Spatial segregation of photosystems in the thylakoid membrane (lateral heterogeneity) observed in plants and in the green algae is usually considered to be absent in photoautotrophs possessing secondary plastids, such as diatoms. Contrary to this assumption, here we show that thylakoid membranes in the chloroplast of a marine diatom, Phaeodactylum tricornutum, contain large areas occupied exclusively by a supercomplex of photosystem I (PSI) and its associated Lhcr antenna. These membrane areas, hundreds of nanometers in size, comprise hundreds of tightly packed PSI-antenna complexes while lacking other components of the photosynthetic electron transport chain. Analyses of the spatial distribution of the PSI-Lhcr complexes have indicated elliptical particles, each 14 × 17 nm in diameter. On larger scales, the red-enhanced illumination exerts a significant effect on the ultrastructure of chloroplasts, creating superstacks of tens of thylakoid membranes.

• MeSH
• chloroplasty metabolismus   účinky záření   ultrastruktura   MeSH
• fotosystém I - proteinový komplex metabolismus   MeSH
• fotosystém II - proteinový komplex metabolismus   MeSH
• multiproteinové komplexy metabolismus   ultrastruktura   MeSH
• rozsivky metabolismus   účinky záření   ultrastruktura   MeSH
• světlo MeSH
• světlosběrné proteinové komplexy metabolismus   MeSH
• transmisní elektronová mikroskopie MeSH
• tylakoidy metabolismus   účinky záření   ultrastruktura   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fotosystém I - proteinový komplex MeSH
• fotosystém II - proteinový komplex MeSH
• multiproteinové komplexy MeSH
• světlosběrné proteinové komplexy MeSH

The arrangement of core antenna complexes (B808-866-RC) in the cytoplasmic membrane of filamentous phototrophic bacterium Chloroflexus aurantiacus was studied by electron microscopy in cultures from different light conditions. A typical nearest-neighbor center-to-center distance of ~18 nm was found, implying less protein crowding compared to membranes of purple bacteria. A mean RC:chlorosome ratio of 11 was estimated for the occupancy of the membrane directly underneath each chlorosome, based on analysis of chlorosome dimensions and core complex distribution. Also presented are results of single-particle analysis of core complexes embedded in the native membrane.

• MeSH
• buněčná membrána metabolismus   ultrastruktura   MeSH
• Chloroflexus metabolismus   MeSH
• elektronová mikroskopie MeSH
• fotosyntetické reakční centrum - proteinové komplexy metabolismus   ultrastruktura   MeSH
• fotosyntéza MeSH
• organely metabolismus   ultrastruktura   MeSH
• Rhodopseudomonas metabolismus   MeSH
• světlo MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fotosyntetické reakční centrum - proteinové komplexy MeSH

Chlorosomes are large light-harvesting complexes found in three phyla of anoxygenic photosynthetic bacteria. Chlorosomes are primarily composed of self-assembling pigment aggregates. In addition to the main pigment, bacteriochlorophyll c, d, or e, chlorosomes also contain variable amounts of carotenoids. Here, we use X-ray scattering and electron cryomicroscopy, complemented with absorption spectroscopy and pigment analysis, to compare the morphologies, structures, and pigment compositions of chlorosomes from Chloroflexus aurantiacus grown under two different light conditions and Chlorobaculum tepidum. High-purity chlorosomes from C. aurantiacus contain about 20% more carotenoid per bacteriochlorophyll c molecule when grown under low light than when grown under high light. This accentuates the light-harvesting function of carotenoids, in addition to their photoprotective role. The low-light chlorosomes are thicker due to the overall greater content of pigments and contain domains of lamellar aggregates. Experiments where carotenoids were selectively extracted from intact chlorosomes using hexane proved that they are located in the interlamellar space, as observed previously for species belonging to the phylum Chlorobi. A fraction of the carotenoids are localized in the baseplate, where they are bound differently and cannot be removed by hexane. In C. tepidum, carotenoids cannot be extracted by hexane even from the chlorosome interior. The chemical structure of the pigments in C. tepidum may lead to π-π interactions between carotenoids and bacteriochlorophylls, preventing carotenoid extraction. The results provide information about the nature of interactions between bacteriochlorophylls and carotenoids in the protein-free environment of the chlorosome interior.

