Photosynthetic Protein Complexes Research Articles

Orchestration Of Photosynthesis-associated Gene Expression And Galactolipid Biosynthesis During Chloroplast Differentiation In Plants.

The chloroplast thylakoid membrane is composed of membrane lipids and photosynthetic protein complexes, and orchestration of thylakoid lipid biosynthesis and photosynthesis-associated protein accumulation is considered important for thylakoid development. Galactolipids consist of ~80% of the thylakoid lipids and their biosynthesis is fundamental for chloroplast development. We previously reported that the suppression of galactolipid biosynthesis decreased the expression of photosynthesis-associated nuclear- and plastid-encoded genes (PhANGs and PhAPGs). However, the mechanism for coordinative regulation between galactolipid biosynthesis in plastids and expression of PhANGs and PhAPGs remains largely unknown. To elucidate this mechanism, we investigated the gene expression patterns in galactolipid-deficient Arabidopsis seedlings during the deetiolation process. We found that galactolipids are crucial for inducing both the transcript accumulation of PhANGs and PhAPGs and the accumulation of plastid-encoded photosynthesis-associated proteins in developing chloroplasts. Genetic analysis indicates the contribution of GENOMES UNCOUPLED1 (GUN1)-mediated plastid-to-nucleus signaling pathway for PhANG regulation in response to galactolipid levels. Previous studies suggested that the accumulation of GUN1 reflects the state of protein homeostasis in plastids and alters the PhANG expression level. Thus we propose a model that galactolipid biosynthesis determines the protein homeostasis in plastids at the initial phase of deetiolation and optimizes the GUN1-dependent signaling to regulate the PhANG expression. This mechanism might contribute to orchestrating the biosynthesis of lipids and proteins for the biogenesis of functional chloroplasts in plants.

Biophysical and molecular characteristics of senescing leaves of two Norway maple varieties differing in anthocyanin content.

Disassembly and degradation of the photosynthetic protein complexes during autumn senescence, a vital step to ensure efficient nutrient relocalization for winter storage, is poorly understood. Concomitantly with the degradation, anthocyanins are often synthesized. However, as to why leaves accumulate red pigments, no consensus exists. One possibility is that anthocyanins protect senescing leaves from excess light. In this study, we investigated the pigment composition, photosynthetic performance, radical production, and degradation of the photosynthetic protein complexes in Norway maple (Acer platanoides) and in its highly pigmented, purple-colored variety (Faassen's black) during autumn senescence, to dissect the possible roles of anthocyanins in photoprotection. Our findings show that senescing Faassen's black was indeed more resistant to Photosystem II (PSII) photoinhibition, presumably due to its high anthocyanin content, than the green maple. However, senescing Faassen's black exhibited low photosynthetic performance, probably due to a poor capacity to repair PSII. Furthermore, an analysis of photosynthetic protein complexes demonstrated that in both maple varieties, the supercomplexes consisting of PSII and its antenna were disassembled first, followed by the degradation of the PSII core, Photosystem I, Cytochrome b6 f, and ATP synthase. Strikingly, the degradation process appeared to proceed faster in Faassen's black, possibly explaining its poor PSII repair capacity. The results suggest that tolerance against PSII photoinhibition may not necessarily translate to a better fitness. Finally, thylakoids isolated from senescing and non-senescing leaves of both maple varieties accumulated very little carbon-centered radicals, suggesting that thylakoids may not be a major source of reactive oxygen species in senescing leaves.

Crosslinker Nanocarriers Delivery to Chloroplasts for In Vivo Mapping of Photosynthetic Membrane Protein Complexes in Living Chlamydomonas reinhardtii Cells.

