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Abstract:
PII proteins are widely distributed signaling proteins in nature, and found in all domains of life. Canonical PII proteins bind to different effector molecules (ATP, ADP, 2-OG), the binding induces conformational changes, and enables the PII protein to bind to different targets to modulate different cellular functions. In general, PII proteins are involved in nitrogen metabolism, sensing the cellular energy state with ATP/ADP binding, and sensing C/N state of the cell. All cyanobacteria contain GlnB gene encoding PII homologues. A close examination of available cyanobacteria genomes on CyanoBase revealed further genes with similarity to glnB but lacking PII signature sequences, we termed the putative gene products PII-like proteins. The available structural information implies that the PII-like proteins have trimeric-protein structures, which are highly similar to the classical PII core architecture. Thus, it is tempting to speculate that PII-like proteins are involved in regulation of different cellular activities, which differ markedly from classical PII proteins [1-3]. To figure out in-vivo cellular function of PII-like proteins, we created different knockout mutants to characterize involvement of PII-like proteins in different physiological functions. The recombinant proteins were titrated with ITC against different effectors molecules to determine the sensory properties of PII-like proteins in comparison to central effector metabolites of classical PII proteins (like, 2-OG). The dynamics of subcellular localization was performed with fusion of PII-like proteins to GFP, and using specific antibodies. Finally, we solved the crystal structures of PII-like proteins for further structure functional analysis.
