Journal
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volume 1847, Issue 2, Pages 189-201Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.bbabio.2014.10.004
Keywords
Bacterial photosynthesis; Light harvesting; Carotenoid; Membrane protein; Antenna; Synthetic biology
Categories
Funding
- Biotechnology and Biological Sciences Research Council (U.K.) [BB/G021546/1]
- European Research Council [338895]
- Government of the People's Republic of China
- Biotechnology and Biological Sciences Research Council (U.K.)
- Engineering and Physical Sciences Research Council
- Photosynthetic Antenna Research Center (PARC)
- Energy Frontier Research Center - US Department of Energy, Office of Science, and Office of Basic Energy Sciences [DE-SC0001035]
- PARCNIGMS [8P41 GM103422-35]
- DOE
- [EP/I012060/1]
- Biotechnology and Biological Sciences Research Council [BB/G021546/1] Funding Source: researchfish
- Engineering and Physical Sciences Research Council [EP/I012060/1] Funding Source: researchfish
- BBSRC [BB/G021546/1] Funding Source: UKRI
- EPSRC [EP/I012060/1] Funding Source: UKRI
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Carotenoids protect the photosynthetic apparatus against harmful radicals arising from the presence of both light and oxygen. They also act as accessory pigments for harvesting solar energy, and are required for stable assembly of many light-harvesting complexes. In the phototrophic bacterium Rhodobacter (Rba.) sphaeroides phytoene desaturase (CrtI) catalyses three sequential desaturations of the colourless carotenoid phytoene, extending the number of conjugated carbon-carbon double bonds, N, from three to nine and producing the yellow carotenoid neurosporene; subsequent modifications produce the yellow/red carotenoids spheroidene/spheroidenone (N = 10/11). Genomic crtl replacements were used to swap the native three-step Rba. sphaeroides CrtI for the four-step Pantoea agglomerans enzyme, which re-routed carotenoid biosynthesis and culminated in the production of 2,2'-diketo-spirilloxanthin under semi-aerobic conditions. The new carotenoid pathway was elucidated using a combination of HPLC and mass spectrometry. Premature termination of this new pathway by inactivating crtC or crtD produced strains with lycopene or rhodopin as major carotenoids. All of the spirilloxanthin series carotenoids are accepted by the assembly pathways for LH2 and RC-LH1-PufX complexes. The efficiency of carotenoid-to-bacteriochlorophyll energy transfer for 2,2'-diketo-spirilloxanthin (15 conjugated C=C bonds; N = 15) in LH2 complexes is low, at 35%. High energy transfer efficiencies were obtained for neurosporene (N = 9;94%), spheroidene (N = 10; 96%) and spheroidenone (N = 11; 95%), whereas intermediate values were measured for lycopene (N = 11; 64%), rhodopin (N = 11; 62%) and spirilloxanthin (N = 13; 39%). The variety and stability of these novel Rba. sphaeroides antenna complexes make them useful experimental models for investigating the energy transfer dynamics of carotenoids in bacterial photosynthesis. (C) 2014 The Authors. Published by Elsevier B.V.
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