title: Engineered biosynthesis of bacteriochlorophyll b in Rhodobacter sphaeroides.
abstract: Bacteriochlorophyll b has the most red-shifted absorbance maximum of all naturally occurring photopigments. It has a characteristic ethylidene group at the C8 position in place of the more common ethyl group, the product of a C8-vinyl reductase, which is carried by the majority of chlorophylls and bacteriochlorophylls used in photosynthesis. The subsequent and first step exclusive to bacteriochlorophyll biosynthesis, the reduction of the C7=C8 bond, is catalyzed by chlorophyllide oxidoreductase. It has been demonstrated that the enzyme from bacteriochlorophyll a-utilizing bacteria can catalyze the formation of compounds carrying an ethyl group at C8 from both ethyl- and vinyl-carrying substrates, indicating a surprising additional C8-vinyl reductase function, while the enzyme from organisms producing BChl b could only catalyze C7=C8 reduction with a vinyl substrate, but this product carried an ethylidene group at the C8 position. We have replaced the native chlorophyllide oxidoreductase-encoding genes of Rhodobacter sphaeroides with those from Blastochloris viridis, but the switch from bacteriochlorophyll a to b biosynthesis is only detected when the native conventional C8-vinyl reductase is absent. We propose a non-enzymatic mechanism for ethylidene group formation based on the absence of cellular C8-vinyl reductase activity.
authors: Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK. Electronic address: d.canniffe@sheffield.ac.uk.
authors: Daniel P
authors: DP
authors: Canniffe
authors: Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK.
authors: C Neil
authors: CN
authors: Hunter
mesh_terms: D001429:Bacteriochlorophylls / Q000096:biosynthesis*; D001483:Base Sequence; D055162:Biocatalysis; D002851:Chromatography, High Pressure Liquid; D017931:DNA Primers; D005798:Genes, Bacterial; D010860:Pigments, Biological / Q000302:isolation & purification; D016133:Polymerase Chain Reaction; D012242:Rhodobacter sphaeroides / Q000235:genetics / Q000378:metabolism*
chemical_list: D001429:Bacteriochlorophylls; D017931:DNA Primers; D010860:Pigments, Biological; C107900:bacteriochlorophyll b
keywords: Bacteriochlorophyll; Chlorophyll; Chlorophyllide oxidoreductase; Pathway engineering; Photosynthesis