Thermodynamic versus Conformational Metastability in Fibril-Forming Lysozyme Solutions

Abstract

The role of intermolecular interaction in fibril-forming protein solutions and its relation with molecular conformation is a crucial aspect for the control and inhibition of amyloid structures. Here, we study the fibril formation and the protein-protein interactions of lysozyme at acidic pH and low ionic strength. The amyloid formation occurs after a long lag time and is preceded by the formation of oligomers, which seems to be off-pathway with respect to fibrillation. By measuring the osmotic isothermal compressibility and the collective diffusion coefficient of lysozyme in solution, we observe that the monomeric solution is kept in a thermodynamically metastable state by strong electrostatic repulsion, even in denaturing conditions. The measured repulsive interaction between monomers is satisfactorily accounted for by classical polyelectrolyte theory. Further, we observe a slow conformational change involving both secondary and tertiary structure, which drives the proteins toward a more hydrophobic conformation. Denatured proteins are driven out of metastability through conformational substates, which are kinetically populated and experience a lower activation energy for fibril formation. Thus, our results highlight the role of electrostatic repulsion, which hinders the aggregation of partially denatured proteins and operates as a gatekeeper favoring the association of those monomers whose conformation is capable of forming amyloid structure.

Protein–Protein Interactions in Dilute to Concentrated Solutions: α-Chymotrypsinogen in Acidic Conditions

“…35,62 R 90 tol is the Rayleigh ratio of toluene and at 632.8 and 532 nm was taken as 14.0 × 10 6 and 28.0 × 10 6 cm –1 , respectively. 67 I , I 0 , and I tol denote the intensity of the sample, buffer, and toluene, respectively. Intensities in SLS were obtained by time-averaging the collected intensities over a time window of 3 min for a given sample.…”

Self-assembling peptide and protein amyloids: from structure to tailored function in nanotechnology

“…the conformational change of the initially folded state into an unfolded or partially folded intermediate 192–194. This is the case, for instance, for insulin,195–198 lysozyme,199,200 β 2 -microglobulin,201,202 enzyme superoxide dismutase (SOD1)203 and light chain immunoglobulin,204 which have been observed to form fibrils under conditions that promote the formation of partially folded species.…”

The severe impact of in vivo-like microfluidic flow and the influence of gemini surfactants on amyloid aggregation of hen egg white lysozyme

“…Amyloid aggregation (AA) is a specic type of protein aggregation process responsible for a number of serious human conformational diseases (proteinopathies), including Alzheimer's disease, Parkinson's disease and others, such as liver cirrhosis or type II diabetes. [1][2][3][4] Although scientists have made much effort to understand processes underlying this fatal aggregation in recent decades, the exact mechanism of AA still remains unclear. 5 This knowledge would be of crucial importance in the quest for a drug against AA.…”