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At least 19 recordsLinked to original sources
PubMed2001

Diffusion of phycobilisomes on the thylakoid membranes of the cyanobacterium Synechococcus 7942. Effects of phycobilisome size, temperature, and membrane lipid composition.

A variant of fluorescence recovery after photobleaching allows us to observe the diffusion of photosynthetic complexes in cyanobacterial thylakoid membranes in vivo. The unicellular cyanobacterium Synechococcus sp. PCC7942 is a wonderful model organism for fluorescence recovery after photobleaching, because it has a favorable membrane geometry and is well characterized and transformable. In Synechococcus 7942 (as in other cyanobacteria) we find that photosystem II is immobile, but phycobilisomes diffuse rapidly on the membrane surface. The diffusion coefficient is 3 x 10(-10) cm(2) s(-1) at 30 degrees C. This shows that the association of phycobilisomes with reaction centers is dynamic; there are no stable phycobilisome-reaction center complexes in vivo. We report the effects of mutations that change the phycobilisome size and membrane lipid composition. 1) In a mutant with no phycobilisome rods, the phycobilisomes remain mobile with a slightly faster diffusion coefficient. This confirms that the diffusion we observe is of intact phycobilisomes rather than detached rod elements. The faster diffusion coefficient in the mutant indicates that the rate of diffusion is partly determined by the phycobilisome size. 2) The temperature dependence of the phycobilisome diffusion coefficient indicates that the phycobilisomes have no integral membrane domain. It is likely that association with the membrane is mediated by multiple weak interactions with lipid head groups. 3) Changing the lipid composition of the thylakoid membrane has a dramatic effect on phycobilisome mobility. The results cannot be explained in terms of changes in the fluidity of the membrane; they suggest that lipids play a role in controlling phycobilisome-reaction center interaction.

Biological Transport↗
PubMed1982

Rod substructure in cyanobacterial phycobilisomes: phycoerythrin assembly in synechocystis 6701 phycobilisomes.

Synechocystis 6701 phycobilisomes consist of a core of three cylindrical elements in an equilateral array from which extend in a fanlike manner six rods, each made up of three to four stacked disks. Previous studies (see Gingrich, J. C., L. K. Blaha, and A. N. Glazer, 1982. J. Cell Biol. 92:261-268) have shown that the rods consist of four disk-shaped complexes of biliproteins with "linker" polypeptides of 27-, 33.5-, 31.5-, and 30.5-kdaltons, listed in order starting with the disk proximal to the core: phycocyanin (alpha beta)6-27 kdalton, phycocyanin (alpha beta)6-33.5 kdalton, phycoerythrin (alpha beta)6-31.5 kdalton, phycoerythrin (alpha beta)6-30.5 kdalton, where alpha beta is the monomer of the biliprotein. Phycoerythrin complexes of the 31.5- and 30.5-kdalton polypeptides were isolated in low salt. In 0.05 M K-phosphate-1 mM EDTA at pH 7.0, these complexes had the average composition (alpha beta)2-31.5 and (alpha beta)-30.5 kdalton polypeptide, respectively. Peptide mapping of purified 31.5- and 30.5-kdalton polypeptides showed that they differed significantly in primary structure. In 0.65 M Na-K-phosphate at pH 8, these phycoerythrin complexes formed rods of stacked disks of composition (alpha beta)6-31.5 or (alpha beta)6-30.5 kdaltons. For the (alpha beta)-30.5 kdalton complex, the yield of rod assemblies was variable and the self-association of free phycoerythrin to smaller aggregates was an important competing reaction. Complementation experiments were performed with incomplete phycobilisomes from Synechocystis 6701 mutant strain CM25. These phycobilisomes are totally lacking in phycoerythrin and the 31.5- and 30.5-kdalton polypeptides, but have no other apparent structural defects. In high phosphate at pH 8, the phycoerythrin-31.5-kdalton complex formed disk assemblies at the end of the rod substructures of CM25 phycobilisomes whereas no interaction with the phycoerythrin-30.5 kdalton complex was detected. In mixtures of both the phycoerythrin-31.5 and -30.5 kdalton complexes with CM25 phycobilisomes, both complexes were incorporated at the distal ends of the rod substructures. The efficiency of energy transfer from the added phycoerythrin in complemented phycobilisomes was approximately 96%. The results show that the ordered assembly of phycoerythrin complexes seen in phycobilisomes is reproduced in the in vitro assembly process.

