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

Ferredoxin-NADP(+) reductase (FNR) and its physiological electron donor fer redoxin (Fd) from the cyanobacterium Anabaena PCC7119 have been co-crystall ized. The unit-cell parameters are a = b = 63.72, c = 158.02 Angstrom and t he space group is P2(1)2(1)2(1). The crystal structure has been solved with 2.4 Angstrom resolution synchrotron data by molecular replacement, anomalo us dispersion and R-min search methods. For the computations, the crystal w as treated as a merohedral twin. The asymmetric unit contains two FNR molec ules and one ferredoxin molecule. The packing of the FNR molecules displays a nearly tetragonal symmetry (space group P4(3)2(1)2), whereas the ferredo xin arrangement is orthorhombic. This study provides the first crystallogra phic model of a dissociable complex between FNR and Fd.