Bioactive compounds and in vitro biological properties of Arthrospira platensis and Athrospira maxima: a comparative study.

Cyanobacteria, especially Arthrospira, are valuable resources of nutrients and natural pigments with many beneficial health-related properties. This study optimized the extraction conditions of Arthrospira to achieve high phenolic contents and antioxidant activities. Under optimized extraction conditions, the bioactive compounds (phenolics and pigment components), antioxidant activities, and inhibitions of the key enzymes relevant to some non-communicable diseases were compared between Arthrospira platensis and Arthrospira maxima. Optimized extraction conditions were determined as 2 h shaking time, 50 °C extraction temperature, and 1% (w/v) solid-to-liquid ratio, giving effective phenolic and phycocyanin contents using aqueous extraction, while 80% (v/v) aqueous ethanolic extraction provided high total chlorophyll content. Most antioxidant activities were higher using 80% (v/v) aqueous ethanolic extracts. Both Arthrospira species inhibited the key enzymes involved in controlling non-communicable diseases including hyperlipidemia (lipase), diabetes (α-amylase, α-glucosidase, and dipeptidyl peptidase-IV), Alzheimer's disease (acetylcholinesterase, butyrylcholinesterase and ß-secretase), and hypertension (angiotensin-converting enzyme). High inhibitory activities were detected against ß-secretase (BACE-1), the enzyme responsible for ß-amyloid plaque formation in the brain that acts as a significant hallmark of Alzheimer's disease. Arthrospira extract and donepezil (Alzheimer's disease drug) synergistically inhibited BACE-1, suggesting the potential of Arthrospira extracts as effective BACE-1 inhibitors. Interestingly, A. maxima exhibited higher bioactive compound contents, antioxidant activities, and key enzyme inhibitions than A. platensis, indicating high potential for future food and medicinal applications.

Spectral Characteristics, In Silico Perspectives, Density Functional Theory (DFT), and Therapeutic Potential of Green-Extracted Phycocyanin from Spirulina.

Phycocyanin (PC) is a naturally occurring green pigment in Spirulina. It was extracted by ultrasonic extraction using green technology, and its structure was studied using IR- and NMR-spectroscopy. Spectral data confirmed the PC structure. This study also involves an in silico assessment of the diverse applications of green pigment PC. Utilizing QSAR, PreADME/T, SwissADME, and Pro-Tox, this study explores the safety profile, pharmacokinetics, and potential targets of PC. QSAR analysis reveals a favorable safety profile, with the parent structure and most metabolites showing no binding to DNA or proteins. PreADME/T indicates low skin permeability, excellent intestinal absorption, and medium permeability, supporting oral administration. Distribution analysis suggests moderate plasma protein binding and cautious blood-brain barrier permeability, guiding formulation strategies. Metabolism assessments highlight interactions with key cytochrome P450 enzymes, influencing drug interactions. Target prediction analysis unveils potential targets, suggesting diverse therapeutic effects, including cardiovascular benefits, anti-inflammatory activities, neuroprotection, and immune modulation. Based on the in silico analysis, PC holds promise for various applications due to its safety, bioavailability, and potential therapeutic benefits. Experimental validation is crucial to elucidate precise molecular mechanisms, ensuring safe and effective utilization in therapeutic and dietary contexts. DFT calculations, including geometry optimization, MEP analysis, HOMO-LUMO energy surface, and quantum reactivity parameters of the PC compound, were obtained using the B3LYP/6-311G(d,p) level. This integrated approach contributes to a comprehensive understanding of PC's pharmacological profile and informs future research directions.

Phycocyanin attenuates skeletal muscle damage and fatigue via modulation of Nrf2 and IRS-1/AKT/mTOR pathway in exercise-induced oxidative stress in rats.

