Structural determinants for protein adsorption/non-adsorption to silica surface

Impact of protein adsorption during biopharmaceutical manufacture & storage

Protein therapeutics contact multiple interfaces during formulation, filtration, fill-finish, and storage processes. Interactions at these interfaces can compromise the conformational and colloidal stability of therapeutic proteins through surface adsorption, potentially leading to aggregation and particle formation. Surface-induced conformational changes in protein higher-order structures, influenced by interfacial hydrophobicity and charge, are key drivers of these effects. The resulting loss of active protein and increased aggregation risk pose significant challenges to the efficacy and safety of the final biotherapeutic product. Thus, it is imperative to develop strategies that minimize protein-surface interactions that may compromise the protein's conformational and colloidal stability during manufacture and storage. This review focuses on current research related to the adsorption behaviour of biotherapeutics at interfaces encountered during fill-finish and storage. Furthermore, the review introduces the factors influencing protein adsorption and interfacial stability and current methodologies and advancements in mitigating interfacial adsorption, emphasizing rational formulation design strategies.

Polysorbates and poloxamer rescue filter-induced serotype-dependent loss of AAVs

Adeno-associated viruses (AAVs) are the leading viral vector for in-vivo gene therapy, and their use is expected to grow rapidly in the next decade. While AAVs are promising tools for treating many genetic diseases, vectors are vulnerable to adsorptive losses to surfaces due to the low concentrations (10-100 μg/mL) during manufacturing, storage, and administration. Here, we examined the filter-induced loss of two AAV serotypes of Clade E and Clade C as a function of the filter type (materials of composition such as polyvinylidene (PVDF), polyethersulfone (PES), and nylon), pore size (0.22 vs 0.45 μm), pH and ionic strength of the formulation, and hydrophobicity and ionic charge of the AAVs. Our results show that both the AAV serotype and the filter used result in varied amounts of adsorptive losses. Increased hydrophobicity of the AAV or the filter resulted in increased levels of adsorption. Altering formulation pH from 5 - 8 or ionic strength from 50 mM - 180 mM NaCl did not have a significant impact on adsorption loss. Additionally, no change in adsorptive loss was observed with an increase in the filter pore size. Three surfactants (polysorbate 20 (PS20), polysorbate 80 (PS80), and poloxamer 188 (P188)) are observed to rescue the filter-dependent loss of AAVs, but to different minimum concentrations. P188 was found to be the most efficient in the case of nylon filters, whereas PS20 is the most efficient with PES filters. A comparison of empty vs. full capsids shows that empty capsids can be used to optimize formulation parameters for full capsids. This study highlights the importance of surfactants in mitigating filter-dependent surface-induced losses observed during AAV manufacturing processes.

Silica-binding peptides: physical chemistry and emerging biomaterials applications

Silica-binding peptides (SBPs) are increasingly recognized as versatile tools for various applications spanning biosensing, biocatalysis, and environmental remediation. This review explores the interaction between these peptides and silica surfaces, offering insights into how variables such as surface silanol density, peptide sequence and composition, and solution conditions influence binding affinity. Key advancements in SBP applications are discussed, including their roles in protein purification, biocatalysis, biosensing, and biomedical engineering. By examining the underlying binding mechanisms and exploring their practical potential, this work provides a comprehensive understanding of how SBPs can drive innovations in materials science and biotechnology.

Vasculo-osteogenic keratin-based nanofibers containing merwinite nanoparticles and sildenafil for bone tissue regeneration

Vascularization of bone tissue constructs plays a pivotal role in facilitating nutrient transport and metabolic waste removal during the processes of osteogenesis and bone regeneration in vivo. In this study, a sildenafil (Sil)-loaded nanofibrous scaffold of keratin/Soluplus/merwinite (KS.Me.Sil) was fabricated through electrospinning and the effectiveness of the scaffold was assessed for bone tissue engineering applications. The KS.Me.Sil nanofibrous scaffold exhibited notably enhanced ultimate tensile strength (3.38 vs 2.61 MPa) and elastic modulus (69.83 vs 46.27 MPa) compared to the KS scaffold. The in vitro release of Ca2+, Si4+ and Mg2+ ions and the release of Sil from the nanofibers as well as biodegradability and bioactivity were evaluated for 14 days. Protein adsorption capability and cytocompatibility of the scaffolds were tested. Alkaline phosphatase activity test, Alizarin red staining and qRT-PCR analysis demonstrated that the KS.Me.Sil nanofibers had the best osteogenic activity among other samples. Also, the results of the chorioallantoic membrane assay showed an almost threefold increase in blood vessel density in the group treated with the KS.Me.Sil nanofibers extract compared to the KS. In conclusion, our findings suggest that the electrospun KS.Me.Sil nanofibrous scaffold offers a robust structure with exceptional osteogenic and angiogenic characteristics, making it a promising candidate for bone tissue engineering applications.

Dual Fractions Proteomic Analysis of Silica Nanoparticle Interactions with Protein Extracts

Dual-fraction proteomics reveals a novel class of proteins impacted by nanoparticle exposure.

BACKGROUND

Nanoparticles (NPs) interact with cellular proteomes, altering biological processes. Understanding these interactions requires comprehensive analyses beyond solely characterizing the NP corona.

METHODS

We utilized a dual-fraction mass spectrometry (MS) approach to analyze both NP-bound and unbound proteins in Saccharomyces cerevisiae sp. protein extracts exposed to silica nanoparticles (SiNPs). We identified unique protein signatures for each fraction and quantified protein abundance changes using spectral counts.

RESULTS

Strong correlations were observed between protein profiles in each fraction and non-exposed controls, while minimal correlation existed between the fractions themselves. Linear models demonstrated equal contributions from both fractions in predicting control sample abundance. Combining both fractions revealed a larger proteomic response to SiNP exposure compared to single-fraction analysis. We identified 302/56 proteins bound/unbound to SiNPs and an additional 196 "impacted" proteins demonstrably affected by SiNPs.

CONCLUSION

This dual-fraction MS approach provides a more comprehensive understanding of nanoparticle interactions with cellular proteomes. It reveals a novel class of "impacted" proteins, potentially undergoing conformational changes or aggregation due to NP exposure. Further research is needed to elucidate their biological functions and the mechanisms underlying their impact.

Unveiling the Broad-Spectrum Virucidal Potential of Purified Clinoptilolite-Tuff

Due to its remarkable surface properties, natural clinoptilolite-tuff interacts with a variety of biochemical, pharmaceutical, chemical, and microbiological entities, including human viruses. In the present work, the virucidal activity of purified clinoptilolite-tuff (PCT) was investigated using a variety of viruses, differing in their structure and composition. Influenza A virus, Herpes Simplex virus, Rhinovirus, and Parvovirus were chosen to represent enveloped and non-enveloped viruses with RNA and DNA genomes. Beside human viruses, Canine Parvovirus and bacteriophages T4 and MS2 were used to represent animal and bacterial viruses, respectively. The virucidal activity of PCT was quantified by examining the residual viral activity on susceptible cell lines upon incubation with PCT. A wide range of antiviral efficiencies was observed, ranging from up to 99% for Herpes Simplex virus to no activity for Rhinovirus and both bacteriophages. This study reveals that the virucidal potential of PCT is not universal and depends on a complex set of factors including virus structure and medium composition. The environmental and medical implications of this research are discussed for uses such as wastewater treatment or wound healing.

