Changes in Secondary Structure and Properties of Bovine Serum Albumin as a Result of Interactions with Gold Surface.

Proteins can alter their shape when interacting with a surface. This study explores how bovine serum albumin (BSA) modifies structurally when it adheres to a gold surface, depending on the protein concentration and pH. We verified that the gold surface induces significant structural modifications to the BSA molecule using circular dichroism, infrared spectroscopy, and atomic force microscopy. Specifically, adsorbed molecules displayed increased levels of disordered structures and ß-turns, with fewer α-helices than the native structure. MP-SPR spectroscopy demonstrated that the protein molecules preferred a planar orientation during adsorption. Molecular dynamics simulations revealed that the interaction between cysteines exposed to the outside of the molecule and the gold surface was vital, especially at pH=3.5. The macroscopic properties of the protein film observed by AFM and contact angles confirm the flexible nature of the protein itself. Notably, structural transformation is joined with the degree of hydration of protein layers.

Changes in Secondary Structure and Properties of Bovine Serum Albumin as a Result of Interactions with a Gold Surface.

The front cover artwork is provided by Prof. Barbara Jachimska's group at the Jerzy Haber Institute of Catalysis and Surface Chemistry, PAS. The image represents the process of changes in the secondary structure of Bovine Serum Albumin (BSA) as a result of its interactions with a gold surface. Read the full text of the Research Article at 10.1002/cphc.202300505.

Dendrimer Platforms for Targeted Doxorubicin Delivery-Physicochemical Properties in Context of Biological Responses.

The unique structure of G4.0 PAMAM dendrimers allows a drug to be enclosed in internal spaces or immobilized on the surface. In the conducted research, the conditions for the formation of the active G4.0 PAMAM complex with doxorubicin hydrochloride (DOX) were optimized. The physicochemical properties of the system were monitored using dynamic light scattering (DLS), circular dichroism (CD), and fluorescence spectroscopy. The Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) method was chosen to determine the preferential conditions for the complex formation. The highest binding efficiency of the drug to the cationic dendrimer was observed under basic conditions when the DOX molecule was deprotonated. The decrease in the zeta potential of the complex confirms that DOX immobilizes through electrostatic interaction with the carrier's surface amine groups. The binding constants were determined from the fluorescence quenching of the DOX molecule in the presence of G4.0 PAMAM. The two-fold way of binding doxorubicin in the structure of dendrimers was visible in the Isothermal calorimetry (ITC) isotherm. Fluorescence spectra and release curves identified the reversible binding of DOX to the nanocarrier. Among the selected cancer cells, the most promising anticancer activity of the G4.0-DOX complex was observed in A375 malignant melanoma cells. Moreover, the preferred intracellular location of the complexes concerning the free drug was found, which is essential from a therapeutic point of view.

Effect of Ionization Degree of Poly(amidoamine) Dendrimer and 5-Fluorouracil on the Efficiency of Complex Formation-A Theoretical and Experimental Approach.

Due to their unique structure, poly(amidoamine) (PAMAM) dendrimers can bind active ingredients in two ways: inside the structure or on their surface. The location of drug molecules significantly impacts the kinetics of active substance release and the mechanism of internalization into the cell. This study focuses on the effect of the protonation degree of the G4PAMAM dendrimer and the anticancer drug 5-fluorouracil (5FU) on the efficiency of complex formation. The most favorable conditions for constructing the G4PAMAM-5FU complex are a low degree of protonation of the dendrimer molecule with the drug simultaneously present in a deprotonated form. The fluorine components in the XPS spectra confirm the formation of the stable complex. Through SAXS and DLS methods, a decrease in the dendrimer's molecular size resulting from protonation changes at alkaline conditions was demonstrated. The gradual closure of the dendrimer structure observed at high pH values makes it difficult for the 5FU molecules to migrate to the interior of the support structure, thereby promoting drug immobilization on the surface. The 1H NMR and DOSY spectra indicate that electrostatic interactions determine the complex formation process. Through MD simulations, the localization profile and the number of 5FU molecules forming the complex were visualized on an atomic scale.

Bovine Serum Albumin as a Platform for Designing Biologically Active Nanocarriers-Experimental and Computational Studies.