Prolonged strenuous exercise induces oxidative stress, leading to oxidative damage, skeletal muscle fatigue, and reduced exercise performance. The body compensates for oxidative stress through antioxidant actions, while related enzymes alone may not overcome excessive oxidative stress during prolonged strenuous exercise. Phycocyanin is an important antioxidant supplement derived from blue-green algae, which may be helpful in this type of situation. This study determined the effects of phycocyanin on exercise performance from prolonged strenuous exercise. Forty Sprague Dawley male rats were divided into 5 groups (n = 8 /group); Control group (C), Exercise group (E), and Exercise with supplement groups receiving low dose (Phycocyanin = 100 mg/kg BW; ELP) and high dose (Phycocyanin = 200 mg/kg BW; EHP) or vitamin C (Vitamin C = 200 mg/kg BW; VC). Phycocyanin was found to decrease oxidative damage markers, muscle fatigue, and muscle atrophy through the activated AKT/mTOR pathway. This was also found to have greater increases in antioxidants via Nrf2 signaling and increases ATP synthesis, GLUT4 transporters, and insulin signaling due to increased IRS-1/AKT signaling. In conclusion, phycocyanin was found to reduce oxidative damage and muscle atrophy, including an increase in insulin signaling in skeletal muscles leading to increased exercise performance in rats.

Mixotrophic Cultivation of Arthrospira platensis (Spirulina) under Salt Stress: Effect on Biomass Composition, FAME Profile and Phycocyanin Content.

Arthrospira platensis holds promise for biotechnological applications due to its rapid growth and ability to produce valuable bioactive compounds like phycocyanin (PC). This study explores the impact of salinity and brewery wastewater (BWW) on the mixotrophic cultivation of A. platensis. Utilizing BWW as an organic carbon source and seawater (SW) for salt stress, we aim to optimize PC production and biomass composition. Under mixotrophic conditions with 2% BWW and SW, A. platensis showed enhanced biomass productivity, reaching a maximum of 3.70 g L-1 and significant increases in PC concentration. This study also observed changes in biochemical composition, with elevated protein and carbohydrate levels under salt stress that mimics the use of seawater. Mixotrophic cultivation with BWW and SW also influenced the FAME profile, enhancing the content of C16:0 and C18:1 FAMES. The purity (EP of 1.15) and yield (100 mg g-1) of PC were notably higher in mixotrophic cultures, indicating the potential for commercial applications in food, cosmetics, and pharmaceuticals. This research underscores the benefits of integrating the use of saline water with waste valorization in microalgae cultivation, promoting sustainability and economic efficiency in biotechnological processes.

Chromatic acclimation in cyanobacteria renders robust photosynthesis and fitness in dynamic light environment: Recent advances and future perspectives.

Cyanobacteria are photoautotrophic organisms that use light and water as a source of energy and electrons, respectively, to fix atmospheric carbon dioxide and release oxygen as a by-product during photosynthesis. However, photosynthesis and fitness of organisms are challenged by seasonal and diurnal fluctuations in light environments. Also, the distribution of cyanobacteria in a water column is subject to changes in the light regime. The quality and quantity of light change significantly in low and bright light environments that either limit photochemistry or result in photoinhibition due to an excess amount of light reaching reaction centers. Therefore, cyanobacteria have to adjust their light-harvesting machinery and cell morphology for the optimal harvesting of light. This adjustment of light-harvesting involves remodeling of the light-harvesting complex called phycobilisome or incorporation of chlorophyll molecules such as chlorophyll d and f into their light-harvesting machinery. Thus, photoacclimation responses of cyanobacteria at the level of pigment composition and cell morphology maximize their photosynthetic ability and fitness under a dynamic light environment. Cyanobacteria exhibit different types of photoacclimation responses that are commonly known as chromatic acclimation (CA). In this work, we discuss different types of CA reported in cyanobacteria and present a molecular mechanism of well-known type 3 CA where phycoerythrin and phycocyanin of phycobilisome changes according to light signals. We also include other aspects of type 3 CA that have been recently studied at a molecular level and highlight the importance of morphogenes, cytoskeleton, and carboxysome proteins. In summary, CA gives a unique competitive benefit to cyanobacteria by increasing their resource utilization ability and fitness.

Energetic Landscape and Terminal Emitters of Phycobilisome Cores from Quantum Chemical Modeling.

Phycobilisomes (PBs) are giant antenna supercomplexes of cyanobacteria that use phycobilin pigments to capture sunlight and transfer the collected energy to membrane-bound photosystems. In the PB core, phycobilins are bound to particular allophycocyanin (APC) proteins. Some phycobilins are thought to be terminal emitters (TEs) with red-shifted fluorescence. However, the precise identification of TEs is still under debate. In this work, we employ multiscale quantum-mechanical calculations to disentangle the excitation energy landscape of PB cores. Using the recent atomistic PB structures from Synechoccoccus PCC 7002 and Synechocystis PCC 6803, we compute the spectral properties of different APC trimers and assign the low-energy pigments. We show that the excitation energy of APC phycobilins is determined by geometric and electrostatic factors and is tuned by the specific protein-protein interactions within the core. Our findings challenge the simple picture of a few red-shifted bilins in the PB core and instead suggest that the red-shifts are established by the entire TE-containing APC trimers. Our work provides a theoretical microscopic basis for the interpretation of energy migration and time-resolved spectroscopy in phycobilisomes.

