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A model for the transmembrane arrangement of a bacterial LH1 antenna complex α/β subunit. Taken from Zuber (1987).
Source publication
This paper describes the main stages involved in the research efforts designed to try and understand the structure and function of purple bacterial antenna complexes. Wherever possible the work has been illustrated by pictures of the major people who carried it out.
Context in source publication
Context 1
... group pinpointed conserved histidine residues as likely ligands for the Mg 2+ at the center of the BChl macrocycles, and correlated some aromatic, potential hydrogen bonding residues with the position of the long wavelength BChl absorption bands. Figure 3 shows a topological model for the α and β components of a purple bacterial LH1 antenna complex from that time (Zuber 1987). As the bio- chemical studies progressed there were several groups of physicists and chemists studying the energy transfer reactions in these antenna complexes, both in native photosynthetic membranes and in isolated, purified complexes. ...
Citations
... Context and motivation for our work is obtained by considering natural light-harvesting systems and the elegant structures with (non- random) arrangements of multiple chromophores in the pigment-pro- tein light-harvesting complexes of photosynthetic organisms [1,2,[10][11][12]. Unfortunately, although these systems function with ex- tremely high performance in natural organisms, there are many chal- lenges in using them for technological purposes. ...
Developing efficient panchromatic light harvesting systems that exploit the energy available from the entire solar spectrum in an economically feasible and scalable fashion is of great importance. Light harvesting by incorporating multiple chromophores into molecular assemblies such as micelles and vesicles is one method for accomplishing this result. In this paper, we describe panchromatic light harvesting in lipid-based vesicle bilayers that contain a random distribution of lipid-bound chromophores. Numerically exact modeling based on Förster theory is developed to establish the criteria for designing a highly efficient panchromatic light-harvesting unit. An approximate modeling method is also developed to greatly reduce the complexity of the modeling problem. Both the exact and approximate models are verified by designing and experimentally testing an efficient three-chromophore light-harvesting system. For the experiments, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(lissamine rhodamine B sulfonyl) (Rhod) as the lowest energy chromophore, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl) (NBD) as an intermediate acceptor, and Marina Blue® 1,2-Dihexadecanoyl-sn-Glycero-3-Phosphoethanolamine (MB) as the highest energy absorber (donor) are selected. From chromophore concentrations and R0 values, modeling predicts an overall efficiency of energy transfer to the terminal acceptor greater than ≈0.6 across a broad excitation wavelength range of ≈250 nm. The predicted transfer efficiency is verified by the experimental results. In addition, comparison of the approximate modeling method with both the numerically exact method and experimental results confirms that the computationally efficient approximate method is sufficiently accurate to guide choices of experimental parameters such as chromophore concentration. Overall, these results show predictive design of panchromatic light-harvesting performance can be performed rapidly and efficiently using an approximate kinetic model for randomly distributed assemblies of multiple chromophores.
... The inner antennae, LH1, form circular structures around the reaction centers (Cogdell and Roszak 2014). The accessory antennae are typically composed of a number of smaller rings surrounding the LH1-RC core complexes (Cogdell et al. 2004). The accessory antennae complexes are not in direct contact with the reaction centers (Walz and Ghosh 1997), but the difference in energy levels provides a cascade-like system of excited states that funnels excitation from the outer LH2s through LH1 to the reaction centers (Hu et al. 1998). ...
Light-harvesting capacity was investigated in six species of aerobic anoxygenic phototrophic (AAP) bacteria using absorption spectroscopy, fluorescence emission spectroscopy, and pigment analyses. Aerobically grown AAP cells contained approx. 140-1800 photosynthetic reaction centers per cell, an order of magnitude less than purple non-sulfur bacteria grown semiaerobically. Three of the studied AAP species did not contain outer light-harvesting complexes, and the size of their reaction center core complexes (RC-LH1 core complexes) varied between 29 and 36 bacteriochlorophyll molecules. In AAP species containing accessory antennae, the size was frequently reduced, providing between 5 and 60 additional bacteriochlorophyll molecules. In Roseobacter litoralis, it was found that cells grown at a higher light intensity contained more reaction centers per cell, while the size of the light-harvesting complexes was reduced. The presented results document that AAP species have both the reduced number and size of light-harvesting complexes which is consistent with the auxiliary role of phototrophy in this bacterial group.
