Exploring the Behavior of Bovine Serum Albumin in Response to Changes in the Chemical Composition of Responsive Polymers: Experimental and Simulation Studies

Elucidating the Role of Optical Activity of Polymers in Protein-Polymer Interactions

Proteins are biomolecules with potential applications in agriculture, food sciences, pharmaceutics, biotechnology, and drug delivery. Interactions of hydrophilic and biocompatible polymers with proteins may impart proteolytic stability, improving the therapeutic effects of biomolecules and also acting as excipients for the prolonged storage of proteins under harsh conditions. The interactions of hydrophilic and stealth polymers such as poly(ethylene glycol), poly(trehalose), and zwitterionic polymers with various proteins are well studied. This study evaluates the molecular interactions of hydrophilic and optically active poly(vitamin B5 analogous methacrylamide) (poly(B5AMA)) with model proteins by fluorescence spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and circular dichroism (CD) spectroscopy analysis. The optically active hydrophilic polymers prepared using chiral monomers of R-(+)- and S-(-)-B5AMA by the photo-iniferter reversible addition fragmentation chain transfer (RAFT) polymerization showed concentration-dependent weak interactions of the polymers with bovine serum albumin and lysozyme proteins. Poly(B5AMA) also exhibited a concentration-dependent protein stabilizing effect at elevated temperatures, and no effect of the stereoisomers of polymers on protein thermal stability was observed. NMR analysis, however, showed poly(B5AMA) stereoisomer-dependent changes in the secondary structure of proteins.

Globular Proteins and Where to Find Them within a Polymer Brush-A Case Study

Protein adsorption by polymerized surfaces is an interdisciplinary topic that has been approached in many ways, leading to a plethora of theoretical, numerical and experimental insight. There is a wide variety of models trying to accurately capture the essence of adsorption and its effect on the conformations of proteins and polymers. However, atomistic simulations are case-specific and computationally demanding. Here, we explore universal aspects of the dynamics of protein adsorption through a coarse-grained (CG) model, that allows us to explore the effects of various design parameters. To this end, we adopt the hydrophobic-polar (HP) model for proteins, place them uniformly at the upper bound of a CG polymer brush whose multibead-spring chains are tethered to a solid implicit wall. We find that the most crucial factor affecting the adsorption efficiency appears to be the polymer grafting density, while the size of the protein and its hydrophobicity ratio come also into play. We discuss the roles of ligands and attractive tethering surfaces to the primary adsorption as well as secondary and ternary adsorption in the presence of attractive (towards the hydrophilic part of the protein) beads along varying spots of the backbone of the polymer chains. The percentage and rate of adsorption, density profiles and the shapes of the proteins, alongside with the respective potential of mean force are recorded to compare the various scenarios during protein adsorption.

Nano Differential Scanning Fluorimetry as a Rapid Stability Assessment Tool in the Nanoformulation of Proteins

The development and production of innovative protein-based therapeutics is a complex and challenging avenue. External conditions such as buffers, solvents, pH, salts, polymers, surfactants, and nanoparticles may affect the stability and integrity of proteins during formulation. In this study, poly (ethylene imine) (PEI) functionalized mesoporous silica nanoparticles (MSNs) were used as a carrier for the model protein bovine serum albumin (BSA). To protect the protein inside MSNs after loading, polymeric encapsulation with poly (sodium 4-styrenesulfonate) (NaPSS) was used to seal the pores. Nano differential scanning fluorimetry (NanoDSF) was used to assess protein thermal stability during the formulation process. The MSN-PEI carrier matrix or conditions used did not destabilize the protein during loading, but the coating polymer NaPSS was incompatible with the NanoDSF technique due to autofluorescence. Thus, another pH-responsive polymer, spermine-modified acetylated dextran (SpAcDEX), was applied as a second coating after NaPSS. It possessed low autofluorescence and was successfully evaluated with the NanoDSF method. Circular dichroism (CD) spectroscopy was used to determine protein integrity in the case of interfering polymers such as NaPSS. Despite this limitation, NanoDSF was found to be a feasible and rapid tool to monitor protein stability during all steps needed to create a viable nanocarrier system for protein delivery.