Optimization of Phycocyanobilin Synthesis in E. coli BL21: Biotechnological Insights and Challenges for Scalable Production.

Phycocyanobilin (PCB) is a small chromophore found in certain phycobiliproteins, such as phycocyanins (PCs) and allophycocyanins (APCs). PCB, along with other phycobilins (PBs) and intermediates such as biliverdin (BV) or phycoerythrobilin (PEB), is attracting increasing biotechnological interest due to its fluorescent and medicinal properties that allow potential applications in biomedicine and the food industry. This study aims to optimize PCB synthesis in Escherichia coli BL21 (DE3) and scale the process to a pre-industrial level. Parameters such as optimal temperature, inducer concentration, initial OD600, and stirring speed were analyzed in shake flask cultures to maximize PCB production. The best results were obtained at a temperature of 28 °C, an IPTG concentration of 0.1 mM, an initial OD600 of 0.5, and an orbital shaking speed of 260 rpm. Furthermore, the optimized protocol was scaled up into a 2 L bioreactor batch, achieving a maximum PCB concentration of 3.8 mg/L. Analysis of the results revealed that biosynthesis of exogenous PBs in Escherichia coli BL21 (DE3) is highly dependent on the metabolic burden of the host. Several scenarios, such as too rapid growth, high inducer concentration, or mechanical stress, can advance entry into the stationary phase. That progressively halts pigment synthesis, leading, in some cases, to its excretion into the growth media and ultimately triggering rapid degradation by the host. These conclusions provide a promising protocol for scalable PCB production and highlight the main biotechnological challenges to increase the yields of the process.

True-solution-scale utilization of natural chlorophyll a in aqueous media through cooperative aggregation with phycocyanin.

The challenge of applying chlorophyll(Chl) in aqueous media has been a significant obstacle to the diversified development of Chl a-related industries. This study presents the first report on the true-solution-scale utilization of Chl in aqueous media through the construction of chlorophyll a-phycocyanin (Chls-PC) composite nanoparticles. This study determined the optimal conditions for Chls-PC preparation: a composite ratio of 1:25, a solvent ratio of 1:4, and a stirring time of 1 h. Fluorescence spectroscopy, transmission electron microscope, and confocal microscopy confirmed Chl a and PC aggregation. Surface hydrophobicity and contact angle measurements showed that Chls-PC water solubility was similar to PC and much higher than Chl. Infrared spectroscopy, quantum chemical calculations, X-ray photoelectron spectroscopy, and molecular dynamics simulations elucidated the water solubilization mechanism of Chls-PC both experimentally and theoretically. This research provides theoretical guidance for the development and production of water-based products using Chl as a raw material.

Role of cultivation parameters in carbohydrate accretion for production of bioethanol and C-phycocyanin from a marine cyanobacterium Leptolyngbya valderiana BDU 41001: A sustainable approach.

The investigation aimed to augment carbohydrate accumulation in the marine cyanobacterium Leptolyngbya valderiana BDU 41001 to facilitate bioethanol production. Under the standardised physiochemical condition (SPC), i.e. 90 µmol photon m-2 s-1 light intensity, initial culture pH 8.5, 35 °C temperature and mixing at 150 rpm increased the carbohydrate productivity ∼70 % than the control, while a 47 % rise in content was obtained under the nitrate (N)-starved condition. Therefore, a two-stage cultivation strategy was implemented, combining SPC at the 1st stage and N starvation at the 2nd stage, resulting in 80 % augmentation of carbohydrate yield, which enhanced the bioethanol yield by ∼86 % as compared to the control employing immobilised yeast fermentation. Moreover, biomass utilisation was maximised by extracting C-phycocyanin, where a ∼77 % rise in productivity was recorded under the SPC. This study highlights the potential of L. valderiana for pilot-scale biorefinery applications, advancing the understanding of sustainable biofuel production.

