The formation of fibrils from protein molecules is one of the phenomena occurring in several diseases, where amyloid fibril formation in Alzheimers disease is one of the most striking. Insulin under stressed conditions (low pH, high temperature) is an often used model system for the study of fibrillation. Such insulin monomer solutions forms fibrils especially when incubated with seeds consisting of fibril fragments. The fibrillation kinetics is a strong function of the concentration of seeds.
We have discovered that a solid surface can be transformed made catalytic providing constantly present seeds or nuclei for the fibrillation process, with an activity comparable to a rather large concentration of seeds in solution. The catalytic surface was obtained after several incubation cycles of a hydrophobic (silicon) surface in a stressed insulin monomer solution. Each incubation cycle consisted of incubation, air transfer and drying followed by measurement of the amount of organic material on the surface with ellipsometry before reincubation into the solution. When the organic layer thickness on the dried surface was about 18 nm, a subsequent incubation caused rapid fibrillation of the monomer solution, a property remaining when the same surface was incubated again in a fresh monomer solution.
The possible nature of the catalyic surface is discussed, with support not only from ellipsometric but also AFM measurements, apparently the 18 nm organic layer presents nucleation points for the formation of fibrils, either directly or through the formation of seeds, which thereafter form fibrils in solution. A simple model based on approaches from heterogeneous catalysis is used to compare the catalytic activity of the surface with that of seeds in solution.
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