Photosynthesis, as the core of solar energy biotransformation, is driven by photosynthetic membrane protein complexes in plants and algae. Current methods for intracellular photosynthetic membrane protein complex analysis mostly require the separation of specific chloroplasts or the change of the intracellular environment, which causes the missing of real-time and on-site information. Thus, we explored a method for in vivo crosslinking and mapping of photosynthetic membrane protein complexes in the chloroplasts of living Chlamydomonas reinhardtii (C. reinhardtii) cells under cultural conditions. Poly(lactic-co-glycolic acid) (PLGA) and poly(lactic-co-glycolic acid)-poly(ethylene glycol) (PLGA-PEG) nanoparticles were fabricated to deliver bis(succinimidyl)propargyl with a nitro compound (BSPNO) into the chloroplasts to crosslink photosynthetic membrane protein complexes. After the in vivo crosslinked protein complexes were extracted and digested, mass spectrometry was employed to detect lysine-specific crosslinked peptides for further elucidating the protein conformations and interactions. With this method, the weak interactions between extrinsic proteins in the luminal side (PsbL and PsbH) and the core subunits (CP47 and CP43) in photosynthetic protein complexes were directly captured in living cells. Additionally, the previously uncharacterized protein (Cre07.g335700) was bound to the light-harvesting proteins, which was related to the biosynthesis of light-harvesting antennae. These results indicated that in vivo analysis of photosynthetic protein complexes based on crosslinker nanocarriers was expected to not only figure out the difficulty in the study of photosynthetic protein complexes in living cells but also provide an approach to explore transient and weak interactions and the function of uncharacterized proteins.

Electrohydrodynamically printed solid-state Photo-electro protein micro-capacitors

The rapid development of portable and scalable electronics requires the production of high-performing, miniaturized energy storage devices with great flexibility and dimensional liberty. In recent years, printed capacitors have emerged as a promising means of meeting these demands. Printed flexible solid-state capacitors are being considered as next-generation energy storage systems because of their flexibility, portability, low cost, scalability, long cycle stability and the option of charging or discharging securely. Here we use sustainable and toxin-free photosynthetic protein complexes to fabricate solid-state flexible Photo-electro micro-capacitors as flexible power packs that are operable under indoor illumination. Electrohydrodynamic (EHD) printing was used to print biohybrid Photo-electro protein micro-capacitors that exhibited high performance uniformity and operational stability. Devices could be connected in either series or parallel configurations to modulate the operating voltage window and charge-discharge time. A specific capacitance of 110 mF g−1 was obtained at a scan rate of 10 mV s−1 and was retained at 91% of the initial value after 10,000 charge/discharge cycles at a current density of 0.063 mA g−1. Devices also displayed mechanical stability and robustness, retaining 93% of initial capacitance after 1000 cycles of bending. The data demonstrate that these micro-capacitors can deliver an economical and practical option as flexible energy storage and delivery devices for applications where exposure is primarily to indoor light.

Quantification of energy-converting protein complexes in plant thylakoid membranes

Knowledge about the exact abundance and ratio of photosynthetic protein complexes in thylakoid membranes is central to understanding structure-function relationships in energy conversion. Recent modeling approaches for studying light harvesting and electron transport reactions rely on quantitative information on the constituent complexes in thylakoid membranes. Over the last decades several quantitative methods have been established and refined, enabling precise stoichiometric information on the five main energy-converting building blocks in the thylakoid membrane: Light-harvesting complex II (LHCII), Photosystem II (PSII), Photosystem I (PSI), cytochrome b6f complex (cyt b6f complex), and ATPase. This paper summarizes a few quantitative spectroscopic and biochemical methods that are currently available for quantification of plant thylakoid protein complexes. Two new methods are presented for quantification of LHCII and the cyt b6f complex, which agree well with established methods. In addition, recent improvements in mass spectrometry (MS) allow deeper compositional information on thylakoid membranes. The comparison between mass spectrometric and more classical protein quantification methods shows similar quantities of complexes, confirming the potential of thylakoid protein complex quantification by MS. The quantitative information on PSII, PSI, and LHCII reveal that about one third of LHCII must be associated with PSI for a balanced light energy absorption by the two photosystems.