Effects of light quality and intensity on phycobiliprotein productivity in two Leptolyngbya strains isolated from southern Bahia's Atlantic Forest.

Cyanobacterial phycocyanin and phycoerythrin are gaining commercial interest due to their nutrition and healthcare values. This research analyzed the biomass accumulation and pigment production of two strains of Leptolyngbya under different combinations of light colors and intensities. The results showed that while Leptolyngbya sp.4 B1 (B1) produced all phycobiliproteins, Leptolyngbya sp.5 F2 (F2) only had phycocyanin and allophycocyanin. Both the color of the light and its light intensity affect the biomass accumulation and phycoerythrin concentration in strain B1. Although white light at medium intensity (50 µmol m-2 s-1) causes greater biomass accumulation (1.66 ± 0.13 gDW L-1), low-intensity (25 µmol m-2 s-1) green light induces lower biomass accumulation with twice the pigment content (87.70 ± 2.46 mg gDW -1), culminating in 71% greater productivity. In contrast, for the F2 strain, light intensity positively influenced biomass and pigment accumulation, being observed 2.25 ± 0.10 gDW L-1 under white light at 100 µmol m-2 s-1 and higher phycocyanin concentration (138.38 ± 3.46 mg gDW -1) under red light at 100 µmol m-2 s-1. These findings provide insights into optimizing the growth conditions by altering the intensity and wavelength of light for future production of phycocyanin and phycoerythrin from local cyanobacteria.

Probing the structural stability of R-phycocyanin under pressure.

The red macroalgae Porphyra, commonly known as Nori, is widely used as food around the world due to its high nutrient content, including the significant abundance of colored phycobiliproteins (PBPs). Among these, R-phycocyanin (R-PC) stands out for its vibrant purple color and numerous bioactive properties, making it a valuable protein for the food industry. However, R-PC's limited thermal stability necessitates alternative processing methods to preserve its color and bioactive properties. Our study aimed to investigate the in-situ stability of oligomeric R-PC under high pressure (HP) conditions (up to 4000 bar) using a combination of absorption, fluorescence, and small-angle X-ray scattering (SAXS) techniques. The unfolding of R-PC is a multiphase process. Initially, low pressure induces conformational changes in the R-PC oligomeric form (trimers). As pressure increases above 1600 bar, these trimers dissociate into monomers, and at pressures above 3000 bar, the subunits begin to unfold. When returned to atmospheric pressure, R-PC partially refolds, retaining 50% of its original color absorbance. In contrast, heat treatment causes irreversible and detrimental effects on R-PC color, highlighting the advantages of HP treatment in preserving both the color and bioactive properties of R-PC compared to heat treatment.

Molecular origins of absorption wavelength variation among phycocyanobilin-binding proteins.

Phycocyanobilin (PCB)-binding proteins, including cyanobacteriochromes and phytochromes, function as photoreceptors and exhibit a wide range of absorption maximum wavelengths. To elucidate the color-tuning mechanisms among these proteins, we investigated seven crystal structures of six PCB-binding proteins: Anacy_2551g3, AnPixJg2, phosphorylation-responsive photosensitive histidine kinase, RcaE, Sb.phyB(PG)-PCB, and Slr1393g3. Employing a quantum chemical/molecular mechanical approach combined with a polarizable continuum model, our analysis revealed that differences in absorption wavelengths among PCB-binding proteins primarily arise from variations in the shape of the PCB molecule itself, accounting for a ∼150 nm difference. Remarkably, calculated excitation energies sufficiently reproduced the absorption wavelengths of these proteins spanning ∼200 nm, including 728 nm for Anacy_2551g3. However, assuming the hypothesized lactim conformation resulted in a significant deviation from the experimentally measured absorption wavelength for Anacy_2551g3. The significantly red-shifted absorption wavelength of Anacy_2551g3 can unambiguously be explained by the significant overlap of molecular orbitals between the two pyrrole rings at both edges of the PCB chromophore without the need to hypothesize lactim formation.

W/O/W Pickering emulsions stabilized by complex modified phycocyanin.