Cyanobacteria↗
PubMed1978

Cyanobacterial phycobilisomes. Characterization of the phycobilisomes of Synechococcus sp. 6301.

A procedure is described for the preparation of stable phycobilisomes from the unicellular cyanobacterium Synechococcus sp. 6301 (also known as Anacystis nidulans). Excitation of the phycocyanin in these particles at 580 nm leads to maximum fluorescence emission, from allophycocyanin and allophycocyanin B, at 673 nm. Electron microscopy shows that the phycobilisomes are clusters of rods. The rods are made up of stacks of discs which exhibit the dimensions of short stacks made up primarily of phycocyanin (Eiserling, F. A., and Glazer, A. N. (1974) J. Ultrastruct. Res. 47, 16-25). Loss of the clusters, by dissociation into rods under suitable conditions, is associated with loss of energy transfer as shown by a shift in fluorescence emission maximum to 652 nm. Synechococcus sp. 6301 phycobilisomes were shown to contain five nonpigmented polypeptides in addition to the colored subunits (which carry the covalently bound tetrapyrrole prosthetic groups) of the phycobiliproteins. Evidence is presented to demonstrate that these colorless polypeptides are genuine components of the phycobilisome. The nonpigmented polypeptides represent approximately 12% of the protein of the phycobilisomes; phycocyanin, approximately 75%, and allophycocyanin, approximately 12%. Spectroscopic studies that phycocyanin is in the hexamer form, (alpha beta)6, in intact phycobilisomes, and that the circular dichroism and absorbance of this aggregate are little affected by incorporation into the phycobilisome structure.

Antigen-Antibody Reactions↗
PubMed1986

Functional linkage between phycobilisome and reaction center in two phycobilisome oxygen-evolving photosystem II preparations isolated from the thermophilic cyanobacterium Synechococcus sp.

Photosystem II oxygen-evolving preparations with attached phycobilisomes were isolated from the thermophilic cyanobacterium Synechococcus sp. with beta-octylglucoside or digitonin. Fluorescence emission spectra of the two preparations determined at 77 K largely lacked a far red band which originates from photosystem I. The spectrum of the digitonin preparation was otherwise similar to that of intact cells, whereas the beta-octylglucoside preparation showed a pronounced band at 687 nm, which is considered to be emitted from phycobilisomes. The relative yield of phycobilin fluorescence was similar between the digitonin preparations and the cells but was considerably larger in the beta-octylglucoside preparations at room temperature. The quantum yield of ferricyanide photoreduction determined with light which is absorbed mainly by phycobiliproteins was 0.85 for the digitonin preparation and 0.57 for the beta-octylglucoside preparation. The results indicate that excitation energy is transferred from phycobilisomes to photosystem II reaction centers in the digitonin preparation as efficiently as in intact cells, while a significant portion of light energy harvested by phycobilisomes is not utilized by the primary photochemistry in the beta-octylglucoside preparation. Digitonin and beta-octylglucoside preparations had 65 and 48 chlorophyll a molecules per photosystem II reaction center, respectively. The beta-octylglucoside preparation contained twice as much phycocyanin and allophycocyanin per photosystem II reaction center as the digitonin preparation, which has a phycobiliprotein-to-photosystem II reaction center ratio very similar to that of cells. It is concluded that whereas the beta-octylglucoside preparation contains a considerable amount of free phycobilisomes, all phycobilisomes present in the digitonin preparation are physically and functionally linked to photosystem II reaction center complexes.

Cell Fractionation↗
PubMed1982

A M(r) 95,000 polypeptide in Porphyridium cruentum phycobilisomes and thylakoids: Possible function in linkage of phycobilisomes to thylakoids and in energy transfer.

Two pigmented polypeptides with the same molecular weight (M(r) 95,000) were isolated from the photosynthetic apparatus of Porphyridium cruentum by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. A blue polypeptide from phycobilisomes had absorption and fluorescence emission spectra similar to those of allophycocyanin. A green-pigmented polypeptide from photosynthetic membranes (free of phycobilisomes) contained chlorophyll a. Several properties were common to the M(r) 95,000 polypeptides from both sources: (i) identical molecular weights, (ii) identical gel electrophoresis patterns after limited protease digestion, and (iii) immunological crossreactivity with an IgG fraction directed against the M(r) 95,000 polypeptide from phycobilisomes. On the basis of this evidence, a common polypeptide exists in phycobilisomes and thylakoids, and it probably anchors the phycobilisome to the thylakoid membrane. The fluorescence emission overlap of the blue and green polypeptides suggests that they are involved in the transfer of energy from phycobilisomes to thylakoids.

