Understanding Conformational Changes in Human Serum Albumin and Its Interactions with Gold Nanorods: Do Flexible Regions Play a Role in Corona Formation?

Temperature dependent human serum albumin Corona formation: A case study on gold nanorods and nanospheres

Protein molecules interact with nanoparticles to form a protein layer on the surface called the protein corona. Corona formation can be affected by the temperature and shape of the nanoparticles thereby impacting the fate of the nanoparticles inside physiological systems. We have investigated the human serum albumin (HSA) corona formation and its interactions with gold nanospheres and nanorods at different temperatures (18-42 °C). UV-Vis, fluorescence, isothermal titration calorimetry (ITC), x-ray photoelectron spectroscopy (XPS) and circular dichroism (CD) experiments have been performed to determine the changes due to the shape and temperature. UV-Vis spectra show a greater propensity of corona induced aggregation in the nanorods compared to the nanospheres. The Stern-Volmer plot indicates that static quenching is predominant in the HSA-AuNP interactions with higher quenching efficiency for nanorods than nanospheres. ITC analyses show that HSA-nanorods are involved in more favorable interactions compared to HSA-nanospheres. XPS studies indicate a more electron rich environment on the AuNRs surface and higher AuS interactions in AuNSs. CD spectra show higher secondary structural changes with temperature in case of HSA-AuNR interactions compared to HSA-AuNS interactions. The changes in the protein corona due to nanoparticle shape and variable temperature have been investigated through protein adsorption and composition, types of interactions and protein conformation.

Cataractous Eye Protein Isolate Stabilized Gold Nanoparticles Prevent Their Ethanol-Induced Aggregation

Due to their distinctive optical, electrical, and catalytic characteristics, gold nanoparticles (AuNPs) have found increasing use for a wide range of applications, including biomedicine and catalysis. Inherent agglomeration propensities impair their functional qualities, stability, and biocompatibility. This work investigates the potential applications of the cataractous eye protein isolate (CEPI), a waste product rich in proteins from cataract surgery, as a novel AuNP stabilizing agent. It was found that CEPI can successfully stabilize AuNPs under a variety of situations, preventing ethanol-induced aggregation and preserving their structural integrity. Using spectroscopic and analytical techniques, including UV-Vis spectroscopy, dynamic light scattering (DLS), circular dichroism (CD) spectroscopy, and fluorescence quenching studies, we confirmed the successful binding of CEPI to AuNPs and the enhanced stability of the conjugates. A shift in the localized surface plasmon resonance (LSPR) peak and modifications to the secondary structure of the CEPI were indicative of strong binding and protective effects between CEPI and AuNPs. These findings suggest that CEPI, an underutilized biomaterial, can serve as an effective and biocompatible stabilizer for AuNPs, with potential applications in biomedical and therapeutic fields.

Protein corona formation on different-shaped CdSe/CdS semiconductor nanocrystals

Nanoparticles (NPs) have been widely studied and applied in medical and pharmaceutical fields. When NPs enter the in vivo environment, they are covered with protein molecules to form the so-called "protein corona". Because NPs and proteins are comparable in size, the shape of NPs has a significant impact on NP-protein interactions. Although NPs of various shapes have been synthesized, how the shape of NPs affects the protein corona is poorly understood, and little is known about the underlying molecular mechanism. In the present study, we synthesized spherical, football-shaped, and rod-shaped semiconductor nanocrystals (SNCs) as model NPs and compared their interaction with human serum albumin (HSA) using fluorescence correlation spectroscopy, fluorescence quenching, Fourier-transform infrared spectroscopy, and thermodynamic analysis. Based on the binding enthalpy and entropy and secondary structural changes of HSA, with the help of hydrodynamic diameter changes of SNCs, we concluded that HSA adopts a conformation or orientation that is appropriate for the local curvature of SNCs. This study demonstrates the effect of NP shape on their interaction with proteins and provides a mechanistic perspective.

