Structural and functional dynamics of tyrosine amino acid in phycocyanin of hot-spring cyanobacteria: A possible pathway for internal energy transfer

Characterization of a Novel Monoclonal Antibody with High Affinity and Specificity against Aflatoxins: A Discovery from Rosetta Antibody-Ligand Computational Simulation

Aflatoxin B1 (AFB1) accumulates in crops, where it poses a threat to human health. To detect AFB1, anti-AFB1 monoclonal antibodies have been developed and are widely used. While the sensitivity and specificity of these antibodies have been extensively studied, information regarding the atomic-level docking of AFB1 (and its derivatives) with these antibodies is limited. Such information is crucial for understanding the key interactions that are required for high affinity and specificity in aflatoxin binding. First, a 3D comparative model of anti-AFB1 antibody (Ab-4B5G6) was predicted from the sequence using RosettaAntibody. We then utilized RosettaLigand to dock AFB1 onto ten homology models, producing a total of 10,000 binding modes. Interestingly, the best-scoring mode predicted strong interactions involving four sites within the heavy chain: ALA33, ASN52, HIS95, and TRP99. Importantly, these strong binding interactions exclusively involve the variable domain of the heavy chain. The best-scoring mode with AFB1 was also obtained through AF multimer combined with RosettaLigand, and two interactions at TRP and HIS were consistent with those found by Rosetta antibody-ligand computational simulation. The role of tryptophan in π interactions in antibodies was confirmed through mutation experiments, and the resulting mutant (W99A) exhibited a >1000-fold reduction in binding affinity for AFB1 and analogs, indicating the effect of tryptophan on the stability of CDR-H3 region. Additionally, we evaluated the binding of two glycolic acid-derived molecular derivatives (with impaired hydrogen bonding potential), and these derivatives (AFB2-GA and AFG2-GA) demonstrated a very weak binding affinity for Ab-4B5G6. The heavy chain was successfully isolated, and its sensitivity and specificity were consistent with those of the intact antibody. The homology models of variable heavy (VH) single-domain antibodies were established by RosettaAntibody, and the docking analysis revealed the same residues, including Ala, His, and Trp. Compared to the potential binding mode of fragment variable (FV) region, the results from a model of VH indicated that there are seven models involved in hydrophobic interaction with TYR32, which is usually referred to as polar amino acid and has both hydrophobic and hydrophilic features depending on the circumstances. Our work encompasses the entire process of Rosetta antibody-ligand computational simulation, highlighting the significance of variable heavy domain structural design in enhancing molecular interactions.

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.

Performance and degradation mechanism of phycocyanin by Cu-TiO2 photocatalytic treatment

The efficiency, transformation products, and mechanism of phycocyanin removal from water by simulated sunlight/Cu-decorated TiO₂ photocatalyst treatment were studied. After 360 min of photocatalytic degradation, the removal rate of PC was higher than 96%, about 47% of DON was oxidized into NH⁴⁺-N, NO^3- and NO^2-. ·OH was the main active species in the photocatalytic system, which contributes about 55.7% to PC degradation efficiency, H⁺ and ·O^2- also contributed to the photocatalytic activity. The degradation process of phycocyanin is firstly caused by the attack of free radicals, which leads to the disintegration of the chromophore group PCB and the apoprotein, and then apoprotein peptide chain was broken to generate small molecule dipeptides, amino acids, and their derivatives. Amino acid residues sensitive to free radical action in phycocyanin peptide chain include most hydrophobic amino acids such as leucine, isoleucine, proline, valine, phenylalanine, and some hydrophilic amino acids which are easily oxidized such as lysine and arginine. Small molecular peptides (dipeptides), amino acids, and their derivatives are broken off and released into water bodies for further reaction and degradation into smaller molecular weight substances. During this process, part of organic nitrogen was transferred to inorganic nitrogen. When photocatalytic oxidation lasts for 300 min, NH⁴⁺ increases from 0.41 mg/L to 2.21 mg/L, and DON removal rate reaches 47%. The Cu-TiO₂ photocatalyst was found to decrease the CHCl₃ formation potential; however, it exacerbated the production of dichloroacetamide (DCAcAm) and dichloroacetonitrile (DCAN) beyond their initial levels. The divergent trends of these disinfection by-products are due to the fundamental differences in the precursor material.

Construction of fluorescent logic gates for the detection of mercury(II) and ciprofloxacin based on phycocyanin

Chemical pollutants such as heavy metals and antibiotics in the environment pose a huge threat to humans and animals. Our studies have demonstrated that the fluorescence of phycocyanin showed quenching responses towards both mercury (Hg2+) and ciprofloxacin (CIP), which acted in accordance with the "OR" molecular logic gate. In order to discriminate Hg2+ and CIP in application scenarios, cysteine (Cys) was utilized to design another "INHIBIT" logic gate, in which Hg2+ and Cys were the two inputs. Thus, an intelligent biosensor with dual-target identification capacity was successfully developed by using a fluorescent natural protein in an ingenious logic gate system.

