The effects of surface adsorption on the thermal stability of proteins

Abstract

The effect of surface adsorption on the structure and stability of proteins is a matter of increasing interest in biotechnology. Therefore, we have examined the effect of adsorption to silica on the thermal stability of 7 proteins employing differential scanning calorimetry (DSC) and front surface fluorescence (FSF) spectroscopy. In general, it was found that surface adsorption decreased the thermal stability of the bound protein. Using lysozyme for further studies, DSC, FSF, and FTIR spectroscopies, as well as enzymatic activity measurements, were used to explore the effect of decreasing surface apolarity on stability. It was observed that increasing surface apolarity produced decreasing stability and increasing structural alteration of the adsorbed protein.

Thermodynamic Analysis of Proteins Adsorbed on Silica Particles: Electrostatic Effects

“…Apparently, electrostatic interactions are a driving force for adsorption because a higher ionic strength decreases the electrostatic attraction between the negatively charged silica and the positively charged proteins. This trend is generally observed for adsorption of positively charged proteins on silica surfaces (1,3,8,14,21). One should take into account that, although the addition of CaCl 2 only marginally increases the ionic strength, the preferential coadsorption of bivalent over monovalent cations results in a more effective screening of electrostatic interactions within the adsorbed protein layer (23,27).…”

“…A more common method for studying the stability of proteins is by following the equilibrium unfolding of the native state with a denaturing agent, such as guanidine hydrochloride, or by modifying the pH or temperature. As temperature perturbations alone do not significantly alter the amount of protein on most surfaces (14,15), thermal denaturation is an obvious method of choice. A powerful tool for performing thermodynamic investigations of protein stability is differential scanning calorimetry (DSC) (16)(17)(18).…”

“…A powerful tool for performing thermodynamic investigations of protein stability is differential scanning calorimetry (DSC) (16)(17)(18). DSC can be successfully employed to study the thermodynamics of proteins in the adsorbed state if proteins are adsorbed onto relatively small colloidal particles that allow a relatively high protein concentration in the sample (14,19,20). DSC measures the temperature-dependent excess heat that is absorbed upon unfolding of a protein and the accumulated excess heat reflects the enthalpy that stabilizes the protein in the native state.…”

“…For example, strong interactions between protein molecules and the surface, such as occur upon adsorption onto hydrophobic surfaces, often lead to structural alterations in the protein structure (1,3,5,6,9,12,14). For the contact of proteins with hydrophilic silica surfaces, both similar structural features as adopted by the protein in solution (5,12,13) and adsorption-induced structural changes (14, 21) have been observed.…”

Protein unfolding during reversed‐phase chromatography: I. Effect of surface properties and duration of adsorption

“…In a complementary study, Sane et al (1999) investigated secondary structure changes in the same system, showing that loading can influence conformation and chromatographic behavior. Despite these and other spectroscopic analyses of protein conformation on RPC surfaces (Steadman et al, 1992), several questions remain unanswered. Among these, the impact of alkyl chain length and pore size are poorly understood, although these parameters are commonly considered in media selection.…”