... Approximately 14 B875 complexes surround and contact the RC, whereas the B800-850 complexes are positioned around the B875-RC complex [16,17]. It was believed that R. sphaeroides contained a single set of B800-850 polypeptides, but a second B800-850 complex has been discovered that can aid light-energy capture in this [18] and other photosynthetic bacteria [19]. ...
Anoxygenic photosynthetic bacteria have provided us with crucial insights into the process of solar energy capture, pathways of metabolic and societal importance, specialized differentiation of membrane domains, function or assembly of bioenergetic enzymes, and into the genetic control of these and other activities. Recent insights into the organization of this bioenergetic membrane system, the genetic control of this specialized domain of the inner membrane and the process by which potentially photosynthetic and non-photosynthetic cells protect themselves from an important class of reactive oxygen species will provide an unparalleled understanding of solar energy capture and facilitate the design of solar-powered microbial biorefineries.
A time line of important research relating to anoxygenic photosynthetic organisms is presented. The time line includes discoveries of organisms, metabolic capabilities, molecular complexes and genetic systems. It also pinpoints important milestones in our understanding of the structure, function, organization, assembly and regulation of photosynthetic complexes.
A compact donor-acceptor molecular dyad has been synthesized by attaching an N,N-dimethylamino fragment to a naphthalic anhydride residue. The dyad shows fluorescence from an intramolecular charge-transfer state (i.e., charge-recombination fluorescence) in solution, with the photo-physical properties being strongly dependent on the solvent polarity. Similar emission is seen for single crystals of the target compound, the molecules being aligned head-to-head, although time-resolved emission profiles display dual-exponential kinetics. A second polymorph with the head-to-tail alignment also gives rise to two lifetimes that differ somewhat from those of the first structure, which are assigned to bulk and surface-bound molecules. Growing the crystal in the presence of Rhodamine B localizes the dye around the surface. Excitation of the crystal is followed by sub-ps exciton migration along the aligned stacks, with occasional crossing to adjacent stacks and trapping at the surface. Rhodamine B present at very low levels acts as the acceptor for excitons entering the surface layer. Crystals embedded in a polyester resin form an artificial light-harvesting antenna able to sensitize an amorphous silicon solar cell.
Photosynthesis is the basis of life on the earth and the development of the vast range of simple organisms existing today can often be traced back to the earliest geological times. Most life forms depend directly or indirectly on the synthetic processes which harvest the sun's energy, utilising a range of pigments such as the chlorophylls and carotenoids, which not only determine the colour of each organism, but often also serve a protective role against the adverse effects of ultraviolet radiation. Recent research has elucidated the detailed photochemical mechanisms and the complex nature of the light-harvesting pigment–protein complexes. This review covers algae and fungi and their symbiotic forms in lichens and corals, particularly with respect to the pigments they synthesise and the commercial uses to which these and other metabolites have been (and may in the future be) put.
Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) have been employed in studying the structural information of various biological systems, particularly in systems without high-resolution structural information available. In this report, we briefly present some principles and biological applications of neutron scattering and DLS, compare the differences in information that can be obtained with small-angle X-ray scattering (SAXS), and then report recent studies of SANS and DLS, together with other biophysical approaches, for light-harvesting antenna complexes and reaction centers of purple and green phototrophic bacteria.
As an outgoing Editor of the Historical Corner of Photosynthesis Research, I present here the following list of papers of historical interest for the benefit of all. The first paper I published was: Govindjee (1988) The Discovery of Chlorophyll-protein Complex by Emil L. Smith during 1937-1941. Photosynth Res 16:285-289. In order to bring to the readers this List of references on the historical papers published in this journal (and some even elsewhere), I have organized these papers under the following headings (some are arbitrarily assigned to a particular section since they may fit in more than one section): (I) biographies (that include obituaries and tributes, arranged alphabetically, with dates of birth and death); (II) recognitions of scientists (arranged alphabetically) by others; (III) personal perspectives (arranged alphabetically); (IV) historical papers (first chronologically, by the year of publication, and then alphabetically by the names of the editors); (V) special issues of Photosynthesis Research (chronologically by the year of publication and then alphabetically by the names of editors); and lastly (VI) Conferences (available reports in Photosynthesis Research).
A time line of important research relating to anoxygenic photosynthetic organisms is presented. The time line includes discoveries of organisms, metabolic capabilities, molecular complexes and genetic systems. It also pinpoints important milestones in our understanding of the structure, function, organization, assembly and regulation of photosynthetic complexes.
