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Biochimica Et Biophysica Acta Jul 2004Allophycocyanin is a biliprotein located in the core of the phycobilisome. The biliprotein is isolated and purified as a trimer (alpha3beta3), where a monomer is an... (Review)
Review
Allophycocyanin is a biliprotein located in the core of the phycobilisome. The biliprotein is isolated and purified as a trimer (alpha3beta3), where a monomer is an alphabeta structure. Each alpha and beta subunit has a single noncyclic tetrapyrrole chromophore, called phycocyanobilin. The trimer of allophycocyanin has an unusual absorption maximum at 650 nm with a shoulder at 620 nm, while the monomer has an absorption maximum at 615 nm. Two explanations have been proposed for the 650-nm maximum. In one, this maximum is produced by the interaction of a particular local protein environment for three of the chromophores, causing them to red shift, while the other three chromophores are at a higher energy. Energy is transferred from the high- to the low-energy chromophores by Förster resonance energy transfer, the donor-acceptor model. In the second proposal, there is strong exciton coupling between two chromophores of the trimer that closely approach across the monomer-monomer interface. The strong interaction causes exciton splitting and a red shift in the absorption. There are three of these strongly coupled chromophore pairs, and energy is transferred between the two-exciton states of a pair by internal conversion. A variety of biophysical methods have been used to examine this question. Although evidence supporting both models has been produced, sophisticated ultra fast fluorescence results from a plethora of approaches now firmly point to the latter strong coupling hypothesis as being more likely. Between the different strongly coupled pairs, Förster resonance energy transfer should occur. For monomers of allophycocyanin, Förster resonance energy transfer occurs between the two chromophores.
Topics: Biopolymers; Energy Transfer; Phycocyanin; Spectrophotometry
PubMed: 15238265
DOI: 10.1016/j.bbabio.2004.04.005 -
Journal of the Royal Society, Interface Apr 2018Bilins are linear tetrapyrrole chromophores with a wide range of visible and near-visible light absorption and emission properties. These properties are tuned upon...
Bilins are linear tetrapyrrole chromophores with a wide range of visible and near-visible light absorption and emission properties. These properties are tuned upon binding to natural proteins and exploited in photosynthetic light-harvesting and non-photosynthetic light-sensitive signalling. These pigmented proteins are now being manipulated to develop fluorescent experimental tools. To engineer the optical properties of bound bilins for specific applications more flexibly, we have used first principles of protein folding to design novel, stable and highly adaptable bilin-binding four-α-helix bundle protein frames, called maquettes, and explored the minimal requirements underlying covalent bilin ligation and conformational restriction responsible for the strong and variable absorption, fluorescence and excitation energy transfer of these proteins. Biliverdin, phycocyanobilin and phycoerythrobilin bind covalently to maquette Cys A blue-shifted tripyrrole formed from maquette-bound phycocyanobilin displays a quantum yield of 26%. Although unrelated in fold and sequence to natural phycobiliproteins, bilin lyases nevertheless interact with maquettes during co-expression in to improve the efficiency of bilin binding and influence bilin structure. Bilins bind and to Cys residues placed in loops, towards the amino end or in the middle of helices but bind poorly at the carboxyl end of helices. Bilin-binding efficiency and fluorescence yield are improved by Arg and Asp residues adjacent to the ligating Cys on the same helix and by His residues on adjacent helices.
Topics: Biomimetic Materials; Energy Metabolism; Energy Transfer; Models, Molecular; Photosynthesis; Phycobiliproteins; Protein Engineering; Protein Folding
PubMed: 29618529
DOI: 10.1098/rsif.2018.0021 -
Advances in Biochemical... 2009Fluorescence spectroscopy is widely used in chemical and biological research. Until recently most of the fluorescence experiments have been performed in the far-field... (Review)
Review
Fluorescence spectroscopy is widely used in chemical and biological research. Until recently most of the fluorescence experiments have been performed in the far-field regime. By far-field we imply at least several wavelengths from the fluorescent probe molecule. In recent years there has been growing interest in the interactions of fluorophores with metallic surfaces or particles. Near-field interactions are those occurring within a wavelength distance of an excited fluorophore. The spectral properties of fluorophores can dramatically be altered by near-field interactions with the electron clouds present in metals. These interactions modify the emission in ways not seen in classical fluorescence experiments. Fluorophores in the excited state can create plasmons that radiate into the far-field and fluorophores in the ground state can interact with and be excited by surface plasmons. These reciprocal interactions suggest that the novel optical absorption and scattering properties of metallic nanostructures can be used to control the decay rates, location, and direction of fluorophore emission. We refer to these phenomena as plasmon-controlled fluorescence (PCF). An overview of the recent work on metal-fluorophore interactions is presented. Recent research combining plasmonics and fluorescence suggest that PCF could lead to new classes of experimental procedures, novel probes, bioassays, and devices.
