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PubMed1977

Subunit structure and chromophore composition of rhodophytan phycoerythrins. Porphyridium cruentum B-phycoerythrin and b-phycoerythrin.

A comparative study is presented of the two phycoerythrins of the unicellular red alga Porphyridium cruentum. Native B-phycoerythrin has a molecular weight of 236,000 +/- 18,000 in 0.05 M potassium phosphate at pH 7.0, and an absorption spectrum with maxima at 545 nm (epsilonM = 2.41 X 10(6) M-1 cm-1) and 563 nm, and a shoulder at 498 nm. The protein carries 38 phycoerythrobilin and at least two phycourobilin prosthetic groups per 240,000 daltons. B-Phycoerythrin is composed of three dissimilar subunits, alpha and beta, each of 17,500 daltons, and gamma of 30,200 daltons. Physical, chemical, and spectroscopic data are consistent with a subunit structure (alphabeta)6gamma for B-phycoerythrin. The alpha and beta subunits carry solely phycoerythrobilin chromophores, while the gamma subunit carries both phycoerythrobilin and phycourobilin groups. The NH2-terminal sequences of the alpha and beta subunits determined by sequential Edman degradation, are shown below: alpha subunit: Met-Lys-Ser-Val-Ile-(Gly-Arg-Phe: beta subunit: Met-Leu-Asp-Ala-Phe-(Thr)-Arg-Val-Val-Val-Asn-Ala-Asx-Ala-( )-Ala-Ala-Tyr-Val. The NH2 terminus of the gamma subunit is blocked. b-Phycoerythrin is polydisperse and exhibits native molecular weights ranging from approximately 40,000 to approximately 260,000, depending on pH, ionic strength, and protein concentration. The absorption spectrum is characterized by maxima at 543 nm (epsilonM = 3.41 X 10(5) M-1 cm-1/35,000 daltons) and 563 nm. The protein carries six phycoerythrobilin groups per 35,000 daltons. b-Phycoerythrin is made up of two dissimilar types of subunits, alpha and beta, of 17,500 daltons each. The alpha and beta subunits derived from b-phycoerythrin appeared equivalent to the corresponding subunits of B-phycoerythrin on the basis of the following criteria: (a) identical chromatographic behavior on Bio-Rex 70 in acid urea; (b) similar amino acid compositions; (c) identical mobilities on polyacrylamide gels in the presence of sodium dodecyl sulfate; (d) similar phycoerythrobilin contents; (e) identical NH2-terminal sequences. These data support, but do not establish unambiguously, the conclusion that b-phycoerythrin may be a component of B-phycoerythrin. The absence or presence, and relative height, of an absorption peak (or shoulder) at 498 nm represents the major difference among the absorption spectra of different classes of phycoerythrins. The present study shows that this spectral feature is dependent on the presence and amount of phycourobilin chromophores in the native protein and is correlated with the presence of the gamma subunit.

Amino Acid Sequence↗
PubMed1979

The protein-chromophore bond in B phycoerythrin from Porphyridium cruentum. Radiosulfur labeling experiments.

Red algae of the species Porphyridium cruentum were grown in a minimum sulfate medium containing 35SO42-. 35S-labeled phycoerythrin was extracted. B Phycoerythrin, b phycoerythrin and R phycocyanin could be separated from other proteins by using a carrier-free electrophoresis on columns. The final ratio A545/A280 of B phycoerythrin thus obtained was greater than or equal to 5. 35S-labeled B phycoerythrin was digested proteolytically with trypsin and pepsin. The resulting 35S-containing bilipeptides were separated by isoelectric focusing. Zones of enhanced chromophore concentration always showed an enhanced radioactivity. Peptide fractions with a low molar ratio sulfur/chromophore (1.1-1.8) were purified to remove sucrose and the carrier ampholyte. A modified, optimized Edman degradation followed. A butylacetate-soluble, red Edman product was obtained that contained most of the chromophore and the bulk of the radioactivity. This product was purified by two-dimensional thin-layer chromatography. The main spot of the chromatogram was subjected to acidic hydrolysis. The major part of the radioactivity in the hydrolysate cochromatographed with cysteine. That proves cysteine to be the binding amino acid in all cases investigated.

Chemical Phenomena↗
PubMed1975

Characterization of R-phycocyanin. Chromophore content of R-phycocyanin and C-phycoerythrin.