Static Disorder has Dynamic Impact on Energy Transport in Biomimetic Light-Harvesting Complexes.

Despite extensive studies, many questions remain about what structural and energetic factors give rise to the remarkable energy transport efficiency of photosynthetic light-harvesting protein complexes, owing largely to the inability to synthetically control such factors in these natural systems. Herein, we demonstrate energy transfer within a biomimetic light-harvesting complex consisting of identical chromophores attached in a circular array to a protein scaffold derived from the tobacco mosaic virus coat protein. We confirm the capability of energy transport by observing ultrafast depolarization in transient absorption anisotropy measurements and a redshift in time-resolved emission spectra in these complexes. Modeling the system with kinetic Monte Carlo simulations recapitulates the observed anisotropy decays, suggesting an inter-site hopping rate as high as 1.6 ps–1. With these simulations, we identify static disorder in orientation, site energy, and degree of coupling as key remaining factors to control to achieve long-range energy transfer in these systems. We thereby establish this system as a highly promising, bottom-up model for studying long-range energy transfer in light-harvesting protein complexes.

Chloroplast envelope ATPase PGA1/AtFtsH12 is required for chloroplast protein accumulation and cytosol-chloroplast protein homeostasis in Arabidopsis

The establishment of photosynthetic protein complexes during chloroplast development requires the influx of a large number of chloroplast proteins that are encoded by the nuclear genome, which is critical for cytosol and chloroplast protein homeostasis and chloroplast development. However, the mechanisms regulating this process are still not well understood in higher plants. Here, we report the isolation and characterization of the pale green Arabidopsis pga1-1 mutant, which is defective in chloroplast development and chloroplast protein accumulation. Using genetic and biochemical evidence, we reveal that PGA1 encodes AtFtsH12, a chloroplast envelope-localized protein of the FtsH family proteins. We determined a G703R mutation in the GAD motif of the conserved ATPase domain renders the pga1-1 a viable hypomorphic allele of the essential gene AtFtsH12. In de-etiolation assays, we showed that the accumulation of photosynthetic proteins and the expression of photosynthetic genes were impaired in pga1-1. Using the FNRctp-GFP and pTAC2-GFP reporters, we demonstrated that AtFtsH12 was required for the accumulation of chloroplast proteins in vivo. Interestingly, we identified an increase in expression of the mutant AtFtsH12 gene in pga1-1, suggesting a feedback regulation. Moreover, we found that cytosolic and chloroplast proteostasis responses were triggered in pga1-1. Together, taking advantage of the novel pga1-1 mutant, we demonstrate the function of AtFtsH12 in chloroplast protein homeostasis and chloroplast development.

De novo protein design of photochemical reaction centers

Natural photosynthetic protein complexes capture sunlight to power the energetic catalysis that supports life on Earth. Yet these natural protein structures carry an evolutionary legacy of complexity and fragility that encumbers protein reengineering efforts and obfuscates the underlying design rules for light-driven charge separation. De novo development of a simplified photosynthetic reaction center protein can clarify practical engineering principles needed to build new enzymes for efficient solar-to-fuel energy conversion. Here, we report the rational design, X-ray crystal structure, and electron transfer activity of a multi-cofactor protein that incorporates essential elements of photosynthetic reaction centers. This highly stable, modular artificial protein framework can be reconstituted in vitro with interchangeable redox centers for nanometer-scale photochemical charge separation. Transient absorption spectroscopy demonstrates Photosystem II-like tyrosine and metal cluster oxidation, and we measure charge separation lifetimes exceeding 100 ms, ideal for light-activated catalysis. This de novo-designed reaction center builds upon engineering guidelines established for charge separation in earlier synthetic photochemical triads and modified natural proteins, and it shows how synthetic biology may lead to a new generation of genetically encoded, light-powered catalysts for solar fuel production.

Chloroplast-localized PITP7 is essential for plant growth and photosynthetic function in Arabidopsis.

