Crystallization and preliminary X-ray studies of ferredoxin-NAD(P) ⁺ reductase from Chlorobium tepidum

Ferredoxin-NAD(P)⁺ reductase (FNR) is a key enzyme that catalyzes the photoreduction of NAD(P)⁺ to generate NAD(P)H during the final step of the photosynthetic electron-transport chain. FNR from the green sulfur bacterium Chlorobium tepidum is a homodimeric enzyme with a molecular weight of 90 kDa; it shares a high level of amino-acid sequence identity to thioredoxin reductase rather than to conventional plant-type FNRs. In order to understand the structural basis of the ferredoxin-dependency of this unique photosynthetic FNR, C. tepidum FNR has been heterologously expressed, purified and crystallized in two forms. Form I crystals belong to space group C222₁ and contain one dimer in the asymmetric unit, while form II crystals belong to space group P4₁22 or P4₃22. Diffraction data were collected from a form I crystal to 2.4 Å resolution on the synchrotron-radiation beamline NW12 at the Photon Factory.