Due to the specificity of their structure, protein systems are adapted to carry various ligands. The structure of many proteins potentially allows for two types of immobilization of a therapeutic agent, either on the outer surface of the protein or within the protein structure. The existence of two active sites in BSA's structure, the so-called Sudlow I and II, was confirmed. The conducted research involved determining the effectiveness of BSA as a potential carrier of 5-fluorouracil (5FU). 5-fluorouracil is a broad-spectrum anticancer drug targeting solid tumors. The research was carried out to estimate the physicochemical properties of the system using complementary measurement techniques. The optimization of the complex formation conditions made it possible to obtain significant correlations between the form of the drug and the effective localization of the active substance in the structure of the protein molecule. The presence of two amino groups in the 5FU structure contributes to the deprotonation of the molecule at high pH values (pH > 8) and the transition to the anionic form (AN1 and AN3). To investigate the binding affinity of the tautomeric form with BSA, UV-vis absorption, fluorescence quenching, zeta potential, QCM-D, and CD spectroscopic studies were performed. The experimental research was supported by molecular dynamics (MD) simulations and molecular docking. The simulations confirm the potential location of 5FU tautomers inside the BSA structure and on its surface.

Adsorption and Conformation Behavior of Lysozyme on a Gold Surface Determined by QCM-D, MP-SPR, and FTIR.

The physicochemical properties of protein layers at the solid-liquid interface are essential in many biological processes. This study aimed to link the structural analysis of adsorbed lysozyme at the water/gold surface at pH 7.5 in a wide range of concentrations. Particular attention was paid to the protein's structural stability and the hydration of the protein layers formed at the interface. Complementary methods such as multi-parameter surface plasmon resonance (MP-SPR), quartz crystal microbalance with energy dissipation (QCM-D), and infrared spectroscopy (FTIR) were used for this purpose. The MP-SPR and QCM-D studies showed that, during the formation of a monolayer on the gold surface, the molecules' orientation changes from side-on to end-on. In addition, bilayer formation is observed when adsorbing in the high-volume concentration range >500 ppm. The degree of hydration of the monolayer and bilayer varies depending on the degree of surface coverage. The hydration of the system decreases with filling the layer in both the monolayer and the bilayer. Hydration for the monolayer varies in the range of 50-70%, because the bilayer is much higher than 80%. The degree of hydration of the adsorption layer has a crucial influence on the protein layers' viscoelastic properties. In general, an increase in the filling of a layer is characterized by a rise in its rigidity. The use of infrared spectroscopy allowed us to determine the changes taking place in the secondary structure of lysozyme due to its interaction with the gold surface. Upon adsorption, the content of II-structures corresponding to ß-turn and random lysozyme structures increases, with a simultaneous decrease in the content of the ß-sheet. The increase in the range of ß-turn in the structure determines the lysozyme structure's stability and prevents its aggregation.

Poly(amidoamine) Dendrimers as Nanocarriers for 5-Fluorouracil: Effectiveness of Complex Formation and Cytotoxicity Studies.

Two generations of positively charged poly(amidoamine) dendrimers (PAMAMs) were selected for study as potential carriers for the anticancer drug 5-fluorouracil (5FU), a drug primarily used in the treatment of colorectal cancer. Analytical techniques, such as UV-Vis spectrophotometry, NMR Spectroscopy and Laser Doppler Velocimetry (LDV), have shown that the most critical factor determining the formation of a PAMAM-5FU complex is the starting components' protonation degree. The tests confirmed the system's ability to attach about 20 5FU molecules per one dendrimer molecule for the G4PAMAM dendrimer and about 25 molecules for the G6PAMAM dendrimer, which gives a system yield of 16% for the fourth generation and 5% for sixth generation dendrimers. Additionally, using the QCM-D method, the adsorption efficiency and the number of drug molecules immobilized in the dendrimer structure were determined. A new aspect in our study was the determination of the change in zeta potential (ζ) induced by the immobilization of 5FU molecules on the dendrimer's outer shell and the importance of this effect in the direct contact of the carrier with cells. Cytotoxicity tests (resazurin reduction and MTS tests) showed no toxicity of dendrimers against mouse fibroblast cells (L929) and a significant decrease in cell viability in the case of four human malignant cell lines: malignant melanoma (A375), glioblastoma (SNB-19), prostate cancer (Du-145) and colon adenocarcinoma (HT-29) during incubation with PAMAM-5FU complexes. The purpose of our work was to investigate the correlation between the physicochemical properties of the carrier and active substance and the system efficiency and optimizing conditions for the formation of an efficient system based on PAMAM dendrimers as nanocarriers for 5-fluorouracil. An additional aspect was to identify potential application properties of the complexes, as demonstrated by cytotoxicity tests.