Elucidation of binding dynamics of tyrosine kinase inhibitor tepotinib, to human serum albumin, using spectroscopic and computational approach

Tepotinib (TPT), an anticancer drug, is a fibroblast growth factor receptor inhibitor approved by the FDA for the chemotherapy of urothelial carcinoma. The binding of anticancer medicines to HSA can affect their pharmacokinetics and pharmacodynamics. The absorption, fluorescence emission, circular dichroism, molecular docking, and simulation studies were used to evaluate the binding relationship between TPT and HSA. The absorption spectra exhibited a hyperchromic effect upon the interaction of TPT with HSA. The Stern-Volmer and binding constant of the HSA-TPT complex demonstrates that fluorescence quenching is triggered by a static rather than a dynamic process. Further, the displacement assays and molecular docking results revealed that TPT preferred binding to site III of HSA. Circular dichroism spectroscopy confirmed that TPT binding to HSA induces conformational changes and reduces α-helical content. The thermal CD spectra reveal that tepotinib enhances protein's stability in the temperature range of 20 to 90 °C. The findings of MDS studies provide further evidence for the stability of the HSA-TPT complex. Consequently, the findings of the present investigation provide a clear picture of the impacts of TPT on HSA interaction. These interactions are thought to make the microenvironment around HSA more hydrophobic than in its native state.

Glycation reduces the binding dynamics of aflatoxin B1 to human serum albumin: a comprehensive spectroscopic and computational investigation

Aflatoxin B1 (AFB1), a potent mutagen, is synthesized by Aspergillus parasiticus and Aspergillus flavus. Human serum albumin (HSA) is a globular protein with diverse roles. As AFB1 is ingested with food and is transported in the body via blood, it becomes pertinent to comprehend the effect of the binding of this toxin on the structure and conformation of HSA, which may help to get insight into the toxic effect of the exposure of the mycotoxin. In this study, multi-spectroscopic approaches have been used to evaluate the binding efficiency of AFB1 with both the native HSA (nHSA) and the glycated HSA (gHSA). Steady-state fluorescence spectroscopy reveals the static type of fluorescence quenching in the fluorescence emission spectra of nHSA and gHSA in the presence of AFB1. The binding constant (Kb) is calculated to be 6.88 × 104 M-1 for nHSA, while a reduced Kb value of 2.95 × 104 M-1 has been obtained for gHSA. The circular dichroism study confirms the change in the secondary structure of nHSA and gHSA in the presence of AFB1, followed by alterations in the melting temperature (Tm) of nHSA and gHSA. In silico computational findings envisaged the amino acid residues and bonds involved in the binding of nHSA and gHSA with AFB1. The comprehensive study analyzes the binding effectiveness of AFB1 with nHSA and gHSA and shows reduced binding of AFB1 to gHSA.Communicated by Ramaswamy H. Sarma.

Biomolecular Interactions of Cytotoxic Ruthenium Compounds with Thiosemicarbazone or Benzothiazole Schiff Base Chelates

Herein we illustrate the formation and characterization of new paramagnetic ruthenium compounds, trans-P-[RuCl(PPh₃ )₂ (pmt)]Cl (1) (Hpmt=1-((pyridin-2-yl)methylene)thiosemicarbazide), trans-P-[RuCl(PPh₃ )₂ (tmc)]Cl (2) (Htmc=1-((thiophen-2-yl)methylene)thiosemicarbazide) and a diamagnetic ruthenium complex, cis-Cl, trans-P-[RuCl₂ (PPh₃ )₂ (btm)] (3) (btm=2-((5-hydroxypentylimino)methyl)benzothiazole). Agarose gel electrophoresis experiments of the metal compounds illustrated dose-dependent binding to gDNA by 1-3, while methylene blue competition assays suggested that 1 and 2 are also DNA intercalators. Assessment of the effects of the compounds on topoisomerase function indicated that 1-3 are capable of inhibiting topoisomerase I activity in terms of the ability to nick supercoiled plasmid DNA. The cytotoxic activities of the metal complexes were determined against a range of cancer cell lines versus a non-tumorigenic control cell line, and the complexes were, in general, more cytotoxic towards the cancer cells, displaying IC₅₀ values in the low micromolar range. Time-dependent stability studies showed that in the presence of strong nucleophilic species (such as DMSO), the chloride co-ligands of 1-3 are rapidly substituted by the former as proven by the suppression of the substitution reactions in the presence of an excess amount of chloride ions. The metal complexes are significantly stable in both DCM and an aqueous phosphate buffer containing 2 % DMSO.

