Desolvation of BSA-ligand complexes measured using the quartz crystal microbalance and dual polarization interferometer

The Binding of Drug Molecules to Serum Albumin: The Effect of Drug Hydrophobicity on Binding Strength and Protein Desolvation

In this work, dual polarization interferometry (DPI) and quartz crystal microgravimetry with dissipation monitoring (QCM-D) were used to examine the binding characteristics and structure-activity relationships of 12 common drugs on a model bovine serum albumin (BSA) film. By taking advantage of the different hydration sensitivities of DPI and QCM-D, we were able to quantify changes in the solvent state upon drug binding to BSA. Quantifying the changes in water mass within binding pockets and upon drug-protein binding allows for a more complete understanding of binding phenomena between drug molecules and serum proteins. For the drugs tested, a quantitative structure-activity relationship (QSAR) was used to establish a correlation between drug binding (K_D) and hydrophobicity (ClogP), with the latter being related to the drug's ability to desolvate the BSA upon binding. Understanding these relationships provides insight into the role of water at the protein-ligand interface and is of particular importance in the area of ligand binding within the field of drug design. This study underscores the importance of hydrophobicity to drug binding kinetics and may be used to further understand and improve drug design and delivery protocols.

A study of polyethylene glycol backfilling for enhancing target recognition using QCM-D and DPI

Polyethylene glycol (PEG) is a promising candidate for protein resistance and preserving protein function in biomedical applications. In this study, a PEG-based bifunctional platform with antifouling for plasma proteins and high sensitivity for biomolecules was designed. Long PEG chains (PEG₂₄) were used to install functional biomolecules, and short PEG chains (PEG₄) served as a protective layer to backfill the surface and suppress nonspecific protein adsorption. Quartz crystal microbalance with dissipation (QCM-D) and dual polarization interferometry (DPI) were combined to investigate the dynamic process of PEG₄ backfilling and the recognition capacity of biomolecules with different ratios of PEG₄ and PEG₂₄ in real time. The amount of PEG₄ chain backfilling affected the flexibility of PEG₂₄ and exposed sites. The recognition capacity was improved by increasing the ratios of PEG₄ to PEG₂₄. Therefore, when the feeding ratio of PEG₄ to PEG₂₄ was 9 : 1, a highly efficient and sensitive platform was constructed for immobilization of antibodies and recognition of antigens either in pure PBS or in a complex biological environment.

pH Dependence of Adsorbed Fibrinogen Conformation and Its Effect on Platelet Adhesion

Quartz crystal microbalance with dissipation (QCM-D) and dual polarization interferometry (DPI) were used to investigate fibrinogen (Fib) adsorption behavior on different surfaces by changing the pH value. Moreover, integrin adhesion to the adsorbed Fibs was studied using DPI. Qualitative and quantitative studies of platelet adhesion to the adsorbed Fibs were performed using scanning electron microscopy (SEM), confocal laser scanning microscope (CLSM), and released lactate dehydrogenase (LDH) assay. Experimental results indicated that the conformation and orientation of the absorbed Fibs depended on surface property and pH cycling. For the hydrophilic surface, Fibs adsorbed at pH 7.4 and presented a αC-hidden orientation. As a result, no integrin adhesion was observed, and a small number of platelets were adhered because the αC-domains were hidden under the Fib molecule. By changing the rinsing solution pH from 7.4 to 3.2 and then back to 7.4, the adsorbed Fib orientation became αC-exposed via the transformation of Fib conformation during pH cycling. Therefore, integrin adhesion was more likely to occur, and more platelets were adhered and activated. For the hydrophobic surface, the adsorbed Fibs became more spread and stretched due to the strong interaction between the Fibs and surface. αC-exposed orientation remained unchanged when the rinsing solution pH changed from 7.4 to 3.2 and then back to 7.4. Therefore, a large number of integrins and platelets were adhered to the adsorbed Fibs, and almost all of the adhered platelets were activated.