Unraveling the impact of tungsten disulfide quantum dots on human serum albumin conformational dynamics and fibrillation pathways: An integrated multi-spectroscopic, biochemical, and molecular docking investigation

Herein, the intricate molecular interplay between human serum albumin (HSA) and tungsten disulfide quantum dots (WS2 QDs) was probed using spectroscopic techniques and sophisticated molecular simulation methods. Fluorescence spectroscopy demonstrated that under physiological conditions, WS2 QDs forge a non-fluorescent ground-state complex with HSA, facilitated by hydrogen bonding and van der Waals forces, ultimately resulting in the static quenching of the protein's intrinsic fluorescence. Complementary site competition experiments and molecular docking simulations reinforced a precise 1: 1 binding stoichiometry, predominantly targeting HSA's Site I. Three-dimensional fluorescence spectroscopy revealed that WS2 QDs perturb the HSA polypeptide backbone, subtly modifying the microenvironment surrounding aromatic amino acid residues. This alteration was further corroborated by circular dichroism spectroscopy, marked by a decrease in helical content and a transition towards irregular peptide conformations. Thermal stability assays illuminated the reduced thermal resilience of the HSA - WS2 QD complex. Laser confocal microscopy coupled with thioflavin T staining yielded compelling evidence that WS2 QDs effectively inhibit amyloid fibril formation in both HSA and lysozyme, underscoring their potential as potent anti-amyloidogenic agents. This comprehensive study offers pivotal insights into multifaceted impact of WS2 QDs on protein structure and function, thereby expanding their horizon of potential applications within the burgeoning field of nanomedicine.

Thin Film Formation of HSA in the Presence of CTAB-Capped Gold Nanorods through Phase Separation

Phase behavior in protein-nanoparticle systems in light of protein corona formation has been investigated. We report the formation of HSA thin films following the addition of a solid protein to a solution of CTAB-capped gold nanorods (AuNRs) via phase separation. The phase separation behavior was observed through UV-vis spectroscopy, turbidity assays, and DLS studies. UV-vis spectra for the protein-AuNR solution indicated a possible self-assembly formation by CTAB-HSA complexes and AuNR-HSA conjugates. The turbidity was found to increase linearly up to 30-50% v/v for each component. The growth phase slope is proportional to the concentration of the components, AuNRs, and HSA, with no lag phase. Dynamic light scattering (DLS) shows the formation of larger aggregates with time, implying a segregated phase of AuNR-HSA and a CTAB-HSA-AuNR network. ζ-potential values confirm surface modification, implying protein corona formation on nanorods. The thin films were also characterized using SEM, AFM, SAXS, XPS, FTIR, and TGA studies. SEM images show a smooth surface with a reduced number of pores, indicating the compactness of the deposited structure. AFM shows two different structural pattern formations with the deposition, indicating possible self-assembly of the protein-conjugated nanoparticles. FTIR studies indicate a change in the hydrogen bonding network and confirm the CTAB-HSA-AuNR complex network formation. The XPS studies indicate Au-S bond formation, along with Au-S-S-Au interactions. SAXS studies indicate the formation of aggregates (oligomers), as well as the presence of dominant attractive intermolecular interactions in the thin films.

Does the surface charge of the nanoparticles drive nanoparticle-cell membrane interactions?

Classical Coulombic interaction, characterized by electrostatic interactions mediated through surface charges, is often regarded as the primary determinant in nanoparticles' (NPs) cellular association and internalization. However, the intricate physicochemical properties of particle surfaces, biomolecular coronas, and cell surfaces defy this oversimplified perspective. Moreover, the nanometrological techniques employed to characterize NPs in complex physiological fluids often exhibit limited accuracy and reproducibility. A more comprehensive understanding of nanoparticle-cell membrane interactions, extending beyond attractive forces between oppositely charged surfaces, necessitates the establishment of databases through rigorous physical, chemical, and biological characterization supported by nanoscale analytics. Additionally, computational approaches, such as in silico modeling and machine learning, play a crucial role in unraveling the complexities of these interactions.