Topics: Chemistry Techniques, Analytical; Metals; Optical Phenomena; Phycobiliproteins; Quantum Dots; Spectrometry, Fluorescence
PubMed: 19082931
DOI: 10.1007/10_2008_9 -
Microbes and Environments 2012Host-like genes are often found in viral genomes. To date, multiple host-like genes involved in photosynthesis and the pentose phosphate pathway have been found in... (Review)
Review
Host-like genes are often found in viral genomes. To date, multiple host-like genes involved in photosynthesis and the pentose phosphate pathway have been found in phages of marine cyanobacteria Synechococcus and Prochlorococcus. These gene products are predicted to redirect host metabolism to deoxynucleotide biosynthesis for phage replication while maintaining photosynthesis. A cyanophage, Ma-LMM01, infecting the toxic cyanobacterium Microcystis aeruginosa, was isolated from a eutrophic freshwater lake and assigned as a member of a new lineage of the Myoviridae family. The genome encodes a host-like NblA. Cyanobacterial NblA is known to be involved in the degradation of the major light harvesting complex, the phycobilisomes. Ma-LMM01 nblA gene showed an early expression pattern and was highly transcribed during phage infection. We speculate that the co-option of nblA into Microcystis phages provides a significant fitness advantage to phages by preventing photoinhibition during infection and possibly represents an important part of the co-evolutionary interactions between cyanobacteria and their phages.
Topics: Bacterial Proteins; Bacteriophages; Biological Evolution; Fresh Water; Genome, Viral; Microcystis; Myoviridae; Phycobilisomes
PubMed: 23047146
DOI: 10.1264/jsme2.me12037 -
Proceedings of the National Academy of... Dec 2017The light-harvesting phycobilisome in cyanobacteria and red algae requires the lyase-catalyzed chromophorylation of phycobiliproteins. There are three functionally...
The light-harvesting phycobilisome in cyanobacteria and red algae requires the lyase-catalyzed chromophorylation of phycobiliproteins. There are three functionally distinct lyase families known. The heterodimeric E/F type is specific for attaching bilins covalently to α-subunits of phycocyanins and phycoerythrins. Unlike other lyases, the lyase also has chromophore-detaching activity. A subclass of the E/F-type lyases is, furthermore, capable of chemically modifying the chromophore. Although these enzymes were characterized >25 y ago, their structures remained unknown. We determined the crystal structure of the heterodimer of CpcE/F from sp. PCC7120 at 1.89-Å resolution. Both subunits are twisted, crescent-shaped α-solenoid structures. CpcE has 15 and CpcF 10 helices. The inner (concave) layer of CpcE (helices h2, 4, 6, 8, 10, 12, and 14) and the outer (convex) layer of CpcF (h16, 18, 20, 22, and 24) form a cavity into which the phycocyanobilin chromophore can be modeled. This location of the chromophore is supported by mutations at the interface between the subunits and within the cavity. The structure of a structurally related, isomerizing lyase, PecE/F, that converts phycocyanobilin into phycoviolobilin, was modeled using the CpcE/F structure as template. A HC motif critical for the isomerase activity of PecE/F is located at the loop between h20 and h21, supporting the proposal that the nucleophilic addition of Cys-88 to C10 of phycocyanobilin induces the isomerization of phycocyanobilin into phycoviolobilin. Also, the structure of NblB, involved in phycobilisome degradation could be modeled using CpcE as template. Combined with CpcF, NblB shows a low chromophore-detaching activity.
Topics: Bacterial Proteins; Lyases; Molecular Dynamics Simulation; Nostoc; Phycobilins; Phycocyanin; Protein Domains
PubMed: 29180420
DOI: 10.1073/pnas.1715495114 -
Biochimica Et Biophysica Acta Jun 2005Cyanobacteria and red algae have intricate light-harvesting systems comprised of phycobilisomes that are attached to the outer side of the thylakoid membrane. The... (Review)
Review
Cyanobacteria and red algae have intricate light-harvesting systems comprised of phycobilisomes that are attached to the outer side of the thylakoid membrane. The phycobilisomes absorb light in the wavelength range of 500-650 nm and transfer energy to the chlorophyll for photosynthesis. Phycobilisomes, which biochemically consist of phycobiliproteins and linker polypeptides, are particularly wonderful subjects for the detailed analysis of structure and function due to their spectral properties and their various components affected by growth conditions. The linker polypeptides are believed to mediate both the assembly of phycobiliproteins into the highly ordered arrays in the phycobilisomes and the interactions between the phycobilisomes and the thylakoid membrane. Functionally, they have been reported to improve energy migration by regulating the spectral characteristics of colored phycobiliproteins. In this review, the progress regarding linker polypeptides research, including separation approaches, structures and interactions with phycobiliproteins, as well as their functions in the phycobilisomes, is presented. In addition, some problems with previous work on linkers are also discussed.
