Protein-surface interactions adsorption

Protein adsorption has been studied with a variety of techniques such as ellipsome-try [107,108], ESCA [109], surface forces measurements [102], total internal reflection fluorescence (TIRE) [103,110], electron microscopy [111], and electrokinetic measurement of latex particles [112,113] and capillaries [114], The TIRE technique has recently been adapted to observe surface diffusion [106] and orientation [IIS] in adsorbed layers. These experiments point toward the significant influence of the protein-surface interaction on the adsorption characteristics [105,108,110]. A very important interaction is due to the hydrophobic interaction between parts of the protein and polymeric surfaces [18], although often electrostatic interactions are also influential [ 116]. Protein desorption can be affected by altering the pH [117] or by the introduction of a complexing agent [118]. 

Separations in hydrophobic interaction chromatography have been modeled as a function of the ionic strength of the buffer and of the hydrophobicity of the column, and tested using the elution of lysozyme and ovalbumin from octyl-, butyl- and phenyl-Sepharose phases.2 The theoretical framework used preferential interaction analysis, a theory competitive to solvophobic theory. Solvophobic theory views protein-surface interaction as a two-step process. In this model, the protein appears in a cavity in the water formed above the adsorption site and then adsorbs to the phase, with the free energy change... 

It is recommended that any reader seriously interested in protein adsorption obtain Teaching Aids for Macromolecular Structures 28), which is commercially available for about 20.00. These aids clearly show the dramatic potential of surface protein structural visualization for the development of hypotheses of protein-surface interactions. 

Apparently, no single factor can be used to predict the process of adsorption there are always several different properties of protein and adsorbent that determine the protein-surface interaction. As a summary, the following general guidelines can be given ... 

Both the nature of protein-surface interactions and inherent properties of a specific enzyme will contribute to the catalytic activity of an immobilized biocatalyst. Adsorption of an enzyme onto a surface can induce conformational changes which affect the rate and specificity of the catalyst. The total amount of enzyme loading, enzyme distribution within the immobilization support, and microenvironment surroimding the supported enzyme can all influence enzyme-catalyst activity, specificity and stability. ... 

At present, the protein/surface interactions that determine adsorption kinetics are unclear. To clarify these interactions, the effects of polymer surface properties on protein adsorption and desorption rates have been investigated. BSA adsorption from a 1 mg% solution (1 mg% = 1 mg/100 mL) was studied using several polymers chosen for their wide range of surface properties and functionalities (22, Cheng, Y.L. et al.. J. Coll. Int. Sci., in press). The polymers and their surface properties (under the conditions of the BSA adsorption experiments) are listed in Table I. 

Protein-surface interactions are highly complex, complicating the ability to precisely control the concentration, conformation, and bioactivity of the adsorbed protein. Numerous materials have been modified in order to achieve better control over the adsorption process, thereby enabling better characterization of the material and greater control over cell function. A few of these modifications will be discussed in the following sections. 

At the solid-water interface, terminally attached PEO will interact with water molecules and extend into the bulk aqueous medium. Using the surface force technique, Luckam (22) has observed that steric repulsion with PEO mainly occurs due to osmotic repulsion between interdigitated PEO chains. Jeon et al. (23,24) have theoretically modeled protein-surface interactions in the presence of PEO and found that steric repulsion by surface-bound PEO chains is mainly responsible for the prevention of protein adsorption on PEO-rich surfaces. 

To get some control over protein adsorption, one has to understand the protein-surface interactions in advance. To this end, adsorption isotherms have been obtained for a wide variety of surfaces, from hydrophilic to hydrophobic. Techniques for controlling the surface wettability include varying the terminating groups of SAMs or the ratio of monomers in copolymers. The effects on protein adsorption of factors such as liquid polarity, temperature, pH, solute t)q)e (e.g., electrolyte), and solute concentration have been widely studied [4]. 

Force measurements have been performed with scanning probe techniques to study protein properties and protein-surface interactions. Apart from specific recognition and specific interactions,"" single-molecule force spectroscopy,adhesion forces between ligand-receptor pairs, " and protein adsorption... 

Zhou et al (2003) developed a new residue-based protein-surface interaction potential model to explore the adsorption and orientation of two antibodies, IgGl and IgG2a. The Monte Carlo simulation results showed that when electrostatic interactions dominate, there are preferred... 

Oberholzer and Lenhoff [32] proposed a method for calculating adsorption isotherms for small globular proteins in aqueous solution based on colloidal descriptions of protein-protein and protein-surface interaction energies. The influence of the structure of the adsorbed protein layer on the energetics was obtained through Brownian dynamics simulations. The qualitative influence of experimental variables such as solution pH, ionic strength, and protein size on the predicted adsorption of proteins was explored. 

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