Lysozyme adsorption at a silica surface using simulation and experiment: effects of pH on protein layer structure.

Hen Egg White Lysozyme (HEWL) is a widely used exemplar to study protein adsorption on surfaces and interfaces. Here we use fully atomistic Molecular Dynamics (MD) simulations, Multi-Parametric Surface Plasmon Resonance (MP-SPR), contact angle and zeta potential measurements to study HEWL adsorption at a silica surface. The simulations provide a detailed description of the adsorption mechanism and indicate that at pH7 the main adsorption driving force is electrostatics, supplemented by weaker hydrophobic forces. Moreover, they reveal the preferred orientation of the adsorbed protein and show that its structure is only slightly altered at the interface with the surface. This provides the basis for interpreting the experimental results, which indicate the surface adsorbs a close-packed monolayer at about pH10 where the surface has a large negative zeta potential and the HEWL is positively charged. At higher pH, the adsorption amount of the protein layer is greatly reduced due to the loss of charge on the protein. At lower pH, the smaller zeta potential of the surface leads to lower HEWL adsorption. These interpretations are complemented by the contact angle measurements that show how the hydrophobicity of the surface is greatest when the surface coverage is highest. The simulations provide details of the hydrophobic residues exposed to solution by the adsorbed HEWL, completing the picture of the protein layer structure.

Effect of Alkaline Conditions on Forming an Effective G4.0 PAMAM Complex with Doxorubicin.

In this study, special attention was paid to the correlation between the degree of ionization of the components and the effective formation of the complex under alkaline conditions. Using UV-Vis, 1H NMR, and CD, structural changes of the drug depending on the pH were monitored. In the pH range of 9.0 to 10.0, the G4.0 PAMAM dendrimer can bind 1 to 10 DOX molecules, while the efficiency increases with the concentration of the drug relative to the carrier. The binding efficiency was described by the parameters of loading content (LC = 4.80-39.20%) and encapsulation efficiency (EE = 17.21-40.16%), whose values increased twofold or even fourfold depending on the conditions. The highest efficiency was obtained for G4.0PAMAM-DOX at a molar ratio of 1:24. Nevertheless, regardless of the conditions, the DLS study indicates system aggregation. Changes in the zeta potential confirm the immobilization of an average of two drug molecules on the dendrimer's surface. Circular dichroism spectra analysis shows a stable dendrimer-drug complex for all the systems obtained. Since the doxorubicin molecule can simultaneously act as a therapeutic and an imaging agent, the theranostic properties of the PAMAM-DOX system have been demonstrated by the high fluorescence intensity observable on fluorescence microscopy.

Novel diagnostic and prognostic factors for the advanced melanoma based on the glycosylation-related changes studied by biophysical profiling methods.

Melanoma is a life-threatening disease due to the early onset of metastasis and frequent resistance to the applied treatment. For now, no single histological, immunohistochemical or serological biomarker was able to provide a precise predictive value for the aggressive behavior in melanoma patients. Thus, the search for quantifying methods allowing a simultaneous diagnosis and prognosis of melanoma patients is highly desirable. By investigating specific molecular interactions with some biosensor-based techniques, one can determine novel prognostic factors for this tumor. In our previous study, we have shown the possibility of a qualitative in vitro distinguishing the commercially available melanoma cells at different progression stages based on the measurements of the lectin Concanavalin A interacting with surface glycans present on cells. Here, we present the results of the quantitative diagnostic and prognostic study of both commercial and patient-derived melanoma cells based on the evaluation of two novel factors: lectin affinity and glycan viscoelastic index obtained from the quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. Two approaches to the QCM-D measurements were applied, the first uses the ability of melanoma cells to grow as a monolayer of cells on the sensor (cell-based sensors), and the second shortens the time of the analysis (suspension cell based-sensors). The results were confirmed by the complementary label-free (atomic force microscopy, AFM; and surface plasmon resonance, SPR) and labeling (lectin-ELISA; and microscale thermophoresis, MST) techniques. This new approach provides additional quantitative diagnosis and a personalized prognosis which can be done simultaneously to the traditional histopathological analysis.