Topics: Cyanobacteria; Peptides; Phycobilisomes; Rhodophyta
PubMed: 15922288
DOI: 10.1016/j.bbabio.2005.04.001 -
Journal of Bacteriology Jan 1999To optimize the utilization of photosynthate and avoid damage that can result from the absorption of excess excitation energy, photosynthetic organisms must rapidly...
To optimize the utilization of photosynthate and avoid damage that can result from the absorption of excess excitation energy, photosynthetic organisms must rapidly modify the synthesis and activities of components of the photosynthetic apparatus in response to environmental cues. During nutrient-limited growth, cyanobacteria degrade their light-harvesting complex, the phycobilisome, and dramatically reduce the rate of photosynthetic electron transport. In this report, we describe the isolation and characterization of a cyanobacterial mutant that does not degrade its phycobilisomes during either sulfur or nitrogen limitation and exhibits an increased ratio of phycocyanin to chlorophyll during nutrient-replete growth. The mutant phenotype was complemented by a gene encoding a polypeptide with similarities to polypeptides that catalyze covalent bond formation between linear tetrapyrrole chromophores and subunits of apophycobiliproteins. The complementing gene, designated nblB, is expressed at approximately the same level in cells grown in nutrient-replete medium and medium devoid of either sulfur or nitrogen. These results suggest that the NblB polypeptide may be a constitutive part of the machinery that coordinates phycobilisome degradation with environmental conditions.
Topics: Amino Acid Sequence; Bacterial Proteins; Cyanobacteria; Genetic Complementation Test; Genome, Bacterial; Light-Harvesting Protein Complexes; Lyases; Molecular Sequence Data; Mutagenesis; Open Reading Frames; Phenotype; Phycobilisomes; Plant Proteins; Plasmids; Sequence Alignment; Sequence Homology, Amino Acid
PubMed: 9882677
DOI: 10.1128/JB.181.2.610-617.1999 -
Protein Science : a Publication of the... Apr 2022The orange carotenoid protein (OCP) is responsible for nonphotochemical quenching (NPQ) in cyanobacteria, a defense mechanism against potentially damaging effects of...
The orange carotenoid protein (OCP) is responsible for nonphotochemical quenching (NPQ) in cyanobacteria, a defense mechanism against potentially damaging effects of excess light conditions. This soluble two-domain protein undergoes profound conformational changes upon photoactivation, involving translocation of the ketocarotenoid inside the cavity followed by domain separation. Domain separation is a critical step in the photocycle of OCP because it exposes the N-terminal domain (NTD) to perform quenching of the phycobilisomes. Many details regarding the mechanism and energetics of OCP domain separation remain unknown. In this work, we apply metadynamics to elucidate the protein rearrangements that lead to the active, domain-separated, form of OCP. We find that translocation of the ketocarotenoid canthaxanthin has a profound effect on the energetic landscape and that domain separation only becomes favorable following translocation. We further explore, characterize, and validate the free energy surface (FES) using equilibrium simulations initiated from different states on the FES. Through pathway optimization methods, we characterize the most probable path to domain separation and reveal the barriers along that pathway. We find that the free energy barriers are relatively small (<5 kcal/mol), but the overall estimated kinetic rate is consistent with experimental measurements (>1 ms). Overall, our results provide detailed information on the requirement for canthaxanthin translocation to precede domain separation and an energetically feasible pathway to dissociation.
Topics: Bacterial Proteins; Carotenoids; Cyanobacteria; Models, Molecular; Phycobilisomes
PubMed: 35000233
DOI: 10.1002/pro.4273 -
Cell Research Jun 2015Phycobilisomes (PBSs) are light-harvesting antennae that transfer energy to photosynthetic reaction centers in cyanobacteria and red algae. PBSs are supermolecular...
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.
Topics: Anabaena; Microscopy, Electron; Models, Molecular; Photosystem II Protein Complex; Phycobilisomes; Protein Conformation
PubMed: 25998682
DOI: 10.1038/cr.2015.59 -
Nature Communications Sep 2022Light harvesting is fundamental for production of ATP and reducing equivalents for CO fixation during photosynthesis. However, electronic energy transfer (EET) through a...
Light harvesting is fundamental for production of ATP and reducing equivalents for CO fixation during photosynthesis. However, electronic energy transfer (EET) through a photosystem can harm the photosynthetic apparatus when not balanced with CO. Here, we show that CO binding to the light-harvesting complex modulates EET in photosynthetic cyanobacteria. More specifically, CO binding to the allophycocyanin alpha subunit of the light-harvesting complex regulates EET and its fluorescence quantum yield in the cyanobacterium Synechocystis sp. PCC 6803. CO binding decreases the inter-chromophore distance in the allophycocyanin trimer. The result is enhanced EET in vitro and in live cells. Our work identifies a direct target for CO in the cyanobacterial light-harvesting apparatus and provides insights into photosynthesis regulation.
Topics: Carbon Dioxide; Photosynthesis; Phycobilisomes; Phycocyanin; Receptors, Cell Surface; Synechocystis
PubMed: 36075935
DOI: 10.1038/s41467-022-32925-6