Metabolite sensing signal processors in eukaryotic photosynthetic microorganisms: from molecular mechanisms to cellular functions

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Microorganisms are highly evolved in their abilities to regulate distinct sets of cellular functions in response to fluctuations in the environment, such as physicochemical or nutritional changes (Silva-Rocha & de Lorenzo, 2010). Although these systems are highly diverse with respect to specificity and complexity, some sensing signal processors are conserved in the different domains of life. Examples include aspects of signal integration in branched pathways or cross-talk suppression (reviewed by Goulian, 2010) as well as regulation via proteins of the PII family that are present in bacteria, archaea and plants (Chellamuthu et al., 2013; Ermilova et al., 2013). Despite the high degree of similarity between prokaryotic and eukaryotic PII proteins, we could reveal a fundamentally novel property in plant PII proteins: they sense glutamine through a novel low affinity glutamine-binding site (Chellamuthu et al., 2014). In addition to the published results, we found by pull-down analysis, that there are apparently many more PII cellular targets in photosynthetic microorganisms than previously anticipated. Together, these results indicate that we have so far only studied a tip of an iceberg of the cellular functions of PII. The basic idea of the project is, that PII proteins are pivotal metabolite sensing signal processors in oxygenic photosynthetic (micro)organisms. In this project, the group from St. Petersburg will focus on the definition of physiological implications of PII-mediated regulatory networks in green algae. The significance of these circuits in algal physiology and its impact in algal biotechnological use will be addressed. In Tübingen, the molecular biology of PIi interactions, from unsolved structure-function aspects of the controlling enzyme of Arginien synthesis, N-acetyl-glutamate kinase, to the characterization of novel PII controlled enzymes of central metabolism, will be in the centre of research.