Abstract

The abundance of interfaces in vivo has resulted in a significant amount of interest in trying to understand the influence of surfaces and interfaces on protein aggregation. The large surface to volume ratios of high surface area and nanoscale materials being developed for the new generation of nanomedicines and diagnostic applications are a potential concern and highlight the importance of understanding the impact of interfaces on protein aggregation processes.

In this study, fourier transform infra-red spectroscopy was used to monitor the changes in inter-molecular β-sheet content of bovine pancreatic insulin at pH 1 and over a range of temperatures (60°C – 80°C) in bulk solution and at a polystyrene surface (PS). The formation of inter-molecular β-sheet was found to be a two stage process. The first stage in β-sheet growth corresponded to the formation of prefibrillar aggregates (~13nm) and the second stage was attributed to the formation of fibrils. The -sheet formation kinetics were used to show that prefibrillar aggregates play an important role in the nucleation of insulin fibrils. They were also used to determine the nucleation and growth rates associated with fibril formation for both the PS surfaces and bulk solution data. The resulting Arrhenius kinetics enabled the determination of the associated activation energies.

These experiments show that the PS surfaces nucleate fibrils more quickly, but that fibril growth is slower than in bulk solution. These results are interpreted in terms of the differences in concentration, mobility, conformational and colloidal stability of the protein molecules adsorbed at surfaces when compared to similar molecules in bulk solution.