Anti-Inflammatory and Anti-Rheumatic Potential of Selective Plant Compounds by Targeting TLR-4/AP-1 Signaling: A Comprehensive Molecular Docking and Simulation Approaches

Plants are an important source of drug development and numerous plant derived molecules have been used in clinical practice for the ailment of various diseases. The Toll-like receptor-4 (TLR-4) signaling pathway plays a crucial role in inflammation including rheumatoid arthritis. The TLR-4 binds with pro-inflammatory ligands such as lipopolysaccharide (LPS) to induce the downstream signaling mechanism such as nuclear factor κappa B (NF-κB) and mitogen activated protein kinases (MAPKs). This signaling activation leads to the onset of various diseases including inflammation. In the present study, 22 natural compounds were studied against TLR-4/AP-1 signaling, which is implicated in the inflammatory process using a computational approach. These compounds belong to various classes such as methylxanthine, sesquiterpene lactone, alkaloid, flavone glycosides, lignan, phenolic acid, etc. The compounds exhibited different binding affinities with the TLR-4, JNK, NF-κB, and AP-1 protein due to the formation of multiple hydrophilic and hydrophobic interactions. With TLR-4, rutin had the highest binding energy (−10.4 kcal/mol), poncirin had the highest binding energy (−9.4 kcal/mol) with NF-κB and JNK (−9.5 kcal/mol), respectively, and icariin had the highest binding affinity (−9.1 kcal/mol) with the AP-1 protein. The root means square deviation (RMSD), root mean square fraction (RMSF), and radius of gyration (RoG) for 150 ns were calculated using molecular dynamic simulation (MD simulation) based on rutin’s greatest binding energy with TLR-4. The RMSD, RMSF, and RoG were all within acceptable limits in the MD simulation, and the complex remained stable for 150 ns. Furthermore, these compounds were assessed for the potential toxic effect on various organs such as the liver, heart, genotoxicity, and oral maximum toxic dose. Moreover, the blood–brain barrier permeability and intestinal absorption were also predicted using SwissADME software (Lausanne, Switzerland). These compounds exhibited promising physico-chemical as well as drug-likeness properties. Consequently, these selected compounds portray promising anti-inflammatory and drug-likeness properties.

Molecular interactions of esculin with bovine serum albumin and recognition of binding sites with spectroscopy and molecular docking

Esculin is structurally a hydroxycoumarin found in various medicinal plants. This study investigates the binding mode of esculin with bovine serum albumin by employing numerous spectroscopic studies and molecular docking approaches. Ultraviolet absorption spectroscopy revealed ground state complex formation between esculin and bovine serum albumin. At the same time, steady-state fluorescence studies showed quenching in the fluorescence emission spectra of BSA in the presence of esculin. To get insight into the location of the binding pocket of esculin on BSA, warfarin and ibuprofen site markers were used. Competitive site marker displacement assay revealed that esculin binds to Sudlow's site I (subdomain IIA) in bovine serum albumin. Thermodynamic parameters suggested that hydrogen bonding and van der Waals interaction stabilizes the esculin-BSA complex. Förster's non-radiation energy transfer analysis described the high propensity of energy transfer between bovine serum albumin and esculin. The molecular docking approach facilitated locating the binding pocket, amino acid residues involved, types of interacting forces, and binding energy (ΔG) between esculin and BSA. Circular dichroism revealed the effect of the binding of esculin on the secondary structure and helped understand the thermal unfolding profile of BSA in the presence of esculin.Communicated by Ramaswamy H. Sarm.

Metal-Modified Montmorillonite as Plasmonic Microstructure for Direct Protein Detection

Thanks to its negative surface charge and high swelling behavior, montmorillonite (MMT) has been widely used to design hybrid materials for applications in metal ion adsorption, drug delivery, or antibacterial substrates. The changes in photophysical and photochemical properties observed when fluorophores interact with MMT make these hybrid materials attractive for designing novel optical sensors. Sensor technology is making huge strides forward, achieving high sensitivity and selectivity, but the fabrication of the sensing platform is often time-consuming and requires expensive chemicals and facilities. Here, we synthesized metal-modified MMT particles suitable for the bio-sensing of self-fluorescent biomolecules. The fluorescent enhancement achieved by combining clay minerals and plasmonic effect was exploited to improve the sensitivity of the fluorescence-based detection mechanism. As proof of concept, we showed that the signal of fluorescein isothiocyanate can be harvested by a factor of 60 using silver-modified MMT, while bovine serum albumin was successfully detected at 1.9 µg/mL. Furthermore, we demonstrated the versatility of the proposed hybrid materials by exploiting their plasmonic properties to develop liquid label-free detection systems. Our results on the signal enhancement achieved using metal-modified MMT will allow the development of highly sensitive, easily fabricated, and cost-efficient fluorescent- and plasmonic-based detection methods for biomolecules.