The Ca2+ response of a smart forisome protein is dependent on polymerization.

Forisomes are giant self-assembling mechanoproteins that undergo reversible structural changes in response to Ca2+ and various other stimuli. Artificial forisomes assembled from the monomer MtSEO-F1 can be used as smart biomaterials, but the molecular basis of their functionality is not understood. To determine the role of protein polymerization in forisome activity, we tested the Ca2+ association of MtSEO-F1 dimers (the basic polymerization unit) by circular dichroism spectroscopy and microscale thermophoresis. We found that soluble MtSEO-F1 dimers neither associate with Ca2+ nor undergo structural changes. However, polarization modulation infrared reflection absorption spectroscopy revealed that aggregated MtSEO-F1 dimers and fully-assembled forisomes associate with Ca2+ , allowing the hydration of poorly-hydrated protein areas. A change in the signal profile of complete forisomes indicated that Ca2+ interacts with negatively-charged regions in the protein complexes that only become available during aggregation. We conclude that aggregation is required to establish the Ca2+ response of forisome polymers.

Analysis of dendrimer-protein interactions and their implications on potential applications of dendrimers in nanomedicine.

This work addresses how G5.5 PAMAM dendrimers form complexes with bovine serum albumin (BSA). Analytical techniques, such as UV-vis spectrophotometry, dynamic light scattering, electrophoretic mobility, quartz crystal microbalance with dissipation monitoring (QCM-D), circular dichroism (CD), and contact angle were used to analyze the properties of the dendrimers systems. The binding of protein to dendrimers can alter the structure, mobility, conformation and functional activity of the dendrimer. The results show that BSA interactions with G5.5 dendrimer carriers are driven both by electrostatic and hydrophobic forces. Dendrimer surface charge is reduced upon contact with the protein. The protein shell formed on the surface of the carrier is very stable as evidenced by the QCM-D measurements. On the other hand, the CD spectra indicates a change in the secondary structure of the protein. The size of the changes is significantly dependent on the ratio of protein to dendrimer. Understanding the mechanism of interaction of potential carriers with proteins is important for their internalization into the cell.

Adsorption of lysozyme on gold surfaces in the presence of an external electric potential.

Adsorbed protein films consist of essential building blocks of many biotechnological and biomedical devices. The electrostatic potential may significantly modulate the protein behaviour on surfaces, affecting their structure and biological activity. In this study, lysozyme was used to investigate the effects of applied electric potentials on adsorption and the protein structure. The pH and the surface charge determine the amount and secondary structure of adsorbed lysozyme on a gold surface. In-situ measurements using polarization modulation infrared reflection absorption spectroscopy indicated that the concentration of both the adsorbed anions and the lysozyme led to conformational changes in the protein film, which was demonstrated by a greater amount of aggregated ß-sheets in films fabricated at net positive charges of the Au electrode (Eads > Epzc). The changes in secondary structure involved two parallel processes. One comprised changes in the hydration/hydrogen-bond network at helices, leading to diverse helical structures: α-, 310- and/or π-helices. In the second process ß-turns, ß-sheets, and random coils displayed an ability to form aggregated ß-sheet structures. The study illuminates the understanding of electrical potential-dependent changes involved in the protein misfolding process.

It takes two to tango - The case of thebaine 6-O-demethylase.

