PGAM5 abolished phosphatase activity with ASK1 and phospho-Thr peptides as substrates. The Drosophila and Caenorhabditis elegans orthologs of PGAM5 also exhibit specific Ser/Thr phosphatase activity and activate the corresponding Drosophila and C. elegans ASK1 kinases. PGAM5 is unrelated to the other known Ser/Thr phosphatases of the PPP, MPP, and FCP families, and our results suggest that this member of the PGAM family has crossed over from small molecules to protein substrates and been adapted to serve as a specialized activator of ASK1.MAP kinase ͉ protein phosphatase P hosphoglycerate mutase (PGAM) is an evolutionarily conserved enzyme of intermediary metabolism that converts 3-phosphoglycerate (3PG) to 2-phosphoglycerate (2PG) in glycolysis and the founder member of the PGAM protein family (1). Members of this family share a common catalytic domain, designated as the PGAM domain, and function as phosphotransferases and/or phosphohydrolases with small molecule substrates. For instance, 1,3-and 1,2-bisphosphoglycerate and fructose-2,6-bisphosphate are the substrates of well-characterized members of this family, the bisphosphoglycerate mutase (BPGM) and 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFB), respectively. The catalytic core of the PGAM domain centers on a histidine residue that acts as a phospho accepter during catalysis. These biochemical and structural features are also shared with the histidine acid phosphatase family of enzymes, and it has recently been proposed that these 2 families can be integrated into a histidine phosphatase superfamily (2). Whereas members of this superfamily predominantly target small molecule substrates, prostatic acid phosphatase has been shown to catalyze hydrolysis of high energy Phospho-Tyr bonds in substrates such as ErbB2 and EGF receptor (3, 4). In addition, Sts-1/TULA-2 in the PGAM family has been shown to function as a protein tyrosine phosphatase, dephosphorylating tyrosine kinases ZAP-70, Syk, and EGF receptor (5-7). These results open the possibility that enzymes in the PGAM family might regulate cellular functions beyond those in glucose metabolism.PGAM5 is a member of the PGAM family that has been shown to interact with Bcl-X L , an apoptosis regulator (8), and Keap1, a redox-regulated substrate adaptor for a cullindependent ubiquitin ligase complex (9). Although it has been suggested that the latter interaction is involved in the regulation of gene expression by the transcription factor Nrf2 (10), molecular functions of PGAM5 have not been elucidated. In this study, we identified PGAM5 as an interacting p...

Nitric oxide (NO) signaling controls various metabolic pathways in bacteria and higher eukaryotes. Cellular enzymes synthesize and detoxify NO; however, a mechanism that controls its cellular homeostasis has not been identified. Here, we found a nitrogen oxide cycle involving nitrate reductase (Nar) and the NO dioxygenase flavohemoglobin (Fhb), that facilitate inter-conversion of nitrate, nitrite, and NO in the actinobacterium Streptomyces coelicolor. This cycle regulates cellular NO levels, bacterial antibiotic production, and morphological differentiation. NO down-regulates Nar and up-regulates Fhb gene expression via the NO-dependent transcriptional factors DevSR and NsrR, respectively, which are involved in the auto-regulation mechanism of intracellular NO levels. Nitrite generated by the NO cycles induces gene expression in neighboring cells, indicating an additional role of the cycle as a producer of a transmittable inter-cellular communication molecule.

SummaryIn Drosophila, the melanization reaction is an important defense mechanism against injury and invasion of microorganisms. Drosophila tyrosine hydroxylase (TH, also known as Pale) and dopa decarboxylase (Ddc), key enzymes in the dopamine synthesis pathway, underlie the melanin synthesis by providing the melanin precursors dopa and dopamine, respectively. It has been shown that expression of Drosophila TH and Ddc is induced in various physiological and pathological conditions, including bacterial challenge; however, the mechanism involved has not been fully elucidated. Here, we show that ectopic activation of p38 MAPK induces TH and Ddc expression, leading to upregulation of melanization in the Drosophila cuticle. This p38-dependent melanization was attenuated by knockdown of TH and Ddc, as well as by that of Drosophila HR38, a member of the NR4A family of nuclear receptors. In mammalian cells, p38 phosphorylated mammalian NR4As and Drosophila HR38 and potentiated these NR4As to transactivate a promoter containing NR4A-binding elements, with this transactivation being, at least in part, dependent on the phosphorylation. This suggests an evolutionarily conserved role for p38 MAPKs in the regulation of NR4As. Thus, p38-regulated gene induction through NR4As appears to function in the dopamine synthesis pathway and may be involved in immune and stress responses.

The heat shock (HS) response is essential for survival of all organisms. Although the machinery of the HS response has been extensively investigated at the cellular level, it is poorly understood at the level of the organism. Here, we show the crucial role of the mushroom body (MB) in the HS response in Drosophila. Null mutants of the mitochondrial phosphatase Drosophila PGAM5 (dPGAM5) exhibited increased vulnerability to HS, which was reversed by MB-specific expression of the caspase inhibitor p35, and similar vulnerability was induced in wild-type flies by knockdown of MB dPGAM5. Elimination of the MB did not affect the HS response of wild-type flies, but did increase the resistance of dPGAM5-deficient flies to HS. Thus, the MB may possess an apoptosis-dependent toxic function, the suppression of which by dPGAM5 appears to be crucial for HS resistance.