Stability and dispersibility of microplastics in experimental exposure medium and their dimensional characterization by SMLS, SAXS, Raman microscopy, and SEM

The plastic production that contributes to the global plastic reservoir presents a major challenge for society in managing plastic waste and mitigating the environmental damage of microplastic (MP) pollution. In the environment, the formation of biomolecular corona around MPs enhance the stability of MP suspensions, influencing the bioavailability and toxicity of MPs. Essential physical properties including MP stability, dispersibility, agglomeration, and dimensional size must be precisely defined and measured in complex media taking into account the formation of a protein corona. Using static multiple light scattering (SMLS), small angle X-ray scattering (SAXS), Raman microscopy, and scanning electron microscopy (SEM), we measured the particle size, density, stability, and agglomeration state of polyethylene and polypropylene MPs stabilized in aqueous suspension by BSA. SEM analysis revealed the formation of nanoplastic debris as MP suspensions aged. Our results suggest that protein adsorption favors the formation of secondary nanoplastics, potentially posing an additional threat to ecosystems. This approach provides analytical methodologies by integrating SEM, SMLS, and SAXS, for characterizing MP suspensions and highlights the effect of the protein corona on size measurements of micro/nanoplastics. Our analysis demonstrates the detectability of secondary nanoplastics by SEM, paving the way for monitoring and controlling human exposure.

Size Tuning of Mesoporous Silica Adjuvant for One-Shot Vaccination with Long-Term Anti-Tumor Effect

Despite recent clinical successes in cancer immunotherapy, it remains difficult to initiate a long-term anti-tumor effect. Therefore, repeated administrations of immune-activating agents are generally required in most cases. Herein, we propose an adjuvant particle size tuning strategy to initiate a long-term anti-tumor effect by one-shot vaccination. This strategy is based on the size-dependent immunostimulation mechanism of mesoporous silica particles. Hollow mesoporous silica (HMS) nanoparticles enhance the antigen uptake with dendritic cells around the immunization site in vivo. In contrast, hierarchically porous silica (HPS) microparticles prolong cancer antigen retention and release in vivo. The size tuning of the mesoporous silica adjuvant prepared by combining both nanoparticles and microparticles demonstrates the immunological properties of both components and has a long-term anti-tumor effect after one-shot vaccination. One-shot vaccination with HMS-HPS-ovalbumin (OVA)-Poly IC (PIC, a TLR3 agonist) increases CD4+ T cell, CD8+ T cell, and CD86+ cell populations in draining lymph nodes even 4 months after vaccination, as well as effector memory CD8+ T cell and tumor-specific tetramer+CD8+ T cell populations in splenocytes. The increases in the numbers of effector memory CD8+ T cells and tumor-specific tetramer+CD8+ T cells indicate that the one-shot vaccination with HMS-HPS-OVA-PIC achieved the longest survival time after a challenge with E.G7-OVA cells among all groups. The size tuning of the mesoporous silica adjuvant shows promise for one-shot vaccination that mimics multiple clinical vaccinations in future cancer immunoadjuvant development. This study may have important implications in the long-term vaccine design of one-shot vaccinations.

Tuning Electrostatic Interactions To Control Orientation of GFP Protein Adsorption on Silica Surface

The adsorption of green fluorescent protein (GFP) on silica surfaces has been the subject of growing interest due to its potential applications in various fields, including biotechnology and biomedicine. In this study, we used all-atom molecular dynamics simulations to investigate the charge-driven adsorption of wild type GFP and its supercharged variants on silica surfaces. The results showed that the positively charged variant of GFP adsorbed on the negatively charged silica surface with minimal loss in its secondary structure. Further studies were conducted to understand the role of surface charge distribution on two other positively charged variants of GFP, and the results showed that the orientation of GFP on silica can be easily tuned by careful mutations of the charged amino acid residues on the GFP. This study provides valuable molecular insights into the role of electrostatic-driven adsorption of GFP and highlights the importance of charge interactions in the adsorption process.

The Adsorption of P2X2 Receptors Interacting with IgG Antibodies Revealed by Combined AFM Imaging and Mechanical Simulation

The adsorption of proteins onto surfaces significantly impacts biomaterials, medical devices, and biological processes. This study aims to provide insights into the irreversible adsorption process of multiprotein complexes, particularly focusing on the interaction between anti-His6 IgG antibodies and the His6-tagged P2X2 receptor. Traditional approaches to understanding protein adsorption have centered around kinetic and thermodynamic models, often examining individual proteins and surface coverage, typically through Molecular Dynamics (MD) simulations. In this research, we introduce a computational approach employing Autodesk Maya 3D software for the investigation of multiprotein complexes' adsorption behavior. Utilizing Atomic Force Microscopy (AFM) imaging and Maya 3D-based mechanical simulations, our study yields real-time structural and kinetic observations. Our combined experimental and computational findings reveal that the P2X2 receptor-IgG antibody complex likely undergoes absorption in an 'extended' configuration. Whereas the P2X2 receptor is less adsorbed once is complexed to the IgG antibody compared to its individual state, the opposite is observed for the antibody. This insight enhances our understanding of the role of protein-protein interactions in the process of protein adsorption.

Silica deposition in plants: scaffolding the mineralization

BACKGROUND

Silicon and aluminium oxides make the bulk of agricultural soils. Plants absorb dissolved silicon as silicic acid into their bodies through their roots. The silicic acid moves with transpiration to target tissues in the plant body, where it polymerizes into biogenic silica. Mostly, the mineral forms on a matrix of cell wall polymers to create a composite material. Historically, silica deposition (silicification) was supposed to occur once water evaporated from the plant surface, leaving behind an increased concentration of silicic acid within plant tissues. However, recent publications indicate that certain cell wall polymers and proteins initiate and control the extent of plant silicification.

SCOPE

Here we review recent publications on the polymers that scaffold the formation of biogenic plant silica, and propose a paradigm shift from spontaneous polymerization of silicic acid to dedicated active metabolic processes that control both the location and the extent of the mineralization.

CONCLUSION

Protein activity concentrates silicic acid beyond its saturation level. Polymeric structures at the cell wall stabilize the supersaturated silicic acid and allow its flow with the transpiration stream, or bind it and allow its initial condensation. Silica nucleation and further polymerization are enabled on a polymeric scaffold, which is embedded within the mineral. Deposition is terminated once free silicic acid is consumed or the chemical moieties for its binding are saturated.

Role of the Protein Corona in the Colloidal Behavior of Microplastics

Microparticles of polyethylene and polypropylene are largely found in aquatic environments because they are the most produced and persistent plastic materials. Once in biological media, they are covered by a layer of molecules, the so-called corona, mostly composed of proteins. A yeast protein extract from Saccharomyces cerevisiae was used as a protein system to observe interactions in complex biological media. Proteins, acting as surfactants and providing hydrophilic surfaces, allow the dispersion of highly hydrophobic particles in water and stabilize them. After 24 h, the microplastic quantity was up to 1 × 10¹¹ particles per liter, whereas without protein, no particles remained in solution. Label-free imaging of the protein corona by synchrotron radiation deep UV fluorescence microscopy (SR-DUV) was performed. In situ images of the protein corona were obtained, and the adsorbed protein quantity, the coverage rate, and the corona heterogeneity were determined. The stability kinetics of the microplastic suspensions were measured by light transmission using a Turbiscan analyzer. Together, the microscopic and kinetics results demonstrate that the protein corona can very efficiently stabilize microplastics in solution provided that the protein corona quality is sufficient. Microplastic stability depends on different parameters such as the particle's intrinsic properties (size, density, hydrophobicity) and the protein corona formation that changes the particle wettability, electrostatic charge, and steric hindrance. By controlling these parameters with proteins, it becomes possible to keep microplastics in and out of solution, paving the way for applications in the field of microplastic pollution control and remediation.

A proteome scale study reveals how plastic surfaces and agitation promote protein aggregation

Protein aggregation in biotherapeutics can reduce their activity and effectiveness. It may also promote immune reactions responsible for severe adverse effects. The impact of plastic materials on protein destabilization is not totally understood. Here, we propose to deconvolve the effects of material surface, air/liquid interface, and agitation to decipher their respective role in protein destabilization and aggregation. We analyzed the effect of polypropylene, TEFLON, glass and LOBIND surfaces on the stability of purified proteins (bovine serum albumin, hemoglobin and α-synuclein) and on a cell extract composed of 6000 soluble proteins during agitation (P = 0.1-1.2 W/kg). Proteomic analysis revealed that chaperonins, intrinsically disordered proteins and ribosomes were more sensitive to the combined effects of material surfaces and agitation while small metabolic oligomers could be protected in the same conditions. Protein loss observations coupled to Raman microscopy, dynamic light scattering and proteomic allowed us to propose a mechanistic model of protein destabilization by plastics. Our results suggest that protein loss is not primarily due to the nucleation of small aggregates in solution, but to the destabilization of proteins exposed to material surfaces and their subsequent aggregation at the sheared air/liquid interface, an effect that cannot be prevented by using LOBIND tubes. A guidance can be established on how to minimize these adverse effects. Remove one of the components of this combined stress - material, air (even partially), or agitation - and proteins will be preserved.

Immobilization of Kluyveromyces lactis β-Galactosidase on Meso-macroporous Silica: Use of Infrared Spectroscopy to Rationalize the Catalytic Efficiency

Enzyme immobilization on adequate carriers is a challenging strategy. Understanding the enzyme-carrier interactions and their effects on enzyme conformation and bioactivity is critical. In this study, a meso-macropores silica (MMS) was used to immobilize β-galactosidase from the yeast Kluyveromyces lactis (β-gal-KL) by physical adsorption. The bioactivity of the immobilized β-gal-KL was altered, evidenced by the increased K_m , decreased V_max and k_cat , and increased activity at alkaline values. By performing infrared spectroscopy analysis and subsequent secondary structure assessment from the amide I band, the immobilized β-gal-KL suffered a β-sheet (∼31-35 %) to α-helix (∼15-19 %) transition with increased turns (∼21-22 %) with respect to the free β-gal-KL having ∼12 % α-helix, ∼42 % β-sheet, and ∼17 % turns. These findings led us to correlate the observed bioactivity performance to structural alterations to a non-native conformation. The presented line of thought can lead to a better understanding of the reasons causing bioactivity alterations upon enzyme immobilization.

The Assembly Mechanism and Mesoscale Architecture of Protein-Polysaccharide Complexes Formed at the Solid-liquid Interface

Protein-polysaccharide composite materials have generated much interest due to their potential use in medical science and biotechnology. A comprehensive understanding of the assembly mechanism and the mesoscale architecture is needed for fabricating protein-polysaccharide composite materials with desired properties. In this study, complex assemblies were built on silica surfaces through a layer-by-layer (LbL) approach using bovine beta-lactoglobulin variant A (βLgA) and pectin as model protein and polysaccharide, respectively. We demonstrated the combined use of quartz crystal microbalance with dissipation monitoring (QCM-D) and neutron reflectometry (NR) for elucidating the assembly mechanism as well as the internal architecture of the protein-polysaccharide complexes formed at the solid-liquid interface. Our results show that βLgA and pectin interacted with each other and formed a cohesive matrix structure at the interface consisting of intertwined pectin chains that were cross-linked by βLgA-rich domains. Although the complexes were fabricated in an LbL fashion, the complexes appeared to be relatively homogeneous with βLgA and pectin molecules spatially distributed within the matrix structure. Our results also demonstrate that the density of βLgA-pectin complex assemblies increased with both the overall and local charge density of pectin molecules. Therefore, the physical properties of the protein-polysaccharide matrix structure, including density and level of hydration, can be tuned by using polysaccharides with varying charge patterns, thus promoting the development of composite materials with desired properties.

[Advances in separation and analysis of aromatic amino acids in food]

Amino acids are important building blocks of proteins in the human body, which are involved in many metabolic pathways. Patients with metabolic diseases such as phenylketonuria, tyrosinemia, and hepatic encephalopathy are genetically defective and cannot metabolize aromatic amino acids (AAA) in food; hence, a regular diet may lead to permanent physiological damage. For this reason, it is necessary to restrict the intake of AAA in their daily diet by limiting natural protein intake, while ensuring normal intake of low protein foods and supplementation with low-AAA protein equivalents. Sources of low-AAA protein equivalents currently rely on free amino acid complex mixtures and low-AAA peptides (also known as high-Fischer-ratio peptides), which have better absorption availability and palatability. AAA separation and analysis techniques are essential for the preparation and detection of low-AAA peptides. Researchers in this field have explored a variety of efficient adsorption materials to selectively remove AAA from complex protein hydrolysates and thus prepare low-AAA peptide foods, or to establish analysis strategies for AAA. Covering more than 70 publications on AAA removal and separation in the last decade from Web of Science Core Collection and China National Knowledge Infrastructure, this review analyzes the structural characteristics and physicochemical properties of AAA, and summarizes the technological progress of AAA removal based on adsorbents such as activated carbon and resin. The applications of two-dimensional nanomaterials, molecular imprinting, cyclodextrins, and metal-organic frameworks in AAA adsorption and analysis from three dimensions, i. e., sample pretreatment, chiral separation and adsorption sensing, are also reviewed. The mainstream adsorbents for AAA removal, such as activated carbon, still suffer from poor specificity and cause environmental pollution during post-use treatment. Existing AAA separating materials show impressive selective adsorption capability in food samples and chiral mixtures as well as high sensitivity in adsorption sensing. The development of an efficient detection technology for AAA may help in detecting trace AAA in food and in evaluating chiral AAA adulteration in food samples. By exploring the advantages and disadvantages of each type of technology, we provide support for the advancement of the removal and analysis techniques for AAA.

Synergistic anti-tumor efficacy of a hollow mesoporous silica-based cancer vaccine and an immune checkpoint inhibitor at the local site

Immune checkpoint inhibitors elicit durable tumor regression in multiple types of tumor, but may induce potential side effects with low response rates in many tumors. Herein, to increase the therapeutic efficacy of immune checkpoint inhibitors, a hollow mesoporous silica (HMS) nanosphere-based cancer vaccine was combined with an immune checkpoint inhibitor, anti-programmed death-ligand 1 (anti-PD-L1) antibody. The HMS nanospheres function as adjuvants that promote dendritic cell activation and antigen cross-presentation. Mice immunized with the HMS-based cancer vaccine show suppressed tumor growth with increased tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-2 (IL-2) levels in their spleens compared with those without HMS-based cancer vaccine. Moreover, the HMS-based cancer vaccine synergistically acts with the anti-PD-L1 antibody on the tumor. The combination of an HMS-based cancer vaccine and an antibody markedly decreases the required dose of the immune checkpoint inhibitor. Mice locally administered with the HMS-based cancer vaccine and 1/8 dose of a standard anti-PD-L1 antibody (25 µg/mouse) show comparable anti-tumor effect and significantly increased CD4⁺ and CD8⁺ T cell populations, compared with those systemically immunized with the standard anti-PD-L1 antibody done at 200 µg/mouse. Our work presents a promising cancer treatment strategy of combining an immune checkpoint inhibitor with an HMS-based cancer vaccine. STATEMENT OF SIGNIFICANCE: The clinical benefits of checkpoint blockade therapy rekindle the hope of cancer immunotherapy. However, objective response rates in checkpoint blockade therapy remain at about 10-40% owing to multiple immunosuppressive factors. To solve these problems, herein, a hollow mesoporous silica (HMS) nanosphere-based cancer vaccine was combined with an immune checkpoint inhibitor, anti-PD-L1 antibody. The HMS-based cancer vaccine synergistically acts with the anti-PD-L1 antibody on the tumor. Mice locally administered with the HMS-based cancer vaccine and 1/8 dose of a standard anti-PD-L1 antibody (25 µg/mouse) show comparable anti-tumor effect and significantly increased CD4⁺ and CD8⁺ T cell populations, compared with those systemically immunized with the standard anti-PD-L1 antibody done at 200 µg/mouse. Our work presents a promising cancer treatment strategy of combining an immune checkpoint inhibitor with an HMS-based cancer vaccine.

Functionalisation of Inorganic Material Surfaces with Staphylococcus Protein A: A Molecular Dynamics Study

Staphylococcus protein A (SpA) is found in the cell wall of Staphylococcus aureus bacteria. Its ability to bind to the constant Fc regions of antibodies means it is useful for antibody extraction, and further integration with inorganic materials can lead to the development of diagnostics and therapeutics. We have investigated the adsorption of SpA on inorganic surface models such as experimentally relevant negatively charged silica, as well as positively charged and neutral surfaces, by use of fully atomistic molecular dynamics simulations. We have found that SpA, which is itself negatively charged at pH7, is able to adsorb on all our surface models. However, adsorption on charged surfaces is more specific in terms of protein orientation compared to a neutral Au (111) surface, while the protein structure is generally well maintained in all cases. The results indicate that SpA adsorption is optimal on the siloxide-rich silica surface, which is negative at pH7 since this keeps the Fc binding regions free to interact with other species in solution. Due to the dominant role of electrostatics, the results are transferable to other inorganic materials and pave the way for new diagnostic and therapeutic designs where SpA might be used to conjugate antibodies to nanoparticles.

Doxorubicin-loaded polypyrrole nanovesicles for suppressing tumor metastasis through combining photothermotherapy and lymphatic system-targeted chemotherapy

The lymphatic system provides a main route for the dissemination of most malignancies, which was related to high mortality in cancer patients. Traditional intravenous chemotherapy is of limited effectiveness on lymphatic metastasis due to the difficulty in accessing the lymphatic system. Herein, a novel lymphatic-targeting nanoplatform is prepared by loading doxorubicin (DOX) into sub-50 nm polypyrrole nanovesicles (PPy NVs). The PPy NVs possessed hollow spherical morphologies and a negative surface charge, leading to high drug loading capacity. These vesicles can also convert near-infrared (NIR) light into heat and thus can be used for tumor thermal ablation. DOX loaded PPy NVs (PPy@DOX NVs) along with NIR illumination are highly effective against 4T1 breast cancer cells in vitro. More importantly, following subcutaneous (SC) injection, a direct lymphatic migration of PPy@DOX NVs is confirmed through fluorescence observation of the isolated draining nodes. The acidic conditions in metastatic nodes might subsequently trigger the release of the encapsulated DOX NVs based on their pH-sensitive release profile. In a mouse model bearing 4T1 breast cancer, lymphatic metastases, as well as lung metastases, are significantly inhibited by nanocarrier-mediated trans-lymphatic drug delivery in combination with photothermal ablation. In conclusion, this platform holds great potential in impeding tumor growth and metastasis.

Protein-biomolecule interactions play a major role in shaping corona proteome: studies on milk interacted dietary particles

Despite the significance of surface absorbed proteins in determining the biological identity of nanoparticles (NPs) entering the human body, little is known about the surface corona and factors that shape their formation on dietary particles used as food additives. In this study, food grade NPs of silica and titania and their food additive counterparts (E551 and E171) were interacted with milk proteins or with skimmed milk and the levels of protein adsorption were quantified. Characteristics of proteins correlating with their level of adsorption to NPs were determined using partial least squares regression analysis. Results from individual protein-particle interactions revealed the significance of factors such as zeta potential, hydrophobicity and hydrodynamic size of particles, and protein characteristics such as the number of beta strands, isoelectric points, the number of amino acid units (Ile, Tyr, Ala, Gly, Pro, Asp, and Arg), and phosphorylation sites on their adsorption to particles. Similar regression analysis was performed to identify the characteristics of twenty abundant and enriched proteins (identified using LC-MS/MS analysis) for their association with the surface corona of milk-interacted particles. Contrary to individual protein-particle interactions, protein characteristics such as helices, turns, protein structures, disulfide bonds, the number of amino acid units (Cys, Met, Leu, and Trp), and Fe binding sites were significant for their association with the surface corona of milk interacted particles. This difference in factors identified from individual proteins and milk interacted particles suggested possible interactions of proteins with surface adsorbed biomolecules as revealed by scanning transmission X-ray microscopy and other biochemical assays.

