Allophycocyanin and phycocyanin crystal structures reveal facets of phycobilisome assembly

Marx, A.; Adir, Noam

doi:10.1016/j.bbabio.2012.11.006

Cited by 82 publications

(55 citation statements)

References 48 publications

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“…The shape of the density maps of the PC trimer was similar to that of the APC trimer with a small difference due to an additional loop in the PC [17] that can be distinguished in the density map (dashed circles for Rb-1 in Figure 3B). A typical rod cylinder in our reconstruction contains two PC hexamers associated with two Pfam00427 domains and two Pfam01383 domains.…”

Section: Core and Rod Assemblymentioning

confidence: 80%

“…The crystal structures of some isolated components of PBSs from different species have been determined. These include PEs [12,13], PCs [8,[14][15][16][17], APCs [10,[17][18][19], and linker proteins [10,20] (Supplementary information, Figure S1). The structural layouts of various PBSs have also been suggested in electron microscopic images [21,22].…”

Section: Introductionmentioning

confidence: 99%

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Structural organization of an intact phycobilisome and its association with photosystem II

Chang¹,

et al. 2015

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Phycobilisomes (PBSs) are light-harvesting antennae that transfer energy to photosynthetic reaction centers in cyanobacteria and red algae. PBSs are supermolecular complexes composed of phycobiliproteins (PBPs) that bear chromophores for energy absorption and linker proteins. Although the structures of some individual components have been determined using crystallography, the three-dimensional structure of an entire PBS complex, which is critical for understanding the energy transfer mechanism, remains unknown. Here, we report the structures of an intact PBS and a PBS in complex with photosystem II (PSII) from Anabaena sp. strain PCC 7120 using single-particle electron microscopy in combination with biochemical and molecular analyses. In the PBS structure, all PBP trimers and the conserved linker protein domains were unambiguously located, and the global distribution of all chromophores was determined. We provide evidence that ApcE and ApcF are critical for the formation of a protrusion at the bottom of PBS, which plays an important role in mediating PBS interaction with PSII. Our results provide insights into the molecular architecture of an intact PBS at different assembly levels and provide the basis for understanding how the light energy absorbed by PBS is transferred to PSII.

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Section: Core and Rod Assemblymentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Structural organization of an intact phycobilisome and its association with photosystem II

Chang¹,

et al. 2015

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“…The overall geometry of the PCB chromophores in all light-harvesting phycobiliproteins is ZZZasa (ref. 31 and references therein; nomenclature is provided in Fig. 4).…”

Section: Resultsmentioning

confidence: 99%

The terminal phycobilisome emitter, L _CM : A light-harvesting pigment with a phytochrome chromophore

Tang

Ding

Höppner

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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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, L CM . The chromophore domain of L CM 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 L CM 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 L CM . 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.cyanobacteria | phycobilisome | core-membrane linker | photosynthesis | crystal structure T he structural separation of light-harvesting and energy transduction processes allows photosynthetic organisms a flexible adaptation to the diverse light regimes present in terrestrial and aqueous habitats. In cyanobacteria and some phylogenetically related organisms that, together, provide a substantial proportion of global carbon fixation, light is harvested by hundreds of chromophores located in the peripheral antenna, namely, the phycobilisome (PBS). These excitations are then collected and transferred to the energy-transducing photosystems I (PSI) and PSII in the photosynthetic membrane via only two pigments, allophycocyanin B (AP-B) and the core-membrane linker (L CM ) (1-5). AP-B preferentially serves PSI (2); it is structurally similar to the bulk phycobiliproteins of the PBS (6). L CM (denoted as ApcE according to the gene by which it is encoded), preferentially serving PSII (5), is a more complex multidomain protein, with an N-terminal section that binds the phycocyanobilin (PCB) chromophore, and is homologous to phycobiliproteins but carries an additional loop that probably acts as a membrane anchor to PSII (4, 7-10). The Cterminal section consists of two to four repeats (depending on the PBS type) that are homologous to the N-terminal domain (Pfam PF00427) of structural PBS proteins, rod-linkers [Protein Data Bank (PDB) ID codes 3OSJ and 3OHW], and considered to organize the complex PBS core (9). They are probably also the loci for phosphorylation (11).Both AP-B and L CM contain the same PCB chromophores...

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“…PC rods stabilize OCP binding to PBs (Gwizdala et al, 2011), and species-specific changes of this connection could lead to different affinities for the OCP. It was recently shown that a more or less pronounced cavity exists between the APC trimers (Marx and Adir, 2013). This could influence PC rod binding or OCP attachment, but a systematic crystallographic study is needed for verification.…”

Section: Influence Of Pb Structure On the Ocp-pb Interactionmentioning

confidence: 99%

Specificity of the Cyanobacterial Orange Carotenoid Protein: Influences of Orange Carotenoid Protein and Phycobilisome Structures

et al. 2013

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Cyanobacteria have developed a photoprotective mechanism that decreases the energy arriving at the reaction centers by increasing thermal energy dissipation at the level of the phycobilisome (PB), the extramembranous light-harvesting antenna. This mechanism is triggered by the photoactive Orange Carotenoid Protein (OCP), which acts both as the photosensor and the energy quencher. The OCP binds the core of the PB. The structure of this core differs in diverse cyanobacterial strains. Here, using two isolated OCPs and four classes of PBs, we demonstrated that differences exist between OCPs related to PB binding, photoactivity, and carotenoid binding. Synechocystis PCC 6803 (hereafter Synechocystis) OCP, but not Arthrospira platensis PCC 7345 (hereafter Arthrospira) OCP, can attach echinenone in addition to hydroxyechinenone. Arthrospira OCP binds more strongly than Synechocystis OCP to all types of PBs. Synechocystis OCP can strongly bind only its own PB in 0.8 M potassium phosphate. However, if the Synechocystis OCP binds to the PB at very high phosphate concentrations (approximately 1.4 M), it is able to quench the fluorescence of any type of PB, even those isolated from strains that lack the OCP-mediated photoprotective mechanism. Thus, the determining step for the induction of photoprotection is the binding of the OCP to PBs. Our results also indicated that the structure of PBs, at least in vitro, significantly influences OCP binding and the stabilization of OCP-PB complexes. Finally, the fact that the OCP induced large fluorescence quenching even in the two-cylinder core of Synechococcus elongatus PBs strongly suggested that OCP binds to one of the basal allophycocyanin cylinders.

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Allophycocyanin and phycocyanin crystal structures reveal facets of phycobilisome assembly

Cited by 82 publications

References 48 publications

Structural organization of an intact phycobilisome and its association with photosystem II

Structural organization of an intact phycobilisome and its association with photosystem II

The terminal phycobilisome emitter, L _CM : A light-harvesting pigment with a phytochrome chromophore

Specificity of the Cyanobacterial Orange Carotenoid Protein: Influences of Orange Carotenoid Protein and Phycobilisome Structures

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Allophycocyanin and phycocyanin crystal structures reveal facets of phycobilisome assembly

Cited by 82 publications

References 48 publications

Structural organization of an intact phycobilisome and its association with photosystem II

Structural organization of an intact phycobilisome and its association with photosystem II

The terminal phycobilisome emitter, L CM : A light-harvesting pigment with a phytochrome chromophore

Specificity of the Cyanobacterial Orange Carotenoid Protein: Influences of Orange Carotenoid Protein and Phycobilisome Structures

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The terminal phycobilisome emitter, L _CM : A light-harvesting pigment with a phytochrome chromophore