Abstract
Dark-operative protochlorophyllide oxidoreductase (DPOR) catalyzes the stereo-specific reduction of C17=C18 double bond of protochlorophyllide in the bacteriochlorophyll biosynthesis. 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. L-protein delivers electrons to the catalytic component NB-protein coupled with the ATP hydrolysis. In the NB-protein the electrons are transferred to protochlorophyllide via a [4Fe-4S] cluster to convert chlorophyllide a. In the previous work, we reported the crystal structure of NB-protein from Rhodobacter capsulatus. Based on the structure and biochemical analysis, we proposed a reaction scheme of the stereo-specific reduction in which Asp274 and the propionate side chain of the substrate donate the protons to C17 and C18, respectively. In this work, site-directed variants and a substrate analogue were used to trap some reaction intermediates. The sequence of proton and electron transfers in the reaction will be discussed.