Nitrilase immobilization and transposition from a micro-scale batch to a continuous process increase the nicotinic acid productivity

In recent years, many biocatalytic processes have been developed for the production of chemicals and pharmaceuticals. In this context, enzyme immobilization methods have attracted attention for their advantages, such as continuous production and increased stability. Here, enzyme immobilization methods and a collection of nitrilases from biodiversity for the conversion of 3-cyanopyridine to nicotinic acid were screened. Substrate conversion over 10 conversion cycles was monitored to optimize the process. The best immobilization conditions were found with cross-linking using glutaraldehyde to modify the PMMA beads. This method showed good activity over 10 cycles in a batch reactor at 30 and 40°C. Finally, production with a new thermostable nitrilase was examined in a continuous packed bed reactor, showing very high stability of the biocatalytic process at a flow rate of 0.12 ml min^-1 and a temperature of 50°C. The complete conversion of 3-cyanopyridine was obtained over 30 days of operation. Future steps will concern reactor scale-up to increase the production rate with reasonable pressure drops.

Lubricin as a tool for controlling adhesion in vivo and ex vivo

The ability to prevent or minimize the accumulation of unwanted biological materials on implantable medical devices is important in maintaining the long-term function of implants. To address this issue, there has been a focus on materials, both biological and synthetic, that have the potential to prevent device fouling. In this review, we introduce a glycoprotein called lubricin and report on its emergence as an effective antifouling coating material. We outline the versatility of lubricin coatings on different surfaces, describe the physical properties of its monolayer structures, and highlight its antifouling properties in improving implant compatibility as well as its use in treatment of ocular diseases and arthritis. This review further describes synthetic polymers mimicking the lubricin structure and function. We also discuss the potential future use of lubricin and its synthetic mimetics as antiadhesive biomaterials for therapeutic applications.

Serum Lowers Bioactivity and Uptake of Synthetic Amorphous Silica by Alveolar Macrophages in a Particle Specific Manner

Various cell types are compromised by synthetic amorphous silica (SAS) if they are exposed to SAS under protein-free conditions in vitro. Addition of serum protein can mitigate most SAS effects, but it is not clear whether this is solely caused by protein corona formation and/or altered particle uptake. Because sensitive and reliable mass spectrometric measurements of SiO₂ NP are cumbersome, quantitative uptake studies of SAS at the cellular level are largely missing. In this study, we combined the comparison of SAS effects on alveolar macrophages in the presence and absence of foetal calf serum with mass spectrometric measurement of ²⁸Si in alkaline cell lysates. Effects on the release of lactate dehydrogenase, glucuronidase, TNFα and H₂O₂ of precipitated (SIPERNAT^® 50, SIPERNAT^® 160) and fumed SAS (AEROSIL^® OX50, AEROSIL^® 380 F) were lowered close to control level by foetal calf serum (FCS) added to the medium. Using a quantitative high resolution ICP-MS measurement combined with electron microscopy, we found that FCS reduced the uptake of particle mass by 9.9% (SIPERNAT^® 50) up to 83.8% (AEROSIL^® OX50). Additionally, larger particle agglomerates were less frequent in cells in the presence of FCS. Plotting values for lactate dehydrogenase (LDH), glucuronidase (GLU) or tumour necrosis factor alpha (TNFα) against the mean cellular dose showed the reduction of bioactivity with a particle sedimentation bias. As a whole, the mitigating effects of FCS on precipitated and fumed SAS on alveolar macrophages are caused by a reduction of bioactivity and by a lowered internalization, and both effects occur in a particle specific manner. The method to quantify nanosized SiO₂ in cells is a valuable tool for future in vitro studies.

DNA immobilization and detection using DNA binding proteins

The immobilization of sensing bioreceptors is a critical feature affecting the final performance of a biosensor. For DNA detection, the (strept)avidin-biotin affinity interaction is often used for the immobilization of biotin-labeled oligonucleotides or PCR amplicons. Herein, DNA binding proteins are proposed as alternative universal anchors for both DNA immobilization and detection, based on the strong and specific affinity interaction between certain DNA binding proteins and their respective dsDNA binding sites. These binding sites can be incorporated in the target DNA molecule during synthesis and by PCR, eliminating the need for post-synthesis chemical modification and resulting in lower costs. When scCro DNA binding protein was immobilized on microplates and nitrocellulose membrane, both ssDNA and dsDNA targets were successfully detected. The detection limits achieved were similar to those obtained with the streptavidin-biotin system. However, the scCro system resulted in higher signals while using less amount of protein. The adsorption properties of scCro were superior to streptavidin's, making scCro a viable alternative as an anchor biomolecule for the development of DNA assays and biosensors. Finally, a nucleic acid lateral flow assay based solely on two different DNA binding proteins, scCro and dHP, was developed for the detection of a PCR amplicon. Overall, the proposed system appears to be very promising and with potential use for multiplex detection using various DNA binding proteins with different sequence specificities. Further work is required to better understand the adsorption properties of these biomolecules on nitrocellulose, optimize the assays comprehensively, and achieve improved sensitivities.

Interaction of microbial functional amyloids with solid surfaces

HYPOTHESIS

Self-assembling protein subunits hold great potential as biomaterials with improved functions. Among the self-assembled protein structures functional amyloids are promising unique properties such as resistance to harsh physical and chemical conditions their mechanical strength, and ease of functionalization. Curli proteins, which are functional amyloids of bacterial biofilms can be programmed as intelligent biomaterials.

EXPERIMENTS

In order to obtain controllable curli based biomaterials for biomedical applications, and to understand role of each of the curli forming monomeric proteins (namely CsgA and CsgB from Escherichia coli) we characterized their binding kinetics to gold, hydroxyapatite, and silica surfaces.

FINDINGS

We demonstrated that CsgA, CsgB, and their equimolar mixture have different binding strengths for different surfaces. On hydroxyapatite and silica surfaces, CsgB is the crucial element that determines the final adhesiveness of the CsgA-CsgB mixture. On the gold surface, on the other hand, CsgA controls the behavior of the mixture. Those findings uncover the binding behavior of curli proteins CsgA and CsgB on different biomedically valuable surfaces to obtain a more precise control on their adhesion to a targeted surface.