Hydroxyapatite sonosensitization of ultrasound-triggered, thermally responsive hydrogels: An on-demand delivery system for bone repair applications

While bones have the innate capability to physiologically regenerate, in certain cases regeneration is suboptimal, too slow, or does not occur. Biomaterials-based growth factor delivery systems have shown potential for the treatment of challenging bone defects, however, achieving controlled growth factor release remains a challenge. The objective of this study was to develop a thermally responsive hydrogel for bone regeneration capable of ultrasound-triggered on-demand delivery of therapeutic agents. Furthermore, it was hypothesized that incorporation of hydroxyapatite (HA) into the hydrogel could increase sonosensitization, augmenting ultrasound sensitivity to enable controlled therapeutic release to the target tissue. Alginate thermally responsive P(Alg-g-NIPAAm) hydrogels were fabricated and varying quantities of HA (1, 3, 5, and 7% wt./vol.) incorporated. All hydrogels were highly injectable (maximum injection force below 6.5 N) and rheological characterization demonstrated their ability to gel at body temperature. The study demonstrated the ultrasound-triggered release of sodium fluorescein (NaF), bovine serum albumin (BSA), and bone morphogenetic protein 2 (BMP-2) from the hydrogels. Release rates of BSA and BMP-2 were significantly enhanced in the HA containing hydrogels, confirming for the first time the role of HA as a son sensitizer. Together these results demonstrate the potential of these ultrasound-triggered thermally responsive hydrogels for on-demand delivery of therapeutic agents for bone regeneration.

Encapsulation of BSA in hybrid PEG hydrogels: stability and controlled release

Hybrid hydrogels based on silylated polyethylene glycol, Si-PEG, were evaluated as hybrid matrices able to trap, stabilize and release bovine serum albumin (BSA) in a controlled manner. Parameters of the inorganic condensation reaction leading to a siloxane (Si–O–Si) three dimensional network were carefully investigated, in particular the temperature, the surrounding hygrometry and the Si-PEG concentration. The resulting hydrogel structural features affected the stability, swelling, and mechanical properties of the network, leading to different protein release profiles. Elongated polymer assemblies were observed, the length of which ranged from 150 nm to over 5 μm. The length could be correlated to the Si–O–Si condensation rate from 60% (hydrogels obtained at 24 °C) to about 90% (xerogels obtained at 24 °C), respectively. Consequently, the controlled release of BSA could be achieved from hours to several weeks, with respect to the fibers' length and the condensation rate. The protein stability was evaluated by means of a thermal study. The main results gave insight into the biomolecule structure preservation during polymerisation, with ΔG < 0 for encapsulated BSA in any conditions, below the melting temperature (65 °C).

Silylated hybrid hydrogels of polyethylene glycol were designed to trap, stabilize and release a model protein (bovine serum albumin). Fine-tuning sol–gel reactions lead to sustained release of BSA over weeks, with good insight of protein stability.

A novel amalgamation of deep eutectic solvents and crowders as biocompatible solvent media for enhanced structural and thermal stability of bovine serum albumin

This study unravels the effect of a novel solvent medium designed by amalgamation of macromolecular crowders and deep eutectic solvents (DESs) on bovine serum albumin (BSA).

How do biological stimuli modulate conformational changes of biomedical thermoresponsive polymer?

Continuing efforts to develop stimuli-responsive polymers (SRPs) as novel smart materials/biomaterials are anticipated to upgrade the quality life of humans. The details of the molecular, physico chemical and biophysical interactions between SRPs and proteins are not fully understood. Indeed, protein - polymer interactions play a major role in a wide range of biomedical/biomaterial applications. In this regard, we have demonstrated the influence of proteins (β-lactoglobulin (BLG) and stem bromelain (BM) as biological stimuli) on the phase transition behavior of biomedical thermoresponsive poly(N-isopropylacrylamide) (PNIPAM). In order to predict these, we have used a set of biophysical techniques to unveil the influence of biological stimuli on the phase transition behavior of PNIPAM. Absorption spectroscopy, steady-state fluorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) were operated at room temperature to examine the changes in absorbance, fluorescence intensity, molecular interactions and surface morphologies, respectively. Furthermore, temperature dependent fluorescence spectroscopy and dynamic light scattering (DLS) studies were also performed to analyze conformational changes, agglomeration behavior, particle size, coil to globule transition and phase behavior. The significant variations obtained in the phase transition temperature values, conformational changes and agglomeration behavior clearly reflects the different molecular interplay induced in presence of biological stimuli. The results demonstrated that the added proteins act as biological stimuli via preferential interactions between the amide group of the polymer and water molecules. The present study can be useful for the design and development of the next generation smart responsive materials/biomaterials.