Recent studies of chloroplast‐localized Sec14‐like protein (CPSFL1, also known as phosphatidylinositol transfer protein 7, PITP7) showed that CPSFL1 is necessary for photoautotropic growth and chloroplast vesicle formation in Arabidopsis (Arabidopsis thaliana). Here, we investigated the functional roles of CPSFL1/PITP7 using two A. thaliana mutants carrying a putative null allele (pitp7‐1) and a weak allele (pitp7‐2), respectively. PITP7 transcripts were undetectable in pitp7‐1 and less abundant in pitp7‐2 than in the wild‐type (WT). The severity of mutant phenotypes, such as plant developmental abnormalities, levels of plastoquinone‐9 (PQ‐9) and chlorophylls, photosynthetic protein complexes, and photosynthetic performance, were well related to PITP7 transcript levels. The pitp7‐1 mutation was seedling lethal and was associated with significantly lower levels of PQ‐9 and major photosynthetic proteins. pitp7‐2 plants showed greater susceptibility to high‐intensity light stress than the WT, attributable to defects in nonphotochemical quenching and photosynthetic electron transport. PITP7 is specifically bound to phosphatidylinositol phosphates (PIPs) in lipid‐binding assays in vitro, and the point mutations R82, H125, E162, or K233 reduced the binding affinity of PITP7 to PIPs. Further, constitutive expression of PITP7H125Q or PITP7E162K in pitp7‐1 homozygous plants restored autotrophic growth in soil but without fully complementing the mutant phenotypes. Consistent with a previous study, our results demonstrate that PITP7 is essential for plant development, particularly the accumulation of PQ‐9 and photosynthetic complexes. We propose a possible role for PITP7 in membrane trafficking of hydrophobic ligands such as PQ‐9 and carotenoids through chloroplast vesicle formation or direct binding involving PIPs.

Chlorophyll dephytylase 1 and chlorophyll synthase: a chlorophyll salvage pathway for the turnover of photosystems I and II.

Chlorophyll (Chl) is made up of the tetrapyrrole chlorophyllide and phytol, a diterpenoid alcohol. The photosynthetic protein complexes utilize Chl for light harvesting to produce biochemical energy for plant development. However, excess light and adverse environmental conditions facilitate generation of reactive oxygen species, which damage photosystems I and II (PSI and PSII) and induce their turnover. During this process, Chl is released, and is thought to be recycled via dephytylation and rephytylation. We previously demonstrated that Chl recycling in Arabidopsis under heat stress is mediated by the enzymes chlorophyll dephytylase 1 (CLD1) and chlorophyll synthase (CHLG) using chlg and cld1 mutants. Here, we show that the mutants with high CLD1/CHLG ratio, by different combinations of chlg-1 (a knock-down mutant) and the hyperactive cld1-1 alleles, develop necrotic leaves when grown under long- and short-day, but not continuous light conditions, owing to the accumulation of chlorophyllide in the dark. Combination of chlg-1 with cld1-4 (a knock-out mutant) leads to reduced chlorophyllide accumulation and necrosis. The operation of CLD1 and CHLG as a Chl salvage pathway was also explored in the context of Chl recycling during the turnover of Chl-binding proteins of the two photosystems. CLD1 was found to interact with CHLG and the light-harvesting complex-like proteins OHP1 and LIL3, implying that auxiliary factors are required for this process.

