Abstract
Dark-operative protochlorophyllide(Pchlide) oxidoreductase (DPOR) catalyzes the stereo-specific reduction of D-ring double-bond of protochlorophyllide to form chlorophyllide a. DPOR consists of two separable components, L-protein (BchL homodimer) and NB-protein (BchN-BchB heterotetramer), which are homologous to Fe protein and MoFe protein of nitrogenase, respectively. In our previous work, we have solved the crystal structure of NB-protein from Rhodobacter capsulatus and proposed a catalytic mechanism of Pchlide reduction. However, 110 amino acids residues in C-terminal region of BchB were disordered. This region is conserved in BchB(ChlB) but not in NifK of nitroganase MoFe-protein, suggesting that the region has unique role(s) in DPOR reaction. To elucidate the functional significance of the C-terminal region, we have constructed a series of BchB mutants in which the C-terminal region was deleted partially or completely. SDS-PAGE profiles of the purified truncated BchB showed doublets with BchN, indicating that the C-terminal region is not essential for BchN-BchB complex formation. Characterization of the mutant NB-proteins is in progress.
