title: The inactivating factor of glutamine synthetase IF17 is an intrinsically disordered protein, which folds upon binding to its target.
abstract: In cyanobacteria, ammonium is incorporated into carbon skeletons by the sequential action of glutamine synthetase and glutamate synthase (GOGAT). The activity of Synechocystis sp. PCC 6803 glutamine synthetase type I (GS) is controlled by a post-transcriptional process involving protein-protein interactions with two inactivating factors: the 65-residue-long protein (IF7) and the 149-residue-long one (IF17). The sequence of the C terminus of IF17 is similar to IF7; IF7 is an intrinsically disordered protein (IDP). In this work, we study the structural propensities and affinity for GS of IF17 and a chimera protein, IF17N/IF7 (constructed by fusing the first 82 residues of IF17 with the whole IF7) by fluorescence, CD, and NMR. IF17 and IF17N/IF7 are IDPs with residual non-hydrogen-bonded structure, probably formed by α-helical, turn-like, and PPII conformations; several theoretical predictions support these experimental findings. IF17 seems to fold upon binding to GS, as suggested by CD thermal denaturations and steady-state far-UV spectra. The apparent affinity of IF17 for GS, as measured by fluorescence, is slightly smaller (K(D) ~1 μM) than that measured for IF7 (~0.3 μM). The K(D)s determined by CD are similar to those measured by fluorescence, but slightly larger, suggesting possible conformational rearrangements in the IFs and/or GS upon binding. Further, the results with IFN17/IF7 suggest that (i) binding of IF17 to the GS is modulated not only by its C-terminal region but also by its N-terminus and (ii) there are weakly structured (that is, "fuzzy") complexes in the ternary GS-IF system.
authors: Instituto de Bioquı́mica Vegetal y Fotosı́ntesis, CSIC- Universidad de Sevilla, Seville, Spain.
authors: Lorena
authors: L
authors: Saelices
authors: Carla V
authors: CV
authors: Galmozzi
authors: Francisco J
authors: FJ
authors: Florencio
authors: M Isabel
authors: MI
authors: Muro-Pastor
authors: José L
authors: JL
authors: Neira
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002942:Circular Dichroism; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics; D007700:Kinetics; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D011489:Protein Denaturation; D054730:Protein Interaction Domains and Motifs; D011499:Protein Processing, Post-Translational; D055550:Protein Stability; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; C120035:IF17 protein, Synechocystis sp.; C120034:IF7 protein, Synechocystis sp.; D011994:Recombinant Proteins; D005974:Glutamate-Ammonia Ligase