The design of efficient artificial light-harvesting antennas is essential for enabling the widespread use of solar energy. Natural photosynthetic systems offer valuable inspiration, but many rely on complex pigment-protein interactions and have limited spectral coverage, which pose challenges for rational design. Chlorosome mimics, which are self-assembling pigment aggregates inspired by green photosynthetic bacteria, offer structural simplicity, flexible tunability, and strong excitonic coupling through pigment-pigment interactions. However, these pigment aggregates suffer from limited absorption in the green and near-infrared regions and, similarly to other light-harvesting systems, reduced energy transfer efficiency at high donor concentrations. One promising strategy to overcome these limitations is the integration of plasmonic nanoparticles, which enhance local electromagnetic fields, increase spectral coverage, and make new energetic pathways accessible. Although plasmonic enhancement has been widely studied in pigment-protein complexes like Photosystem I and light-harvesting complexes (LHCs), its application to pigment-pigment self-assembled systems remains largely unexplored. This perspective presents recent advances in biomimetic light-harvesting design with chlorosome mimics and explores the potential for plasmonic enhancement of photophysics in these systems. We examine the structure of chlorosomes and their artificial mimics to understand the role of pigment-pigment interactions in facilitating highly efficient energy transfer.

• Publication type
• Journal Article MeSH
• Review MeSH

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
• Chloroplasts metabolism   radiation effects   ultrastructure   MeSH
• Photosystem I Protein Complex metabolism   MeSH
• Photosystem II Protein Complex metabolism   MeSH
• Multiprotein Complexes metabolism   ultrastructure   MeSH
• Diatoms metabolism   radiation effects   ultrastructure   MeSH
• Light MeSH
• Light-Harvesting Protein Complexes metabolism   MeSH
• Microscopy, Electron, Transmission MeSH
• Thylakoids metabolism   radiation effects   ultrastructure   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Photosystem I Protein Complex MeSH
• Photosystem II Protein Complex MeSH
• Multiprotein Complexes MeSH
• Light-Harvesting Protein Complexes 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
• Cell Membrane metabolism   ultrastructure   MeSH
• Chloroflexus metabolism   MeSH
• Microscopy, Electron MeSH
• Photosynthetic Reaction Center Complex Proteins metabolism   ultrastructure   MeSH
• Photosynthesis MeSH
• Organelles metabolism   ultrastructure   MeSH
• Rhodopseudomonas metabolism   MeSH
• Light MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Photosynthetic Reaction Center Complex Proteins 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
• Bacterial Chromatophores MeSH
• Pigments, Biological MeSH
• Chloroflexus cytology   metabolism   MeSH
• X-Ray Diffraction MeSH
• Phycobiliproteins chemistry   physiology   MeSH
• Carotenoids chemistry   metabolism   MeSH
• Molecular Structure MeSH
• Organelles physiology   MeSH
• Light * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Names of Substances
• Pigments, Biological MeSH
• Phycobiliproteins MeSH
• Carotenoids 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
• Bacterial Proteins chemistry   isolation & purification   metabolism   MeSH
• Bacteriochlorophylls chemistry   isolation & purification   metabolism   MeSH
• Chlorobium chemistry   MeSH
• Photosynthesis MeSH
• Energy Transfer * MeSH
• Spectrum Analysis MeSH
• Light MeSH
• Light-Harvesting Protein Complexes chemistry   metabolism   MeSH
• Xanthophylls chemistry   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• astaxanthine MeSH Browser
• bacteriochlorophyll c MeSH Browser
• Bacterial Proteins MeSH
• Bacteriochlorophylls MeSH
• Light-Harvesting Protein Complexes MeSH
• Xanthophylls 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
• Alcohols chemistry   MeSH
• Anisotropy MeSH
• Bacteriochlorophylls chemistry   metabolism   MeSH
• Cellular Structures metabolism   MeSH
• Chlorobium metabolism   MeSH
• Esterification MeSH
• Hexanes chemistry   MeSH
• Protein Structure, Quaternary MeSH
• Scattering, Radiation MeSH
• X-Rays MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Alcohols MeSH
• Bacteriochlorophylls MeSH
• Hexanes MeSH