BACKGROUND: A water-in-oil-in-water (W/O/W) double emulsion can simultaneously load hydrophilic and hydrophobic substances due to its unique two-membrane, three-phase structure. However, thermodynamic instability greatly limits the application of double emulsions in food processing. Further development of Pickering emulsions based on proteins, etc., can improve the stability and loading capacity. It is of great significance to promote their practical application. RESULTS: Herein, we prepared ultrasound pretreatment complex glycation-modified phycocyanin (UMPC) to stabilize a W/O/W Pickering emulsion for the codelivery of vitamin B12 (VB12) and vitamin E (VE). First, an inner water phase and oil phase containing polyglycerin polyricinoleate were homogenized to prepare a W/O emulsion. Subsequently, the W/O emulsion was homogenized with an outer water phase containing UMPC to obtain a W/O/W Pickering emulsion. A gel-like inner phase emulsion with excellent storage and thermal stabilities was obtained under the condition that the W/O emulsion volume ratio was 80% and the UMPC was stabilized by 10 g kg-1. The double emulsion after loading VB12 and VE showed good encapsulation effect during the storage period, the encapsulation rate could reach more than 90%, it also showed excellent protection effect under long-time storage and UV irradiation and the retention rate increased by more than 65%. In addition, the bioavailability of VB12 and VE significantly increased during simulated gastrointestinal digestion and reached 46.02% and 52.43%, respectively. CONCLUSION: These results indicate that the UMPC-stabilized W/O/W Pickering emulsion is an effective carrier for the codelivery of hydrophilic and hydrophobic bioactive molecules and also provides a means for useful exploration of an efficient and stable emulsion system stabilized by biological macromolecules. © 2024 Society of Chemical Industry.

C-Phycocyanin Prevents Oxidative Stress, Inflammation, and Lung Remodeling in an Ovalbumin-Induced Rat Asthma Model.

Asthma is a chronic immunological disease related to oxidative stress and chronic inflammation; both processes promote airway remodeling with collagen deposition and matrix thickening, causing pulmonary damage and lost function. This study investigates the immunomodulation of C-phycocyanin (CPC), a natural blue pigment purified from cyanobacteria, as a potential alternative treatment to prevent the remodeling process against asthma. We conducted experiments using ovalbumin (OVA) to induce asthma in Sprague Dawley rats. Animals were divided into five groups: (1) sham + vehicle, (2) sham + CPC, (3) asthma + vehicle, (4) asthma + CPC, and (5) asthma + methylprednisolone (MP). Our findings reveal that asthma promotes hypoxemia, leukocytosis, and pulmonary myeloperoxidase (MPO) activity by increasing lipid peroxidation, reactive oxygen and nitrogen species, inflammation associated with Th2 response, and airway remodeling in the lungs. CPC and MP treatment partially prevented these physiological processes with similar action on the biomarkers evaluated. In conclusion, CPC treatment enhanced the antioxidant defense system, thereby preventing oxidative stress and reducing airway inflammation by regulating pro-inflammatory and anti-inflammatory cytokines, consequently avoiding asthma-induced airway remodeling.

Functional Modification of Cyanobacterial Phycobiliprotein and Phycobilisomes through Bilin Metabolism Control.

Phycobilisomes (PBSs) are light-harvesting antenna complexes in cyanobacteria that adapt to diverse light environments through the use of phycobiliproteins within the PBS structures. Freshwater cyanobacteria, such as Synechococcus elongatus PCC 7942, thrive under red light because of the presence of phycocyanin (PC) and its chromophore, phycocyanobilin (PCB), in the PBS. Cyanobacteria in shorter-wavelength light environments such as green light, employ phycoerythrin paired with phycoerythrobilin (PEB) along with PC in the PBS. Synthetic biology studies have shown that PEB production can be achieved by expression of the heterologous PEB synthases 15,16-dihydrobiliverdin:ferredoxin oxidoreductase (PebA) and PEB:ferredoxin oxidoreductase (PebB), leading to PEB accumulation and cellular browning. This approach is genetically unstable, and the properties of the resulting PEB-bound PBS complexes remain uncharacterized. In this study, we engineered a novel strain of Synechococcus 7942 PEB1 with finely tuned control of PEB biosynthesis. PEB1 exhibited a reversible change in the color of the culture from green to brown and pink based on PebA and PebB induction levels. High induction led to complete PCB-to-PEB substitution, causing the disassembly of the PBS rod complex. In contrast, low induction levels of PebA and PebB resulted in the formation of a stable chimeric PBS complex with partial PCB-to-PEB substitution. This acclimation enabled efficient light harvesting in the green spectrum and energy transfer to the photosynthetic reaction center. These findings, which improve our understanding of PBS and highlight the structural importance of the bilin composition, provide a foundation for future studies on PBS adaptation in bioengineering, synthetic biology, and renewable energy.

