The Stabilization Effect of Glutaraldehyde on the Spirulina platensis Phycobilisomes

The spectral properties of the glutaraldehyde-treated phycobilisomes were studied. The results showed that glutaraldehyde was effective in preventing phycobilisomes from dilution- induced dissociation and preserving the intra-phycobilisomes energy transfer.

Energy Transfer from Phycobilisomes to Photosystems of Nostoc flagelliforme Born. et Flah. During the Rewetting Course and Its Physiological Significance

: During the non-frost season, the condensation of dew makes Nostoc flagelliforme Born. et Flah., a highly drought-tolerant terrestrial cyanobacterium, frequently undergo rehydration-dehydration. Rehydration begins in the dark at night. After rewetting in the dark, photochemical activity and the structure of photosystem (PS) II were not recovered at all; the structure of PSI, energy transfer in phycobilisomes, and energy transfer from phycobilisomes to PSI were recovered within 5 min, as in the light. The recovery of energy transfer from phycobilisomes to PSII was light dependent and energy transfer from phycobilisomes to PSII was only partially recovered in the dark. These results suggest that the two-trigger control (water and light) of photo synthetic recovery may make N. flagelliforme avoid unnecessary energy consumption and, at the same time, the partial recovery of energy transfer from phycobilisomes to PSII in the dark could help N. flagelliforme accumulate more photosynthetic products during the transient period of rehydration-dehydration.

Computer simulation on kinetics of primary process in photosynthesis of algae (Ⅳ)——Excitation energy transfer in phycobilisomes from blue-green algae

A more exact model of phycobilisomes has been designed with the rods composed of the hexamer disks and an abstract allophycocyanin (APC) core. Based on this model, the excitation energy transfer was simulated using the computer simulation technique. The simulation shows that the excitation energy is transferred from the outlayer disk to the core in a partly reversible way in phycobilisomes, and that the transfer rate from the last disk to the core is less than those between disks. The energy transfer between the two trimers in a hexamer is dominantly through the α84-chromophores (m), while that between the disks is through the β84-chromophores (f) that are also responsible for the transfer of energy into the core.

Diverse Chromatic Acclimation Processes Regulating Phycoerythrocyanin and Rod-Shaped Phycobilisome in Cyanobacteria

In this article,we proposed that CpcC1 and CpcC2 connect distal and middle phycocyanin discs of phycobilisomes,respectively,in Leptolyngbya sp.PCC 6406.However,Ughy and Ajlani (2004) have concluded that CpcC2 and CpcC1 connect distal and middle discs,respectively,based on the mutagenesis results in Synechocystis sp.PCC 6803.Therefore,we replaced the original Figure 2 with a new one containing corrected Figure 2G and corrected one sentence on page 718,"In the hemi-discoidal PBS of Synechocystis sp.PCC6803,CpcC1,CpcC2,and CpcG connect the distal,middle,and basal discs of the PC rods,respectively (Ughy and Ajlani,2004;Arteni et al.,2009)",to "In the hemi-discoidal PBS of Synechocystis sp.PCC6803,CpcC2,CpcC1,and CpcG connect the distal,middle,and basal discs of the PC rods,respectively (Ughy and Ajlani,2004;Arteni et al.,2009) This correction does not affect the conclusions of this work.

A new model of phycobilisome in Spirulina platensis

Phycobilisomes (PBS) were isolated from blue-green alga Spirulina platensis. Scanning tunneling microscope was used to investigate the three-dimensional structure of PBS deposited on freshly cleaved highly oriented py-rolytic graphite (HOPG) in ambient condition at room temperature. The results showed that the rods of PBS radiated from the core to different directions in the space other than arrayed in one plane, which was different from the typical hemi-discoidal model structure. The diameter of PBS was up to 70 nm, and the rod was approximately 50 nm in length. Similar results were observed in Langmuir-Blodgett (LB) film of PBS. The dissociated PBS could reaggregate into rod-like structures and easily form two-dimensional membrane while being absorbed on HOPG, however, no intact PBS was observed. The filling-space model structure of PBS in Spirulina platensis with STM from three-dimensional real space at nanometer scale was found, which showed that this new structural model of PBS surely exists in blue-green algae and red algae. The function of this structural model of PBS was also discussed.

