Chlorophylls and bacteriochlorophylls, together with carotenoids, serve, noncovalently bound to specific apoproteins, as principal light-harvesting and energy-transforming pigments in photosynthetic organisms. In recent years, enormous progress has been achieved in the elucidation of structures and functions of light-harvesting (antenna) complexes, photosynthetic reaction centers and even entire photosystems. It is becoming increasingly clear that light-harvesting complexes not only serve to enlarge the absorption cross sections of the respective reaction centers but are vitally important in short- and long-term adaptation of the photosynthetic apparatus and regulation of the energy-transforming processes in response to external and internal conditions. Thus, the wide variety of structural diversity in photosynthetic antenna "designs" becomes conceivable. It is, however, common for LHCs to form trimeric (or multiples thereof) structures. We propose a simple, tentative explanation of the trimer issue, based on the 2D world created by photosynthetic membrane systems.

• Keywords
• bacteriochlorophylls, carotenoids, chlorophylls, excitation energy transfer, light-harvesting complexes, photoprotection, photosynthesis, photosystems, pigment-protein complexes,
• MeSH
• Bacterial Proteins chemistry   metabolism   MeSH
• Photosynthesis MeSH
• Protein Conformation MeSH
• Models, Molecular MeSH
• Protein Multimerization MeSH
• Energy Transfer MeSH
• Plant Proteins chemistry   metabolism   MeSH
• Plants metabolism   MeSH
• Cyanobacteria metabolism   MeSH
• Light-Harvesting Protein Complexes chemistry   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Bacterial Proteins MeSH
• Plant Proteins MeSH
• Light-Harvesting Protein Complexes MeSH

Photosynthesis is a highly optimized process from which valuable lessons can be learned about the operating principles in nature. Its primary steps involve energy transport operating near theoretical quantum limits in efficiency. Recently, extensive research was motivated by the hypothesis that nature used quantum coherences to direct energy transfer. This body of work, a cornerstone for the field of quantum biology, rests on the interpretation of small-amplitude oscillations in two-dimensional electronic spectra of photosynthetic complexes. This Review discusses recent work reexamining these claims and demonstrates that interexciton coherences are too short lived to have any functional significance in photosynthetic energy transfer. Instead, the observed long-lived coherences originate from impulsively excited vibrations, generally observed in femtosecond spectroscopy. These efforts, collectively, lead to a more detailed understanding of the quantum aspects of dissipation. Nature, rather than trying to avoid dissipation, exploits it via engineering of exciton-bath interaction to create efficient energy flow.

• MeSH
• Algorithms MeSH
• Photosynthesis * MeSH
• Quantum Theory * MeSH
• Energy Transfer * MeSH
• Spectrum Analysis MeSH
• Light-Harvesting Protein Complexes metabolism   MeSH
• Models, Theoretical MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Names of Substances
• Light-Harvesting Protein Complexes MeSH

Absorption of sunlight is the first step in photosynthesis, which provides energy for the vast majority of organisms on Earth. The primary processes of photosynthesis have been studied extensively in isolated light-harvesting complexes and reaction centres, however, to understand fully the way in which organisms capture light it is crucial to also reveal the functional relationships between the individual complexes. Here we report the use of two-dimensional electronic spectroscopy to track directly the excitation-energy flow through the entire photosynthetic system of green sulfur bacteria. We unravel the functional organization of individual complexes in the photosynthetic unit and show that, whereas energy is transferred within subunits on a timescale of subpicoseconds to a few picoseconds, across the complexes the energy flows at a timescale of tens of picoseconds. Thus, we demonstrate that the bottleneck of energy transfer is between the constituents.

• MeSH
• Chlorobi metabolism   MeSH
• Photosynthesis MeSH
• Energy Transfer MeSH
• Sunlight MeSH
• Spectrum Analysis methods   MeSH
• Light MeSH
• Light-Harvesting Protein Complexes chemistry   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Light-Harvesting Protein Complexes MeSH

Chlorobaculum tepidum is a representative of green sulfur bacteria, a group of anoxygenic photoautotrophs that employ chlorosomes as the main light-harvesting structures. Chlorosomes are coupled to a ferredoxin-reducing reaction center by means of the Fenna-Matthews-Olson (FMO) protein. While the biochemical properties and physical functioning of all the individual components of this photosynthetic machinery are quite well understood, the native architecture of the photosynthetic supercomplexes is not. Here we report observations of membrane-bound FMO and the analysis of the respective FMO-reaction center complex. We propose the existence of a supercomplex formed by two reaction centers and four FMO trimers based on the single-particle analysis of the complexes attached to native membrane. Moreover, the structure of the photosynthetic unit comprising the chlorosome with the associated pool of RC-FMO supercomplexes is proposed.

• Keywords
• Chlorosome, Electron microscopy, FMO (Fenna–Matthews–Olson protein), Green sulfur bacteria, Light-harvesting complex, Reaction center,
• MeSH
• Bacterial Proteins chemistry   metabolism   ultrastructure   MeSH
• Chlorobi chemistry   MeSH
• Cytoplasm chemistry   MeSH
• Photosynthetic Reaction Center Complex Proteins chemistry   metabolism   MeSH
• Intracellular Membranes chemistry   MeSH
• Light-Harvesting Protein Complexes chemistry   metabolism   ultrastructure   MeSH
• Microscopy, Electron, Transmission MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Bacterial Proteins MeSH
• FMO bacteriochlorophyll protein, Bacteria MeSH Browser
• Photosynthetic Reaction Center Complex Proteins MeSH
• Light-Harvesting Protein Complexes MeSH