Protein phosphatase PphA from Synechocystis sp. PCC 6803: the physiological framework of PII-P dephosphorylation.
The phosphorylated signal transduction protein P(II) (P(II)-P) in the cyanobacterium Synechocystis sp. strain PCC 6803 is dephosphorylated by PphA, a protein phosphatase of the 2C family (PP2C). In this study, the physiological conditions of P(II)-P dephosphorylation were investigated with respect to the in vivo specificity of P(II)-P towards PphA and the cellular abundance of PphA in cells growing under different nitrogen regimes. Furthermore, the consequences of impaired P(II)-P dephosphorylation with respect to short-term inhibition of glutamine synthetase (GS) were studied. With a contribution of approximately 15 % of total Mn(2+)-dependent p-nitrophenyl phosphate hydrolysis activity, PphA has only a minor impact on the total PP2C activity in Synechocystis extracts. Nevertheless, residual P(II)-P dephosphorylation in PphA-deficient cells could only be observed after prolonged incubation in the presence of ammonium. The abundance of PphA correlates with the phosphorylation state of P(II) under nitrogen-replete conditions and is specifically enhanced by nitrite. Regulation of pphA expression operates at the post-transcriptional level. In the presence of nitrate/nitrite, PphA is present in molar excess over P(II)-P, enabling the cells to rapidly dephosphorylate P(II)-P in response to changing environmental conditions. A PphA-deficient mutant is not impaired in short-term inhibition of GS activity following ammonium treatment. Down-regulation of GS occurs by induction of gif genes (encoding GS inactivating factors 7 and 17), which is controlled by NtcA-mediated gene repression. Thus, impaired P(II)-P dephosphorylation does not affect ammonium-prompted inactivation of NtcA.
Kloft
Nicole
N
Institut für Mikrobiologie und Molekularbiologie, Justus-Liebig-Universität Giessen, 35392 Giessen, Germany.
Rasch
Grit
G
Forchhammer
Karl
K
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D005798:Genes, Bacterial; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D051922:PII Nitrogen Regulatory Proteins; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D015398:Signal Transduction; D046939:Synechocystis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D051922:PII Nitrogen Regulatory Proteins; C404143:PIID regulatory protein, Bacteria; D010749:Phosphoprotein Phosphatases; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen