Protein folding at emulsion oil/water interfaces

Formation of β-Lactoglobulin Self-Assemblies via Liquid-Liquid Phase Separation for Applications beyond the Biological Functions

Proteins are like miracle machines, playing important roles in living organisms. They perform vital biofunctions by further combining together and/or with other biomacromolecules to form assemblies or condensates such as membraneless organelles. Therefore, studying the self-assembly of biomacromolecules is of fundamental importance. In addition to their biological activities, protein assemblies also exhibit extra properties that enable them to achieve applications beyond their original functions. Herein, this study showed that in the presence of monosaccharides, ethylene glycols, and amino acids, β-lactoglobulin (β-LG) can form assemblies with specific structures, which were highly reproducible. The mechanism of the assembly process was studied through multi-scale observations and theoretical analysis, and it was found that the assembling all started from the formation of solute-rich liquid droplets via liquid-liquid phase separation (LLPS). These droplets then combined together to form condensates with elaborate structures, and the condensates finally evolved to form assemblies with various morphologies. Such a mechanism of the assembly is valuable for studying the assembly processes that frequently occur in living organisms. Detailed studies concerning the properties and applications of the obtained β-LG assemblies showed that the assemblies exhibited significantly better performances than the protein itself in terms of autofluorescence, antioxidant activity, and metal ion absorption, which indicates broad applications of these assemblies in bioimaging, biodetection, biodiagnosis, health maintenance, and pollution treatment. This study revealed that biomacromolecules, especially proteins, can be assembled via LLPS, and some unexpected application potentials could be found beyond their original biological functions.

Physiological fluid interfaces: Functional microenvironments, drug delivery targets, and first line of defense

Fluid interfaces, i.e. the boundary layer of two liquids or a liquid and a gas, play a vital role in physiological processes as diverse as visual perception, oral health and taste, lipid metabolism, and pulmonary breathing. These fluid interfaces exhibit a complex composition, structure, and rheology tailored to their individual physiological functions. Advances in interfacial thin film techniques have facilitated the analysis of such complex interfaces under physiologically relevant conditions. This allowed new insights on the origin of their physiological functionality, how deviations may cause disease, and has revealed new therapy strategies. Furthermore, the interactions of physiological fluid interfaces with exogenous substances is crucial for understanding certain disorders and exploiting drug delivery routes to or across fluid interfaces. Here, we provide an overview on fluid interfaces with physiological relevance, namely tear films, interfacial aspects of saliva, lipid droplet digestion and storage in the cell, and the functioning of lung surfactant. We elucidate their structure-function relationship, discuss diseases associated with interfacial composition, and describe therapies and drug delivery approaches targeted at fluid interfaces. STATEMENT OF SIGNIFICANCE: Fluid interfaces are inherent to all living organisms and play a vital role in various physiological processes. Examples are the eye tear film, saliva, lipid digestion & storage in cells, and pulmonary breathing. These fluid interfaces exhibit complex interfacial compositions and structures to meet their specific physiological function. We provide an overview on physiological fluid interfaces with a focus on interfacial phenomena. We elucidate their structure-function relationship, discuss diseases associated with interfacial composition, and describe novel therapies and drug delivery approaches targeted at fluid interfaces. This sets the scene for ocular, oral, or pulmonary surface engineering and drug delivery approaches.

Effect of protein-fatty acid interactions on the formation of starch-lipid-protein complexes

The effect of interactions between beta-lactoglobulin (βLG) and lauric acid (LA) on the formation of ternary maize starch-LA-protein complexes was investigated. Analysis of the secondary structure of βLG by FTIR and changes in fluorescence λmax and intensity indicated that βLG and LA interacted during heating and cooling in a Rapid Visco Analyser (RVA). Results from RVA, DSC and Raman spectroscopy analyses showed that increasing the concentration of βLG from 25 to 200 mg increased the amount of ternary starch-LA-βLG complexes formed. There was little difference in the amounts of the ternary complexes formed when the amount of βLG was 25-150 mg, but a greater amount of starch-LA-βLG complexes was formed when 200 mg of βLG was pre-mixed with LA. From this study, we concluded that prior interaction between βLG and LA had no significant effect on the formation of ternary starch-LA-βLG complexes.

Effectiveness of cell adhesive additives in different supramolecular polymers

Supramolecular motifs in elastomeric biomaterials facilitate the modular incorporation of additives with corresponding motifs. The influence of the elastomeric supramolecular base polymer on the presentation of additives has been sparsely examined, limiting the knowledge of transferability of effective functionalization between polymers. Here it was investigated if the polymer backbone and the additive influence biomaterial modification in two different types of hydrogen bonding supramolecular systems, that is, based on ureido-pyrimidinone or bis-urea units. Two different cell-adhesive additives, that is, catechol or cyclic RGD, were incorporated into different elastomeric polymers, that is, polycaprolactone, priplast or polycarbonate. The additive effectiveness was evaluated with three different cell types. AFM measurements showed modest alterations on nano-scale assembly in ureido-pyrimidinone materials modified with additives. On the contrary, additive addition was highly intrusive in bis-urea materials. Detailed cell adhesive studies revealed additive effectiveness varied between base polymers and the supramolecular platform, with bis-urea materials more potently affecting cell behavior. This research highlights that additive transposition might not always be as evident. Therefore, additive effectiveness requires re-evaluation in supramolecular biomaterials when altering the polymer backbone to suit the biomaterial application.

Synthesis of bio-inspired cellulose nanocrystals-soy protein isolate nanoconjugate for stabilization of oil-in-water Pickering emulsions

The development of hybrid polysaccharide-protein complexes as Pickering emulsion stabilizers has attracted increasing research interest in recent years. This work presents an eco-friendly surface modification strategy to functionalize hydrophilic cellulose nanocrystals (CNC) using hydrophobic soy protein isolate (SPI) via mussel adhesive-inspired poly (l-dopa) (PLD) to develop improved nanoconjugates as stabilizers for oil-in-water Pickering emulsion. The physicochemical properties of the CNC-PLD-SPI nanoconjugate were evaluated by solid-state 13C NMR, FT-IR, TGA, XRD, contact angle analysis, and TEM. The modified CNC (conjugation content of 38.22 ± 1.21%) had lowered crystallinity index, higher thermal stability, and more hydrophobic than unmodified CNC, with an average particle size of 309.9 ± 8.0 nm. Use of amphiphilic CNC-PLD-SPI nanoconjugate with greater conformational flexibility as Pickering stabilizer produced oil-in-water emulsions with greater physical stability.

Applications of serum albumins in delivery systems: Differences in interfacial behaviour and interacting abilities with polysaccharides

One of the major applications of Serum Albumins is their use as delivery systems for lipophilic compounds in biomedicine. Their biomedical application is based on the similarity with Human Serum Albumin (HSA), as a fully biocompatible protein. In general, Bovine Serum Albumin (BSA) is treated as comparable to its human homologue and used as a model protein for fundamental studies since it is available in high amounts and well understood. This protein can act as a carrier for lipophilic compounds or as protective shell in an emulsion-based vehicle. Polysaccharides are generally included in these formulations in order to increase the stability and/or applicability of the carrier. In this review, the main biomedical applications of Albumins as drug delivery systems are first presented. Secondly, the differences between BSA and HSA are highlighted, exploring the similarities and differences between these proteins and their interaction with polysaccharides, both in solution and adsorbed at interfaces. Finally, the use of Albumins as emulsifiers for emulsion-based delivery systems, concretely as Liquid Lipid Nanocapsules (LLNs), is revised and discussed in terms of the differences encountered in the molecular structure and in the interfacial properties. The specific case of Hyaluronic Acid is considered as a promising additive with important applications in biomedicine. The literature works are thoroughly discussed highlighting similarities and differences between BSA and HSA and their interaction with polysaccharides encountered at different structural levels, hence providing routes to control the optimal design of delivery systems.

Globular protein assembly and network formation at fluid interfaces: effect of oil

The formation of viscoelastic networks at fluid interfaces by globular proteins is essential in many industries, scientific disciplines, and biological processes. However, the effect of the oil phase on the structural transitions of proteins, network formation, and layer strength at fluid interfaces has received little attention. Herein, we present a comprehensive study on the effect of oil polarity on globular protein networks. The formation dynamics and mechanical properties of the interfacial networks of three different globular proteins (lysozyme, β-lactoglobulin, and bovine serum albumin) were studied with interfacial shear and dilatational rheometry. Furthermore, the degree of protein unfolding at the interfaces was evaluated by subsequent injection of disulfide bonds reducing dithiothreitol. Finally, we measured the interfacial layer thickness and protein immersion into the oil phase with neutron reflectometry. We found that oil polarity significantly affects the network formation, the degree of interfacial protein unfolding, interfacial protein location, and the resulting network strength. These results allow predicting emulsion stabilization of proteins, tailoring interfacial layers with desired mechanical properties, and retaining the protein structure and functionality upon adsorption.

Partitioning Behavior and Interfacial Activity of Phenolic Acid Derivatives and their Impact on β-Lactoglobulin at the Oil-Water Interface

Proteins are able to stabilize dispersed food systems due to their amphiphilic nature, acting as emulsifiers. Their interfacial properties can be influenced by different methods, including the formation of protein-phenol nanocomplexes. In this study, the interfacial behavior of phenolic compounds and protein-phenol nanocomplexes was first characterized according to the oil-water partitioning behavior of phenolic acid derivatives according to their molecular structure and its impact on interfacial tension. The influence of the phenolic compounds on protein film formation and its properties by dilatational rheology was then evaluated. The most phenolic acid derivatives are predominantly present in the aqueous phase. Despite their hydrophobic benzene body, weak interfacial activity was observed depending on their chemical structure. This result supports possible protein-phenol nanocomplex formation in the aqueous phase and possible interactions at the oil-water interface. Protein-phenol nanocomplexes showed decreased interfacial adsorption properties and decreased viscoelastic interfacial behavior, depending on the expansion of the delocalized π-electrons in the phenol.

Identification and characterization of yak α-lactalbumin and β-lactoglobulin

α-Lactalbumin (α-LA) and β-lactoglobulin (β-LG) were isolated from yak milk and identified by mass spectrometry. The variant of α-LA (L8IIC8) in yak milk had 123 amino acids, and the sequence differed from α-LA from bovine milk. The amino acid at site 71 was Asn (N) in domestic yak milk, but Asp (D) in bovine and wild yak milk sequences. Yak β-LG had 2 variants, β-LG A (P02754) and β-LG E (L8J1Z0). Both domestic yak and wild yak milk contained β-LG E, but it was absent in bovine milk. The amino acid at site 158 of β-Lg E was Gly (G) in yak but Glu (E) in bovine. The yak α-LA and β-LG secondary structures were slightly different from those in bovine milk. The denaturation temperatures of yak α-LA and β-LG were 52.1°C and 80.9°C, respectively. This study provides insights relevant to food functionality, food safety control, and the biological properties of yak milk products.

Functionality of Cricket and Mealworm Hydrolysates Generated after Pretreatment of Meals with High Hydrostatic Pressures

The low consumer acceptance to entomophagy in Western society remains the strongest barrier of this practice, despite these numerous advantages. More positively, it was demonstrated that the attractiveness of edible insects can be enhanced by the use of insect ingredients. Currently, insect ingredients are mainly used as filler agents due to their poor functional properties. Nevertheless, new research on insect ingredient functionalities is emerging to overcome these issues. Recently, high hydrostatic pressure processing has been used to improve the functional properties of proteins. The study described here evaluates the functional properties of two commercial insect meals (Gryllodes sigillatus and Tenebrio molitor) and their respective hydrolysates generated by Alcalase®, conventionally and after pressurization pretreatment of the insect meals. Regardless of the insect species and treatments, water binding capacity, foaming and gelation properties did not improve after enzymatic hydrolysis. The low emulsion properties after enzymatic hydrolysis were due to rapid instability of emulsion. The pretreatment of mealworm meal with pressurization probably induced protein denaturation and aggregation phenomena which lowered the degree of hydrolysis. As expected, enzymatic digestion (with and without pressurization) increased the solubility, reaching values close to 100%. The pretreatment of mealworm meal with pressure further improved its solubility compared to control hydrolysate, while pressurization pretreatment decreased the solubility of cricket meal. These results may be related to the impact of pressurization on protein structure and therefore to the generation of different peptide compositions and profiles. The oil binding capacity also improved after enzymatic hydrolysis, but further for pressure-treated mealworm hydrolysate. Despite the moderate effect of pretreatment by high hydrostatic pressures, insect protein hydrolysates demonstrated interesting functional properties which could potentially facilitate their use in the food industry.

The structure and properties of MFG-E8 and the In vitro assessment of its toxic effects on myoblast cells

Four high-molecular-weight protein fractions of milk fat globule membrane (MFGM) were isolated from bovine milk. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), MALDI-TOF/TOF™ and Liquid chromatography electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) were used to measure the molecular sizes of the MFGM. Fourier transform infrared spectroscopy (FT-IR) and circular dichroism (CD) were performed to determine the conformations of the MFGM. The results showed that the main protein (98.33%) in MFGM protein fraction 2 was Milk fat globule epidermal growth factor-VIII (MFG-E8), with a molecular weight of 47.82 kDa. The secondary structural component measurements showed that the MFG-E8 consisted of 5% helix, 70% sheet and 25% random coil, and the results matched well with the prediction by SSPro 5.1 bioinformatic analysis. The thermograms analysis revealed that Td and△H of MFG-E8 were 60.50°Cand 132.29 kJ/mol. The in vitro digestibility of MFG-E8 showed that it can be enzymatically hydrolyzed in the stomach and relatively stable in the intestinal fluid. The in vitro C₂C₁₂ and Caco2 cell activity tests indicated that MFG-E8 promoted the proliferation of C₂C₁₂ myoblast cells without cytotoxicity. The biological functional properties of MFG-E8 may be related to the fact that MFG-E8 possesses a high level of β-sheet structure. Our results suggested that MFG-E8 possesses broad prospects not only for use in functional food products but also as a source of natural anti-sarcopenia drugs.

Physicochemical and emulsifying properties of mussel water-soluble proteins as affected by lecithin concentration

The effects of lecithin addition at different concentrations (0-2.0%) on the physicochemical and emulsifying properties of mussel water-soluble proteins (MWP) were investigated. In solution system, low lecithin concentration (0.5%-1.0%) induced the aggregation and increased turbidity of composite particles. Lecithin addition caused changes in secondary structure and induced partial unfolding of MWP. Hydrophobic interactions between MWP and lecithin may contribute to the exposure of chromophores and hydrophobic groups of MWP. The interfacial tension decreased with lecithin addition. However, at a high lecithin concentration (1.5%-2.0%), the degree of aggregation and state of unfolding alleviated due to competitive adsorption. In emulsion system, with the low concentration of lecithin addition (0.5%-1.0%), droplet size and surface charge of emulsion decreased. The emulsion activity index, emulsion stability index, percentage of adsorbed protein increased. Both creaming stability and viscoelastic properties improved. At an intermediate lecithin concentration (1.0%), the emulsion showed the highest physical stability, while further addition of lecithin caused a slight deterioration in emulsifying properties. Overall, these results indicated the possibility that the lecithin-MWP mixed emulsifiers can be used to obtain emulsions with desirable properties.

