Isolation and Characterization of Carotenosomes from a Bacteriochlorophyll c-less Mutant of Chlorobium tepidum
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Chlorosomes are the light-harvesting organelles in photosynthetic green bacteria and typically contain large amounts of bacteriochlorophyll (BChl) c in addition to smaller amounts of BChl a, carotenoids, and several protein species. We have isolated vestigial chlorosomes, denoted carotenosomes, from a BChl c-less, bchK mutant of the green sulfur bacterium Chlorobium tepidum. The physical shape of the carotenosomes (86 +/- 17 nm x 66 +/- 13 nm x 4.3 +/- 0.8 nm on average) was reminiscent of a flattened chlorosome. The carotenosomes contained carotenoids, BChl a, and the proteins CsmA and CsmD in ratios to each other comparable to their ratios in wild-type chlorosomes, but all other chlorosome proteins normally found in wild-type chlorosomes were found only in trace amounts or were not detected. Similar to wild-type chlorosomes, the CsmA protein in the carotenosomes formed oligomers at least up to homo-octamers as shown by chemical cross-linking and immunoblotting. The absorption spectrum of BChl a in the carotenosomes was also indistinguishable from that in wild-type chlorosomes. Energy transfer from the bulk carotenoids to BChl a in carotenosomes was poor. The results indicate that the carotenosomes have an intact baseplate made of remarkably stable oligomeric CsmA-BChl a complexes but are flattened in structure due to the absence of BChl c. Carotenosomes thus provide a valuable material for studying the biogenesis, structure, and function of the photosynthetic antennae in green bacteria.
Original language | English |
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Journal | Photosynthesis Research |
Volume | 86 |
Issue number | 1-2 |
Pages (from-to) | 101-11 |
Number of pages | 10 |
ISSN | 0166-8595 |
DOIs | |
Publication status | Published - 2005 |
Bibliographical note
Keywords: Bacterial Proteins; Bacteriochlorophylls; Carotenoids; Cell Fractionation; Chlorobium; Microscopy, Atomic Force; Microscopy, Electron; Mutation; Organelles; Protein Binding; Spectrum Analysis
ID: 14095005