Crystal structure determination at 1.4 angstrom resolution of ferredoxin from the green alga Chlorella fusca

Background: [2Fe-2S] ferredoxins, also call ed plant-type ferredoxins, are low-potential redox proteins that are widely distributed in biological syst ems. In photosynthesis, the plant-type ferredoxins function as the central molecule for distributing electrons from the photolysis of water to a numbe r of ferredoxin-dependent enzymes, as well as to cyclic photophosphorylatio n electron transfer. This paper reports only the second structure of a [2Fe -2S] ferredoxin from a eukaryotic organism in its native form. Results: Ferredoxin from the green algae Chlorella fusca has been purified, characterised, crystallised and its structure determined to 1.4 Angstrom r esolution - the highest resolution structure published to date for a plant- type ferredoxin. The structure has the general features of the plant-type f erredoxins already described, with conformational differences corresponding to regions of higher mobility. Immunological data indicate that a serine r esidue within the protein is partially phosphorylated. A slightly electropo sitive shift in the measured redox potential value, -325 mV, is observed in comparison with other ferredoxins. Conclusions: This high-resolution structure provides a detailed picture of the hydrogen-bonding pattern around the [2Fe-2S] cluster of a plant-type fe rredoxin; for the first time, it was possible to obtain reliable error esti mates for the geometrical parameters. The presence of phosphoserine in the protein indicates a possible mechanism for the regulation of the distributi on of reducing power from the photosynthetic electron-transfer chain.