Perspectives on Protein-Nanoparticle Interactions at the In Vivo Level

The distinct features of nanoparticles have provided a vast opportunity of developing new diagnosis and therapy strategies for miscellaneous diseases. Although a few nanomedicines are available in the market or in the translation stage, many important issues are still unsolved. When entering the body, nanomaterials will be quickly coated by proteins from their surroundings, forming a corona on their surface, the so-called protein corona. Studies have shown that the protein corona has many important biological implications, particularly at the in vivo level. For example, they can promote the immune system to rapidly clear these outer materials and prevent nanoparticles from playing their designed role in therapy. In this Perspective, the available techniques for characterizing protein-nanoparticle interactions are critically summarized. Effects of nanoparticle properties and environmental factors on protein corona formation, which can further regulate the in vivo fate of nanoparticles, are highlighted and discussed. Moreover, recent progress on the biomedical application of protein corona-engineered nanoparticles is introduced, and future directions for this important yet challenging research area are also briefly discussed.

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 β-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.

How Does pH Affect the Adsorption of Human Serum Protein in the Presence of Hydrophobic and Hydrophilic Nanoparticles at Air-Water and Lipid-Water Interfaces?

This study investigates interaction between hydrophilic (11-mercaptoundecanoic acid (MUA)) and hydrophobic (1-undecanethiol (UDT)) gold nanoparticles (GNPs) with human serum albumin (HSA) protein on air-water and lipid-water interfaces at pH 3 and 7. Vibrational sum frequency generation (VSFG) spectroscopy is used to analyze changes in the intensity of interfacial water molecules and the C-H group of the protein. At the air-water interface, the hydrophobic interaction between the HSA protein and hydrophobic GNPs at pH 3 leads to their accumulation at the interface, resulting in an increased C-H intensity of the protein with a slight decrease in water intensity. Whereas, at pH 7, where the negative charge of the protein results in the reduced surface activity of the HSA compared to pH 3, the interaction between alkyl chain of the hydrophobic GNPs and alkyl group of the protein results in the adsorption of the protein-capped GNPs at the interface. This leads to an increased intensity of the C-H group of protein and water molecules. However, negatively charged hydrophilic GNPs do not induce significant changes in the interfacial water structure or the C-H group of the protein due to the electrostatic force of repulsion with the negatively charged HSA at pH 7. In contrast, at the lipid-water interface, both hydrophobic and hydrophilic GNPs interact with HSA protein, causing disordering of interfacial water molecules at pH 3 and ordering at pH 7. Interestingly, similar behavior of the protein with both types of GNPs results in comparable ordering/disordering at the interface depending on the pH of solution. Furthermore, the VSFG results obtained with the deuterated lipid suggest that changes in ordering and disorder occur due to increased protein adsorption in the presence of GNPs, causing alterations in the membrane structure. These findings give a better understanding of the mechanisms that govern protein-nanoparticle interaction and their consequential effects on the structure, function, and behavior of molecules at the biological membrane interface, which is crucial for developing safe and effective nanoparticle-based therapeutics.

Real-Time Optical Tracking of Protein Corona Formation on Single Nanoparticles in Serum

The formation of a protein corona, where proteins spontaneously adhere to the surface of nanomaterials in biological environments, leads to changes in their physicochemical properties and subsequently affects their intended biomedical functionalities. Most current methods to study protein corona formation are ensemble-averaging and either require fluorescent labeling, washing steps, or are only applicable to specific types of particles. Here we introduce real-time all-optical nanoparticle analysis by scattering microscopy (RONAS) to track the formation of protein corona in full serum, at the single-particle level, without any labeling. RONAS uses optical scattering microscopy and enables real-time and in situ tracking of protein adsorption on metallic and dielectric nanoparticles with different geometries directly in blood serum. We analyzed the adsorbed protein mass, the affinity, and the kinetics of the protein adsorption at the single particle level. While there is a high degree of heterogeneity from particle to particle, the predominant factor in protein adsorption is surface chemistry rather than the underlying nanoparticle material or size. RONAS offers an in-depth understanding of the mechanisms related to protein coronas and, thus, enables the development of strategies to engineer efficient bionanomaterials.

