The isolated, twenty-three-residue-long, N-terminal region of the glutamine synthetase inactivating factor binds to its target

- The region Ala7-Ala29 (IF7pep) of the inactivating factor (IF7) of GS binds to GS.
- The binding of IF7pep to GS occurs with the same affinity as that of intact IF7.
- Isolated IF7pep has an intrinsic tendency to populate α-helix-like conformations.
- Isolated IF7pep does not inactivate GS.
- The binding reaction is electrostatically-driven involving several species.

Glutamine synthetase (GS) catalyzes the ATP-dependent formation of glutamine from glutamate and ammonia. The activity of Synechocystis sp. PCC 6803 GS type I is regulated by protein-protein interactions with a 65-residue-long protein (IF7). IF7 binds initially to GS through residues at its N terminus. In this work, we studied the conformational preferences of the N-terminal region of IF7 (IF7pep, residues Ala7-Ala29), its binding to GS and its functional properties. Isolated IF7pep populated a nascent helix in aqueous solution. IF7pep was bound to GS with an affinity constant of 0.4 μM, and a 1:1 stoichiometry. IF7pep did not inactivate GS, suggesting that there were other IF7 regions important to carry out the inactivating function. Binding of IF7pep to GS was electrostatically-driven and it did not follow a kinetic two-state model.

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