Chloroplast pH Homeostasis for the Regulation of Photosynthesis

The pH of various chloroplast compartments, such as the thylakoid lumen and stroma, is light-dependent. Light illumination induces electron transfer in the photosynthetic apparatus, coupled with proton translocation across the thylakoid membranes, resulting in acidification and alkalization of the thylakoid lumen and stroma, respectively. Luminal acidification is crucial for inducing regulatory mechanisms that protect photosystems against photodamage caused by the overproduction of reactive oxygen species (ROS). Stromal alkalization activates enzymes involved in the Calvin–Benson–Bassham (CBB) cycle. Moreover, proton translocation across the thylakoid membranes generates a proton gradient (ΔpH) and an electric potential (ΔΨ), both of which comprise the proton motive force (pmf) that drives ATP synthase. Then, the synthesized ATP is consumed in the CBB cycle and other chloroplast metabolic pathways. In the dark, the pH of both the chloroplast stroma and thylakoid lumen becomes neutral. Despite extensive studies of the above-mentioned processes, the molecular mechanisms of how chloroplast pH can be maintained at proper levels during the light phase for efficient activation of photosynthesis and other metabolic pathways and return to neutral levels during the dark phase remain largely unclear, especially in terms of the precise control of stromal pH. The transient increase and decrease in chloroplast pH upon dark-to-light and light-to-dark transitions have been considered as signals for controlling other biological processes in plant cells. Forward and reverse genetic screening approaches recently identified new plastid proteins involved in controlling ΔpH and ΔΨ across the thylakoid membranes and chloroplast proton/ion homeostasis. These proteins have been conserved during the evolution of oxygenic phototrophs and include putative photosynthetic protein complexes, proton transporters, and/or their regulators. Herein, we summarize the recently identified protein players that control chloroplast pH and influence photosynthetic efficiency in plants.

Chloroplast translational regulation uncovers nonessential photosynthesis genes as key players in plant cold acclimation.

Plants evolved efficient multifaceted acclimation strategies to cope with low temperatures. Chloroplasts respond to temperature stimuli and participate in temperature sensing and acclimation. However, very little is known about the involvement of chloroplast genes and their expression in plant chilling tolerance. Here we systematically investigated cold acclimation in tobacco seedlings over 2 days of exposure to low temperatures by examining responses in chloroplast genome copy number, transcript accumulation and translation, photosynthesis, cell physiology, and metabolism. Our time-resolved genome-wide investigation of chloroplast gene expression revealed substantial cold-induced translational regulation at both the initiation and elongation levels, in the virtual absence of changes at the transcript level. These cold-triggered dynamics in chloroplast translation are widely distinct from previously described high light-induced effects. Analysis of the gene set responding significantly to the cold stimulus suggested nonessential plastid-encoded subunits of photosynthetic protein complexes as novel players in plant cold acclimation. Functional characterization of one of these cold-responsive chloroplast genes by reverse genetics demonstrated that the encoded protein, the small cytochrome b6f complex subunit PetL, crucially contributes to photosynthetic cold acclimation. Together, our results uncover an important, previously underappreciated role of chloroplast translational regulation in plant cold acclimation.

Lipids in photosynthetic protein complexes in the thylakoid membrane of plants, algae, and cyanobacteria.

In the thylakoid membrane of cyanobacteria and chloroplasts, many proteins involved in photosynthesis are associated with or integrated into the fluid bilayer matrix formed by four unique glycerolipid classes, monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol, and phosphatidylglycerol. Biochemical and molecular genetic studies have revealed that these glycerolipids play essential roles not only in the formation of thylakoid lipid bilayers but also in the assembly and functions of photosynthetic complexes. Moreover, considerable advances in structural biology have identified a number of lipid molecules within the photosynthetic complexes such as PSI and PSII. These data have provided important insights into the association of lipids with protein subunits in photosynthetic complexes and the distribution of lipids in the thylakoid membrane. Here, we summarize recent high-resolution observations of lipid molecules in the structures of photosynthetic complexes from plants, algae, and cyanobacteria, and evaluate the distribution of lipids among photosynthetic protein complexes and thylakoid lipid bilayers. By integrating the structural information into the findings from biochemical and molecular genetic studies, we highlight the conserved and differentiated roles of lipids in the assembly and functions of photosynthetic complexes among plants, algae, and cyanobacteria.