C-phycocyanin reinforces autophagy to block pulmonary fibrogenesis by inhibiting lncIAPF biogenesis.

Pulmonary fibrosis is a chronic and irreversible progressive lung disease caused by various factors, such as age and environmental pollution. With countries stepping into an aging society and the seriousness of environmental pollution caused by global industrialization, the incidence of pulmonary fibrosis is annually increasing. However, no effective drug is available for pulmonary fibrosis treatment. C-phycocyanin (C-PC), extracted from blue-green algae, has good water solubility and antioxidation. This study elucidated that C-PC reinforces autophagy to block pulmonary fibrogenesis by inhibiting long noncoding RNA (lncRNA) biogenesis in vivo and in vitro. Cleavage under targets and release using nuclease (CUT & RUN)-PCR, co-immunoprecipitation (Co-IP), and nuclear-cytoplasmic separation experiments clarified that C-PC blocked the nuclear translocation of activating transcription factor 3 (ATF3) to prevent the binding between ATF3 and transcription factor Smad3, thereby hindering lncIAPF transcription. Human antigen R (HuR) truncation experiment and RNA binding protein immunoprecipitation (RIP) were then performed to identify the binding domain with lncIAPF in the 244-322 aa of HuR. lncIAPF exerted its profibrogenic function through the binding protein HuR, a negative regulator of autophagy. In summary, C-PC promoted autophagy via down-regulating the lncIAPF-HuR-mediated signal pathway to alleviate pulmonary fibrosis, showing its potential as a drug for treating pulmonary fibrosis. Exploring how C-PC interacts with biological molecules will help us understand the mechanism of this drug and provide valuable target genes to design new drugs.

Bioactivity of selenium nanoparticles biosynthesized by crude phycocyanin extract of Leptolyngbya sp. SSI24 cultivated on recycled filter cake wastes from sugar-industry.

BACKGROUND: Beet filter cake (BFC) is a food-grade solid waste produced by the sugar industry, constituting a permanent source of pollution. Cyanobacteria are considered a sustainable resource for various bioactive compounds such as phycocyanin pigment with valuable applications. This study aimed to use beet filter cake extract (BFCE) as an alternative medium for the economic cultivation of cyanobacterium Leptolyngbya sp. SSI24 PP723083, then biorefined the bioactive component such as phycocyanin pigment that could be used in the production of selenium nanoparticles. RESULTS: The results of the batch experiment displayed that the highest protein content was in BG11medium (47.9%); however, the maximum carbohydrate and lipid content were in 25% BFCE (15.25 and 10.23%, respectively). In addition, 75% BFCE medium stimulated the phycocyanin content (25.29 mg/g) with an insignificant variation compared to BG11 (22.8 mg/g). Moreover, crude phycocyanin extract from Leptolyngbya sp SSI24 cultivated on BG11 and 75% BFCE successfully produced spherical-shaped selenium nanoparticles (Se-NPs) with mean sizes of 95 and 96 nm in both extracts, respectively. Moreover, XRD results demonstrated that the biosynthesized Se-NPs have a crystalline nature. In addition, the Zeta potential of the biosynthesized Se-NPs equals - 17 mV and - 15.03 mV in the control and 75% BFCE treatment, respectively, indicating their stability. The biosynthesized Se-NPs exhibited higher effectiveness against Gram-positive bacteria than Gram-negative bacteria. Moreover, the biosynthesized Se-NPs from BG11 had higher antioxidant activity with IC50 of 60 ± 0.7 compared to 75% BFCE medium. Further, Se-NPs biosynthesized from phycocyanin extracted from Leptolyngbya sp cultivated on 75% BFCE exhibited strong anticancer activity with IC50 of 17.31 ± 0.63 µg/ml against the human breast cancer cell line. CONCLUSIONS: The BFCE-supplemented medium can be used for the cultivation of cyanobacterial strain for the phycocyanin accumulation that is used for the green synthesis of selenium nanoparticles that have biological applications.

Red/green cyanobacteriochromes acquire isomerization from phycocyanobilin to phycoviolobilin.

