Structural organisation of phycobilisomes from Synechocystis sp. strain PCC 6803 and their interaction with the membrane. Biochim Biophys Acta

Department of Biophysical Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Biochimica et Biophysica Acta (Impact Factor: 4.66). 02/2009; 1787(4):272-9. DOI: 10.1016/j.bbabio.2009.01.009
Source: PubMed


In cyanobacteria, the harvesting of light energy for photosynthesis is mainly carried out by the phycobilisome - a giant, multi-subunit pigment-protein complex. This complex is composed of heterodimeric phycobiliproteins that are assembled with the aid of linker polypeptides such that light absorption and energy transfer to photosystem II are optimised. In this work we have studied, using single particle electron microscopy, the phycobilisome structure in mutants lacking either two or all three of the phycocyanin hexamers. The images presented give much greater detail than those previously published, and in the best two-dimensional projection maps a resolution of 13 A was achieved. As well as giving a better overall picture of the assembly of phycobilisomes, these results reveal new details of the association of allophycocyanin trimers within the core. Insights are gained into the attachment of this core to the membrane surface, essential for efficient energy transfer to photosystem II. Comparison of projection maps of phycobilisomes with and without reconstituted ferredoxin:NADP oxidoreductase suggests a location for this enzyme within the complex at the rod-core interface.

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Available from: Ana Andreea Arteni
    • "Phycobilisomes (PBSs) are supramolecular complexes with molecular weights of typically 5–30 MDa, composed mainly of two structural components: chromophore-bearing phycobiliproteins, and their associated , mostly colorless, linker polypeptides123. Phycobiliprotein complexes are grouped into four major categories based on their spectral properties and chromophore (bilin) compositions: phycoerythrins and phycoerythrocyanins that absorb in the teal to green region of 500–565 nm, as well as phycocyanins (PCs) and allophycocyanins (APCs) that absorb in the orange (~620 nm) to red regions (655 nm), re- spectively4567. The linker peptides aggregate trimeric phycoerythrins (phycoerythrocyanins) and PC units into rods, as well as APC units into core structures; they also connect the rods to the core, and the entire PBS to the thylakoid membrane[3,7891011. Additionally, linkers play an important role in modulating the spectroscopic properties of phycobiliproteins[5,12]. "
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    ABSTRACT: Phycobilisomes are the main light-harvesting protein complexes in cyanobacteria and some algae. It is commonly accepted that these complexes only absorb green and orange light, complementing chlorophyll absorbance. Here, we present a new phycobilisome derived complex that consists only of allophycocyanin core subunits, having red-shifted absorption peaks of 653 and 712nm. These red-shifted phycobiliprotein complexes were isolated from the chlorophyll f-containing cyanobacterium, Halomicronema hongdechloris, grown under monochromatic 730nm-wavelength (far-red) light. The 3D model obtained from single particle analysis reveals a double disk assembly of 120-145Å with two α/β allophycocyanin trimers fitting into the two separated disks. They are significantly smaller than typical phycobilisomes formed from allophycocyanin subunits and core-membrane linker proteins, which fit well with a reduced distance between thylakoid membranes observed from cells grown under far-red light. Spectral analysis of the dissociated and denatured phycobiliprotein complexes grown under both these light conditions shows that the same bilin chromophore, phycocyanobilin, is exclusively used. Our findings show that red-shifted phycobilisomes are required for assisting efficient far-red light harvesting. Their discovery provides new insights into the molecular mechanisms of light harvesting under extreme conditions for photosynthesis, as well as the strategies involved in flexible chromatic acclimation to diverse light conditions.
    No preview · Article · Oct 2015 · Biochimica et Biophysica Acta
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    • "The rod-core linkers (L RC ) bind the rods to the core cylinders. The small core linkers (L C ) stabilize the core cylinders and the membrane-core linker (L MC ) anchors the PBSs to the PSs [34]. "
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    ABSTRACT: In photosynthetic organisms, carotenoids (carotenes or xanthophylls) are important for light harvesting, photoprotection and structural stability of a variety of pigment-protein complexes. Here, we investigated the consequences of altered carotenoid composition for the functional organization of photosynthetic complexes in wild-type and various mutant strains of the cyanobacterium Synechocystis sp. PCC 6803. Although it is generally accepted that xanthophylls do not play a role in cyanobacterial photosynthesis in low-light conditions, we have found that the absence of xanthophylls leads to reduced oligomerization of photosystems I and II. This is remarkable because these complexes do not bind xanthophylls. Oligomerization is even more disturbed in crtH mutant cells, which show limited carotenoid synthesis; in these cells also the phycobilisomes are distorted despite the fact that these extramembranous light-harvesting complexes do not contain carotenoids. The number of phycocyanin rods connected to the phycobilisome core is strongly reduced leading to high amounts of unattached phycocyanin units. In the absence of carotenoids the overall organization of the thylakoid membranes is disturbed: Photosystem II is not formed, photosystem I hardly oligomerizes and the assembly of phycobilisomes remains incomplete. These data underline the importance of carotenoids in the structural and functional organization of the cyanobacterial photosynthetic machinery. Copyright © 2015. Published by Elsevier B.V.
    Full-text · Article · Jun 2015 · Biochimica et Biophysica Acta
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    • "Using cryoelectron microscopy and single particle analysis, Arteni et al. [32] proposed a model suggesting that the location of FNRL is located at the interface between the phycocyanin rods and the allophycocyanin core. Our data from the ΔcpcF mutant (Figs. 4 and 5) support this model. "
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    ABSTRACT: Phycocyanin is an important component of the phycobilisome, which is the principal light-harvesting complex in cyanobacteria. The covalent attachment of the phycocyanobilin chromophore to phycocyanin is catalyzed by the enzyme phycocyanin lyase. The photosynthetic properties and phycobilisome assembly state were characterized in wild type and two mutants which lack holo-α-phycocyanin. Insertional inactivation of the phycocyanin α-subunit lyase (ΔcpcF mutant) prevents the ligation of phycocyanobilin to α-phycocyanin (CpcA), while disruption of the cpcB/A/C2/C1 operon in the CK mutant prevents synthesis of both apo-α-phycocyanin (apo-CpcA) and apo-β-phycocyanin (apo-CpcB). Both mutants exhibited similar light saturation curves under white actinic light illumination conditions, indicating the phycobilisomes in the ΔcpcF mutant are not fully functional in excitation energy transfer. Under red actinic light illumination, wild type and both phycocyanin mutant strains exhibited similar light saturation characteristics. This indicates that all three strains contain functional allophycocyanin cores associated with their phycobilisomes. Analysis of the phycobilisome content of these strains indicated that, as expected, wild type exhibited normal phycobilisome assembly and the CK mutant assembled only the allophycocyanin core. However, the ΔcpcF mutant assembled phycobilisomes which, while much larger than the allophycocyanin core observed in the CK mutant, were significantly smaller than phycobilisomes observed in wild type. Interestingly, the phycobilisomes from the ΔcpcF mutant contained holo-CpcB and apo-CpcA. Additionally, we found that the large form of FNR (FNRL) accumulated to normal levels in wild type and the ΔcpcF mutant. In the CK mutant, however, significantly less FNRL accumulated. FNRL has been reported to associate with the phycocyanin rods in phycobilisomes via its N-terminal domain, which shares sequence homology with a phycocyanin linker polypeptide. We suggest that the assembly of apo-CpcA in the phycobilisomes of ΔcpcF can stabilize FNRL and modulate its function. These phycobilisomes, however, inefficiently transfer excitation energy to Photosystem II.
    Full-text · Article · Aug 2014 · PLoS ONE
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