Supplementary material for "Lipids in photosynthetic protein complexes in the thylakoid membrane of plants, algae, and cyanobacteria"

Supplementary material for "Lipids in photosynthetic protein complexes in the thylakoid membrane of plants, algae, and cyanobacteria"

Experimental and calculated infrared spectra of disubstituted naphthoquinones

In recent years there has been interest in incorporating substituted 1,4-naphthoquinones (NQs) into the A1 binding site in photosystem I (PSI) photosynthetic protein complexes. This interest in part stems from the considerably altered bioenergetics of electron transfer that occur in PSI with such substitutions. Time resolved FTIR studies of PSI complexes with disubstituted NQs incorporated have and currently are being undertaken, and with this in mind it is worth considering FTIR absorption spectra of these disubstituted NQs in solution. Here we present FTIR absorbance spectra for 2-bromo-3-methyl-1,4-naphthoquinone (BrMeNQ), 2-chloromethyl-3-methyl-1,4-naphthoquinone (CMMeNQ) and 2-ethylthio-3-methyl-1,4-naphthoquinone (ETMeNQ) in tetrahydrofuran (THF). The FTIR spectra of these di-substituted naphthoquinones (NQs) were compared to FTIR spectra of 2-methyl-3-phytyl-1,4-naphthoquinone [phylloquinone (PhQ)], 2,3-dimethyl-1,4-naphthoquinone (DMNQ), and 2-methyl-1,4-naphthoquinone (2MNQ). To aid in the assignment of bands in the experimental spectra, density functional theory (DFT) based vibrational frequency calculations for all the substituted NQs in solution were undertaken. The calculated and experimental spectra agree well. By calculating normal mode potential energy distributions, unambiguous quantitative band assignments were made. The calculated and experimental spectra together make predictions about what may be observable in time resolved FTIR difference spectra obtained using PSI with the different NQs incorporated. Time resolved FTIR difference spectra are presented that support these predictions.

Comparative Transcriptome Profiling of Kappaphycus alvarezii (Rhodophyta, Solieriaceae) in Response to Light of Different Wavelengths and Carbon Dioxide Enrichment.

Rhodophyta (red algae) comprises over 6000 species, however, there have only been a few comparative transcriptomic studies due to their under-representation in genomic databases. Kappaphycus alvarezii, a Gigartinales algae, is a valuable source of carrageenan and is extensively cultivated in many countries. The majority of seaweed farming in Southeast Asia is done in intertidal zones under varying light (i.e., spectra and irradiance) and carbon dioxide (CO2) conditions, which affects the rate of photosynthesis. This study conducted transcriptome profiling to investigate the photosynthetic mechanisms in K. alvarezii exposed to different wavelengths of light (i.e., blue, green, and red light, in comparison to white light) and CO2 availability. We analyzed the responses of photosynthetic protein complexes to light and observed that light of different wavelengths regulates a similar set of photosynthetic apparatuses. Under CO2 enrichment, genes encoding C3 and C4 enzymes were found to be actively transcribed, suggesting the likely shift in the carbon metabolism pathway or the involvement of these genes in adaptive physiological processes. This study contributes to the understanding of the regulatory mechanisms of photosynthetic carbon metabolism in red algae and has implications for the culture and commercial production of these economically valuable macroalgae.

Insights into Solution Structures of Photosynthetic Protein Complexes from Small-Angle Scattering Methods

High-resolution structures of photosynthetic pigment–protein complexes are often determined using crystallography or cryo-electron microscopy (cryo-EM), which are restricted to the use of protein crystals or to low temperatures, respectively. However, functional studies and biotechnological applications of photosystems necessitate the use of proteins isolated in aqueous solution, so that the relevance of high-resolution structures has to be independently verified. In this regard, small-angle neutron and X-ray scattering (SANS and SAXS, respectively) can serve as the missing link because of their capability to provide structural information for proteins in aqueous solution at physiological temperatures. In the present review, we discuss the principles and prototypical applications of SANS and SAXS using the photosynthetic pigment–protein complexes phycocyanin (PC) and Photosystem I (PSI) as model systems for a water-soluble and for a membrane protein, respectively. For example, the solution structure of PSI was studied using SAXS and SANS with contrast matching. A Guinier analysis reveals that PSI in solution is virtually free of aggregation and characterized by a radius of gyration of about 75 Å. The latter value is about 10% larger than expected from the crystal structure. This is corroborated by an ab initio structure reconstitution, which also shows a slight expansion of Photosystem I in buffer solution at room temperature. In part, this may be due to conformational states accessible by thermally activated protein dynamics in solution at physiological temperatures. The size of the detergent belt is derived by comparison with SANS measurements without detergent match, revealing a monolayer of detergent molecules under proper solubilization conditions.