R-phycocyanin was purified from two independent isolates of the unicellular red alga Porphyridium cruentum. At pH 7.0 the protein sediments as a single component with s 20,w of 5.98 S (at 2 mg/ml, gamma/2=0.02). Over a protein concentration range of 0.2 to 0.5 mg/ml (gamma/2=0.16), sedimentation equilibrium gave a molecular weight of 103,000 +/- 6,000 with no evidence of heterogeneity. In common with C-phydocyanins, R-phycocyanin consists of alpha and beta subunits of molecular weights of 18,200 and 20,500, determined by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. Isoelectric focusing in polyacrylamide gels resolves two bands, blue (at pI of 5.2), and purple (at pI of 5.3), believed to correspond to the alpha and beta subunits, respectively. The native protein gave a single precipitin band when tested against the homologous antiserum by the Ouchterlony double diffusion technique. No cross-reaction was observed with antiserum to the allophycocyanin from the same organism. The absorption spectrum of native trimeric R-physocyanin at pH 7.0 exhibited epsilomN (555 nm) of 1.51 x 10(5) M(-1) cm(-1), epsilonM (618 nm) 2.55 x 10(5) M(-1) cm(-1), and A 1% 1cm (618 nm) of 70.0. The circular dichroism spectrum of the native protein was characterized by the following molecular ellipticity maxima in deg cm2 per dmol x 10(-5): [theta]311 = -2.36, [theta]343 = -3.27, [theta]552 = 4.67, and [theta]627 = 6.27. All of these values were based on an alphabeta molecular weight of 36,3000, calculated from the amino acid composition. To permit quantitative estimation of the chromophore composition of R-phycocyanin, the absorption properties of Aphanocapsa sp. C-phycoerythrin were determined. At pH 7.0, native C-phycoerythrin exhibited epsilonM (562 nm) of 4.88 x 10(5) M(-1) cm(-1), and A 1% 1cm of 127, based on an alphabeta molecular weight of 38,400 calculated from the amino acid composition. The molar extinction coefficients for polypeptide-bound phycoerythrobilin were calculated from the spectrum of denatured C-phycoerythrin in 8 M urea at pH 1.9, on the assumption that each alphabeta unit contains six such chromophores. The analogous data for phycocyanobilin was available from an earlier study (Glazer, A.N., and Fang, S. (1973) J. Biol. Chem. 248, 659-662). The absorption curve of denatured R-phycocyanin was fitted with high precision by a theoretical curve calculated for a mixture of two phycocyanobilin and one phycoerythrobilin chromophore. The amino acid analyses of R-phycocyanin and of its separated alpha and beta subunits demonstrated a 1:1 stoichiometry for the subunits in the native protein. The absorption spectra of the isolated subunits were consistent with the conclusion that the alpha subunit carries a single phycocyanobilin chromophore, while one phycoerythrobilin and one phycocyanobilin chromophore are bound to the beta subunit...

Amino Acids↗
PubMed1975

Subunits of phycoerythrin from Fremyella diplosiphon: chemical and immunochemical characterization.

The alpha and beta subunits of the phycobiliprotein, phycoerythrin, isolated from the filamentous blue-green alga, Fremyella diplosiphon, have been separated by chromatography on Bio-Rex 70 ion exchange resin. Analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis shows no detectable cross-contamination of these subunit preparations. The molar extinction coefficients at 552 nm of the alpha and beta subunits in 8 M urea are 25,549 and 48,456, respectively. The amino acid compositions of the subunits are very similar. Molecular weights of the alpha and beta subunits are 19,500 and 21,700, respectively, based on the amino acid composition analyses. Antisera prepared against the alpha subunit reacts with the beta subunit, and vice versa. Tryptic peptide maps reveal that the subunits share share at least eight common tryptic peptides. These results indicate that the phycoerythrin subunits are chemically very similar.

Alkylation↗
PubMedDate not supplied

Chromophore content of C-phycoerythrin from various Cyanobacteria.

The molar extinction coefficient for phycoerythrobilin (l a) was calculated by two independent methods. It is different from that of the cleaved chromophore, phycobiliviolin (2). By unfolding with urea or tryptic digestion, the chromophore absorption of C-phycoerythrin (PE) was determined free of any protein influence. The chromophore content of PE from various Cyanobacteria was determined with these data to be either 5 or 6, depending on the organism. This corresponds to a chromophore distribution over phycoerythrin subunits alpha:beta of either 2:3 or 2:4. The phylogenetic significance of varying chromophore content is discussed.

Cyanobacteria↗
PubMed1976

[Spectral effects of denaturation of B- and C-phycoerythrins].

B-phycoerythrin (B-PhE) from red alga Porphyridium cruentum and C-phycoerythrin (C-PhE) from blue-green alga Nostoc punctiforma were isolated. Their absorption and fluorescence spectra were measured at room and liquid nitrogen temperature. The drastic change of fluorescence and absorption maxima under dissociation of the proteins into subunits was observed. Dissociation of the C-PhE into two subunits (molecular weight 16 000 and 12 000) was revealed by SDS-acrylamide gel electrophoresis in 0.01% SDS solution at pH 7.0. The absorption spectra of subunits of both B-PhE and C-PhE were similar. The fluorescence quenching by oxidants and destructive photooxidation were negligible and increased after denaturation.

