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 capsulatus has been purified in recombinant form from Escherichia coli. This protein, called FdVI, resembles ferredoxins involved in iron-sulfur cluster biosynthesis in various prokaryotic and eukaryotic cells. Purified recombinant FdVI was recovered in high yields and appeared to be indistinguishable from the genuine R. capsulatus ferredoxin based on UV-visible absorption and EPR spectroscopy and mass spectrometry. FdVI has been crystallized in the oxidized state by a sitting-drop vapour-diffusion technique using sodium formate as precipitant. Seeding larger drops from a previous hanging-drop-grown small crystal resulted in the formation of long red-brown prismatic needles. Preliminary X-ray diffraction analysis indicated that FdVI crystals are orthorhombic and belong to the space group P2₁2₁2₁, with unit-cell parameters a = 45.87, b = 49.83, c = 54.29 Å.