Thebaine 6-O-demethylase (T6ODM) is an Fe(II)/2-oxoglutarate-dependent dioxygenase catalysing two oxidative O-demethylation reactions in morphine biosynthesis. Its crystal structure revealed a large active site pocket which is at least two times larger than necessary to accommodate a substrate (thebaine or oripavine) molecule. Since so far no crystal structures have been obtained for enzyme-substrate complex, which is necessary to explain the enzyme regiospecificity towards the C6-bound methoxy group, in this work we used computational methods and multi-parametric surface plasmon resonance measurements to elucidate the most likely structure of this complex and the reaction mechanism starting therefrom. Results of simulations and experiments unanimously indicate that the enzyme-substrate complex of T6ODM has a 1:2 stoichiometry. The key residues responsible for substrate binding are: Val-128, Glu-133, Met-150 and Agr-219 for the substrate in the distal position, and Asp-144, Leu-235 and Leu-353 for the proximal substrate molecule. QM/MM and DFT calculations show that the oxo ligand is bound trans to His-295 and the enzyme catalyzes hydroxylation of the C6-bound methoxy group according to the established rebound mechanism. The final stage of the demethylation reaction, which includes deformylation and enol-keton tautomerization steps, is most likely catalysed by water molecules and takes place in the solvent.

Detecting lysozyme unfolding via the fluorescence of lysozyme encapsulated gold nanoclusters.

Protein misfolding plays a critical role in the manifestation of amyloidosis type diseases. Therefore, understanding protein unfolding and the ability to track protein unfolding in a dynamic manner are of considerable interest. Fluorescence-based techniques are powerful tools for gaining real-time information about the local environmental conditions of a probe on the nanoscale. Fluorescent gold nanoclusters (AuNCs) are a new type of fluorescent probes which are <2 nm in diameter, incredibly robust and offer highly sensitive, wavelength tuneable emission. Their small size minimises intrusion and makes AuNCs ideal for studying protein dynamics. Lysozyme has previously been used to encapsulate AuNCs. The unfolding dynamics of lysozyme under different environmental conditions have been well-studied and being an amyloid type protein makes lysozyme an ideal candidate for encapsulating AuNCs in order to test their sensitivity to protein unfolding. In this study, we tracked the fluorescence characteristics of AuNCs encapsulated in lysozyme while inducing protein unfolding using urea, sodium dodecyl sulphate (SDS) and elevated temperature and compared them to complimentary circular dichroism spectra. It is found that AuNC fluorescence emission is quenched upon induced protein unfolding either due to a decrease in Forster Resonance Energy Transfer (FRET) efficiency between tryptophan and AuNCs or solvent exposure of the AuNC. Fluorescence lifetime measurements confirmed quenching to be collisional via oxygen dissolved in a solution which increases as the AuNC was exposed to the solvent during unfolding. Moreover, the longer decay component τ1 was observed to decrease as the protein unfolded, due to the increased collisional quenching. It is suggested that AuNC sensitivity to solvent exposure might be utilised in the future as a new approach to studying and possibly even detecting amyloidosis type diseases.

Properties of polyethylene glycol supported tetraarylporphyrin in aqueous solution and its interaction with liposomal membranes.

5,10,15,20-Tetrakis(4-hydroxyphenyl)porphyrin was functionalized by covalent attachment of poly(ethylene glycol) (PEG) chains of various molecular weights, 350, 2000, and 5000 Da. The properties of PEG-functionalized tetraarylporphyrins in aqueous solution and their interactions with liposomes have been studied. Electronic absorption spectroscopy, dynamic light scattering, atomic force microscopy, and fluorescence quenching were used to monitor aggregation of porphyrin chromophores and behavior of the attached PEG chains in the aqueous solution. The tendency for aggregation of porphyrin chromophores in aqueous solution and the efficiency of fluorescence quenching by KI decrease with increasing length of PEG chain linked to the porphyrin ring. The experimental results indicate that polymer clusters are present in aqueous solution of all pegylated porphyrins. The interactions between the pegylated porphyrins and phosphatidylcholine liposomes in the aqueous solution were studied using the fluorescence methods. The apparent binding constants of porphyrin chromophores to liposomes were determined. The degree of binding was found to be dependent on the molecular weight of the attached polymer.

Which physical and structural factors of liposome carriers control their drug-loading efficiency?