Journal Article↗
PubMed2003

Characterization of apcC, the nuclear gene for the phycobilisome core linker polypeptide L(c)(7.8) from the glaucocystophyte alga Cyanophora paradoxa. Import of the precursor into isolated cyanelles and integration of the mature protein into intact phycobilisomes.

Phycobilisomes are the complex and highly efficient light-harvesting antenna systems of cyanobacteria, glaucocystophyte algae and red algae. In the glaucocystophyte Cyanophora paradoxa, seven genes for (chromophoric) phycobilisome components are known thus far, which all reside on the cyanelle genome. Here, we report the sequence of apcC, specifying the precursor to the colorless polypeptide L(c)(7.8), the first core linker reported for a eukaryote. The precursor was efficiently imported in vitro into isolated cyanelles. Fractionation into thylakoid membranes and stroma and into intact phycobilisomes and soluble proteins, respectively, indicated a low but significant incorporation of the imported linker polypeptide into the phycobilisomes.

Algal Proteins↗
PubMed1981

A terminal energy acceptor of the phycobilisome: the 75,000-dalton polypeptide of Synechococcus 6301 phycobilisomes--a new biliprotein.

A rapid procedure is described for the isolation of "linker" polypeptides (Lundell, D. J., R. C. Williams, and A. N. Glazer. 1981. J. Biol. Chem. 256:3580-3592) of cyanobacterial phycobilisomes. The 75,000-dalton component of the core of Synechococcus 6301 phycobilisomes isolated by this procedure has been shown to carry a bilin similar in spectroscopic properties to phycocyanobilin. "Renatured" 75,000-dalton polypeptide has absorption maxima at 610 and 665 nm and a fluorescence emission maximum at 676 nm, similar to that of intact phycobilisomes. A complex of allophycocyanin and a 40,000-dalton bilin-carrying fragment of the 75,000-dalton polypeptide, obtained by limited tryptic digestion, is described. This complex, which lacks allophycocyanin B, shows a fluorescence emission maximum at 676 nm. The above data indicate that the 75,000-dalton polypeptide functions as a terminal energy acceptor in the phycobilisome.

Cyanobacteria↗
PubMed1978

Biliprotein assemble in the disc-shaped phycobilisomes of Rhodella violacea. On the molecular composition of energy-transfering complexes (tripartite units) forming the periphery of the phycobilisome.

Heterogeneous complexes with a molecular weight of about 790000 containing B-phycoerythrin (Bangiales phycoerythrin) and C-phycocyanin (Cyanophyceae phycocyanin) in a molar pigment ratio of 2:1 were isolated from purified, dissociated phycobilisomes. Electron microscopical investigations revealed structures of three discs aggregated face to face with an apparent distance of 1.5 nm between each disc. Two discs may represent phycoerythrin and one phycocyanin. The complexes are structurally identical with tripartite units of the phycobilisome periphery. Fluorescence data confirmed the integrity of isolated tripartite units. Excitation at 546 nm gives a fluorescence maximum at 644 nm, indicating intermolecular transfer of excitation energy from phycoerythrin to phycocyanin. Comparative subunit analyses and spectral data suggested that no allophycocyanin is present. Cross-linking experiments gave evidence for a polar arrangement of phycocyanin within the complex. This pigment itself is an aggregate of two smaller molecules each having a molecular weight of about 140000. Tripartite units contain all the phycoerythrin and phycocyanin of the phycobilisome. On this basis, a phycobilisome model is proposed which combines the aspects of biliprotein distribution, energy transfer and fine structure.

Macromolecular Substances↗
PubMed1981

Cyanobacterial phycobilisomes. Phycocyanin assembly in the rod substructures of anabaena variabilis phycobilisomes.