Immunogenic Potential and Therapeutic Efficacy of Multi-Epitope Encapsulated Silk Fibroin Nanoparticles against Pseudomonas aeruginosa-Mediated Urinary Tract Infections

Pseudomonas aeruginosa (P. aeruginosa) causing urinary tract infections (UTIs) are a major concern among hospital-acquired infections. The need for an effective vaccine that reduces the infections is imperative. This study aims to evaluate the efficacy of a multi-epitope vaccine encapsulated in silk fibroin nanoparticles (SFNPs) against P. aeruginosa-mediated UTIs. A multi-epitope is constructed from nine proteins of P. aeruginosa using immunoinformatic analysis, expressed, and purified in BL21 (DE3) cells. The encapsulation efficiency of the multi-epitope in SFNPs is 85% with a mean particle size of 130 nm and 24% of the encapsulated antigen is released after 35 days. The vaccine formulations adjuvanted with SFNPs or alum significantly improve systemic and mucosal humoral responses and the cytokine profile (IFN-γ, IL-4, and IL-17) in mice. Additionally, the longevity of the IgG response is maintained for at least 110 days in a steady state. In a bladder challenge, mice treated with the multi-epitope admixed with alum or encapsulated in SFNPs demonstrate significant protection of the bladder and kidneys against P. aeruginosa. This study highlights the promising therapeutic potential of a multi-epitope vaccine encapsulated in SFNPs or adjuvanted with alum against P. aeruginosa infections.

pH-Responsible Doxorubicin-Loaded Fe3O4@CaCO3 Nanocomposites for Cancer Treatment

A magnetic nanocomposite (MNC) is an integrated nanoplatform that combines a set of functions of two types of materials. A successful combination can give rise to a completely new material with unique physical, chemical, and biological properties. The magnetic core of MNC provides the possibility of magnetic resonance or magnetic particle imaging, magnetic field-influenced targeted delivery, hyperthermia, and other outstanding applications. Recently, MNC gained attention for external magnetic field-guided specific delivery to cancer tissue. Further, drug loading enhancement, construction stability, and biocompatibility improvement may lead to high progress in the area. Herein, the novel method for nanoscale Fe3O4@CaCO3 composites synthesis was proposed. For the procedure, oleic acid-modified Fe3O4 nanoparticles were coated with porous CaCO3 using an ion coprecipitation technique. PEG-2000, Tween 20, and DMEM cell media was successfully used as a stabilization agent and template for Fe3O4@CaCO3 synthesis. Transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and dynamic light scattering (DLS) data were used for the Fe3O4@CaCO3 MNC’s characterization. To improve the nanocomposite properties, the concentration of the magnetic core was varied, yielding optimal size, polydispersity, and aggregation ability. The resulting Fe3O4@CaCO3 had a size of 135 nm with narrow size distributions, which is suitable for biomedical applications. The stability experiment in various pH, cell media, and fetal bovine serum was also evaluated. The material showed low cytotoxicity and high biocompatibility. An excellent anticancer drug doxorubicin (DOX) loading of up to 1900 µg/mg (DOX/MNC) was demonstrated. The Fe3O4@CaCO3/DOX displayed high stability at neutral pH and efficient acid-responsive drug release. The series of DOX-loaded Fe3O4@CaCO3 MNCs indicated effective inhibition of Hela and MCF-7 cell lines, and the IC 50 values were calculated. Moreover, 1.5 μg of the DOX-loaded Fe3O4@CaCO3 nanocomposite is sufficient to inhibit 50% of Hela cells, which shows a high prospect for cancer treatment. The stability experiments for DOX-loaded Fe3O4@CaCO3 in human serum albumin solution indicated the drug release due to the formation of a protein corona. The presented experiment showed the “pitfalls” of DOX-loaded nanocomposites and provided step-by-step guidance on efficient, smart, anticancer nanoconstruction fabrication. Thus, the Fe3O4@CaCO3 nanoplatform exhibits good performance in the cancer treatment area.