Heat-induced self-assembling of BSA at the isoelectric point

Mechanisms of denitrifying granular sludge disintegration and calcium ion-enhanced re-granulation in acidic wastewater treatment

Granular sludge is an alternative technology for the direct treatment of acidic nitrate-containing wastewater. Rapid remediation of disintegrated granules is essential to achieve efficient nitrogen removal. In this study, denitrifying granules were inactivated and disintegrated when the influent nitrate-nitrogen concentration was elevated from 240 to 360 mg L-1 in acidic wastewater (pH = 4.1) in a sequencing batch reactor. Tightly bound extracellular polymeric substances (TB-EPS) decreased by 60%, and extracellular protein (PN) was the main component of the reduced EPS. The three-dimensional excitation emission matrices (3D-EEM) results confirmed that the PNs that decreased were mainly tryptophan-like, tyrosine-like, and aromatic. This study further confirmed that the decrease in PN was mainly from the destruction of C=O (amide I) and N-H functional groups. Overloading of nitrogen-inhibited denitrifying activity and the destruction and dissolution of TB-EPS by acidic pH were responsible for granule disintegration, with PNs playing a major role in maintaining granule stability. Based on this, new granules with an average particle size of 454.4 μm were formed after calcium chloride addition; EPS nearly doubled during granule formation with PN as the dominant component, accounting for 64.7-78.4% of the EPS. Atomic force microscopy (AFM) revealed that PN-PN adhesion increased by 1.6-4.9 times in the presence of calcium ions, accelerating the re-granulation of disintegrated particles. This study provides new insights into the disintegration and remediation of granular sludge under acidic conditions.

The Effect of Nanoscale Modification of Nisin by Different Milk-Derived Proteins on Its Physicochemical Properties and Antibacterial Activity

Nisin is used as a natural food preservative because of its broad-spectrum antimicrobial activity against Gram-positive bacteria. However, free nisin is susceptible to various factors that reduce its antimicrobial activity. Milk protein, a protein derived from milk, has self-assembly properties and is a good carrier of bioactive substances. In this study, lactoferrin-nisin nanoparticles (L-N), bovine serum albumin-nisin nanoparticles (B-N), and casein-nisin nanoparticles (C-N) were successfully prepared by a self-assembly technique, and then their properties were investigated. The studies revealed that lactoferrin (LF) and nisin formed L-N mainly through hydrophobic interactions and hydrogen bonding, and L-N had the best performance. The small particle size (29.83 ± 2.42 nm), dense reticular structure, and good thermal stability, storage stability, and emulsification of L-N laid a certain foundation for its application in food. Further bacteriostatic studies showed that L-N enhanced the bacteriostatic activity of nisin, with prominent inhibitory properties against Listeria monocytogenes, Staphylococcus aureus, and Bacillus cereus, which mainly disrupted the cell membrane of the bacteria. The above results broaden our understanding of milk protein-nisin nanoparticles, while the excellent antibacterial activity of L-N makes it promising for application as a novel food preservative, which will help to improve the bioavailability of nisin in food systems.

Experimental procedures to investigate fibrillation of proteins

The unwanted phenomenon of protein fibrillation is observed in vivo and during therapeutic protein development in the industry. Protein aggregation is associated with various degenerative disorders and might induce immune-related challenges post-administration of biopharmaceutics. A pipeline for early detection, identification, and removal of pre-formed fibrils is needed to improve the quality, efficacy, and effectiveness of the formulation. Protein fibril formation is accompanied by unfolding, secondary structural changes and the formation of larger aggregates. However, most detection processes come with extensive sample preparation steps and inefficient repeatability, incurring a financial burden on research. The current article summarizes and critically discusses six simple yet powerful methods to detect aggregation phenomena in the line of detecting fibrillar aggregates in heat-induced bovine serum albumin protein. Comparing the native and heat-induced protein samples would provide insights about aggregates. Easy, inexpensive and optimized protocols for detecting the fibrillation of proteins are explained. The procedures mentioned here detected the appearance of β-sheet-rich fibrils in the heat-induced protein sample. The aggregation is characterized by enhanced thioflavin-T fluorescence, alteration in the intrinsic fluorescence, decrease in helicity and subsequent increase in β-sheet and appearance of particles with larger hydrodynamic diameters. •This article summarizes various analytical techniques to easily characterize the fibrillation of proteins.•Various techniques to detect the formation of β-sheet rich structures, changes in the secondary structures and size of aggregates have been discussed.•The stated methodologies are validated on a model protein, albumin.

