title: Structural basis for the allosteric control of the global transcription factor NtcA by the nitrogen starvation signal 2-oxoglutarate.
abstract: 2-oxogluatarate (2-OG), a metabolite of the highly conserved Krebs cycle, not only plays a critical role in metabolism, but also constitutes a signaling molecule in a variety of organisms ranging from bacteria to plants and animals. In cyanobacteria, the accumulation of 2-OG constitutes the signal of nitrogen starvation and NtcA, a global transcription factor, has been proposed as a putative receptor for 2-OG. Here we present three crystal structures of NtcA from the cyanobacterium Anabaena: the apoform, and two ligand-bound forms in complex with either 2-OG or its analogue 2,2-difluoropentanedioic acid. All structures assemble as homodimers, with each subunit composed of an N-terminal effector-binding domain and a C-terminal DNA-binding domain connected by a long helix (C-helix). The 2-OG binds to the effector-binding domain at a pocket similar to that used by cAMP in catabolite activator protein, but with a different pattern. Comparative structural analysis reveals a putative signal transmission route upon 2-OG binding. A tighter coiled-coil conformation of the two C-helices induced by 2-OG is crucial to maintain the proper distance between the two F-helices for DNA recognition. Whereas catabolite activator protein adopts a transition from off-to-on state upon cAMP binding, our structural analysis explains well why NtcA can bind to DNA even in its apoform, and how 2-OG just enhances the DNA-binding activity of NtcA. These findings provided the structural insights into the function of a global transcription factor regulated by 2-OG, a metabolite standing at a crossroad between carbon and nitrogen metabolisms.
authors.affiliation: Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China.
authors.forename: Meng-Xi
authors.initials: MX
authors.lastname: Zhao
authors.forename: Yong-Liang
authors.initials: YL
authors.lastname: Jiang
authors.forename: Yong-Xing
authors.initials: YX
authors.lastname: He
authors.forename: Yi-Fei
authors.initials: YF
authors.lastname: Chen
authors.forename: Yan-Bin
authors.initials: YB
authors.lastname: Teng
authors.forename: Yuxing
authors.initials: Y
authors.lastname: Chen
authors.forename: Cheng-Cai
authors.initials: CC
authors.lastname: Zhang
authors.forename: Cong-Zhao
authors.initials: CZ
authors.lastname: Zhou
mesh_terms: D017033:Anabaena / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D000818:Animals; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism; D002373:Cyclic AMP Receptor Protein / Q000235:genetics / Q000378:metabolism; D007656:Ketoglutaric Acids / Q000378:metabolism* / Q000494:pharmacology; D009584:Nitrogen / Q000378:metabolism*; D009603:Nitroso Compounds; D011485:Protein Binding / Q000235:genetics; D017433:Protein Structure, Secondary / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D053778:Thiazolidines; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D002373:Cyclic AMP Receptor Protein; D007656:Ketoglutaric Acids; D009603:Nitroso Compounds; D053778:Thiazolidines; D014157:Transcription Factors; C040387:N-nitrosothiazolidine-4-carboxylic acid; D009584:Nitrogen