scholarly journals Light’s interaction with pigments in chloroplasts: The murburn perspective, with special relevance to carotenoids

2020 ◽  
Author(s):  
Kelath Murali Manoj ◽  
Afsal Manekkathodi
Keyword(s):  
Light Harvesting ◽  
Reaction Centers ◽  
Oxygenic Photosynthesis ◽  
Physiological Data ◽  
Light Harvesting Complexes ◽  
Light Reaction ◽  
Historical Perspectives ◽  
Electron Emitters ◽  
Theoretical Foundations ◽  
Special Relevance

The prevailing understanding on photolytic photophosphorylation, the light reaction of oxygenic photosynthesis, considers the vast majority of the diverse pigments, chlorophyll binding proteins (CBPs) and light harvesting complexes (LHCs) as photon-energy relaying facets; only the two photosystems’ (PS) reaction centers’ chlorophyll a couplets are deemed to serve as photo-excitable electron emitters. Highlighting the historical perspectives involved, we present reasons why this conventional perception is unmet by theoretical foundations, unsupported by molecular awareness on the various pigments and unverified by physiological data available on chloroplasts. Further, we propose a simple diffusible reactive oxygen species (DROS)-based mechanism for correlating the functions of various light harvesting LHCs and CBPs with the reaction centers of PS I & II.

scholarly journals The terminal phycobilisome emitter, LCM: A light-harvesting pigment with a phytochrome chromophore

2015 ◽  
Vol 112 (52) ◽  
pp. 15880-15885 ◽  
Author(s):  
Kun Tang ◽  
Wen-Long Ding ◽  
Astrid Höppner ◽  
Cheng Zhao ◽  
Lun Zhang ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Transient Absorption ◽  
Light Harvesting ◽  
Reaction Centers ◽  
Protein Fold ◽  
Light Harvesting Complexes ◽  
Exciton Coupling ◽  
Femtosecond Transient Absorption ◽  
Orange Carotenoid Protein ◽  
Sensory Photoreceptors

Photosynthesis relies on energy transfer from light-harvesting complexes to reaction centers. Phycobilisomes, the light-harvesting antennas in cyanobacteria and red algae, attach to the membrane via the multidomain core-membrane linker, LCM. The chromophore domain of LCM forms a bottleneck for funneling the harvested energy either productively to reaction centers or, in case of light overload, to quenchers like orange carotenoid protein (OCP) that prevent photodamage. The crystal structure of the solubly modified chromophore domain from Nostoc sp. PCC7120 was resolved at 2.2 Å. Although its protein fold is similar to the protein folds of phycobiliproteins, the phycocyanobilin (PCB) chromophore adopts ZZZssa geometry, which is unknown among phycobiliproteins but characteristic for sensory photoreceptors (phytochromes and cyanobacteriochromes). However, chromophore photoisomerization is inhibited in LCM by tight packing. The ZZZssa geometry of the chromophore and π-π stacking with a neighboring Trp account for the functionally relevant extreme spectral red shift of LCM. Exciton coupling is excluded by the large distance between two PCBs in a homodimer and by preservation of the spectral features in monomers. The structure also indicates a distinct flexibility that could be involved in quenching. The conclusions from the crystal structure are supported by femtosecond transient absorption spectra in solution.

Overexpression of Thalassiosira pseudonana violaxanthin de-epoxidase-like 2 (VDL2) increases fucoxanthin while stoichiometrically reducing diadinoxanthin cycle pigment abundance

2020 ◽  
Author(s):  
Olga Gaidarenko ◽  
Dylan W. Mills ◽  
Maria Vernet ◽  
Mark Hildebrand
Keyword(s):  
Light Harvesting ◽  
Photosynthetic Pigment ◽  
Carotenoid Biosynthesis ◽  
Thalassiosira Pseudonana ◽  
Physiological Data ◽  
Biosynthesis Pathway ◽  
Chloroplast Targeting ◽  
Light Harvesting Complexes ◽  
Carotenoid Biosynthesis Pathway ◽  
Transcriptomic Responses