Effect of multi-frequency countercurrent ultrasound treatment on extraction optimization, functional and structural properties of protein isolates from Walnut (Juglans regia L.) meal

This study evaluated the effects of ultrasound treatment on walnut meal protein (WMP) extraction and techno-functional properties. The Box-Behnken Design (BBD) was adopted for the optimization of the traditional and ultrasound-assisted extraction (UAE) processes. Standard protocols were used to assay the techno-functional characteristics. The extraction models' statistical results exhibited adequacy with the least desirability index of 95.8%. The UAE enhanced the WMP extraction yield, purity, and chemical score by 30.15%, 16.27%, and 9.74%, respectively, while reducing the extraction time by 25% over the control. The emulsion and foam stabilities and bulk density increased by 34.5%, 39.8%, and 6.1%, respectively, over the control. The α-helix decreased while β-sheet, β-turns and random coil secondary structure components increased significantly (p < .05) by 95.76%, 101.3%, 105.1%, and 85.7% correspondingly. The dual-frequency combination (20/40 kHz/kHz) was the best frequency mode. WMP could serve as a functional additive in manufactured foods as texture and flavor enhancer. PRACTICAL APPLICATIONS: Walnut meal protein (WMP) has a well-balanced amino acid profile and its economic use could be practically increased as a food ingredient by ultrasound-assisted extraction. By this technique, WMP could be employed for the development of enhanced food ingredients rather than being discarded as animal feed. This study showed a positive effect of ultrasonic-assisted alkaline pretreatment on WMP extraction, functionality and structure characteristics. In addition to process improvement, ultrasound is energy efficient and environmentally friendly. Therefore, the applicability of this technique to improve the functionality of plant proteins from industrial by-products to be included in food products is promising.

Encapsulation of Vitamin D3 in Pickering Emulsion Stabilized by Nanofibrillated Mangosteen Cellulose: Effect of Environmental Stresses

Vitamin D₃ was encapsulated in 10% wt soybean oil-in-water (O/W) Pickering emulsions stabilized by either nanofibrillated cellulose (NFC) or whey protein isolate (WPI) at 0.3%, 0.5%, and 0.7% w/w. The vitamin D₃ -enriched emulsions were tested for their stability against temperature (30 °C to 90 °C), pH (2 to 8), and ionic strength (0 to 500 mM NaCl). The mean particle diameter (d₃₂ ), ζ-potential, and creaming stability of the oil droplets in the emulsions were measured, as well as their vitamin D₃ encapsulation efficiency (EE). After preparation, the oil droplet size (d₃₂ ) of the emulsions stabilized by NFC increased with increasing emulsifier concentration, whereas the droplet size of emulsions stabilized by WPI decreased. NFC provided good stability to the emulsions through a combination of steric and electrostatic repulsion. The EE of vitamin D₃ increased with increasing emulsifier concentration. Heating or ionic strength did not significantly (P < 0.05) affect the emulsions properties and EE. On the other hand, the NFC-stabilized emulsions were sensitive to highly acidic conditions (pH 2), with an increase in particle size and decrease in EE. The WPI-stabilized emulsions aggregated around the isoelectric point of the adsorbed proteins (pI ≈ 4.8). Increasing NFC or WPI concentration improved the stability and EE of the emulsions against environmental stresses. NFC-stabilized emulsions had good long-term stability. The results show that NFC can be used as an effective emulsifier for creating vitamin-enriched emulsions with good stability. PRACTICAL APPLICATION: This study can be used to develop more effective encapsulation technologies for fat-soluble vitamins in emulsion-based food products. Encapsulation using nanofibrillated cellulose effectively protected the encapsulated vitamins against environmental stresses which occur in industrial food production (such as pH changes, salt addition, and thermal processing). Moreover, nanofibrillated cellulose extracted from mangosteen rind is a nature-derived emulsifier that is environmental friendly.

Secondary Structural Changes in Proteins as a Result of Electroadsorption at Aqueous-Organogel Interfaces

The electroadsorption of proteins at aqueous-organic interfaces offers the possibility to examine protein structural rearrangements upon interaction with lipophilic phases, without modifying the bulk protein or relying on a solid support. The aqueous-organic interface has already provided a simple means of electrochemical protein detection, often involving adsorption and ion complexation; however, little is yet known about the protein structure at these electrified interfaces. This work focuses on the interaction between proteins and an electrified aqueous-organic interface via controlled protein electroadsorption. Four proteins known to be electroactive at such interfaces were studied: lysozyme, myoglobin, cytochrome c, and hemoglobin. Following controlled protein electroadsorption onto the interface, ex situ structural characterization of the proteins by FTIR spectroscopy was undertaken, focusing on secondary structural traits within the amide I band. The structural variations observed included unfolding to form aggregated antiparallel β-sheets, where the rearrangement was specifically dependent on the interaction with the organic phase. This was supported by MALDI ToF MS measurements, which showed the formation of protein-anion complexes for three of these proteins, and molecular dynamic simulations, which modeled the structure of lysozyme at an aqueous-organic interface. On the basis of these findings, the modulation of protein secondary structure by interfacial electrochemistry opens up unique prospects to selectively modify proteins.

