Phycobilisomes Supply Excitations to Both Photosystems in a Megacomplex in Cyanobacteria

Liu, Haijun; Zhang, Hao; Niedzwiedzki, Dariusz M.; Prado, Mindy; He, Guannan; Gross, Michael L.; Blankenship, Robert E.

doi:10.1126/science.1242321

Cited by 306 publications

(261 citation statements)

References 55 publications

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“…This protrusion fits well with the hole on the cytoplasmic side of PSII and forms a tight interaction between PBS and PSII, which is likely required for an efficient energy transfer from PBS to PSII. The tight association between PBS and PSII agrees with a recent report that demonstrated the formation of the PBS-PSII-PSI megacomplex in vivo via protein cross-linking and mass spectrometry analyses [27]. It should also be noted that EM imaging showed peripheral rods attached to the bottom of the cores of PBSs isolated from the ∆apcF mutant ( Figure 4C).…”

Section: Discussionsupporting

confidence: 77%

“…Early reports showed that state transitions occurred in a time range of subseconds to seconds [25] and that this process is controlled by the redox state of electron carriers between PSI and PSII [26]. Liu et al [27] recently reported the isolation of a PBS-PSII-PSI mega-complex, and suggested that PBS does not need to change its spatial position during state transitions. In this study, we investigated the three-dimensional (3D) structures of the intact PBS and PBS-PSII complexes from Anabaena 7120 using single-particle electron microscopy (EM) analysis.…”

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: Discussionsupporting

confidence: 77%

Section: Introductionmentioning

confidence: 99%

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

Chang¹,

et al. 2015

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“…Figure 6 shows that, using a different method to immobilize membranes, PSII complexes can be imaged at low resolution, and they likely sit alongside PSI complexes. The mixed PSI/PSII T. elongatus membranes identified in Figures 5A and 5B, and those from Synechocystis ( Figure 7) and Synechococcus 7002 (Supplemental Figure 10) could be the origin of the megacomplex consisting of PSI, PSII, and a phycobilisome (Liu et al, 2013); the PSI-PSII contact zones shown in this work could provide sites for docking phycobilisomes, which are then proposed to donate excitation energy to either one of these photosystems (Liu et al, 2013). The regions with PSI and PSII in close proximity in Figures 5A and 5B also create the conditions for "spillover" of excitations from PSII to PSI (Biggins and Bruce, 1989).…”

Section: Discussionmentioning

confidence: 99%

Lateral Segregation of Photosystem I in Cyanobacterial Thylakoids

et al. 2017

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Photosystem I (PSI) is the dominant photosystem in cyanobacteria and it plays a pivotal role in cyanobacterial metabolism. Despite its biological importance, the native organization of PSI in cyanobacterial thylakoid membranes is poorly understood. Here, we use atomic force microscopy (AFM) to show that ordered, extensive macromolecular arrays of PSI complexes are present in thylakoids from Thermosynechococcus elongatus, Synechococcus sp PCC 7002, and Synechocystis sp PCC 6803. Hyperspectral confocal fluorescence microscopy and three-dimensional structured illumination microscopy of Synechocystis sp PCC 6803 cells visualize PSI domains within the context of the complete thylakoid system. Crystallographic and AFM data were used to build a structural model of a membrane landscape comprising 96 PSI trimers and 27,648 chlorophyll a molecules. Rather than facilitating intertrimer energy transfer, the close associations between PSI primarily maximize packing efficiency; short-range interactions with Complex I and cytochrome b 6 f are excluded from these regions of the membrane, so PSI turnover is sustained by long-distance diffusion of the electron donors at the membrane surface. Elsewhere, PSI-photosystem II contact zones provide sites for docking phycobilisomes and the formation of megacomplexes. PSI-enriched domains in cyanobacteria might foreshadow the partitioning of PSI into stromal lamellae in plants, similarly sustained by long-distance diffusion of electron carriers.

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“…Orange carotenoid protein (OCP) is a specific 35 kDa watersoluble protein that plays an essential role in non-photochemical quenching (NPQ) of the cyanobacterial light-harvesting antennae, phycobilisomes (1)(2)(3)(4). OCP acts as a blue-green light intensity sensor (5).…”

Section: Introductionmentioning

confidence: 99%

Fluorescent Labeling Preserving OCP Photoactivity Reveals Its Reorganization during the Photocycle

Maksimov

Sluchanko

Mironov

et al. 2017

Biophysical Journal

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Orange carotenoid protein (OCP), responsible for the photoprotection of the cyanobacterial photosynthetic apparatus under excessive light conditions, undergoes significant rearrangements upon photoconversion and transits from the stable orange to the signaling red state. This is thought to involve a 12-Å translocation of the carotenoid cofactor and separation of the N-and C-terminal protein domains. Despite clear recent progress, the detailed mechanism of the OCP photoconversion and associated photoprotection remains elusive. Here, we labeled the OCP of Synechocystis with tetramethylrhodamine-maleimide (TMR) and obtained a photoactive OCP-TMR complex, the fluorescence of which was highly sensitive to the protein state, showing unprecedented contrast between the orange and red states and reflecting changes in protein conformation and the distances from TMR to the carotenoid throughout the photocycle. The OCP-TMR complex was sensitive to the light intensity, temperature, and viscosity of the solvent. Based on the observed Fö rster resonance energy transfer, we determined that upon photoconversion, the distance between TMR (donor) bound to a cysteine in the C-terminal domain and the carotenoid (acceptor) increased by 18 Å , with simultaneous translocation of the carotenoid into the N-terminal domain. Time-resolved fluorescence anisotropy revealed a significant decrease of the OCP rotation rate in the red state, indicating that the light-triggered conversion of the protein is accompanied by an increase of its hydrodynamic radius. Thus, our results support the idea of significant structural rearrangements of OCP, providing, to our knowledge, new insights into the structural rearrangements of OCP throughout the photocycle and a completely novel approach to the study of its photocycle and non-photochemical quenching. We suggest that this approach can be generally applied to other photoactive proteins.

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Phycobilisomes Supply Excitations to Both Photosystems in a Megacomplex in Cyanobacteria

Cited by 306 publications

References 55 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

Lateral Segregation of Photosystem I in Cyanobacterial Thylakoids

Fluorescent Labeling Preserving OCP Photoactivity Reveals Its Reorganization during the Photocycle

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