Structural and functional characterization of the ga-substituted ferredoxin from Synechocystis sp. PCC6803, a mimic of the native protein.

In photosynthetic organisms, ferredoxin (Fd) interacts with many proteins, acting as a shuttle for electrons from Photosystem I to a group of enzymes involved in NADP+ reduction, sulfur and nitrogen assimilation, and the regulation of carbon assimilation. The study of the dynamic interactions between ferredoxin and these enzymes by nuclear magnetic resonance is severely hindered by the paramagnetic [2Fe-2S] cluster of a ferredoxin. To establish whether ferredoxin in which the cluster has been replaced by Ga is a suitable diamagnetic mimic, the solution structure of Synechocystis Ga-substituted ferredoxin has been determined and compared with the structure of the native protein. The ensemble of 10 structures with the lowest energies has an average root-mean-square deviation of 0.30 ± 0.05 A for backbone atoms and 0.65 ± 0.04 A for all heavy atoms. Comparison of the NMR structure of GaFd with the crystal structure of the native Fd indicates that the general structural fold found for the native, iron-contain...