Identification and quantification of proteins at adsorption layer of emulsion stabilized by pea protein isolates

This study adopted the method of quantitative proteomics to analyze the adsorbed proteins in oil-in-water emulsions stabilized by pea protein isolate (PPI). Adsorbed proteins were precipitated by an optimized precipitation method and precipitates were labeled and subjected to a reversed-phase high performance liquid chromatography coupled to tandem mass spectrometry (RPLC-ESI-MS/MS) for protein identification and quantification. In total, 77 proteins were identified, of which 49 proteins with significant differences were observed. There were 25 upregulated proteins (fold change > 1) and 24 downregulated proteins (fold change < 1). The interfacial adsorption abilities of these proteins were compared according to the classification of protein families. The results showed that all isoforms of vicilins exhibited high adsorption abilities at the oil-water interface. Compared with vicilin, convicilin showed opposite adsorption capacity. Different legumin families showed significantly different affinities on the oil-water interface. In contrast to albumin-1, albumin-2 was preferentially adsorbed to the interface. The amino acid sequence alignment and hydropathy profile analysis of these proteins showed that the proteins well-balanced between hydrophobic and hydrophilic amino acid groups displayed high interfacial activity. In contrast, a long hydrophilic or hydrophobic fragment could adversely influence protein interfacial activity. This study provides an insight into the interfacial behaviors of proteins by supplying detailed quantitative information of interfacial layer.

Molecular Dynamics Simulation of Protein Biosurfactants

Surfaces and interfaces are ubiquitous in nature and are involved in many biological processes. Due to this, natural organisms have evolved a number of methods to control interfacial and surface properties. Many of these methods involve the use of specialised protein biosurfactants, which due to the competing demands of high surface activity, biocompatibility, and low solution aggregation may take structures that differ from the traditional head–tail structure of small molecule surfactants. As well as their biological functions, these proteins have also attracted interest for industrial applications, in areas including food technology, surface modification, and drug delivery. To understand the biological functions and technological applications of protein biosurfactants, it is necessary to have a molecular level description of their behaviour, in particular at surfaces and interfaces, for which molecular simulation is well suited to investigate. In this review, we will give an overview of simulation studies of a number of examples of protein biosurfactants (hydrophobins, surfactin, and ranaspumin). We will also outline some of the key challenges and future directions for molecular simulation in the investigation of protein biosurfactants and how this can help guide future developments.

Poly(lactic-co-glycolic acid) devices: Production and applications for sustained protein delivery

Injectable or implantable poly(lactic-co-glycolic acid) (PLGA) devices for the sustained delivery of proteins have been widely studied and utilized to overcome the necessity of repeated administrations for therapeutic proteins due to poor pharmacokinetic profiles of macromolecular therapies. These devices can come in the form of microparticles, implants, or patches depending on the disease state and route of administration. Furthermore, the release rate can be tuned from weeks to months by controlling the polymer composition, geometry of the device, or introducing additives during device fabrication. Slow-release devices have become a very powerful tool for modern medicine. Production of these devices has initially focused on emulsion-based methods, relying on phase separation to encapsulate proteins within polymeric microparticles. Process parameters and the effect of additives have been thoroughly researched to ensure protein stability during device manufacturing and to control the release profile. Continuous fluidic production methods have also been utilized to create protein-laden PLGA devices through spray drying and electrospray production. Thermal processing of PLGA with solid proteins is an emerging production method that allows for continuous, high-throughput manufacturing of PLGA/protein devices. Overall, polymeric materials for protein delivery remain an emerging field of research for the creation of single administration treatments for a wide variety of disease. This review describes, in detail, methods to make PLGA devices, comparing traditional emulsion-based methods to emerging methods to fabricate protein-laden devices. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Implantable Materials and Surgical Technologies > Nanomaterials and Implants Biology-Inspired Nanomaterials > Peptide-Based Structures.