ABSTRACTDespite the ubiquity and ecological importance of diatoms, much remains to be understood about their physiology and metabolism, including their carotenoid biosynthesis pathway. Early carotenoid biosynthesis steps are well-conserved, while the identity of the enzymes that catalyze the later steps and their order remain unclear. Those steps lead to the biosynthesis of the final pathway products: the main accessory light-harvesting pigment fucoxanthin (Fx) and the main photoprotective pigment pool comprised of diadinoxanthin (Ddx) and its reversibly de-epoxidized form diatoxanthin (Dtx). We used sequence comparison to known carotenoid biosynthesis enzymes to identify novel candidates in the diatom Thalassiosira pseudonana. Microarray and RNA-seq data was used to select candidates with transcriptomic responses similar to known carotenoid biosynthesis genes and to create full-length gene models, and we focused on those that encode proteins predicted to be chloroplast-localized. We identified a violaxanthin de-epoxidase-like gene (Thaps3_11707, VDL2) that when overexpressed results in increased Fx abundance while stoichiometrically reducing Ddx+Dtx. Based on transcriptomics, we hypothesize that Thaps3_10233 may also contribute to Fx biosynthesis, in addition to VDL2. Separately using antisense RNA to target VDL2, VDL1, and both LUT1-like copies (hypothesized to catalyze an earlier step in the pathway) simultaneously, reduced the overall cellular photosynthetic pigment content, including chlorophylls, suggesting destabilization of light-harvesting complexes by Fx deficiency. Based on transcriptomic and physiological data, we hypothesize that the two predicted T. pseudonana zeaxanthin epoxidases have distinct functions and that different copies of phytoene synthase and phytoene desaturase may serve to initiate carotenoid biosynthesis in response to different cellular needs. Finally, nine carotene cis/trans isomerase (CRTISO) candidates identified based on sequence identity to known CRTISO proteins were narrowed to two most likely to be part of the T. pseudonana carotenoid biosynthesis pathway based on transcriptomic responses and predicted chloroplast targeting.

Enhanced Photocurrent Generation by Photosynthetic Bacterial Reaction Centers through Molecular Relays, Light-Harvesting Complexes, and Direct Protein–Gold Interactions

Langmuir ◽  
2011 ◽  
Vol 27 (16) ◽  
pp. 10282-10294 ◽  
Author(s):  
Mart-Jan den Hollander ◽  
J. Gerhard Magis ◽  
Philipp Fuchsenberger ◽  
Thijs J. Aartsma ◽  
Michael R. Jones ◽  
...  
Keyword(s):  
Light Harvesting ◽  
Reaction Centers ◽  
Light Harvesting Complexes ◽  
Photocurrent Generation ◽  
Bacterial Reaction Centers

scholarly journals Structural Diversity of Photosystem I and Its Light-Harvesting System in Eukaryotic Algae and Plants

2021 ◽  
Vol 12 ◽  
Author(s):  
Tianyu Bai ◽  
Lin Guo ◽  
Mingyu Xu ◽  
Lirong Tian
Keyword(s):  
Photosystem I ◽  
Light Harvesting ◽  
Structural Diversity ◽  
Spatial Arrangement ◽  
Oxygenic Photosynthesis ◽  
Light Harvesting Complexes ◽  
X Ray Crystallography ◽  
Photosynthetic Organisms ◽  
Eukaryotic Algae ◽  
Structural Details

Photosystem I (PSI) is one of the most efficient photoelectric apparatus in nature, converting solar energy into condensed chemical energy with almost 100% quantum efficiency. The ability of PSI to attain such high conversion efficiency depends on the precise spatial arrangement of its protein subunits and binding cofactors. The PSI structures of oxygenic photosynthetic organisms, namely cyanobacteria, eukaryotic algae, and plants, have undergone great variation during their evolution, especially in eukaryotic algae and vascular plants for which light-harvesting complexes (LHCI) developed that surround the PSI core complex. A detailed understanding of the functional and structural properties of this PSI-LHCI is not only an important foundation for understanding the evolution of photosynthetic organisms but is also useful for designing future artificial photochemical devices. Recently, the structures of such PSI-LHCI supercomplexes from red alga, green alga, diatoms, and plants were determined by X-ray crystallography and single-particle cryo-electron microscopy (cryo-EM). These findings provide new insights into the various structural adjustments of PSI, especially with respect to the diversity of peripheral antenna systems arising via evolutionary processes. Here, we review the structural details of the PSI tetramer in cyanobacteria and the PSI-LHCI and PSI-LHCI-LHCII supercomplexes from different algae and plants, and then discuss the diversity of PSI-LHCI in oxygenic photosynthesis organisms.

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