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Functional assembly of the foreign carotenoid lycopene into the photosynthetic apparatus of Rhodobacter sphaeroides , achieved by replacement of the native 3‐step phytoene desaturase with its 4‐step counterpart from Erwinia herbicola
Author(s) -
GarciaAsua Guillermo,
Cogdell Richard J.,
Hunter C. Neil
Publication year - 2002
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2002.02871.x
Subject(s) - rhodobacter sphaeroides , phytoene desaturase , phytoene , carotenoid , lycopene , bacteriochlorophyll , biology , rhodospirillaceae , biochemistry , photosynthesis , photochemistry , enzyme , chemistry , biosynthesis
Summary Photosynthetic organisms synthesize a diverse range of carotenoids. These pigments are important for the assembly, function and stability of photosynthetic pigment–protein complexes, and they are used to quench harmful radicals. The photosynthetic bacterium Rhodobacter sphaeroides was used as a model system to explore the origin of carotenoid diversity. Replacing the native 3‐step phytoene desaturase (CrtI) with the 4‐step enzyme from Erwinia herbicola results in significant flux down the spirilloxanthin pathway for the first time in Rb. sphaeroides . In Rb. sphaeroides , the completion of four desaturations to lycopene by the Erwinia CrtI appears to require the absence of CrtC and, in a crtC background, even the native 3‐step enzyme can synthesize a significant amount (13%) of lycopene, in addition to the expected neurosporene. We suggest that the CrtC hydroxylase can intervene in the sequence of reactions catalyzed by phytoene desaturase. We investigated the properties of the lycopene‐synthesizing strain of Rb. sphaeroides . In the LH2 light‐harvesting complex, lycopene transfers absorbed light energy to the bacteriochlorophylls with an efficiency of 54%, which compares favourably with other LH2 complexes that contain carotenoids with 11 conjugated double bonds. Thus, lycopene can join the assembly pathway for photosynthetic complexes in Rb. sphaeroides , and can perform its role as an energy donor to bacteriochlorophylls.