Crystallization and preliminary X-ray diffraction analysis of a [2Fe-2S] ferredoxin (FdVI) from Rhodobacter capsulatus

A [2Fe-2S] ferredoxin found in the photosynthetic bacterium Rhodobacter cap sulatus has been purified in recombinant form from Escherichia coli. This p rotein, called FdVI, resembles ferredoxins involved in iron-sulfur cluster biosynthesis in various prokaryotic and eukaryotic cells. Purified recombin ant FdVI was recovered in high yields and appeared to be indistinguishable from the genuine R. capsulatus ferredoxin based on UV-visible absorption an d EPR spectroscopy and mass spectrometry. FdVI has been crystallized in the oxidized state by a sitting-drop vapour-diffusion technique using sodium f ormate as precipitant. Seeding larger drops from a previous hanging-drop-gr own small crystal resulted in the formation of long red-brown prismatic nee dles. Preliminary X-ray diffraction analysis indicated that FdVI crystals a re orthorhombic and belong to the space group P2(1)2(1)2(1), with unit-cell parameters a = 45.87, b = 49.83, c = 54.29 Angstrom.