A new mechanism for reduced cell adhesion: Adsorption dynamics of collagen on a nanoporous gold surface

Nanostructured materials such as nanoparticles and nanoporous materials strongly affect cell behaviors such as cell viability. Because cellular uptake of nanoporous materials does not occur, mechanisms for the effects of nanoporous materials on cells are different from those of nanoparticles. The effects of nanoporous materials on cells are thought to result from large conformational changes in the extracellular matrix (ECM) induced by the nanoporous materials, although the mechanotransduction and the critical focal adhesion cluster size also have an effect on the cell response. However, we show that the adhesion of mesenchymal stem cells to a gold surface is reduced for nanoporous gold (NPG), despite the conformational changes in collagen induced by NPG being below the detection limits of the experimental analyses. The adsorption dynamics of collagen on NPG are investigated by molecular dynamics simulations to determine the origin of the reduced cell adhesion to NPG. The adsorption energy of collagen on NPG is lower than that on flat gold (FG) despite there being little difference between the global conformation of collagen segments adsorbed on NPG compared with FG. This finding is related to the surface strain of NPG and the limited movement of collagen amino acids owing to interchain hydrogen bonds. The results obtained in this study provide new insight into the interactions between nanostructured materials and the ECM.

Probing the binding modes and dynamics of histidine on fumed silica surfaces by solid-state NMR

Silica nanoparticles can be designed to exhibit a diverse range of morphologies (e.g. non-porous, mesoporous), physical properties (e.g. hydrophobic, hydrophilic) and a wide range of chemical and biomolecular surface functionalizations. In the present work, the adsorption complex of histidine (His) and fumed silica nanoparticles (FSN) is probed using thermal analysis (TGA/DTG) and a battery of solid-state (SS) NMR methods supported by DFT chemical shift calculations. Multinuclear (1H/13C/15N) one- and two-dimensional magic angle spinning (MAS) SSNMR experiments were applied to determine site-specific interactions between His and FSN surfaces as a function of adsorption solution concentration, pH and hydration state. By directly comparing SSNMR observables (linewidth, chemical shift and relaxation parameters) for His-FSN adsorption complexes to various crystalline, amorphous and aqueous His forms, the His structural and dynamic environment on FSN surfaces could be determined at an atomic level. The observed 13C and 15N MAS NMR chemical shifts, linewidths and relaxation parameters show that the His surface layer on FSN has a significant dependence on pH and hydration state. His is highly dynamic on FSN surfaces under acidic conditions (pH 4) as evidenced by sharp resonances with near isotropic chemical shifts regardless of hydration level indicating a non-specific binding arrangement while, a considerably more rigid His environment with defined protonation states is observed at near neutral pH with subtle variations between hydrated and anhydrous complexes. At near neutral pH, less charge repulsion occurs on the FSN surface and His is more tightly bound as evidenced by considerable line broadening likely due to chemical shift heterogeneity and a distribution in hydrogen-bonding strengths on the FSN surface. Multiple His sites exchange with a tightly bound water layer in hydrated samples while, direct interaction with the FSN surface and significant chemical shift perturbations for imidazole ring nitrogen sites and some carbon resonances are observed after drying. The SSNMR data was used to propose an interfacial molecular binding model between His and FSN surfaces under varying conditions setting the stage for future multinuclear, multidimensional SSNMR studies of His-containing peptides on silica nanoparticles and other nanomaterials of interest.

Characterization of the nano-bio interaction between metallic oxide nanomaterials and freshwater microalgae using flow cytometry

Since nanomaterials (NMs) are particulate contaminants, their first contact with organisms is a physical encounter ruled by physic-chemical processes that can determinate the potential NMs accumulation, toxicity, and trophic transfer. Freshwater ecosystems often become a final depository for NMs, so they can get in contact with the biota, especially primary organisms as algae. There are almost none comparative studies of this interaction using various NMs in the same conditions. This work identifies, analyzes, and compares the algae-NMs interaction by flow cytometry after a short-term contact test in which three freshwater algae (Raphidocelis subcapitata, Desmodesmus subspicatus, and Chlorella vulgaris) interact individually with a set of twelve metallic oxide NMs. Dose-response profiles and differences in the algae-NMs interaction were found according to each algae species (C. vulgaris had the most affinity, starting the interaction from 0.5 mg/L and D. subspicatus had the less affinity starting at 5 mg/L). Flow cytometry results were confirmed by optical microscopy. Some NMs characteristics were identified as key-factors that govern the algae-NMs interaction: NMs composition (no interaction for SiO₂ NMs), surface electric charge (higher interaction for the positively charged NMs and lower interaction for the negatively charged ones) and crystalline form (for TiO₂ NMs). The presented method can be useful for a rapid determination of the interaction between free cells organisms as microalgae and (nano)particulate substances.

In Situ Analysis of Weakly Bound Proteins Reveals Molecular Basis of Soft Corona Formation

Few experimental techniques allow the analysis of the protein corona in situ. As a result, little is known on the effects of nanoparticles on weakly bound proteins that form the soft corona. Despite its biological importance, our understanding of the molecular bases driving its formation is limited. Here, we show that hemoglobin can form either a hard or a soft corona on silica nanoparticles depending on the pH conditions. Using cryoTEM and synchrotron-radiation circular dichroism, we show that nanoparticles alter the structure and the stability of weakly bound proteins in situ. Molecular dynamics simulation identified the structural elements driving protein-nanoparticle interaction. Based on thermodynamic analysis, we show that nanoparticles stabilize partially unfolded protein conformations by enthalpy-driven molecular interactions. We suggest that nanoparticles alter weakly bound proteins by shifting the equilibrium toward the unfolded states at physiological temperature. We show that the classical approach based on nanoparticle separation from the biological medium fails to detect destabilization of weakly bound proteins, and therefore cannot be used to fully predict the biological effects of nanomaterials in situ.

From Protein Corona to Colloidal Self-Assembly: The Importance of Protein Size in Protein-Nanoparticle Interactions

Protein adsorption on nanoparticles is an important field of study, particularly with regard to nanomedicine and nanotoxicology. Many factors can influence the composition and structure of the layer(s) of adsorbed proteins, the so-called protein corona. However, the role of protein size has not been specifically investigated, although some evidence has indicated its potential important role in corona composition and structure. To assess the role of protein size, we studied the interactions of hemoproteins (spanning a large size range) with monodisperse silica nanoparticles. We combined various techniques-adsorption isotherms, isothermal titration calorimetry, circular dichroism, and transmission electron cryomicroscopy-to address this issue. Overall, the results show that small proteins behaved as typical model proteins, forming homogeneous monolayers on the nanoparticle surface (protein corona). Their adsorption is purely enthalpy-driven, with subtle structural changes. In contrast, large proteins interact with nanoparticles via entropy-driven mechanisms. Their structure is completely preserved during adsorption, and any given protein can directly bind to several nanoparticles, forming bridges in these newly formed protein-nanoparticle assemblies. Protein size is clearly an overlooked factor that should be integrated into proteomics and toxicological studies.