Phycocyanin complexes with "linker" polypeptides (Lundell, D. J., Williams, R. C., and Glazer, A. N. (1981) J. Biol. Chem. 256, 3580-3592) of 27 and 32.5 kilodaltons have been isolated from dissociated Anabaena variabilis phycobilisomes. In 0.05 M phosphate at pH 7.0, these "trimeric" complexes have the molar composition (alpha beta)3 . 27,000 and (alpha beta)3 . 32,500, where alpha and beta are the subunits of phycocyanin and 27,000 and 32,500 denote single copies of the linker polypeptides. The (alpha beta)3 . 27,000 and (alpha beta)3 . 32,500 complexes have lambda max at 638 and 629 nm and fluorescence emission maxima at 651 and 646 nm, respectively. In 0.6 M phosphate at pH 8.0, the (alpha beta)3 . 27,000 complex forms an (alpha beta)6 . 27,000 disc-shaped aggregate as seen in the electron microscope, whereas the (alpha beta)3 . 32,500 complex forms discs, (alpha beta)6 . 32,500, and stacked disc rods of varying lengths. The former material, containing the 27,000 polypeptide, when mixed with the (alpha beta)6 . 32,500 discs, limits their assembly into rods. The spectroscopic properties of the discs and rods assembled in vitro indicate that energy transfer in phycobilisome rod substructures proceeds from (alpha beta)6 . 32,500 discs to the (alpha beta)6 . 27,000 disc proximal to the core and thence to the core.

Circular Dichroism↗
PubMed1993

Core substructure in phycobilisomes of red algae. II. The central part of the tricylindrical core--APCM--a constituent of hemidiscoidal phycobilisomes of Rhodella violacea.

The central part of the tricylindrical core of phycobilisomes from Rhodella violacea was isolated by hydroxylapatite adsorption chromatography followed by density gradient centrifugation. In the electron microscope negatively stained APCM complexes showed a tricylindrical face view with an edge length of 20 to 24 nm and a thickness of 9 to 10 nm in profile view. These complexes had a M(r) of 900,000, and a sedimentation coefficient 24S. The fluorescence emission maximum at room temperature lay at 671 nm when excited at 590 nm. The presence of the high molecular linker polypeptide LCM exclusively in APCM and the existence of beta AP19.5, alpha AP18, and beta AP17 were demonstrated in SDS-polyacrylamide gel electrophoresis. The presence of "trimeric" allophycocyanin complexes in a separate band, with a sedimentation coefficient 6S, confirms the uncoupling of these complexes from the core; their maximal fluorescence at 680 nm in the second derivative hints at alpha AP-8. The results indicate a high conformity in the molecular organization of the core of hemidiscoidal phycobilisomes of red algae (Rhodella violacea) and cyanobacteria (Mastigocladus laminosus).

Bacterial Proteins↗
PubMed2003

Interaction of ferredoxin:NADP+ oxidoreductase with phycobilisomes and phycobilisome substructures of the cyanobacterium Synechococcus sp. strain PCC 7002.

The enzyme ferredoxin-NADP(+) oxidoreductase (FNR) from Synechococcus sp. PCC 7002 has an extended structure comprising three domains (FNR-3D) (Schluchter, W. M., and Bryant, D. A. (1992) Biochemistry 31, 3092-3102). Phycobilisome (PBS) preparations from wild-type cells contained from 1.0 to 1.6 molecules of FNR-3D per PBS, with an average value of 1.3 FNR per PBS. A maximum of two FNR-3D molecules could be specifically bound to wild-type PBS via the N-terminal, CpcD-like domain of the enzyme when exogenous recombinant FNR-3D (rFNR-3D) was added. To localize the enzyme within the PBS, the interaction of PBS and their substructures with rFNR-3D was further investigated. The binding affinity of rFNR-3D for phycocyanin (PC) hexamers, which contained a 22-kDa proteolytic fragment derived from CpcG, the L(RC)(27) linker polypeptide, was higher than its affinity for PC hexamers containing no linker protein. PBS from a cpcD3 mutant, which lacks the 9-kDa, PC-associated rod linker, incorporated up to six rFNR-3D molecules per PBS. PBS of a cpcC mutant, which has peripheral rods that contain single PC hexamers, also incorporated up to six rFNR-3D molecules per PBS. Direct competition binding experiments showed that PBS from the cpcD3 mutant bound more enzyme than PBS from the cpcC mutant. These observations support the hypothesis that the enzyme binds preferentially to the distal ends of the peripheral rods of the PBS. These data also show that the relative affinity order of the PC complexes for FNR-3D is as follows: (alpha(PC)beta(PC))(6)-L(R)(33) > (alpha(PC)beta(PC))(6)-L(RC)(27) > (alpha(PC)beta(PC))(6). The data suggest that, during the assembly of the PBS, FNR-3D could be displaced to the periphery according to its relative binding affinity for different PC subcomplexes. Thus, FNR-3D would not interfere with the light absorption and energy transfer properties of PC in the peripheral rods of the PBS. The implications of this localization of FNR within the PBS with respect to its function in cyanobacteria are discussed.