ISOLATION AND PROTEIN COMPOSITION OF PHYCOBILISOMES FROM RED ALGA Bangia fuscopurpurea

The phycobilisomes, composed of chromophoric biliproteins and colorless accessory linker proteins, serve as light-harvesting antennae in blue-green and red algae. Studies have been thoroughly made in many species of blue-green algae and some species of red algae. However, the composition of the accessory undenatured proteins of phycobilisomes has

Diverse Chromatic Acclimation Processes Regulating Phycoerythrocyanin and Rod-Shaped Phycobilisome in Cyanobacteria

Cyanobacteria have evolved various photoacclimation processes to perform oxygenic photosynthesis under different light environments.Chromatic acclimation(CA)is a widely recognized and ecologically important type of photoacclimation,whereby cyanobacteria alter the absorbing light colors of a supermolecular antenna complex called the phycobilisome.To date,several CA variants that regulate the green-absorbing phycoerythrin(PE)and/or the red-absorbing phycocyanin(PC)within the hemi-discoidal form of phycobilisome have been characterized.In this study,we identified a unique CA regulatory gene cluster encoding yellow-green-absorbing phycoerythrocyanin(PEC)and a rod-membrane linker protein(CpcL)for the rod-shaped form of phycobilisome.Using the cyanobacterium Leptolyngbya sp.PCC 6406,we revealed novel CA variants regulating PEC(CA7)and the rod-shaped phycobilisome(CAO),which maximize yellowgreen light-harvesting capacity and balance the excitation of photosystems,respective!y.Analysis of the distribution of CA gene clusters in 445 cyanobacteria genomes revealed eight CA variants responding to green and red light,which are classified based on the presence of PEC,PE,cpcL,and CA photosensor genes.Phylogenetic analysis further suggested that the emergence of CA7 was a single event and preceded that of heterocystous strains,whereas the acquisition of CAO occurred multiple times.Taken together,these results offer novel insights into the diversity and evolution of the complex cyanobacterial photoacclimation mechanisms.

Synthesis and energy transfer of model conjugate of phycobilisome rods

The conjugate of R-phycoerythrin (R-PE) and C-phycocyanin (C-PC) was synthesized through a heterobifunctional coupling reagent, N-succinimidyl 3-(2-pyridyldithio) propionate. The molar ratio of R-PE to C-PC was determined by absorption spectra, and the result was 2:1. The energy transfer phenomena were observed from steady-state fluorescence spectra. The calculated result showed that the energy transfer efficiency from R-PE to C-PC was 88%. The energy transfer kinetics was determined by picosecond time-resolved fluorescence spectra. The time constant of energy transfer from R-PE to C-PC was 80 ps, which was much longer than that in the rood of native phycobilisomes.

Synthesis and characterization of model conjugate of phycobilisomes

PHYCOBILISOMES are light-harvesting protein-pigment complexes located on the cytoplasmic

Fluorescence recovery after photobleaching:analyses of cyanobacterial phycobilisomes reveal intrinsic fluorescence recovery

Fluorescence recovery after photobleaching(FRAP)has been used to study the dynamics of the cyanobacterial photosynthesis apparatus since 1997.Fluorescence recovery of cyanobacteria during FRAP was conventionally interpreted as a result of phycobilisome(PBS)diffusion on the surface of the thylakoid membrane.The mechanism of state transition in cyanobacteria has been widely attributed to PBS diffusion.However,in red algae,another PBS-containing group,the intrinsic photoprocess was found to contribute greatly to the fluorescence recovery of PBS,which raises questions concerning the role of FRAP in red algal PBS.Therefore,it is important to re-evaluate the nature of PBS fluorescence recovery in cyanobacteria.In the present study,four cyanobacterial strains with different phenotypes and PBS compositions were used to investigate their FRAP characteristics.Fluorescence recovery of PBS was observed in wholly photobleached cells in all four cyanobacterial strains,in which the contribution of PBS diffusion to the fluorescence recovery was not possible.Moreover,the fluorescence recovered in isolated PBSs and PBS-thylakoid membranes after photobleaching further demonstrated the intrinsic photoprocess nature of fluorescence recovery.These findings suggest that the intrinsic photoprocess contributed to the fluorescence recovery following photobleaching when measured by the FRAP method.