Amyloidogenic and non-amyloidogenic molten globule conformation of β-lactoglobulin in self-crowded regime

Molecular insights on the β-lactoglobulin thermal unfolding and aggregation are derived from FTIR and UV Resonance Raman (UVRR) investigations. We propose an in situ and in real-time approach that thanks to the identification of specific spectroscopic markers can distinguish the two different unfolding pathways pursued by β-lactoglobulin during the conformational transition from the folded to the molten globule state, as triggered by the pH conditions. For both the investigated pH values (1.4 and 7.5) the greatest conformational variation of β-lactoglobulin occurs at 80 °C and a high degree of structural reversibility after cooling is observed. In acidic condition β-lactoglobulin exposes to the solvent its hydrophobic moieties in a much higher extent than in neutral solution, resulting on a highly open conformation. Moving from the diluted to the self-crowded regime, the solution pH and consequently the different molten globule conformation select the amyloid or non-amyloid aggregation pathway. At acidic condition the amyloid aggregates form during the heating cycle leading to the formation of transparent hydrogel. On the contrary, in neutral condition the amyloid aggregates never form. Information on the secondary structure conformational change of β-lactoglobulin and the formation of amyloid aggregates are obtained by FTIR spectroscopy and are related to the information of the structural changes localized around the aromatic amino acid sites by UVRR technique. Our results highlight a strong involvement of the chain portions where tryptophan is located on the formation of amyloid aggregates.

Rapid, sensitive detection of PFOA with smartphone-based flow rate analysis utilizing competitive molecular interactions during capillary action

Perfluorinated-alkyl substances (PFAS) pose an unmet threat to the public because they are not strictly monitored and regulated. Perfluorinated-carbon alkyl chains (PFOA), a type of PFAS, at 70 fg/μL is the current health and safety recommendation. Current testing methods for PFOA and PFAS chemicals include HPLC-MS/MS and molecularly imprinted polymers, which are expensive, time-consuming, and require training. In this work, PFOA and PFOS detection was performed on a paper microfluidic chip using competitive interactions between PFOA/PFOS, cellulose fibers, and various reagents (L-lysine, casein, and albumin). Such interactions altered the surface tension at the wetting front and, subsequently, the capillary flow rate. A smartphone captured the videos of this capillary action. The samples flowed through the channel in less than 2 min. Albumin worked the best in detecting PFOA, followed by casein. The detection limit was 10 ag/μL in DI water and 1 fg/μL in effluent (processed) wastewater. Specificity to other non-fluorocarbon surfactants was also tested, using anionic sodium dodecyl sulfate (SDS), non-ionic Tween 20, and cationic cetrimonium bromide (CTAB). A combination of the reagents successfully distinguished PFOA from all three surfactants at 100% accuracy. This low-cost, handheld assay can be an accessible alternative for rapid in situ estimation of PFOA concentration.

Phase Behavior, Self-Assembly, and Adhesive Potential of Cellulose Nanocrystal-Bovine Serum Albumin Amyloid Composites