Amino Acid Sequence↗
PubMed1983

Light-Harvesting System of the Red Alga Gracilaria tikvahiae: II. Phycobilisome Characteristics of Pigment Mutants.

Phycobilisomes were isolated from wild type Gracilaria tikvahiae and a number of its genetically characterized Mendelian and non-Mendelian pigment mutants in which the principal lesions result in an increase or decrease in the accumulation of phycoerythrin. Both the size and phycoerythrin content of the phycobilisomes are proportional to the phycoerythrin content of the crude algal extracts. In most of the strains examined, the structure and function of the phycocyanin-allophycocyanin phycobilisome cores are the same as in wild type. The phycobilisome architecture is derived from wild type by the addition or removal of phycoerythrin. The same pattern is observed for the phycobilisome of mos(2) which contains a large excess of phycocyanin that is not bound to the phycobilisome. The single exception is a yellow, non-Mendelian mutant, NMY-1, which makes functional phycobilisomes composed of phycoerythrin and allophycocyanin with almost no phycocyanin. Characterization of the ;linker' polypeptides of the phycobilisome indicates that a 29 kilodalton protein is required for the stable incorporation of phycocyanin into the phycobilisome. Evidence is provided for the requirement of nuclear and cytoplasmic genes in phycobilisome synthesis and assembly. The symmetry properties of the phycobilisome are considered and a structural model for the reaction center II-phycobilisome organization is presented.

Journal Article↗
PubMed2004

[Effect of CHAPS on the stability of Spirulina platensis phycobilisomes].

The Spirulina platensis phycobilisomes were isolated by sucrose density gradients ultracentrifugation, and the fluorescence emission maximum of the phycobilisomes at room temperature was at 671 nm. The effects of ionic strength and the zwitterionic detergent CHAPS on the stability of the Spirulina platensis phycobilisomes were studied by room temperature fluorescence spectrum. The phycobilisomes were stable in 1.0 mol x L(-1) phosphate buffer solution, and their fluorescence emission maximum could remain unchanged for 7 days. The fluorescence emission maximum of phycobilisomes was blue-shifted to 648 nm when the concentration of the phosphate buffer solution was diluted to 0.1 mol x L(-1) with deionized water, which suggested that the phycobilisomes had been dissociated. The phycobilisomes were readily dissociated in phosphate buffer solutions of low concentrations (< 0.6 mol x L(-1)) and the speed of the dissociation increased with decreasing the concentration of the phosphate buffer solution. The fluorescence emission maximum of the phycobilisomes in 1.0 mol x L(-1) phosphate buffer solution was blue-shifted to 648 nm when 10 mmol x L(-1) CHAPS was added into the phycobilisomes solution, suggesting that CHAPS could dissociate phycobilisomes under high ionic strength conditions. The results might be useful for isolating intact substructures of phycobilisomes.

Cholic Acids↗
PubMed1982

Molecular architecture of a light-harvesting antenna. Isolation and characterization of phycobilisome subassembly particles.