Application of Photoinduced Electron Transfer with Copper Nanoclusters toward Finding Characteristics of Protein Pockets

Proteins possess various domains and subdomain pockets with varying hydrophobicity/hydrophilicity. The local polarities of these domains play a major role in oxidation-reduction-based biological processes. Herein, we have synthesized ultrasmall fluorescent copper nanoclusters (Cu NCs) that are directed to bind to the different domain-specific pockets of the model protein bovine serum albumins (BSA). Potential electron acceptors, methyl viologen (MV) derivatives, were chosen such that they specifically reach the various domains following their hydrophobicity/hydrophilicity. Here, we have used MV²⁺, HMV⁺, and DHMV²⁺, possessing hydrophilic, intermediate, and hydrophobic specificities. Being electron acceptors, these derivatives draw electrons from the Cu NCs through photoinduced electron transfer (PET). The rate of PET varies at the different domains of BSA based on the local environment which has been analyzed. Here, PET is confirmed by steady state as well as time-resolved fluorescence spectroscopy. This study would provide a measurable way to identify the location of the different domains of a protein which is scalable by changing the superficial conditions without unfolding the protein.

Polymethacrylate Coated Electrospun PHB Fibers as a Functionalized Platform for Bio-Diagnostics: Confirmation Analysis on the Presence of Immobilized IgG Antibodies against Dengue Virus

In this article, a combination of far field electrospinning (FFES) and free-radical polymerization has been used to create a unique platform for protein immobilization via the physical attachment of biomolecules to the surface of the fiber mats. The large specific surface area of the fibers with its tailored chemistry provides a desirable platform for effective analyte-surface interaction. The detailed analysis of protein immobilization on a newly developed bio-receptive surface plays a vital role to gauge its advantages in bio-diagnostic applications. We relied on scanning electron microscopy (SEM), diameter range analysis, and X-ray photoelectron spectroscopy (XPS), along with thermal gravimetric analysis (TGA), water-in-air contact angle analysis (WCA), Fourier transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM) to study our developed platforms and to provide valuable information regarding the presence of biomolecular entities on the surface. Detailed analyses of the fiber mats before and after antibody immobilization have shown obvious changes on the surface of the bioreceptive surface including: (i) an additional peak corresponding to the presence of an antibody in TGA analysis; (ii) extra FTIR peaks corresponding to the presence of antibodies on the coated fiber platforms; and (iii) a clear alteration in surface roughness recorded by AFM analysis. Confirmation analyses on protein immobilization are of great importance as they underlay substantial grounds for various biosensing applications.

Synthesis of Novel Temperature- and pH-Sensitive ABA Triblock Copolymers P(DEAEMA-co-MEO₂MA-co-OEGMA)-b-PEG-b-P(DEAEMA-co-MEO₂MA-co-OEGMA): Micellization, Sol⁻Gel Transitions, and Sustained BSA Release

Novel temperature- and pH-responsive ABA-type triblock copolymers, P(DEAEMA-co-MEO₂MA-co-OEGMA)-b-PEG-b-P(DEAEMA-co-MEO₂MA-co-OEGMA), composed of a poly(ethylene glycol) (PEG) middle block and temperature- and pH-sensitive outer blocks, were synthesized by atom transfer radical polymerization (ATRP). The composition and structure of the copolymer were characterized by ¹H NMR and gel permeation chromatography (GPC). The temperature- and pH-sensitivity, micellization, and the sol⁻gel transitions of the triblock copolymers in aqueous solutions were studied using transmittance measurements, surface tension, viscosity, fluorescence probe technique, dynamic light scattering (DLS), zeta-potential measurements, and transmission electron microscopy (TEM). The lower critical solution temperature (LCST) of the triblock copolymer, which contains a small amount of a weak base group, (N,N-diethylamino) ethyl methacrylate (DEAEMA), can be tuned precisely and reversibly by changing the solution pH. When the copolymer concentration was sufficiently high, increasing temperature resulted in the free-flowing solution transformation into a micellar gel. The sol-to-gel transition temperature (Tsol⁻gel) in aqueous solution will continue to decrease as solution concentration increases.