Cyanobacteriochromes (CBCRs) are unique cyanobacteria-specific photoreceptors that share a distant relation with phytochromes. Most CBCRs contain conserved cysteine residues known as canonical Cys, while some CBCRs have additional cysteine residues called second Cys within the DXCF motif, leading to their classification as DXCF CBCRs. They typically undergo a process where they incorporate phycocyanobilin (PCB) and subsequently isomerize it to phycoviolobilin (PVB). Conversely, CBCRs with conserved Trp residues and without the second Cys are called extended red/green (XRG) CBCRs. Typical XRG CBCRs bind PCB without undergoing PCB-to-PVB isomerization, displaying red/green reversible photoconversion, and there are also atypical CBCRs that exhibit diverse photoconversions. We discovered novel XRG CBCRs with Cys residue instead of the conserved Trp residue. These novel XRG CBCRs exhibited the ability to isomerize PCB to PVB, displaying green/teal reversible photoconversion. Through sequence- and structure-based comparisons coupled with mutagenesis experiments, we identified three amino acid residues, including the Cys residue, crucial for facilitating PCB-to-PVB isomerization. This research expands our understanding of the diversity of XRG CBCRs, highlighting the remarkable molecular plasticity of CBCRs.

Green and sustainable extraction of phycocyanin from Spirulina platensis by temperature-sensitive polymer-based aqueous two-phase system and mechanism study.

In this study, a sustainable and environmentally friendly method was developed for the enrichment and purification of phycocyanin from Spirulina platensis. This was achieved by utilizing a temperature-sensitive polymer, Pluronic F68, in an aqueous two-phase solvent system. The phase behavior of the temperature-sensitive polymer-based biphasic system was evaluated. The extraction conditions were optimized by both single-factor experiments and response surface methodology. Under the optimal conditions, the upper polymer-rich phase was recycled for sustainable phycocyanin extraction, resulting in a grade of 3.23 during the third extraction cycle. Pluronic F68 could be efficiently recovered and reused during the extraction process. The interaction mechanism between Pluronic F68 and phycocyanin was systematically studied using FT-IR and fluorescence analysis. This was further complemented by static and dynamic calculation of molecular motion through molecular docking and molecular dynamics simulation, indicating that hydrophobic segment of Pluronic F68 played a key role in the binding process with phycocyanin.

Teal-light absorbing cyanobacterial phytochrome superfamily provides insights into the diverse mechanisms of spectral tuning and facilitates the engineering of photoreceptors for optogenetic tools.

Cyanobacteriochromes (CBCRs) are distinctive tetrapyrrole (bilin)-binding photoreceptors exclusively found in cyanobacteria. Unlike canonical phytochromes, CBCRs require only a GAF (cGMP-phosphodiesterase/adenylate cyclase/FhlA) domain for autolyase activity to form a bilin adduct via a Cys residue and cis-trans photoisomerization. Apart from the canonical Cys, which attaches covalently to C31 in the A-ring of the bilin, some GAF domains of CBCRs contain a second-Cys in the Asp-Xaa-Cys-Phe (DXCF) motif, responsible for isomerization of phycocyanobilin (PCB) to phycoviolobilin (PVB) and/or for the formation of a reversible 2nd thioether linkage to the C10. Unlike green/teal-absorbing GAF proteins lacking ligation activity, the second-Cys in another teal-absorbing lineage (DXCF blue/teal group) exhibits both isomerization and ligation activity due to the presence of the Tyr instead of His next to the canonical Cys. Herein, we discovered an atypical CBCR GAF protein, Tpl7205g1, belonging to the DXCF blue/teal group, but having His instead of Tyr next to the first-Cys. Consistent with its subfamily, the second-Cys of Tpl7205g1 did not form a thioether linkage at C10 of PCB, showing only isomerization activity. Instead of forming 2nd thioether linkage, this novel GAF protein exhibits a pH-dependent photocycle between protonated 15Z and deprotonated 15E. Site-directed mutagenesis to the GAF scaffolds revealed its combined characteristics, including properties of teal-DXCF CBCRs and red/green-absorbing CBCRs (XRG CBCRs), suggesting itself as the evolutionary bridge between the two CBCR groups. Our study thus sheds light on the expanded spectral tuning characteristics of teal-light absorbing CBCRs and enhances feasibility of engineering these photoreceptors.