Tuning C-Phycocyanin Photoactivity via pH-Mediated Assembly-Disassembly

Environment-triggered protein conformational changes have garnered wide interest in both fundamental research, for deciphering in vivo acclimatory responses, and practical applications, for designing stimuli-responsive probes. Here, we propose a protein-chromophore regulatory mechanism that allows for manipulation of C-phycocyanin (C-PC) from Spirulina platensis by environmental pH and UV irradiation. Using small-angle X-ray scattering, a pH-mediated C-PC assembly-disassembly pathway, from monomers to nonamers, was unraveled. Such flexible protein matrices impart tunability to the embedded tetrapyrroles, whose photochemical behaviors were found to be modulated by protein assembly states. UV irradiation on C-PC triggers pH-dependent singlet oxygen (¹O₂) generation and conformational changes. Intermolecular photo-crosslinking occurs at pH 5.0 via dityrosine species, which bridges solution-based C-PC oligomers into unprecedented dodecamers and 24-mers. These supramolecular assemblies impart C-PC at pH 5.0, which significantly enhanced ¹O₂ yield, fluorescence, and photostability relative to those at other pH values, a finding that makes C-PC appealing for tumor-targeted photodynamic therapy.

The formation of phycocyanin-EGCG complex for improving the color protection stability exposing to light

Phycocyanin (PC) is a natural pigment-protein complex in food dye applications. In this study, a phycocyanin-epigallocatechin gallate (EGCG) complex (PE) was prepared and the effects of EGCG on the structure and color stability of PC were evaluated. The fluorescence results showed that the binding number n was 62.1 ± 3.41 (EGCG/PC) and the binding constant K was 4.39 (±0.2) × 10⁵ M^-1, indicating a weak-binding interaction. Fourier transform-infrared analysis showed that EGCG caused structural changes in PC by partially uncoiling α-helix and increasing β-sheet content. The EGCG induced a PC association at a reaction molar ratio above 40:1 (EGCG/PC). Moreover, EGCG protected phycocyanobilin against color fading, making PE more stable relative to PC under 8-days storage in light. This study provides a novel scheme to stabilize PC by forming a complex with polyphenols, which will facilitate the PC application as a natural blue pigment in food.

In vitro and in vivo impact assessment of eco-designed CuO nanoparticles on non-target aquatic photoautotrophic organisms

This work has assessed the impact of copper oxide nanoparticles (CuONPs), designed via green route, toward photosynthetic apparatus on aquatic photoautotrophic organisms. In order to filling knowledge gaps, in vitro and in vivo assays were performed, using cyanobacterial phycocyanin (C-PC) from Arthrospira platensis and Lemna valdiviana plants (duckweed), respectively. Impairment in light energy transfer became evident in C-PC exposed to CuONPs, giving rise to an increase of light absorption and a suppression of fluorescence emission. Fourier transform infrared spectroscopy (FTIR) results showed that C-PC structures might be altered by the nanoparticles, also revealed that CuONPs preferably interacts with -NH functional groups. The data also revealed that CuONPs affected the chlorophyll a content in duckweed leaves. In addition, photosystem II (PSII) performance was significantly affected by CuONPs, negatively impacting the PSII photochemical network. In summary, the results point out that, even eco-friendly designed, CuONPs may negatively affect the photosynthetic process when accumulated by aquatic photoautotrophs.

In vitro assessment of the toxicity of lead (Pb2+) to phycocyanin

This work reports the influence of lead (Pb²⁺) on fluorescence characteristics and protein structure of phycocyanin molecules experimentally in vitro. The fluorescence intensity decreases with the increasing concentration of Pb²⁺ from 0 to 5 × 10^-5 mol L^-1, showing the fluorescence quenching of phycocyanin by Pb²⁺. The quenching process is suggested to be static regarding the calculation results and the experimental results of time-resolved fluorescence decay profiles. The synchronous fluorescence spectra show that the effect of Pb²⁺ on the Tyr residues of phycocyanin is more significant than the Trp residues. The forming of aggregation by the interaction of Pb²⁺ with phycocyanin molecules is suggested from the results of resonance light scattering spectra. The UV-Vis spectra of the protein skeleton of phycocyanin have a red-shift of about 10 nm with increasing the Pb²⁺ concentration from 0 to 5 × 10^-5 mol L^-1, indicating a change in the protein skeleton and its secondary structure. With the increasing Pb²⁺ concentration, the two negative peaks (209 nm and 218 nm) on circular dichroism spectra become smaller, showing a decrease of the α-helix structure. These results may give people a deeper understanding of that how the heavy metal (Pb²⁺) can affect the chemo-physical properties of phycocyanin.