Conformational and Organizational Insights into Serum Proteins during Competitive Adsorption on Self-Assembled Monolayers

Abstract

Physicochemical interactions of proteins with surfaces mediate the interactions between the implant and the biological system. Surface chemistry of the implant is crucial as it regulates the events at the interface. The objective of this study was to explore the performance of modified surfaces for such interactions relevant to various biomedical applications. Because of a wide range of surface wettability, we aimed to study protein behavior (i.e., conformational changes and their packing) during competitive protein adsorption. Three serum proteins (bovine serum albumin, BSA; fibrinogen, FB; and immunoglobulin G, IgG) were tested for their conformational changes and orientation upon adsorption on hydrophilic (COOH and amine), moderately hydrophobic (mixed and hybrid), and hydrophobic (octyl) surfaces generated via silanization. Modified surfaces were characterized using Fourier-transform infrared spectroscopy, contact angle, and atomic force microscopy (AFM) techniques. Adsorbed masses of proteins from single and binary protein solutions on different surfaces were quantified along with their secondary structure analyses. Maximum adsorbed protein masses were found to be on negatively charged and hydrophobic (octyl) surfaces because of ionic and hydrophobic interactions between protein molecules and surfaces, respectively. Side-on and end-on orientations of adsorbed protein molecules were analyzed using theoretical and AFM analyses. We observed compact and elongated forms of BSA molecules on hydrophilic and hydrophobic surfaces, respectively. We further found a linear increase in the α-helix content of BSA and β-sheet contents of FB and IgG proteins with the increasing side-on (%)-oriented protein molecules on the surfaces. This indicates that side-on orientations of adsorbed FB and IgG lead to the formation of β-sheets. Sodium dodecyl sulfate polyacrylamide gel electrophoresis was employed to quantify the protein types and their ratio in competitively adsorbed proteins on different surfaces. A theoretical analysis was also used to determine the % secondary structures of competitively adsorbed proteins from BSA/FB and BSA/IgG solutions, which very well agreed with experimental results. The competitive protein adsorption from both BSA/FB and BSA/IgG solutions was found to be entropy-driven, as revealed by thermodynamic studies performed using isothermal titration calorimetry.

Nanolamellar Tantalum Interfaces in the Osteoblast Adhesion

“…As expected, the relative 'hydrophobic' Ta40 exhibited the strongest fluorescence intensity, corresponding to a significantly greater adsorption amount of BSA, in an agreement with that a higher and stronger protein adsorption to hydrophobic surfaces compared to hydrophilic surfaces. 45,46 isotropically grown cells shown later in SEM observations. This is because, the shallow nanolamellas (less than 12 nm, Figure 1b), cannot control the direction of cell growth.…”

Conformation Variation and Tunable Protein Adsorption through Combination of Poly(acrylic acid) and Antifouling Poly(N-(2-hydroxyethyl) acrylamide) Diblock on a Particle Surface

“…For the PSV@PAA and BSA system, the interaction process could be divided into 4 stages (pH 107, pH 75, pH 53 and pH 32) [19]. The turbidity remains near zero with a pH from 10 to 7, which indicates almost no interaction, because both protein and polymer brushes are negatively charged when Ph > pI, which is also proved by basically unchanged diameters, as illustrated in Figure 4a.…”

“…Generally, protein adsorption to polymer brushes is a highly complicated process, which is often controlled by surface properties such as hydrophilicity/hydrophobicity; surface potential; roughness and external parameters, including pH, temperature, salt concentration, etc. [15][16][17][18][19]. It is not likely that a single factor is solely responsible for the adsorption behavior but, rather, a combination of many [20].…”

Design of engineered surfaces for prospective detection of SARS-CoV-2 using quartz crystal microbalance-based techniques

“…Typically, adsorbed amount increase with an increase in surface hydrophobicity [23,24]. The protein adsorption is reported to be entropy driven and the conformations of the adsorbed protein molecules are found to depend on the surface chemistry [25,26], which plays a key role in the detection process. A recent study reported that acetylcholinesterase adsorbed in the 'end-on' orientation on the positively charged surface and in the 'back-on' orientation on the negatively charged surfaces and thus its catalytic activities were altered [26].…”