A limiting factor for photosynthetic organisms is their light-harvesting efficiency, that is the efficiency of their conversion of light energy to chemical energy. Small modifications or variations ...of chlorophylls allow photosynthetic organisms to harvest sunlight at different wavelengths. Oxygenic photosynthetic organisms usually utilize only the visible portion of the solar spectrum. The cyanobacterium Acaryochloris marina carries out oxygenic photosynthesis but contains mostly chlorophyll d and only traces of chlorophyll a. Chlorophyll d provides a potential selective advantage because it enables Acaryochloris to use infrared light (700-750nm) that is not absorbed by chlorophyll a. Recently, an even more red-shifted chlorophyll termed chlorophyll f has been reported. Here, we discuss using modified chlorophylls to extend the spectral region of light that drives photosynthetic organisms.
Martin Kamen was a giant of twentieth century science. Trained as a physical chemist, he was the co-discoverer of radioactive Carbon 14, which has transformed many areas of science as a tracer and as ...a way to date artifacts. He later switched to the study of metabolism and biochemistry and made important contributions to the understanding of nitrogen fixation and photosynthesis. Finally, he studied cytochromes, primarily from anoxygenic photosynthetic bacteria.
This review serves as an introduction to the variety of light-harvesting (LH) structures present in phototrophic prokaryotes. It provides an overview of the LH complexes of purple bacteria, green ...sulfur bacteria (GSB), acidobacteria, filamentous anoxygenic phototrophs (FAP), and cyanobacteria. Bacteria have adapted their LH systems for efficient operation under a multitude of different habitats and light qualities, performing both oxygenic (oxygen-evolving) and anoxygenic (non-oxygen-evolving) photosynthesis. For each LH system, emphasis is placed on the overall architecture of the pigment-protein complex, as well as any relevant information on energy transfer rates and pathways. This review addresses also some of the more recent findings in the field, such as the structure of the CsmA chlorosome baseplate and the whole-cell kinetics of energy transfer in GSB, while also pointing out some areas in need of further investigation.
Photosynthetic pigment-protein complexes (PPCs) accomplish light-energy capture and photochemistry in natural photosynthesis. In this review, we examine three pigment protein complexes in oxygenic ...photosynthesis: light-harvesting antenna complexes and two reaction centers: Photosystem II (PSII), and Photosystem I (PSI). Recent technological developments promise unprecedented insights into how these multi–component protein complexes are assembled into higher order structures and thereby execute their function. Furthermore, the interfacial domain between light-harvesting antenna complexes and PSII, especially the potential roles of the structural loops from CP29 and the PB–loop of ApcE in higher plant and cyanobacteria, respectively, are discussed. It is emphasized that the structural nuances are required for the structural dynamics and consequently for functional regulation in response to an ever–changing and challenging environment.
•Structural similarities of higher plant LHC-PSII assembly and Cyanobacterial PBS-PSII assembly•The structural loop of higher plant CP29 and cyanobacterial PB-loop play similar functional roles mediating complex assembly•The PsbW-PsbI-CP43-D1-PsbO axis acts as a hub sensing proton status
Evolution of photosynthesis Hohmann-Marriott, Martin F; Blankenship, Robert E
Annual review of plant biology,
01/2011, Letnik:
62
Journal Article
Recenzirano
Energy conversion of sunlight by photosynthetic organisms has changed Earth and life on it. Photosynthesis arose early in Earth's history, and the earliest forms of photosynthetic life were almost ...certainly anoxygenic (non-oxygen evolving). The invention of oxygenic photosynthesis and the subsequent rise of atmospheric oxygen approximately 2.4 billion years ago revolutionized the energetic and enzymatic fundamentals of life. The repercussions of this revolution are manifested in novel biosynthetic pathways of photosynthetic cofactors and the modification of electron carriers, pigments, and existing and alternative modes of photosynthetic carbon fixation. The evolutionary history of photosynthetic organisms is further complicated by lateral gene transfer that involved photosynthetic components as well as by endosymbiotic events. An expanding wealth of genetic information, together with biochemical, biophysical, and physiological data, reveals a mosaic of photosynthetic features. In combination, these data provide an increasingly robust framework to formulate and evaluate hypotheses concerning the origin and evolution of photosynthesis.
Femtosecond pulsed excitation of light-harvesting complexes creates oscillatory features in their response. This phenomenon has inspired a large body of work aimed at uncovering the origin of the ...coherent beatings and possible implications for function. Here we exploit site-directed mutagenesis to change the excitonic level structure in Fenna-Matthews-Olson (FMO) complexes and compare the coherences using broadband pump-probe spectroscopy. Our experiments detect two oscillation frequencies with dephasing on a picosecond timescale-both at 77 K and at room temperature. By studying these coherences with selective excitation pump-probe experiments, where pump excitation is in resonance only with the lowest excitonic state, we show that the key contributions to these oscillations stem from ground-state vibrational wavepackets. These experiments explicitly show that the coherences-although in the ground electronic state-can be probed at the absorption resonances of other bacteriochlorophyll molecules because of delocalization of the electronic excitation over several chromophores.
How Cyanobacteria went green Blankenship, Robert E.
Science (American Association for the Advancement of Science),
03/2017, Letnik:
355, Številka:
6332
Journal Article
Recenzirano
One of the most important developments in Earth's history is the change from the anaerobic environment of the early Earth to the aerobic and highly oxidizing environment that we have today, with 21% ...atmospheric oxygen (O2) (1). Many geologists, atmospheric scientists, and biologists have studied this dramatic change in the redox state of Earth-the "great oxidation event" (2)-to understand when and how it took place. On page 1436 of this issue, Soo et al. report exciting new evidence toward answers to both these questions (3).
Photosynthetic antenna complexes capture and concentrate solar radiation by transferring the excitation to the reaction center that stores energy from the photon in chemical bonds. This process ...occurs with near-perfect quantum efficiency. Recent experiments at cryogenic temperatures have revealed that coherent energy transfer—a wave-like transfer mechanism—occurs in many photosynthetic pigment-protein complexes. Using the Fenna–Matthews–Olson antenna complex (FMO) as a model system, theoretical studies incorporating both incoherent and coherent transfer as well as thermal dephasing predict that environmentally assisted quantum transfer efficiency peaks near physiological temperature; these studies also show that this mechanism simultaneously improves the robustness of the energy transfer process. This theory requires long-lived quantum coherence at room temperature, which never has been observed in FMO. Here we present evidence that quantum coherence survives in FMO at physiological temperature for at least 300 fs, long enough to impact biological energy transport. These data prove that the wave-like energy transfer process discovered at 77 K is directly relevant to biological function. Microscopically, we attribute this long coherence lifetime to correlated motions within the protein matrix encapsulating the chromophores, and we find that the degree of protection afforded by the protein appears constant between 77 K and 277 K. The protein shapes the energy landscape and mediates an efficient energy transfer despite thermal fluctuations.
In photosynthetic organisms, photons are captured by light-harvesting antenna complexes, and energy is transferred to reaction centers where photochemical reactions take place. We describe here the ...isolation and characterization of a fully functional megacomplex composed of a phycobilisome antenna complex and photosystems I and II from the cyanobacterium Synechocystis PCC 6803. A combination of in vivo protein cross-linking, mass spectrometry, and time-resolved spectroscopy indicates that the megacomplex is organized to facilitate energy transfer but not intercomplex electron transfer, which requires diffusible intermediates and the cytochrome b 6 f complex. The organization provides a basis for understanding how phycobilisomes transfer excitation energy to reaction centers and how the energy balance of two photosystems is achieved, allowing the organism to adapt to varying ecophysiological conditions.
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