Ensilicated tetanus antigen retains immunogenicity: in vivo study and time-resolved SAXS characterization

Our recently developed ensilication approach can physically stabilize proteins in silica without use of a pre-formed particle matrix. Stabilisation is done by tailor fitting individual proteins with a silica coat using a modified sol-gel process. Biopharmaceuticals, e.g. liquid-formulated vaccines with adjuvants, frequently have poor thermal stability; heating and/or freezing impairs their potency. As a result, there is an increase in the prevalence of vaccine-preventable diseases in low-income countries even when there are means to combat them. One of the root causes lies in the problematic vaccine ‘cold chain’ distribution. We believe that ensilication can improve vaccine availability by enabling transportation without refrigeration. Here, we show that ensilication stabilizes tetanus toxin C fragment (TTCF), a component of the tetanus toxoid present in the diphtheria, tetanus and pertussis (DTP) vaccine. Experimental in vivo immunization data show that the ensilicated material can be stored, transported at ambient temperatures, and even heat-treated without compromising the immunogenic properties of TTCF. To further our understanding of the ensilication process and its protective effect on proteins, we have also studied the formation of TTCF-silica nanoparticles via time-resolved Small Angle X-ray Scattering (SAXS). Our results reveal ensilication to be a staged diffusion-limited cluster aggregation (DLCA) type reaction. An early stage (tens of seconds) in which individual proteins are coated with silica is followed by a subsequent stage (several minutes) in which the protein-containing silica nanoparticles aggregate into larger clusters. Our results suggest that we could utilize this technology for vaccines, therapeutics or other biopharmaceuticals that are not compatible with lyophilization.

Improving sensitivity for the targeted LC-MS/MS analysis of the peptide bradykinin using a design of experiments approach

The nonapeptide bradykinin is endogenously present only in low picomolar plasma concentrations, subsequently making reliable detection using liquid chromatography coupled to mass spectrometry (LC-MS/MS) challenging. Furthermore, non-specific adsorption during sample preparation and storage can lead to unpredictable peptide losses. To overcome these issues, a design of experiments (DoE) approach was applied, which consisted of a screening to identify impacting factors, optimisation and confirmation runs. On the one hand, different injection solvent compositions and sample collection materials were investigated in order to decrease non-specific adsorption. On the other hand, the addition of modifiers, which are known to enhance the signal intensity in LC-MS/MS, to the chromatographic mobile phase was examined. Polypropylene was the most suitable material among those investigated and resulted in a factor increase of 12.0 compared to LC-MS glass. The advantages of protein low-binding polypropylene versus standard polypropylene were fully compensated by the optimisation of the injection solvent. The latter substantially contributed to a decrease of non-specific adsorption of bradykinin. In this regard, bradykinin further benefitted from an organic fraction and a high amount of formic acid. Based on the DoE results, the final optimised injection solvent-consisting of 8.7% formic acid in 49.4/5.3/36.6 water/methanol/dimethyl sulfoxide (v/v/v)-was established. Furthermore, optimisation of the mobile phase composition yielded a signal intensity increase by a factor of 7.7. The transferability of the optimisation results conducted in neat solutions were successfully confirmed in human plasma. The applicability of this approach was further supported by the successful determination of low-abundance endogenous bradykinin levels in human plasma using LC-MS/MS.

Probing Protein Denaturation during Size-Exclusion Chromatography Using Native Mass Spectrometry

Size-exclusion chromatography employing aqueous mobile phases with volatile salts at neutral pH combined with electrospray-ionization mass spectrometry (SEC-ESI-MS) is a useful tool to study proteins in their native state. However, whether the applied eluent conditions actually prevent protein–stationary phase interactions, and/or protein denaturation, often is not assessed. In this study, the effects of volatile mobile phase additives on SEC retention and ESI of proteins were thoroughly investigated. Myoglobin was used as the main model protein, and eluents of varying ionic strength and pH were applied. The degree of interaction between protein and stationary phase was evaluated by calculating the SEC distribution coefficient. Protein-ion charge state distributions obtained during offline and online native ESI-MS were used to monitor alterations in protein structure. Interestingly, most of the supposedly mild eluent compositions induced nonideal SEC behavior and/or protein unfolding. SEC experiments revealed that the nature, ionic strength, and pH of the eluent affected protein retention. Protein–stationary phase interactions were effectively avoided using ammonium acetate at ionic strengths above 0.1 M. Direct-infusion ESI-MS showed that the tested volatile eluent salts seem to follow the Hofmeister series: no denaturation was induced using ammonium acetate (kosmotropic), whereas ammonium formate and bicarbonate (both chaotropic) caused structural changes. Using a mobile phase of 0.2 M ammonium acetate (pH 6.9), several proteins (i.e., myoglobin, carbonic anhydrase, and cytochrome c) could be analyzed by SEC-ESI-MS using different column chemistries without compromising their native state. Overall, with SEC-ESI-MS, the effect of nonspecific interactions between protein and stationary phase on the protein structure can be studied, even revealing gradual structural differences along a peak.

Protein Corona Composition of Silica Nanoparticles in Complex Media: Nanoparticle Size does not Matter

Biomolecules, and particularly proteins, bind on nanoparticle (NP) surfaces to form the so-called protein corona. It is accepted that the corona drives the biological distribution and toxicity of NPs. Here, the corona composition and structure were studied using silica nanoparticles (SiNPs) of different sizes interacting with soluble yeast protein extracts. Adsorption isotherms showed that the amount of adsorbed proteins varied greatly upon NP size with large NPs having more adsorbed proteins per surface unit. The protein corona composition was studied using a large-scale label-free proteomic approach, combined with statistical and regression analyses. Most of the proteins adsorbed on the NPs were the same, regardless of the size of the NPs. To go beyond, the protein physicochemical parameters relevant for the adsorption were studied: electrostatic interactions and disordered regions are the main driving forces for the adsorption on SiNPs but polypeptide sequence length seems to be an important factor as well. This article demonstrates that curvature effects exhibited using model proteins are not determining factors for the corona composition on SiNPs, when dealing with complex biological media.

Albumin-driven disassembly of lipidic nanoparticles: the specific case of the squalene-adenosine nanodrug

In the field of nanomedicine, nanostructured nanoparticles (NPs) made of self-assembling prodrugs emerged in the recent years with promising properties. In particular, squalene-based drug nanoparticles have already shown their efficiency through in vivo experiments. However, a complete pattern of their stability and interactions in the blood stream is still lacking. In this work we assess the behavior of squalene-adenosine (SQAd) nanoparticles - whose neuroprotective effect has already been demonstrated in murine models - in the presence of fetal bovine serum (FBS) and of bovine serum albumin (BSA), the main protein of blood plasma. Extensive physicochemical characterizations were performed using Small Angle Neutron Scattering (SANS), cryogenic transmission electron microscopy (Cryo-TEM), circular dichroism (CD), steady-state fluorescence spectroscopy (SSFS) and isothermal titration calorimetry (ITC) as well as in silico by means of ensemble docking simulations with human serum albumin (HSA). Significant changes in the colloidal stability of the nanoparticles in the presence of serum albumin were observed. SANS, CD and SSFS analyses demonstrated an interaction between SQAd and BSA, with a partial disassembly of the nanoparticles in the presence of BSA and the formation of a complex between SQAd and BSA. The interaction free energy of SQAd nanoparticles with BSA derived from ITC experiments, is about -8 kcal mol^-1 which is further supported in silico by ensemble docking simulations. Overall, our results show that serum albumin partially disassembles SQAd nanoparticles by extracting individual SQAd monomers from them. As a consequence, the SQAd nanoparticles would act as a circulating reservoir in the blood stream. The approach developed in this study could be extended to other soft organic nanoparticles.