The correlation between structural and physical properties of lipid membrane and its drug-loading efficiency were studied. The properties of bilayer were altered by incorporation of several lipidic modifiers: cholesterol, oleic acid, methyl oleate, and pegylated lipid. By using the molecular probe technique it was demonstrated that the membrane properties, such as micropolarity, microviscosity and free volume were considerably changed by incorporation of the modifiers. The partitioning of two different porphyrins between the bulk aqueous phase and the modified liposomes was studied using the fluorescence methods, and liposome-binding constants were determined. It was found that cholesterol reduced the partitioning of both porphyrins into liposomal bilayer. On the contrary, the incorporation of methyl oleate and pegylated lipid causes a pronounced increase in the value of the binding constants of both porphyrins. It was concluded that the free volume rather than hydrophobicity of bilayer is a governing factor in the solute partitioning into lipid bilayers.

Polyallylamine hydrochloride coating enhances the fluorescence emission of Human Serum Albumin encapsulated gold nanoclusters.

Protein encapsulated gold nanoclusters have received much attention due to the possibility of using them as a non-toxic fluorescent probe or marker for biomedical applications, however one major disadvantage currently is their low brightness and quantum yield in comparison to currently used fluorescent markers. A method of increasing the fluorescence emission of Human Serum Albumin (HSA) encapsulated gold nanoclusters (AuNCs) via a Polyallylamide hydrochloride (PAH) coating is described. PAH molecules with a molecular weight of ~17,500 Da were found to enhance the fluorescence emission of HSA-AuNCs by 3-fold when the protein/polymer concentration ratio is 2:1 in solution. Interestingly, the fluorescence lifetime of the AuNCs was found to decrease while the native tryptophan (TRP) fluorescence lifetime also decreased during the fluorescence emission intensity enhancement caused by the PAH binding. Coinciding with the decrease in fluorescence lifetime, the zeta potential of the system was observed to be zero during maximum fluorescence intensity enhancement, causing the formation of large aggregates. These results suggest that PAH binds to the HSA-AuNCs acting as a linker; causing aggregation and rigidification, which results in a decrease in separation between native TRP of HSA and AuNCs; improving Förster Resonance Energy Transfer (FRET) and increasing the fluorescence emission intensity. These findings are critical to the development of brighter protein encapsulated AuNCs.

Energy Landscape of Negatively Charged BSA Adsorbed on a Negatively Charged Silica Surface.

We study the energy landscape of the negatively charged protein bovine serum albumin adsorbed on a negatively charged silica surface at pH 7. We use fully atomistic molecular dynamics (MD) and steered MD (SMD) to probe the energy of adsorption and the pathway for the surface diffusion of the protein and its associated activation energy. We find an adsorption energy ∼1.2 eV, which implies that adsorption is irreversible even on experimental time scales of hours. In contrast, the activation energy for surface diffusion is ∼0.4 eV so that it is observable on the MD simulation time scale of 100 ns. This analysis paves the way for a more detailed understanding of how a protein layer forms on biomaterial surfaces, even when the protein and surface share the same electrical polarity.

Mechanism of actin polymerization by myosin subfragment-1 probed by dynamic light scattering.

Monomeric actin (G-actin) polymerizes spontaneously into helical filaments in the presence of inorganic salts. The slowest, rate-limiting step of the polymerization process is formation of actin trimers, the smallest oligomers that serve as nuclei for fast filament growth (filament elongation) by monomer addition at the filament ends. In low ionic-strength solutions, actin can be polymerized by myosin subfragment-1 (S1). In early works it has been suggested that G-actin-S1 1:1 complexes (GS) assemble into filaments according to the nucleation-filament elongation scheme. Subsequent studies indicated that one S1 molecule can bind two actin monomers, and that oligomerization of the initial complexes is a fast reaction. This has led to suggest an alternative mechanism, with a ternary G(2)S complex and its oligomers being predominant intermediates of S1-induced assembly of G-actin into filaments. We used dynamic light scattering to analyze the initial steps of S1-induced polymerization of actin. Our results suggest formation of GS complexes and their oligomers in the presence of S1 equimolar to or in excess over actin. We confirm formation of G(2)S complexes as intermediates of S1-induced polymerization in the presence of actin in excess over S1.