Canniffe DP, Hunter CN. Engineered biosynthesis of bacteriochlorophyll b in Rhodobacter sphaeroides.
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014;
1837:1611-6. [PMID:
25058304 PMCID:
PMC4331041 DOI:
10.1016/j.bbabio.2014.07.011]
[Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Subscribe] [Scholar Register] [Received: 05/27/2014] [Revised: 07/11/2014] [Accepted: 07/15/2014] [Indexed: 12/03/2022]
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.
We engineer the production of a foreign photopigment in Rhodobacter sphaeroides.
Native COR-encoding genes are replaced with those from Blastochloris viridis.
Bacteriochlorophyll b is produced upon additional deletion of conventional 8VR.
We propose that loss of 8VR activity by COR leads to ethylidene bond formation.
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