Abstract
PII proteins are multitasking information-processing proteins occurring in bacteria, archaea, and plastids, decoding the metabolic state of the cells and providing this information to various regulatory targets. Research in recent years identified a wide range of novel PII targets mainly through ligand fishing assays, indicating that PII proteins evolved into major regulatory hubs of cellular metabolism. PII proteins orchestrate not only key steps of nitrogen and carbon metabolism but rather control a wide range of transporters and can also regulate the production of signaling molecules (c-di-GMP) and cofactors (NAD+). A recently identified class of PII-interacting proteins, which by themselves have no enzymatic activity, modulate cellular processes through protein interactions, further extending the regulatory range of PII proteins.
Highlights
PII proteins are multitasking information-processing proteins occurring in bacteria, archaea, and plastids, decoding the metabolic state of the cells and providing this information to various regulatory targets
A brief retrospect on PII research – from nitrogen signaling to global metabolic control The first PII signaling protein was identified in the late 1960s as a small regulatory protein that affected covalent modification of glutamine synthetase activity in Escherichia coli
This protein was regarded as a specialized signal transduction module in Proteobacteria that responds to the carbon/nitrogen balance by sensing cellular glutamine [2] and 2-oxoglutarate (2-OG) levels [3,4]
Summary
PII proteins are multitasking information-processing proteins occurring in bacteria, archaea, and plastids, decoding the metabolic state of the cells and providing this information to various regulatory targets. PII proteins orchestrate key steps of nitrogen and carbon metabolism but rather control a wide range of transporters and can regulate the production of signaling molecules (c-di-GMP) and cofactors (NAD+). By the middle of the first decade of the new millennium, PII proteins were recognized to control various reactions in anabolic nitrogen metabolism, from ammonia uptake and nitrogen fixation to arginine biosynthesis, as well as controlling nitrogen-dependent gene expression They were termed 'sensors of 2-OG that regulate nitrogen metabolism' [9]. A novel class of PII-interactors occurs in cyanobacteria and archaea: small proteins without enzymatic activity that modulate cellular processes through a network of protein interactions to extend further the regulatory range of PII proteins.
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