Rapid C8-vinyl reduction of divinyl-chlorophyllide a by BciA from Rhodobacter capsulatus

Divinyl-chlorophyllide a (DV-Chlide a) is a universal precursor for chlorophyll or bacteriochlorophyll biosynthesis in all photosynthetic organisms. Previous mutational analyses revealed that BciA works for reduction of the C8-vinyl group of DV-Chlide a. Chlorophyllide oxidoreductase (COR) reduces the C7=C8 double bond of Chlide a bearing the C8-ethyl group, but also potentially catalyzes the reduction of the C8-vinyl group of DV-Chlide a. In this study, we prepared a recombinant BciA protein from the purple photosynthetic bacterium Rhodobacter capsulatus and analyzed its C8-vinyl reduction activity towards DV-Chlide a. BciA formed a functional oligomeric complex consisting of at least three rigid dimers. BciA required NADPH as an electron donor for its C8-vinyl reduction activity. The enzymatic activity of BciA towards the substrate DV-Chlide a was much higher than that of COR towards Chlide a. Phylogenetic distribution and the enzymatic parameters of BciA and COR suggest that BciA is a more recently acquired auxiliary C8-vinyl reductase, attained to meet the high demand for bacteriochlorophylls used to produce large amounts of light-harvesting complexes. (C) 2017 Elsevier B.V. All rights reserved.