Synechococcus 6301 mutant, strain AN112, produces phycobilisomes containing two major biliproteins, phycocyanin and allophycocyanin, and two major linker polypeptides of 27 and 75 kilodaltons (27K and 75K). These phycobilisomes have a molecular weight of approximately 2.5 X 10(6) and are the smallest of these particles known to date. Sucrose density gradient centrifugation of AN112 phycobilisomes partially dissociated in 50 mM N-[tris(hydroxymethyl)methyl]glycine, 5 mM CaCl2, 10% (w/v) glycerol, pH 7.8, separated three distinct fractions: (1) free trimeric biliproteins, (2) hexameric complexes of phycocyanin with 27K (11 S particles), and (3) phycobilisome subassemblies equivalent in mass to approximately 25% of the intact phycobilisome (18 S particles). The 18 S particles contained equimolar amounts of phycocyanin and allophycocyanin, which represented approximately 30 and 50%, respectively, of the content of these biliproteins in the AN112 phycobilisome. The 18 S particles also contained 75% and 100%, respectively, of 27K and 75K polypeptides; i.e. 75K was present in a 2-fold higher amount than in the intact phycobilisome. The absorption spectrum (lambda max 648 nm) of the 18 S particles was similar to that of allophycocyanin. Upon excitation at 580 nm, these particles exhibited a fluorescence emission spectrum consisting of 680 and 660 nm components, identical with that of intact phycobilisomes. The circular dichroism spectra of AN112 phycobilisomes and of the 18 S particles, in the region between 650 and 700 nm, were also very similar. Allophycocyanin B, which fluoresces at 680 nm, was found in fraction 1, and was totally absent from the 18 S particle. Thus, the long wavelength emission of the 18 S particle must have arisen from another terminal energy acceptor. The most probable candidate is the 75K polypeptide, which has been shown to carry a bilin chromophore and emit near 680 nm (Lundell, D. J., Yamanaka, G., and Glazer, A. N. (1980) J. Cell Biol. 91, 315-319). The 27K polypeptide, present in both fractions 2 and 3, was a component of different complexes in the two fractions. Fraction 2 displayed the physical and spectroscopic properties characteristic of the phycocyanin-linker complex, (alpha beta)6.27K. However, in the 18 S particle, 27K functioned in the assembly and attachment of phycocyanin trimers to a core domain. Based on the analysis of the components in fractions 1-3, a model is proposed which describes the structure of the AN112 phycobilisome, with emphasis on the roles of the linker polypeptides in the assembly of the core.

Circular Dichroism↗
PubMed1998

Cyanobacterial phycobilisomes

Cyanobacterial phycobilisomes harvest light and cause energy migration usually toward photosystem II reaction centers. Energy transfer from phycobilisomes directly to photosystem I may occur under certain light conditions. The phycobilisomes are highly organized complexes of various biliproteins and linker polypeptides. Phycobilisomes are composed of rods and a core. The biliproteins have their bilins (chromophores) arranged to produce rapid and directional energy migration through the phycobilisomes and to chlorophyll a in the thylakoid membrane. The modulation of the energy levels of the four chemically different bilins by a variety of influences produces more efficient light harvesting and energy migration. Acclimation of cyanobacterial phycobilisomes to growth light by complementary chromatic adaptation is a complex process that changes the ratio of phycocyanin to phycoerythrin in rods of certain phycobilisomes to improve light harvesting in changing habitats. The linkers govern the assembly of the biliproteins into phycobilisomes, and, even if colorless, in certain cases they have been shown to improve the energy migration process. The Lcm polypeptide has several functions, including the linker function of determining the organization of the phycobilisome cores. Details of how linkers perform their tasks are still topics of interest. The transfer of excitation energy from bilin to bilin is considered, particularly for monomers and trimers of C-phycocyanin, phycoerythrocyanin, and allophycocyanin. Phycobilisomes are one of the ways cyanobacteria thrive in varying and sometimes extreme habitats. Various biliprotein properties perhaps not related to photosynthesis are considered: the photoreversibility of phycoviolobilin, biophysical studies, and biliproteins in evolution. Copyright 1998 Academic Press.

Journal Article↗
PubMed1990

Phycobilisome Heterogeneity in the Red Alga Porphyra umbilicalis.

Phycobilisomes were isolated from Rhodophyceae brought from the field (Porphyra umbilicalis) or grown in culture under laboratory conditions (Antithamnion glanduliferum). In P. umbilicalis two kinds of well-coupled (ellipsoidal and hemidiscoidal) phycobilisomes were detected, in contrast to A. glanduliferum cultured algae in which only one kind of well-coupled, ellipsoidaltype phycobilisome appeared. The new phycobilisome-type particle detected in P. umbilicalis is characterized by an impoverishment in R-phycoerythrin and by sedimentation at lower density. The comparison between both phycobilisomes of P. umbilicalis allows determination of the presence of one colorless linker polypeptide (30 kilodaltons) associated with R-phycocyanin and allophycocyanin and two (40 and 38 kilodaltons) associated to R-phycoerythrin. The percentage of linker polypeptides associated with this pigment is low in the new phycobilisome-like particle detected. This suggests that part of the R-phycoerythrin is less strongly bound to the phycobilisome than the other pigments. This feature could probably explain the existence of two kinds of phycobilisomes as intermediary steps of phycobilisome organization in algae exposed to rapid changes in environmental factors. In contrast, algae growing in culture and adapted to specific conditions do not present intermediary organization steps. Polypeptide composition and identification are given for this phycobilisome-like particle.

