Glutamine synthetase (GS) catalyzes the ATP-dependent formation of glutamine from glutamate and ammonia. The activity of Synechocystis sp. PCC 6803 GS is regulated, among other mechanisms, by protein-protein interactions with a 65-residue-long, intrinsically disordered protein (IDP), named IF7. IDPs explore diverse conformations in their free states and, in some cases, in their molecular complexes. We used both nuclear magnetic resonance (NMR) at 11.7 T and small angle X-ray scattering (SAXS) to study the size and the dynamics in the picoseconds-to-nanosecond (ps-ns) timescale of: (i) isolated IF7; and (ii) the IF7/GS complex. Our SAXS findings, together with MD results, show: (i) some of the possible IF7 structures in solution; and, (ii) that the presence of IF7 affected the structure of GS in solution. The joint use of SAXS and NMR shows that movements of each amino acid of IF7 were uncorrelated with those of its neighbors. Residues of IF7 with the largest values of the relaxation rates (R1, R2 and ηxy), in the free and bound species, were mainly clustered around: (i) the C terminus of the protein; and (ii) Ala30. These residues, together with Arg8 (which is a hot-spot residue in the interaction with GS), had a restricted mobility in the presence of GS. The C-terminal region, which appeared more compact in our MD simulations of isolated IF7, seemed to be involved in non-native contacts with GS that help in the binding between the two macromolecules.

中文翻译：

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谷氨酰胺合成酶内源性无序抑制剂IF7的动力学及其与其伴侣的相互作用。

谷氨酰胺合成酶（GS）催化由谷氨酸和氨形成的ATP依赖性谷氨酰胺。集胞藻的活动。PCC 6803 GS除其他机理外，还受到与65个残基长的固有无序蛋白（IDP）（称为IF7）的蛋白相互作用的调节。国内流离失所者在其自由状态下以及在某些情况下在其分子复合物中探索各种构象。我们使用11.7 T的核磁共振（NMR）和小角X射线散射（SAXS）来研究皮秒到纳秒（ps-ns）时标的大小和动力学：（i）孤立的IF7；（ii）IF7 / GS综合体。我们的SAXS调查结果以及MD结果表明：（i）溶液中可能存在的IF7结构；（ii）IF7的存在影响溶液中GS的结构。SAXS和NMR的联合使用表明IF7的每个氨基酸的运动与其邻居的运动无关。在游离和结合物种中，具有最大弛豫率值（R1，R2和ηxy）的IF7残基主要集中在：（i）蛋白质的C末端；（ii）Ala30。这些残基与Arg8（在与GS相互作用中是热点残基）一起在GS存在下具有受限的迁移率。C末端区域在我们对分离的IF7的MD模拟中显得更为紧凑，似乎参与了与GS的非天然接触，这有助于两个大分子之间的结合。主要集中在：（i）蛋白的C末端；（ii）Ala30。这些残基与Arg8（在与GS相互作用中是热点残基）一起在GS存在下具有受限的迁移率。C末端区域在我们对分离的IF7的MD模拟中显得更为紧凑，似乎参与了与GS的非天然接触，这有助于两个大分子之间的结合。主要集中在：（i）蛋白的C末端；（ii）Ala30。这些残基与Arg8（在与GS相互作用中是热点残基）一起在GS存在下具有受限的迁移率。C末端区域在我们对分离的IF7的MD模拟中显得更为紧凑，似乎参与了与GS的非天然接触，这有助于两个大分子之间的结合。