Effect of grafted PEG chain conformation on albumin and lysozyme adsorption: A combined study using QCM-D and DPI

In this study, elucidation of protein adsorption mechanism is performed using dual polarization interferometry (DPI) and quartz crystal microbalance with dissipation (QCM-D) to study adsorption behaviors of bovine serum albumin (BSA) and lysozyme (LYZ) on poly (ethylene glycol) (PEG) layers. From the analysis of DPI, PEG2000 and PEG5000 show tight and loose mushroom conformations, respectively. Small amount of LYZ could displace the interfacial water surrounding the tight mushroomed PEG2000 chains by hydrogen bond attraction, leading to protein adsorption. The loose mushroomed PEG5000 chains exhibit a more flexible conformation and high elastic repulsion energy that could prevent protein adsorption of all BSA and most of LYZ. From the analysis of QCM, PEG2000 and PEG5000 show tight and extended brush conformations. The LYZ adsorbed mass has critical regions of PEG2000 (0.19 chain/nm(2)) and PEG5000 (0.16 chain/nm(2)) graft density. When graft density of PEG is higher than the critical region (brush conformations), the attraction of hydrogen bonds between PEG and LYZ is the dominant factor. When graft density of PEG is lower than the critical region (mushroom conformations), elastic repulsion between PEG and proteins is driven by the high conformation entropy of PEG chains, which is the dominant force of steric repulsion in PEG-protein systems. Therefore, the adsorption of BSA is suppressed by the high elastic repulsion energy of PEG chains, whereas the adsorption of LYZ is balanced by the interactions between the repulsion of entropy elasticity and the attraction of hydrogen bonds.

Protein-ligand interactions investigated by thermal shift assays (TSA) and dual polarization interferometry (DPI)

Over the last decades, a wide range of biophysical techniques investigating protein-ligand interactions have become indispensable tools to complement high-resolution crystal structure determinations. Current approaches in solution range from high-throughput-capable methods such as thermal shift assays (TSA) to highly accurate techniques including microscale thermophoresis (MST) and isothermal titration calorimetry (ITC) that can provide a full thermodynamic description of binding events. Surface-based methods such as surface plasmon resonance (SPR) and dual polarization interferometry (DPI) allow real-time measurements and can provide kinetic parameters as well as binding constants. DPI provides additional spatial information about the binding event. Here, an account is presented of new developments and recent applications of TSA and DPI connected to crystallography.

Plasma proteins adsorption mechanism on polyethylene-grafted poly(ethylene glycol) surface by quartz crystal microbalance with dissipation

Protein adsorption has a vital role in biomaterial surface science because it is directly related to the hemocompatibility of blood-contacting materials. In this study, monomethoxy poly(ethylene glycol) (mPEG) with two different molecular weights was grafted on polyethylene as a model to elucidate the adsorption mechanisms of plasma protein through quartz crystal microbalance with dissipation (QCM-D). Combined with data from platelet adhesion, whole blood clotting time, and hemolysis rate, the blood compatibility of PE-g-mPEG film was found to have significantly improved. Two adsorption schemes were developed for real-time monitoring of protein adsorption. Results showed that the preadsorbed bovine serum albumin (BSA) on the surfaces of PE-g-mPEG films could effectively inhibit subsequent adsorption of fibrinogen (Fib). Nonspecific protein adsorption of BSA was determined by surface coverage, not by the chain length of PEG. Dense PEG brush could release more trapped water molecules to resist BSA adsorption. Moreover, the preadsorbed Fib could be gradually displaced by high-concentration BSA. However, the adsorption and displacement of Fib was determined by surface hydrophilicity.

A comprehensive study of lysozyme adsorption using dual polarization interferometry and quartz crystal microbalance with dissipation

Protein adsorption plays a crucial role in biomaterial surface science as it is directly linked to the biocompatibility of artificial biomaterial devices. Here, elucidation of protein adsorption mechanism is effected using dual polarization interferometry and a quartz crystal microbalance to characterize lysozyme layer properties on a silica surface at different coverage values. Lysozyme is observed to adsorb from sparse monolayer to multilayer coverage. At low coverage an irreversibly adsorbed layer is formed with slight deformation consistent with side-on orientation. At higher coverage values dynamic re-orientation effects are observed which lead to monolayer surface coverages of 2-3 ng/mm² corresponding to edge-on or/and end-on orientations. These monolayer thickness values ranged between 3 and 4.5 nm with a protein density value of 0.60 g/mL and with 50 wt% solvent mass. Further increase of coverage results formation of a multilayer structure. Using the hydration content and other physical layer properties a tentative model lysozyme adsorption is proposed.