Heterogenous Expression of Synechocystis sp. PCC 6803 Deg Proteases and Their Possible Roles on Phycobiliprotein Degradation in vitro

The Synechocystis sp. PCC 6803 genome harbours a Deg gene family consisting of three members, htrA （degP, slr1204）, hhoA （degQ, sll1679） and hhoB （degS, sll1427）. This work provided biochemical characterization of HhoA, HtrA and HhoB from Synechocystis sp. PCC 6803. Firstly mature HhoA, HhoB and HtrA from Synechocystis sp. PCC 6803 were cloned and expressed as soluble recombinant his-tagged fusion protein in Escherichia coli. Then the proteolytic activity of HhoA, HhoB and HtrA was tested using casein, bovine serum albumin, five recombinant chromoproteins and cyanobacterial phycocyanin as substrates in vitro. The experimental results showed that HhoA and HtrA had proteolytic activity on casein, five recombinant chromoproteins and cyanobacterial phycocyanin. No proteolytic activity of HhoB was found using all substrates in vitro, indicating functional difference among Deg proteases from Synechocystis sp. PCC 6803. Therefore, the results indicated the biochemical properties of HhoA and HtrA on hydrolysis of proteins and phycobiliproteins in vitro, which implicated that they were proteases possibly involved in phycobiliprotein degradation in vivo.

The Energy Transfer Processes between Carotenoid and Chlorophyll Regulated by Electron Exchange Mechanism

The energy transfer efficiency between carotenoids and chlorophyll depend on temperature and viscosity of the media. A 3.5 ps process was detected by the pico-second time-resolved spectra and the process was proved to be regulated by electron exchange mechanism.

Emerging Perspectives on the Mechanisms, Regulation, and Distribution of Light Color Acclimation in Cyanobacteria

Chromatic acclimation （CA） provides many cyanobacteria with the ability to tailor the properties of their light-harvesting antennae to the spectral distribution of ambient light. CA was originally discovered as a result of its dramatic cellular phenotype in red and green light. However, discoveries over the past decade have revealed that many pairs of light colors, ranging from blue to infrared, can trigger CA responses. The capacity to undergo CA is widespread geographically, occurs in most habitats around the world, and is found within all major cyanobacterial groups. In addition, many other cellular activities have been found to be under CA control, resulting in distinct physiological and morphological states for cells under different light-color conditions. Several types of CA appear to be the result of convergent evolution, where different strategies are used to achieve the final goal of optimizing light-harvesting antenna composition to maximize photon capture. The regulation of CA has been found to occur primarily at the level of RNA abundance. The CA-regulatory pathways uncovered thus far are two-component systems that use phytochrome-class photoreceptors with sensor-kinase domains to control response regulators that function as transcription factors. However, there is also at least one CA- regulatory pathway that operates at the post-transcriptional level. It is becoming increasingly clear that large numbers of cyanobacterial species have the capacity to acclimate to a wide variety of light colors through the use of a range of different CA processes.

Progress in the study on structure and function of the antenna of algae

IN the evolution series, algae possess a position between green plants and photosynthetic bacteria. The photosynthetic apparatus of algae and plants are very similar because both of them contain the two phótosynthetic reaction centers of PSⅡ and PSⅠ and have the same photosynthetic function. Therefore, study of the photosynthesis of algae has a common significance. On the other hand, the light-harvesting antennae of plants are chlorophyll a/b-protein complex in thylakoids while those of algae are the phycobilisomes. A phycobilisome is a large super-

Energy transfer kinetics of phycoerythrocyanins (PECs) from the cyanobacterium Anabaena variabilis(Ⅰ)

The excitation energy transfer processes in nionomeric phycoerythrocyanins ( PEC)have been studied in detail using steady-state and time-resolved fluorescence spectra techniques as well as the deconvolution fech nique of spectra.The results indicate that the energy transfer processes should take place between α84 PVB md β8 or β155-PCB chromophores,the time constants of energy transfer are 34.7 and 130 ps individually;the component with lifetime of 1.57 ns originates from the fluorescence lifetime of the terminal emitter of β84 and /or β155 PCB chre-mophores; and the component with lifetime of 515 ps might be assigned to the energy transfer between two PCB chro mophores of β subunit.

