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Hexanol-Induced Order-Disorder Transitions in Lamellar Self-Assembling Aggregates of Bacteriochlorophyll c in Chlorobium tepidum Chlorosomes

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dc.creator Arellano, Juan B.
dc.creator Torkkeli, Mika
dc.creator Tuma, Roman
dc.creator Laurinmäki, Pasi A.
dc.creator Melo, Thor Bernt
dc.creator Ikonen, Teemu P.
dc.creator Butcher, Sarah J.
dc.creator Serimaa, Ritva E.
dc.creator Psencik, Jakub
dc.date 2008-03-05T08:23:33Z
dc.date 2008-03-05T08:23:33Z
dc.date 2008-03
dc.date.accessioned 2017-01-31T01:00:34Z
dc.date.available 2017-01-31T01:00:34Z
dc.identifier Langmuir 24(5): 2035–2041 (2008)
dc.identifier 0743-7463
dc.identifier http://hdl.handle.net/10261/3151
dc.identifier 10.1021/la703024e
dc.identifier.uri http://dspace.mediu.edu.my:8181/xmlui/handle/10261/3151
dc.description Chlorosomes are light-harvesting complexes of green photosynthetic bacteria. Chlorosomes contain bacteriochlorophyll (BChl) c, d, or e aggregates that exhibit strong excitonic coupling. The short-range order, which is responsible for the coupling, has been proposed to be augmented by pigment arrangement into undulated lamellar structures with spacing between 2 and 3 nm. Treatment of chlorosomes with hexanol reversibly converts the aggregated chlorosome chlorophylls into a form with spectral properties very similar to that of the monomer. Although this transition has been extensively studied, the structural basis remains unclear due to variability in the obtained morphologies. Here we investigated hexanol-induced structural changes in the lamellar organization of BChl c in chlorosomes from Chlorobium tepidum by a combination of X-ray scattering, electron cryomicroscopy, and optical spectroscopy. At a low hexanol/pigment ratio, the lamellae persisted in the presence of hexanol while the short-range order and exciton interactions between chlorin rings were effectively eliminated, producing a monomer-like absorption. The result suggested that hexanol hydroxyls solvated the chlorin rings while the aliphatic tail partitioned into the hydrophobic part of the lamellar structure. This partitioning extended the chlorosome along its long axis. Further increase of the hexanol/pigment ratio produced round pigment-hexanol droplets, which lost all lamellar order. After hexanol removal the spectral properties were restored. In the samples treated under the high hexanol/pigment ratio, lamellae reassembled in small domains after hexanol removal while the shape and long-range order were irreversibly lost. Thus, all the interactions required for establishing the short-range order by self-assembly are provided by BChl c molecules alone. However, the long-range order and overall shape are imposed by an external structure, e.g., the proteinaceous chlorosome baseplate.
dc.description This study was supported by the Spanish Ministry of Science and Education (Grant No. BFU2004-04914-C02-02 to J.B.A.), the Academy of Finland (Research Fellowship No. 1118462 to R.T.), the Czech Ministry of Education, Youth and Sports and Czech Science Foundation (Projects Nos. MSM0021620835 and 206/05/2739 to J.P.). Electron microscopy was carried out in the Electron Microscopy Unit of the Institute of Biotechnology, University of Helsinki.
dc.description Peer reviewed
dc.format 18673 bytes
dc.format image/gif
dc.language eng
dc.publisher American Chemical Society
dc.relation http://pubs.acs.org/doi/abs/10.1021/la703024e
dc.rights openAccess
dc.subject Chlorosomes
dc.subject Lamellar aggregates
dc.subject Hexanol
dc.subject Bacteriochlorophyll
dc.subject Chlorobium tepidum
dc.subject Order-disorder transitions
dc.title Hexanol-Induced Order-Disorder Transitions in Lamellar Self-Assembling Aggregates of Bacteriochlorophyll c in Chlorobium tepidum Chlorosomes
dc.type Artículo


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