Chemical Phenomena↗
PubMed1978

On the linkages between chromophore and protein in biliproteins, VII. Amino acid sequence in the chromophore regions of C-phycoerythrin from Pseudanabaena W 1173 and Phormidium persicinum.

Bilipeptides from all chromophore regions were prepared by trypsin digestion of C-phycoerythrin from Pseudanabaena W 1173 and Phormidium persicinum. Analytical separation and quantitative determination of bilipeptides was achieved by isoelectric focusing, preparative isolation by gel chromatography and ion-exchange chromatography. Amino acid analysis revealed cysteine as the only amino acid common to all chromopeptides. Amino acid sequences were determined by Edman degradation and the dansyl-Edman technique. Sequences are different in all 5 and 6 chromophore regions, respectively. Possible homologies are discussed. A thioether linkage between ring A of the chromophore and cysteine was found in the bilipeptides (as before in biliproteins). A second linkage (serine ester) was found in only one peptide (CM 4.I from Pseudanabaena W 1173). This peptide absorbs as cation at a longer wavelength (559 nm) than the other bilipeptides (542 - 550 nm).

Amino Acid Sequence↗
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↗
PubMed1977

Occurrence and nature of chromatic adaptation in cyanobacteria.

Forty-four axenic strains of cyanobacteria that synthesize phycoerythrin were screened to ascertain the effect of light quality on pigment synthesis. Cellular pigment compositions were determined after photoautotrophic growth with low light fluxes (7.0 X 10(2) ergs/cm2 per s) of green, red, and white light, and in the case of facultative heterotrophs, after dark growth at the expense of sugars. Twelve strains did not adapt chromatically: the cells contained fixed proportions of phycoerythrin, phycocyanin, and allophycocyanin under the growth conditions used. In the remaining strains, the cellular ratio of phycoerythrin to phycocyanin was much higher after growth in green than in red light. Quantitative data on the cellular pigment contents, supplemented by measurements of the differential rates of pigment synthesis on representative strains, show that chromatic adaptation may involve a light-induced modulation either of phycoerythrin synthesis alone (7 strains) or of both phycoerythrin and phycocyanin synthesis (25 strains). Facultative hetrotrophs able to adapt chromatically have a phycobiliprotein composition after dark growth which closely resembles that after growth in red light. Light quality does not affect the differential rate of chlorophyll synthesis. The physiological and taxonomic implications of these findings are discussed.

Adaptation, Physiological↗
PubMed1977

Isolation and characterization of disc-shaped phycobilisomes from the red alga Rhodella violacea.

Disc-shaped phycobilisomes were purified from Triton X100 treated cell homogenates of the unicellular marine red alga, Rhodella violacea. Their absorption spectrum had principal maxima at 544 and 568 nm (B-phycoerythrin), 624 nm (C-phycocyanin) and a distinct shoulder at 652 nm (allophycocyanin). Intermolecular energy transfer within the phycobilisomes was clearly demonstrated by fluorescence data. Excited at 546 nm intact phycobilisomes showed a main fluorescence emission maximum at 665 nm, a minor one at 577 nm and a shoulder at 730 nm. Dissociated phycobilisomes revealed a composition of 58% B-phycoerythrin, 25% C-phycocyanin and 17% allophycocyanin under the cultural conditions used. Analytical methods resolved no other components than phycobiliproteins. In addition to the defined C-phycocyanin and two isoproteins of B-phycoerythrin a stable heterogeneous aggregate of B-phycoerythrin/C-phycocyanin was separated in considerable amounts. In the electron microscope negatively stained phycobilisomes appeared as elliptical aggregates having dimensions slightly above the values found in ultrathin sections and a detailed subunit structure. All observations and data suggest a new rhodophytan phycobilisome type in Rhodella violacea.

Cell Fractionation↗
PubMed1978

Picosecond time-resolved energy transfer in Porphyridium cruentum. Part I. In the intact alga.

The wavelength-resolved fluorescence emission kinetics of the accessory pigments and chlorophyll a in Porphyridium cruentum have been studied by pico-second laser spectroscopy. Direct excitation of the pigment B-phycoerythrin with a 530 nm, 6 ps pulse produced fluorescence emission from all of the pigments as a result of energy transfer between the pigments to the reaction centre of Photosystem II. The emission from B-phycoerythrin at 576 nm follows a nonexponential decay law with a mean fluorescence lifetime of 70 ps, whereas the fluorescence from R-phycocyanin (640 nm), allophycocyanin (660 nm) and chlorophyll a (685 nm) all appeared to follow an exponential decay law with lifetimes of 90 ps, 118 ps and 175 ps respectively. Upon closure of the Photosystem II reaction centres with 3-(3,4-dichlorophenyl)-1,1-dimethylurea and preillumination the chlorophyll a decay became non-exponential, having a long component with an apparent lifetime of 840 ps. The fluorescence from the latter three pigments all showed finite risetimes to the maximum emission intensity of 12 ps for R-phycocyanin, 24 ps for allophycocyanin and 50 ps for chlorophyll a. A kinetic analysis of these results indicates that energy transfer between the pigments is at least 99% efficient and is governed by an exp --At1/2 transfer function. The apparent exponential behaviour of the fluorescence decay functions of the latter three pigments is shown to be a direct result of the energy transfer kinetics, as are the observed risetimes in the fluorescence emissions.