Structural organization is ubiquitous throughout nature and contributes to the outstanding mechanical/adhesive performance of organisms including geckoes, barnacles, and crustaceans. Typically, these types of structures are composed of polysaccharide and protein-based building blocks, and therefore, there is significant research interest in using similar building blocks in the fabrication of high-performance synthetic materials. Via evaporation-induced self-assembly, the organization of cellulose nanocrystals (CNCs) into a chiral nematic regime results in the formation of structured CNC films with prominent mechanical, optical, and photonic properties. However, there remains an important knowledge gap in relating equilibrium suspension behavior to dry film structuring and other functional properties of CNC-based composite materials. Herein, we systematically investigate the phase behavior of composite suspensions of rigid CNCs and flexible bovine serum albumin (BSA) amyloids in relation to their self-assembly into ordered films and structural adhesives. Increasing the concentration of BSA amyloids in the CNC suspensions results in a clear decrease in the anisotropic fraction volume percent via the preferential accumulation of BSA amyloids in the isotropic regime (as a result of depletion interactions). This translates to a blue shift or compression of the chiral nematic pitch in dried films. Finally, we also demonstrate the synergistic adhesive potential of CNC-BSA amyloid composites, with ultimate lap shear strengths in excess of 500 N/mg. We anticipate that understanding the systematic relationships between material interactions and self-assembly in suspension such as those investigated here will pave the way for a new generation of structured composite materials with a variety of enhanced functionalities.

Injectable redox albumin-based hydrogel with in-situ loaded dihydromyricetin

Albumin is widely used in clinics due to its demonstrated biological safety and functional flexibility. Hydrogels derived from natural albumin possess high moisture retention ability and good biodegradability, making albumin ideal biomaterials compared with synthetic polymers. Herein, by reducing disulfide bonds in bovine serum albumin molecules with glutathione and re-oxidizing the free thiols using dimethyl sulfoxide (DMSO) as additional oxidant, three-dimensional network was assembled, leading to the formation of hydrogel. Meanwhile, DMSO is also an excellent solvent for many drugs, and the hydrophobic drug dihydromyricetin (DMY) can be well dissolved in DMSO. During the crosslinking reaction, DMSO participated in fabricating a porous albumin hydrogel network. At the same time, increased loading of DMY and sustained release of DMY were achieved, improving bioavailability of hydrophobic drug DMY. Rheological test and cytotoxicity assay proved excellent elasticity and biocompatibility of the hydrogel. Self-healing property and narrow-needle injection provided potential application of the hydrogel as biomedical materials. This method for formation hydrogels and in situ loading of drugs may expand to preparing other drug loaded hydrogels and find wide applications.

Quantitative estimation of chemical microheterogeneity through the determination of fuzzy entropy

Chemical micro-heterogeneity is an attribute of all living systems and most of the soft and crystalline materials. Its characterization requires a plethora of techniques. This work proposes a strategy for quantifying the degree of chemical micro-heterogeneity. First of all, our approach needs the collection of time-evolving signals that can be fitted through poly-exponential functions. The best fit is determined through the Maximum Entropy Method. The pre-exponential terms of the poly-exponential fitting function are used to estimate Fuzzy Entropy. Related to the possibility of implementing Fuzzy sets through the micro-heterogeneity of chemical systems. Fuzzy Entropy becomes a quantitative estimation of the Fuzzy Information that can be processed through micro-heterogeneous chemical systems. We conclude that our definition of Fuzzy Entropy can be extended to other kinds of data, such as morphological and structural distributions, spectroscopic bands and chromatographic peaks. The chemical implementation of Fuzzy sets and Fuzzy logic will promote the development of Chemical Artificial Intelligence.

Development of a rapid, high-sensitivity, low-cost fluorescence method for protein surface hydrophobicity determination using a Nanodrop fluorospectrometer

A microvolumetric method for surface hydrophobicity (H₀) determination of proteins using a Nanodrop fluorospectrometer was developed. This method reduces the protein and fluorophore quantities that are necessary for sample preparations and readings by two and three orders of magnitude, respectively, compared to conventional methods. In addition, readings can be obtained in just 2-6 s. Bovine serum albumin (BSA) and 1-anilino 8-naphthalene sulfonic acid (ANS) were used for the first optimization of appropriate fluorophore-protein conditions for H₀ determination (20 μM ANS, 0.5-4 μM BSA, pH 5). Based on validation guidelines, the novel method shows linear behavior, good intraday precision, accuracy, and sensitivity. This method was robust against several factors, as determined by a Youden-Steiner test. Additional surface hydrophobicity determinations using several proteins demonstrate suitable method applicability. The present microvolumetric method provides a reliable technique to determine the H₀ of proteins for pharmaceutical, biotechnological, and food applications.