Adsorption and conformations of lysozyme and α-lactalbumin at a water-octane interface

As proteins contain both hydrophobic and hydrophilic amino acids, they will readily adsorb onto interfaces between water and hydrophobic fluids such as oil. This adsorption normally causes changes in the protein structure, which can result in loss of protein function and irreversible adsorption, leading to the formation of protein interfacial films. While this can be advantageous in some applications (e.g., food technology), in most cases it limits our ability to exploit protein functionality at interfaces. To understand and control protein interfacial adsorption and function, it is necessary to understand the microscopic conformation of proteins at liquid interfaces. In this paper, molecular dynamics simulations are used to investigate the adsorption and conformation of two similar proteins, lysozyme and α-lactalbumin, at a water-octane interface. While they both adsorb onto the interface, α-lactalbumin does so in a specific orientation, mediated by two amphipathic helices, while lysozyme adsorbs in a non-specific manner. Using replica exchange simulations, both proteins are found to possess a number of distinct interfacial conformations, with compact states similar to the solution conformation being most common for both proteins. Decomposing the different contributions to the protein energy at oil-water interfaces suggests that conformational change for α-lactalbumin, unlike lysozyme, is driven by favourable protein-oil interactions. Revealing these differences between the factors that govern the conformational change at interfaces in otherwise similar proteins can give insight into the control of protein interfacial adsorption, aggregation, and function.

Effect of 2 Emulsion-Based Adjuvants on the Structure and Thermal Stability of Staphylococcus aureus Alpha-Toxin

The effects of 2 squalene-based emulsion adjuvant systems (MedImmune emulsion 0 [ME.0] and Stable Emulsion [SE]) on the structure and stability of the recombinant protein antigen alpha-toxin (AT), a potential vaccine candidate for Staphylococcus aureus infection, were investigated using Fourier-transform infrared spectroscopy and both steady-state and time-resolved intrinsic fluorescence spectroscopy as well as differential scanning calorimetry (DSC). A component study, performed to identify the effects of the individual emulsion's components, showed negligible interactions between AT and ME.0. DSC analysis showed the ME.0 emulsion thermally destabilized AT, probably because of changes in the buffer composition of AT upon mixing. The SE emulsion caused increased alpha-helix and decreased beta-sheet content in AT, and a significant blue shift in the fluorescence spectra relative to that of AT in solution. DSC analysis showed SE exerted a dramatic thermal stabilization effect on AT, probably attributable to an interaction between AT and SE. Size exclusion chromatography showed a complete loss in the recovery of AT when mixed with SE, but not ME.0, indicating a high degree of interaction with SE. This work successfully characterized the biophysical properties of AT in the presence of 2 emulsion adjuvants including a component study to rationalize how emulsion components affect protein antigen stability.

Supramolecular surface functionalization via catechols for the improvement of cell-material interactions

Optimization of cell-material interactions is crucial for the success of synthetic biomaterials in guiding tissue regeneration. To do so, catechol chemistry is often used to introduce adhesiveness into biomaterials. Here, a supramolecular approach based on ureido-pyrimidinone (UPy) modified polymers is combined with catechol chemistry in order to achieve improved cellular adhesion onto supramolecular biomaterials. UPy-modified hydrophobic polymers with non-cell adhesive properties are developed that can be bioactivated via a modular approach using UPy-modified catechols. It is shown that successful formulation of the UPy-catechol additive with the UPy-polymer results in surfaces that induce cardiomyocyte progenitor cell adhesion, cell spreading, and preservation of cardiac specific extracellular matrix production. Hence, by functionalizing supramolecular surfaces with catechol functionalities, an adhesive supramolecular biomaterial is developed that allows for the possibility to contribute to biomaterial-based regeneration.