• MeSH
• bakteriální chromatofory MeSH
• biologické pigmenty MeSH
• Chloroflexus cytologie   metabolismus   MeSH
• difrakce rentgenového záření MeSH
• fykobiliproteiny chemie   fyziologie   MeSH
• karotenoidy chemie   metabolismus   MeSH
• molekulární struktura MeSH
• organely fyziologie   MeSH
• světlo * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• biologické pigmenty MeSH
• fykobiliproteiny MeSH
• karotenoidy MeSH

Chlorosomes, the light-harvesting antennae of green photosynthetic bacteria, are based on large aggregates of bacteriochlorophyll molecules. Aggregates with similar properties to those in chlorosomes can also be prepared in vitro. Several agents were shown to induce aggregation of bacteriochlorophyll c in aqueous environments, including certain lipids, carotenes, and quinones. A key distinguishing feature of bacteriochlorophyll c aggregates, both in vitro and in chlorosomes, is a large (>60 nm) red shift of their Q(y) absorption band compared with that of the monomers. In this study, we investigate the self-assembly of bacteriochlorophyll c with the xanthophyll astaxanthin, which leads to the formation of a new type of complexes. Our results indicate that, due to its specific structure, astaxanthin molecules competes with bacteriochlorophylls for the bonds involved in the aggregation, thus preventing the formation of any significant red shift compared with pure bacteriochlorophyll c in aqueous buffer. A strong interaction between both the types of pigments in the developed assemblies, is manifested by a rather efficient (~40%) excitation energy transfer from astaxanthin to bacteriochlorophyll c, as revealed by fluorescence excitation spectroscopy. Results of transient absorption spectroscopy show that the energy transfer is very fast (<500 fs) and proceeds through the S(2) state of astaxanthin.

• MeSH
• bakteriální proteiny chemie   izolace a purifikace   metabolismus   MeSH
• bakteriochlorofyly chemie   izolace a purifikace   metabolismus   MeSH
• Chlorobium chemie   MeSH
• fotosyntéza MeSH
• přenos energie * MeSH
• spektrální analýza MeSH
• světlo MeSH
• světlosběrné proteinové komplexy chemie   metabolismus   MeSH
• xanthofyly chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• astaxanthine MeSH Prohlížeč
• bacteriochlorophyll c MeSH Prohlížeč
• bakteriální proteiny MeSH
• bakteriochlorofyly MeSH
• světlosběrné proteinové komplexy MeSH
• xanthofyly MeSH

Chlorosomes from green photosynthetic bacteria are large photosynthetic antennae containing self-assembling aggregates of bacteriochlorophyll c, d, or e. The pigments within chlorosomes are organized in curved lamellar structures. Aggregates with similar optical properties can be prepared in vitro, both in polar as well as non-polar solvents. In order to gain insight into their structure we examined hexane-induced aggregates of purified bacteriochlorophyll c by X-ray scattering. The bacteriochlorophyll c aggregates exhibit scattering features that are virtually identical to those of native chlorosomes demonstrating that the self-assembly of these pigments is fully encoded in their chemical structure. Thus, the hexane-induced aggregates constitute an excellent model to study the effects of chemical structure on assembly. Using bacteriochlorophyllides transesterified with different alcohols we have established a linear relationship between the esterifying alcohol length and the lamellar spacing. The results provide a structural basis for lamellar spacing variability observed for native chlorosomes from different species. A plausible physiological role of this variability is discussed. The X-ray scattering also confirmed the assignments of peaks, which arise from the crystalline baseplate in the native chlorosomes.

• MeSH
• alkoholy chemie   MeSH
• anizotropie MeSH
• bakteriochlorofyly chemie   metabolismus   MeSH
• buněčné struktury metabolismus   MeSH
• Chlorobium metabolismus   MeSH
• esterifikace MeSH
• hexany chemie   MeSH
• kvarterní struktura proteinů MeSH
• radiační rozptyl MeSH
• rentgenové záření MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• alkoholy MeSH
• bakteriochlorofyly MeSH
• hexany MeSH