Closing the Gap for Electronic Short-Circuiting: Photosystem I Mixed Monolayers Enable Improved Anisotropic Electron Flow in Biophotovoltaic Devices.

Well‐defined assemblies of photosynthetic protein complexes are required for an optimal performance of semi‐artificial energy conversion devices, capable of providing unidirectional electron flow when light‐harvesting proteins are interfaced with electrode surfaces. We present mixed photosystem I (PSI) monolayers constituted of native cyanobacterial PSI trimers in combination with isolated PSI monomers from the same organism. The resulting compact arrangement ensures a high density of photoactive protein complexes per unit area, providing the basis to effectively minimize short‐circuiting processes that typically limit the performance of PSI‐based bioelectrodes. The PSI film is further interfaced with redox polymers for optimal electron transfer, enabling highly efficient light‐induced photocurrent generation. Coupling of the photocathode with a [NiFeSe]‐hydrogenase confirms the possibility to realize light‐induced H2 evolution.

Reassessing the rationale behind herbicide biosensors: The case of a photosystem II/redox polymer-based bioelectrode

Interfacing photosynthetic protein complexes with electrodes is frequently used for the identification of electron transfer mechanisms and the fabrication of biosensors. Binding of herbicide compounds to the terminal plastoquinone QB at photosystem II (PSII) causes disruption of electron flow that is associated with a diminished performance of the associated biodevice. Thus, the principle of electron transport inhibition at PSII can be used for herbicide detection and has inspired the fabrication of several biosensors for this purpose. However, the biosensor performance may reveal a more complex behavior than generally expected. As we present here for a photobioelectrode constituted by PSII embedded in a redox polymer matrix, the effect caused by inhibitors does not only impact the electron transfer from PSII but also the properties of the polymer film used for immobilization and electrical wiring of the protein complexes. Incorporation of phenolic inhibitors into the polymer film surprisingly translates into enhanced photocurrents and, in particular cases, in a higher stability of the overall electrode architecture. The achieved results stress the importance to evaluate first the possible influence of analytes of interest on the biosensor architecture as a whole and provide important insights for consideration in future design of bioelectrochemical devices.

Composition, phosphorylation and dynamic organization of photosynthetic protein complexes in plant thylakoid membrane

The photosystems (PS), catalyzing the photosynthetic reactions of higher plants, are unevenly distributed in the thylakoid membrane: PSII, together with its light harvesting complex (LHC)II, is enriched in the appressed grana stacks, while PSI–LHCI resides in the non-appressed stroma thylakoids, which wind around the grana stacks. The two photosystems interact in a third membrane domain, the grana margins, which connect the grana and stroma thylakoids and allow the loosely bound LHCII to serve as an additional antenna for PSI. The light harvesting is balanced by reversible phosphorylation of LHCII proteins. Nevertheless, light energy also damages PSII and the repair process is regulated by reversible phosphorylation of PSII core proteins. Here, we discuss the detailed composition and organization of PSII–LHCII and PSI–LHCI (super)complexes in the thylakoid membrane of angiosperm chloroplasts and address the role of thylakoid protein phosphorylation in dynamics of the entire protein complex network of the photosynthetic membrane. Finally, we scrutinize the phosphorylation-dependent dynamics of the protein complexes in context of thylakoid ultrastructure and present a model on the reorganization of the entire thylakoid network in response to changes in thylakoid protein phosphorylation.