Crystallographic studies of the interaction between the ferredoxin-NADP⁺ reductase and ferredoxin from the cyanobacterium Anabaena: looking for the elusive ferredoxin molecule

Ferredoxin-NADP⁺ reductase (FNR) and its physiological electron donor ferredoxin (Fd) from the cyanobacterium Anabaena PCC7119 have been co-crystallized. The unit-cell parameters are a = b = 63.72, c = 158.02 Å and the space group is P2₁2₁2₁. The crystal structure has been solved with 2.4 Å resolution synchrotron data by molecular replacement, anomalous dispersion and R_min search methods. For the computations, the crystal was treated as a merohedral twin. The asymmetric unit contains two FNR molecules and one ferredoxin molecule. The packing of the FNR molecules displays a nearly tetragonal symmetry (space group P4₃2₁2), whereas the ferredoxin arrangement is orthorhombic. This study provides the first crystallographic model of a dissociable complex between FNR and Fd.