Project description:Chlorophototrophic organisms have a charge-separating reaction centre (RC) complex that receives energy from a dedicated light-harvesting (LH) antenna. In the purple phototrophic bacteria, these two functions are embodied by the 'core' photosynthetic component, the RC-LH1 complex. RC-LH1 complexes sit within a membrane bilayer, with the central RC wholly or partly surrounded by a curved array of LH1 subunits that bind a series of bacteriochlorophyll (BChl) and carotenoid pigments. Decades of research have shown that the absorption of light initiates a cascade of energy, electron, and proton transfers that culminate in the formation of a quinol, which is subsequently oxidized by the cytochrome bc1 complex. However, a full understanding of all these processes, from femtosecond absorption of light to millisecond quinone diffusion, requires a level of molecular detail that was lacking until the remarkable recent upsurge in the availability of RC-LH1 structures. Here, we survey 13 recently determined RC-LH1 assemblies, and we compare the precise molecular arrangements of pigments and proteins that allow efficient light absorption and the transfer of energy, electrons and protons. We highlight shared structural features, as well as differences that span the bound pigments and cofactors, the structures of individual subunits, the overall architecture of the complexes, and the roles of additional subunits newly identified in just one or a few species. We discuss RC-LH1 structures in the context of prior biochemical and spectroscopic investigations, which together enhance our understanding of the molecular mechanisms of photosynthesis in the purple phototrophic bacteria. A particular emphasis is placed on how the remarkable and unexpected structural diversity in RC-LH1 complexes demonstrates different evolutionary solutions for maximising pigment density for optimised light harvesting, whilst balancing the requirement for efficient quinone diffusion between RC and cytochrome bc1 complexes through the encircling LH1 complex.

Project description:Peripheral light harvesting (LH) antenna complexes have been studied extensively in the purple nonsulfur bacterium Rhodopseudomonas palustris because it produces different types of LH complexes under high light intensities (LH2 complex) and low light intensities (LH3 and LH4 complex). The ability of R. palustris to alter its peripheral LH complexes in response to changes in light intensity is attributed to the multiple operons that encode the a and b peptides that make up these complexes, whose expression is affected by light intensity, light quality, and oxygen tension. However, low resolution structures, amino acid similarities between the complexes, and a lack of transcriptional analysis made it difficult to determine the LH complexes composition and functions under different light intensities. It was also unclear how much diversity of the R. palustris LH complexes exists in nature.Results: To gain insight into the composition of the LH complexes, their function under high light intensities and low light intensities, and their prevalence in the environment we undertook an integrative genomics approach using 15 closely related R. palustris strains isolated from the environment and 5 R. palustris ecotypes whose genomes have been sequenced. We sequenced the genomes for the 15 closely related strains and using RNA-seq carried out transcriptomic analysis on all 20 strains grown under high light intensity and low light intensity. We were able to determine that even closely related R. palustris strains had differences in their pucBA gene content and expression, even under the same growth conditions. We also found that the LH2 complex could compensate for the lack of an LH4 complex under LL intensities but not under extremely LL intensities. Conclusions: This is the first time an integrative genomics approach has been used to study light harvesting in the environment. The variation observed in LH gene composition and expression in environmental isolates of R. palustris likely reflects how these strains have adapted to specific light conditions in the environment. We have also shown that there is redundancy between some of the LH complexes under certain light intensities, which may partially explain why multiple operons encoding LH complexes have evolved and been maintained in R. palustris.

Project description:Peripheral light harvesting (LH) antenna complexes have been studied extensively in the purple nonsulfur bacterium Rhodopseudomonas palustris because it produces different types of LH complexes under high light intensities (LH2 complex) and low light intensities (LH3 and LH4 complex). The ability of R. palustris to alter its peripheral LH complexes in response to changes in light intensity is attributed to the multiple operons that encode the a and b peptides that make up these complexes, whose expression is affected by light intensity, light quality, and oxygen tension. However, low resolution structures, amino acid similarities between the complexes, and a lack of transcriptional analysis made it difficult to determine the LH complexes composition and functions under different light intensities. It was also unclear how much diversity of the R. palustris LH complexes exists in nature.Results: To gain insight into the composition of the LH complexes, their function under high light intensities and low light intensities, and their prevalence in the environment we undertook an integrative genomics approach using 15 closely related R. palustris strains isolated from the environment and 5 R. palustris ecotypes whose genomes have been sequenced. We sequenced the genomes for the 15 closely related strains and using RNA-seq carried out transcriptomic analysis on all 20 strains grown under high light intensity and low light intensity. We were able to determine that even closely related R. palustris strains had differences in their pucBA gene content and expression, even under the same growth conditions. We also found that the LH2 complex could compensate for the lack of an LH4 complex under LL intensities but not under extremely LL intensities. Conclusions: This is the first time an integrative genomics approach has been used to study light harvesting in the environment. The variation observed in LH gene composition and expression in environmental isolates of R. palustris likely reflects how these strains have adapted to specific light conditions in the environment. We have also shown that there is redundancy between some of the LH complexes under certain light intensities, which may partially explain why multiple operons encoding LH complexes have evolved and been maintained in R. palustris. Examing the variation observed in LH gene composition and expression in various environmental isolates

Dataset Information

The molecular mechanisms of light adaption in light-harvesting complexes of purple bacteria revealed by a multiscale modeling.

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The molecular mechanisms of light adaption in light-harvesting complexes of purple bacteria revealed by a multiscale modeling.

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