A flexible, robust microbead-based assay for quantification and normalization of target protein concentrations

Although there are many methods for quantifying the concentration of specific proteins in samples, current techniques are technically challenging or do not easily lend themselves to normalization. Here, we describe a microbead-based assay for quantifying specific protein concentration(s) that is high-throughput, inexpensive, simple-to-use, and intrinsically incorporates normalization against the sample total protein content. This assay, termed the FRANC assay, exploits high affinity biotin-streptavidin binding to couple sample proteins to streptavidin-labelled magnetic microbeads. Proteins are then antibody-probed, followed by labeling of proteins on the microbead with fluorescent dye, and flow cytometry-based analysis. The FRANC assay demonstrates detection limits for target proteins in the femtogram range, with a linear range up to as much as 10 ng. Normalization of target protein concentrations resulted in an 80% reduction in variability as compared to non-normalized measurements. We conclude that the FRANC assay offers attractive advantages over current methods for quantifying specific protein(s) in samples.

Platform for Screening Abiotic/Biotic Interactions Using Indicator Displacement Assays

This paper describes novel adaptations of optically sectioned planar format assays to screen compounds for their affinities to materials surfaces. The novel platform, which we name optically sectioned indicator displacement assays (O-IDA), makes use of displaceable dyes in a format adaptable to high-throughput multiwell plate technologies. We describe two approaches: the first being where the dye exhibits fluorescence in both the surface bound and unbound state and the second, where fluorescence is lost upon displacement of the dye from the surface. Half maximal inhibitory concentration (IC₅₀), binding affinity (K_i), and binding free energy (ΔG_ads) values can be extracted from the raw data. Representative biomolecules were tested for interactions with silica in an aqueous environment and ZnO(0001)-Zn and (10-10) facets in a nonaqueous environment. We provide the first experimental values for both the binding of small molecules to silica and the facet-dependent ZnO binding affinity of key amino acids associated with ZnO-specific oligopeptides. The specific data will be invaluable to those studying interactions at interfaces both experimentally and computationally. O-IDA provides a general framework for the high-throughput screening of molecule binding to materials surfaces, which has important applications in drug delivery, (bio-) catalysis, biosensing, and biomaterial engineering.

Protein-Nanoparticle Interactions: What Are the Protein-Corona Thickness and Organization?

Protein adsorption on a surface is generally evaluated in terms of the evolution of the proteins' structures and functions. However, when the surface is that of a nanoparticle, the protein corona formed around it possesses a particular supramolecular structure that gives a "biological identity" to the new object. Little is known about the actual shape of the protein corona. Here, the protein corona formed by the adsorption of model proteins (myoglobin and hemoglobin) on silica nanoparticles was studied. Small-angle neutron scattering and oxygenation studies were combined to assess both the structural and functional impacts of the adsorption on proteins. Large differences in the oxygenation properties could be found while no significant global shape changes were seen after adsorption. Moreover, the structural study showed that the adsorbed proteins form an organized yet discontinuous monolayer around the nanoparticles.

Ensilication Improves the Thermal Stability of the Tuberculosis Antigen Ag85b and an Sbi-Ag85b Vaccine Conjugate

There is an urgent need for the development of vaccine thermostabilisation methodologies as the maintenance of a continuous and reliable cold chain remains a major hurdle to the global distribution of safe and effective vaccines. Ensilication, a method that encases proteins in a resistant silica cage has been shown to physically prevent the thermal denaturation of a number of model proteins. In this study we investigate the utility of this promising approach in improving the thermal stability of antigens and vaccine conjugates highly relevant to the development of candidate tuberculosis vaccines, including antigen 85b conjugated with the Staphylococcus aureus-protein based adjuvant Sbi. Here we analyse the sensitivity of these constructs to thermal denaturation and demonstrate for the first time the benefits of ensilication in conferring these vaccine-relevant proteins with protection against temperature-induced loss of structure and function without the need for refrigeration. Our results reveal the potential of ensilication in facilitating the storage and transport of vaccines at ambient temperatures in the future and therefore in delivering life-saving vaccines globally, and in particular to remote areas of developing countries where disease rates are often highest.

Confining a Protein-Containing Water Nanodroplet inside Silica Nanochannels

Incorporation of biological systems in water nanodroplets has recently emerged as a new frontier to investigate structural changes of biomolecules, with perspective applications in ultra-fast drug delivery. We report on the molecular dynamics of the digestive protein Pepsin subjected to a double confinement. The double confinement stemmed from embedding the protein inside a water nanodroplet, which in turn was caged in a nanochannel mimicking the mesoporous silica SBA-15. The nano-bio-droplet, whose size fits with the pore diameter, behaved differently depending on the protonation state of the pore surface silanols. Neutral channel sections allowed for the droplet to flow, while deprotonated sections acted as anchoring piers for the droplet. Inside the droplet, the protein, not directly bonded to the surface, showed a behavior similar to that reported for bulk water solutions, indicating that double confinement should not alter its catalytic activity. Our results suggest that nanobiodroplets, recently fabricated in volatile environments, can be encapsulated and stored in mesoporous silicas.

Proteomic Sample Preparation through Extraction by Unspecific Adsorption on Silica Beads for ArgC-like Digestion

Sample preparation for mass-spectrometry-based proteomic analyses usually requires intricate, multistep workflows that are often limited in capacity or suffer from sample loss. Here, we introduce a lean adsorption-based protocol (ABP) for the extraction of proteins from fresh cell lysates that enables us to modify and tag protein samples under harsh conditions, such as organic solvents, high salt concentrations, or low pH values. This offers high versatility while also reducing the required steps in the preparation process significantly. Protein identifications are slightly increased compared to traditional acetone precipitation followed by an in-solution digestion (AP/IS) or filter aided sample preparation (FASP) and proved complementary to both methods regarding proteome coverage. When combined with ArgC-like digestion, this approach delivered 5386 uniquely identified proteins, a substantial increase of 18.27% over tryptic digestion (4554), while decreasing spectra complexity due to a lower number of peptide to spectra matches per protein and the number of missed cleaved peptides. In addition, an increased number of identified membrane proteins and histones as well as improved fragmentation and intensity coverage were observed through comprehensive data analysis.