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[摘要]：P-II proteins control key processes of nitrogen metabolism in bacteria, archaea, and plants in response to the central metabolites ATP, ADP, and 2-oxoglutarate (2-OG), signaling cellular energy and carbon and nitrogen abundance. This metabolic information is integrated by P-II and transmitted to regulatory targets (key enzymes, transporters, and transcription factors), modulating their activity. In oxygenic phototrophs, the controlling enzyme of arginine synthesis, N-acetyl-glutamate kinase (NAGK), is a major P-II target, whose activity responds to 2-OG via P-II. Here we show structures of the Synechococcus elongatus P-II protein in complex with ATP, Mg2+, and 2-OG, which clarify how 2-OG affects P-II-NAGK interaction. P-II trimers with all three sites fully occupied were obtained as well as structures with one or two 2-OG molecules per P-II trimer. These structures identify the site of 2-OG located in the vicinity between the subunit clefts and the base of the T loop. The 2-OG is bound to a Mg2+ ion, which is coordinated by three phosphates of ATP, and by ionic interactions with the highly conserved residues K58 and Q39 together with B-and T-loop backbone interactions. These interactions impose a unique T-loop conformation that affects the interactions with the P-II target. Structures of P-II trimers with one or two bound 2-OG molecules reveal the basis for anticooperative 2-OG binding and shed light on the intersubunit signaling mechanism by which P-II senses effectors in a wide range of concentrations. |
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