Journal Article↗
PubMed1983

Phycobilisome composition and possible relationship to reaction centers.

The photosynthetic apparatus was studied in Anacystis nidulans wild type and in a spontaneous pigment mutant 85Y which had improved growth in far-red light (greater than 650 nm). Two phycobiliproteins, C-phycocyanin (lambda max 625) and allophycocyanin (lambda max 650), were present in a molar ratio of approximately 3:1 in the wild type and approximately 0.4:1 in the mutant. Phycobilisomes of wild type cells were larger (57 X 30 nm) than those of the mutant 85Y (28 X 15 nm). In the mutant they seemed to consist primarily of the allophycocyanin core. Fluorescence emission maxima of wild type and mutant 85Y phycobilisomes were at 680 nm (23 degrees C) and 685 nm (-196 degrees C). Excitation maxima of phycobilisomes were at 630 and 650 nm for the wild type and the mutant 85Y, respectively. The phycobilisomes of wild type cells whether grown in white or far-red light had the same size and pigment composition. A typical wild type cell in white light had a thylakoid area of 22.8 microns 2, but in far-red light the area was reduced to 13.5 microns 2, which was close to that of 85Y at 13.6 microns 2. Chlorophyll molecules per cell decreased in far-red light from 1.1 X 10(7) in wild type (white light) to 4.5 X 10(6) in mutant 85Y (far-red). The number of phycobilisomes per cell (approx 2 X 10(4)), calculated from the phycobiliprotein content and phycobilisome size, was about the same in wild type (white light) and mutant 85Y (far-red light), but the number of phycobilisomes per unit area of thylakoid was significantly greater in mutant 85Y than in wild type. The present results suggest that the phycobilisomes are linked with reaction centers and that the PSII complement (photo-system II and phycobilisome) was fully maintained in far-red light.

Binding Sites↗
PubMed1989

Spectroscopic studies of cyanobacterial phycobilisomes lacking core polypeptides.

Synechococcus sp. PCC 7002 (Agmenellum quadruplicatum PR6) genes encoding two highly conserved phycobilisome core polypeptides, a small linker polypeptide (LC8, apcC) and the allophycocyanin-B alpha-subunit (alpha APB, apcD), respectively, were interrupted by insertion of restriction fragments carrying the neomycin phosphotransferase gene of Tn5. The interrupted genes were used to transform Synechococcus sp. PCC 7002 to kanamycin resistance. The apcC- mutant assembled phycobilisomes lacking the LC8 polypeptide and the apcD- mutant assembled phycobilisomes lacking alpha APB. No other differences between the compositions of the mutant and wild-type phycobilisomes were detected. The apcC- strain grew about 25% more slowly than the wild-type, and its phycobilisomes dissociated more rapidly in 0.33 M Na/K-PO4 (pH 8.0) or in 0.75 M Na/K-PO4 at pH 8.0, at 40 degrees C, than did those of the wild-type. The phycobilisomes of this mutant were indistinguishable from those of the wild-type with respect to absorption and circular dichroism spectra, as well as time-resolved fluorescence emission. Steady-state emission spectra indicate a small decrease in long wavelength (680 nm) emission from the apcC- phycobilisomes and a complementary increase in shorter wavelength (665 nm) emission, relative to wild-type phycobilisomes. Strain apcD- phycobilisomes appear to be functionally indistinguishable from those of the wild-type, in spite of the absence of the two alpha APB subunits which bear terminal acceptor bilins. The only spectroscopic difference was seen in the steady-state fluorescence emission, for which the emission of the mutant was about 15% higher than that of the wild-type and was slightly blue-shifted. A phenotype has yet to be found for the apcD- mutation.

Cloning, Molecular↗