Reversibility of the Adsorption of Lysozyme on Silica

Abstract

A central paradigm that underpins our understanding of the interaction of proteins with solid surfaces is that protein adsorption leads to changes in secondary structure. The bound proteins tend to denature, and these non-native, adsorbed structures are likely stabilized through the loss of α-helices with the concomitant formation of intermolecular β-sheets. The goal of this work is to critically assess the impact this behavior has on protein desorption, where irreversible conformational changes might lead to protein aggregation or result in other forms of instability. The adsorption, desorption, and structural transitions of lysozyme are examined on fumed silica nanoparticles as a function of the amount of protein adsorbed. Surprisingly, the data indicate not only that adsorption is reversible but also that protein desorption is predictable in a coverage-dependent manner. Additionally, there is evidence of a two-state model which involves exchange between a native-like dissolved state and a highly perturbed adsorbed state. Since the in situ circular dichroism (CD) derived secondary structures of the adsorbed proteins are essentially unaffected by changes in surface coverage, these results are not consistent with previous claims that surface-induced denaturation is coverage dependent. Inspired by results from homopolymer adsorption experiments, we speculate that more local descriptors, such as the number of amino acids per chain that are physically adsorbed on the surface, likely control the desorption process.

Bridging interactions of proteins with silica nanoparticles: The influence of pH, ionic strength and protein concentration

“…The present results support earlier reports [7][8][9][10][11][42][43][44] that the adsorption of lysozyme on silica surfaces is mainly due to electrostatic interactions. This is concluded from the fact that the sharply increasing protein binding curve (Fig.…”

“…[1][2][3] Much research has therefore been devoted to better understand the fundamentals of protein adsorption. [4][5][6][7][8][9][10][11] It is well-established that proteins adsorb strongly onto hydrophobic surfaces, even under electrostatically adverse conditions, because the driving force for adsorption originating from dehydration of a hydrophobic surface largely outweighs electrostatic repulsion. 12,13 Protein adsorption onto hydrophilic surfaces depends on the conformational stability of the protein, and a distinction between structurally inexible ("hard") and pliable ("so") proteins has been introduced to account for differences in the adsorption behavior.…”

Single-molecule resolution of protein structure and interfacial dynamics on biomaterial surfaces

“…In addition, our results suggest that desorption of denatured OPH may result in an increase in the concentration of denatured protein in solution, which may induce aggregation in solution. Desorption from a denatured state has been proposed to explain the observation of denatured proteins accumulating in solution after surface contact (35,39). However, to our knowledge, these results are the first to confirm the occurrence of this phenomenon at the molecular level.…”

“…Widely used methods for probing such effects entail measuring changes in infrared absorbance, circular dichroism, or intrinsic fluorescence after exposure of the interface to protein solution (2,(31)(32)(33)(34)(35)(36). These methods can detect shifts in the average secondary structure of the adsorbed protein layer over time without a priori knowledge of protein structure.…”

Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments

“…for the 13-mer DDDDAAAAARRRR 267,268 ) and concomitant formation of -sheets. 269,270 This is no absolute rule however. Some peptides have been specifically designed that strongly adsorb to silica particles and form helices on the surface, 235 while they were not structured in the solution.…”