Energy transfer kinetics of phycoerythrocyanin trimer from cyanobacterium Anabaena variabilis (II)

The excitation energy transfer processes in trimeric PEC have been studied by using steady state and time resolved fluorescence spectra techniques in detail. The results indicate that the energy transfer processes should take place between α 84 PVB and β 84 or β 155 PCB chromophores with the time constants 34.7 ps and 175-200 ps individually; in contrast with monomeric PEC, from time resolved fluorescence anisotropic spectrum technique, the decay constant of 45 ps which was assigned to the energy transfer time among three β 84 PCB chromophores was observed and the energy levels of β 84 and/or β 155 PCB chromophores were confirmed to turn over in trimeric PEC.

Molecular mechanisms for interaction of glycine betaine with supra-molecular phycobiliprotein complexes

Glycine betaine(GB) is a biologically important small molecule protecting cells,proteins and enzymes in vivo and in vitro under environmental stresses.Recently,it was found that GB could also relax the structure and inactivate the function of phycobiliproteins and phycobilisome(PBS),a kind of supramolecular complexes,in cyanobacterial cells.The molecular mechanisms for the opposite phenomena are quite ambiguous.Taking PBS and a trimeric or monomeric C-phycocyanin(C-PC) as models,the molecular mechanism for the interaction of GB with supra-molecular complexes or nuclear proteins was investigated.The energetic decoupling of PBS components induced by GB suggests that the PBS core-membrane linking polypeptide was the most sensitive site while the rod-core linker was the next.Biochemistry analysis proves that PBS structure was loosened but not dissociated into the components.On the basis of the results and structure knowledge,it was proposed that GB screened the electrostatic attraction of the opposite charges on a linker and a protein leading to a much looser structure.It was observed that GB induced a spectral blue shift for trimeric C-PC but a red shift for a monomeric C-PC(a nuclear protein),which were ascribed to GB's screening of the electrostatic attraction of a linker to a protein and strengthening of the hydrophobic interaction between C-PC monomers.The trimers and monomers' forming of the same products under high concentration of GB was ascribed to a compromise of the opposite interaction forces.

Excitation energy transfer mechanism in C-phycocyanin hexamer

Excitation energy transfer processes and mechanism in C-PC hexamer have been studied in detail by picosecond time-resolved fluorescencs isotropic and anisotropic spectroscopy methods. The experimental results show that there are two types of principal channels, with large probability or amplitude, for linking two trimers viam?m and s?s energy transfer pathways, the energy-transfer time constants of them are about 20 and 10 ps, respectively. Indeed, there exists the evidence for energy-transfer channels of s?f steps in the same monomer and threef?f steps in the same trimer of the C-PC hexamer unit, with small probability or amplitude, and the time constants of them might be ca. 50 and 45 ps separately. Also, the present results show that the hexamer possesses an optimal structure for energy-transfer and for the first time confirm that the dominant energy-transfer processes except those between 1 m?2f, 2m?3f and 3m?1f and so on, in isolated C-PC hexamer, could be described by F?rster dipole-dipole resonance mechanism.

RESONANCE RAMAN SCATTERING OF PHYCO BILISOMES AND PHYCO BILIPROTEINS FROM CYANOBACTERIUM Westiellopsis prolifica

Phycobilisome is a kind of supramolecular light-harvesting pigment protein complex, which can facilitate the absorption and transfer of light energy to the photosynthetic reaction centers in cyanobacteria and red algae. The phycobilisomes (hereafter called PBS)