Linking PII regulation with central carbon control in Synechocystis PCC 6803

• Applicant: Professor Dr. Karl Forchhammer
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 452840821

The ability of cells to precisely sense the carbon/nitrogen (C/N) balance and execute appropriate responses upon perturbation is a key requirement for maintenance of cellular homeostasis. In prokaryotes, the versatile PII signaling proteins are important players in this respect. They act as multitasking signal processors, integrating the signal from the C/N status reporter metabolite 2-OG with that from the energy state of the cell through interdependent ATP/ADP binding. Depending on the integrated signals, PII orchestrates metabolic activities in response to environmental changes through binding to various targets. Research in the last decade has revealed that the principle of PII signalling has remained conserved during evolution, whereas different molecular machines (enzymes, transporters, transcription factors) have acquired the ability to read out the metabolic information that has been integrated and calculated by PII proteins through diverse interactions with PII. Recently, we discovered several novel targets of PII in the model cyanobacterium Synechocystis PCC 6803, which indicates that PII orchestrates cellular activities even wider than thought so-far. Among these targets are three transport systems for the major nitrogen sources, the ammonium transporter AMT1, the ABC-type nitrate/nitrite uptake system NRT and the ABC-type urea uptake system URT, furthermore phosphoenolpyruvate carboxylase, as well as two small peptides of unknown function, Sll0944 and Ssr0692. Preliminary data indicate that Sll0944 has a pivotal role in the acclimation of cyanobacteria to nitrogen deprivation. Mutation of Sll0944 leads to gradual loss of viability under N-starvation and to a concomitant massive over-accumulation of polyhydroxybutyrate, never reported to this extent before. By pull-down analysis, we could identify the central carbon-distributing enzyme PGAM (2-3 phosphoglycerate independent phosphoglycerate mutase) as dominant target of Sll0944, with potential involvement of the carboxysome associated protein CcmP. In the current proposal, we aim to identify the role of these proteins in Synechocystis nitrogen acclimation and the functional implication of PII interaction. Therefore, we propose a project that systematically dissects and characterizes, from activity to structural level, the interactions of the PII/Sll0944/PGAM/CcmP interaction network. Since these proteins are highly conserved in cyanobacteria, we will obtain fundamental insights in bacterial metabolic control of global relevance.

• DFG Programme: Research Grants