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Abstract

PII proteins constitute one of the most widely distributed families of signal transduction proteins, whose representatives are present in archaea, bacteria and plants. They play a pivotal role to control the nitrogen metabolism in response to the central metabolites ATP, ADP and 2- oxoglutarate (2-OG). These signals from energy status, carbon and nitrogen metabolism are integrated and transmitted to the regulatory targets (key enzymes, transporters and transcription factors). In oxygenic phototrophic organisms, from cyanobacteria to higher plants, the controlling enzyme of arginine synthesis, N-acetyl-glutamate kinase (NAGK), is a major PII target, whose activity responds to the cellular 2- OG and energy status via PII signalling. Novel crystal structures of PII signal transduction proteins from oxygenic phototrophs in the presence of signaling metabolites and in complex with NAGK give deeper insights into their control mechanism and sheds light on the evolutionary adaptation of PII signal transduction.