Chlorophyll↗
PubMed1978

Picosecond time-resolved energy transfer in Porphyridium cruentum. Part II. In the isolated light harvesting complex (phycobilisomes).

The transfer of excitation energy between phycobiliproteins in isolated phycobilisomes has been observed on a picosecond time scale. The photon density of the excitation pulse has been carefully varied so as to control the level of exciton interactions induced in the pigment bed. The 530 nm light pulse is absorbed predominantly by B-phycoerythrin, and the fluorescence of this component rises within the pulse duration and shows a mean 1/e decay time of 70 ps. The main emission band, centred at 672 nm, is due to allophycocyanin and is prominent because of the absence of energy transfer to chlorophyll. Energy transfer to this pigment from B-phycoerythrin via R-phycocyanin produces a risetime of 120 ps to the fluorescence maximum. The lifetime of the allophycocyanin fluorescence is found to be about 4 ns using excitation pulses of low photon densities (10(13) photons.cm-2), but decreases to about 2 ns at higher photon densities. The relative quantum yield of the allophycocyanin fluorescence decreases almost 10 fold over the range of laser pulse intensities, 10(13)--10(16) photons-cm-2. Fluorescence quenching by exciton-exciton annihilation is only observed in allophycocyanin and could be a consequence of the long lifetime of the single exciton in this pigment.

Energy Transfer↗
PubMed1975

Letter: Sequences of the N-terminus portions of biliproteins.

The N-terminal sequences of the separated polypeptide chains of biliproteins isolated from several Cyanophyta, Rhodophyta, and Cryptophyta have been determined. The portions of the sequences determined for the alpha (fast) chain of C-phycocyanin from both procaryotic and eucaryotic cells are extremely conservative. Methionine is the N-terminal amino acid in most of the species studied. The N-terminus and subsequent sequence of phycoerythrin alpha chains are almost identical with those of the C-phycocyanin alpha chain. The beta (slow) chain of C-phycocyanin is also rather conservative in amino acid substitution but has more variation than the alpha chain. The variations are consistent with single base changes in codons and conserve the size and functional characteristics of the amino acid. The sequence homologies are consistent with the phylogenetic relationship between Cyanophyta and the chloroplast of Rhodophyta. There are no other reported sequences of polypeptide chains of the same or related proteins from such different strains of microorganisms that show such close sequence homology.

Amino Acid Sequence↗
PubMed2026

Gloeotrichia echinulata genomes from the United States are nontoxigenic and likely geosmin producers.

Six Gloeotrichia echinulata genomes derived from planktonic harmful algal blooms (HABs) with similar colonial morphology have been sequenced from lakes in the west and northeast regions of USA, four of them to completion. The c. 7 Mbp genomes exhibit a high level of conservation, with 98-99% pairwise genome-wide average nucleotide identity and high levels of synteny, representing a single species cluster. We observed strong conservation of gene clusters responsible for the synthesis of the secondary metabolites and bioactive peptides that are characteristic of HAB-forming cyanobacteria. All six G. echinulata genomes lack genes for the synthesis of classic cyanotoxins, including microcystin, but possess genes responsible for the synthesis of the taste and odor compound geosmin. Interestingly, the geoA geosmin synthase gene in three genomes is homologous to other cyanobacterial geoA genes, while the other three geoA genes are related to actinomyces geoA. Phylogenomic analysis places the G. echinulata genomes within a clade of benthic Nostocales, reflecting an ecological niche featuring extensive growth on the sediment surface before colonies disperse into the epilimnion for planktonic growth. We identify genes conserved in all six genomes that could represent physiological adaptations supporting active growth on sediments and pelagic recruitment independent of wind-driven mixing: phycoerythrin light harvesting complexes for optimal photosynthesis at depth; gliding motility to access patchy nutrient distributions; and gas vesicles with relatively small GvpC proteins that predict resistance to higher hydrostatic pressure. The strong genomic similarity across geographically distant populations suggests that G. echinulata in the United States is a tightly related non-toxigenic species group with predictable properties relevant to public health and drinking water management.

Cyanobacteria↗