Multi-length scale structural investigation of lysozyme self-assembly

Reactive amyloid oligomers are responsible for cytotoxicity in amyloid pathologies and because of their unstable nature characterizing their behavior is a challenge. The physics governing the self-assembly of proteins in crowded conditions is extremely complex and its comprehension, despite its paramount relevance to understanding molecular mechanisms inside cells and optimizing pharmaceutical processes, remains inconclusive. Here, we focus on the amyloid oligomerization process in self-crowded lysozyme aqueous solutions in acidic conditions. We reveal that the amyloid oligomers form at high protein concentration and low pH. Through multi-length scale spectroscopic investigations, we find that amyloid oligomers can further interconnect with each other by weak and non-specific interactions forming an extended network that leads to the percolation of the whole system. Our multi-length scale structural analysis follows the thermal history of amyloid oligomers from different perspectives and highlights the impact of hierarchical self-assembly of biological macromolecules on functional properties.

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Use of multi-length scale spectroscopies to characterize unstable amyloid oligomers

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Lysozyme form thermo-labile amyloid oligomers in self-crowded conditions

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Amyloid oligomers interact and form an extended hydrogel network

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Amyloid oligomers are responsible for the existence of the hydrogel matrix

Self-Healing Behavior of Polymer/Protein Hybrid Hydrogels

The paper presents the viscoelastic properties of new hybrid hydrogels containing poly(vinyl alcohol) (PVA), hydroxypropylcellulose (HPC), bovine serum albumin (BSA) and reduced glutathione (GSH). After heating the mixture at 55 °C, in the presence of GSH, a weak network is formed due to partial BSA unfolding. By applying three successive freezing/thawing cycles, a stable porous network structure with elastic properties is designed, as evidenced by SEM and rheology. The hydrogels exhibit self-healing properties when the samples are cut into two pieces; the intermolecular interactions are reestablished in time and therefore the fragments repair themselves. The effects of the BSA content, loaded deformation and temperature on the self-healing ability of hydrogels are presented and discussed through rheological data. Due to their versatile viscoelastic behavior, the properties of PVA/HPC/BSA hydrogels can be tuned during their preparation in order to achieve suitable biomaterials for targeted applications.

Protein Hydration in a Bioprotecting Mixture

We combined broad-band depolarized light scattering and infrared spectroscopies to study the properties of hydration water in a lysozyme-trehalose aqueous solution, where trehalose is present above the concentration threshold (30% in weight) relevant for biopreservation. The joint use of the two different techniques, which were sensitive to inter-and intra-molecular degrees of freedom, shed new light on the molecular mechanism underlying the interaction between the three species in the mixture. Thanks to the comparison with the binary solution cases, we were able to show that, under the investigated conditions, the protein, through preferential hydration, remains strongly hydrated even in the ternary mixture. This supported the water entrapment scenario, for which a certain amount of water between protein and sugar protects the biomolecule from damage caused by external agents.

Albumin-based dynamic double cross-linked hydrogel with self-healing property for antimicrobial application

Hydrogels as ideal material are widely used in biomedical field against bacterial infection. Hydrogels synthesized from natural protein possess better biocompatibility than that synthesized from synthetic polymers. In this work, we designed bovine serum albumin (BSA) based hydrogel via double dynamic crosslinking. The cleavage and rearrangement of disulfide bonds of BSA triggered by glutathione (GSH) forms a disulfide bridge network, and tetrakis (hydroxymethyl) phosphonium sulfate (THPS) grafts the amino groups of BSA by a Mannich-type reaction to form a second network. Integrating THPS into the BSA/GSH system enables gel formation and endows excellent antimicrobial properties. Rheological tests showed the hydrogel featuring elasticity, good mechanical strength and self-healing properties. Antibacterial and cytotoxicity tests proved the hydrogel excellent bacteriostatic ability and low cytotoxicity. This albumin-based hydrogel with low cost is expected to realize wide biomedical applications.