Self-Assembly, Dynamics, and Polymorphism of hIAPP(20–29) Aggregates at Solid–Liquid Interfaces

Abstract

The misfolding and subsequent assembly of proteins and peptides into insoluble amyloid structures play important roles in the development of numerous diseases. The dynamics of self-assembly and the morphology of the resulting aggregates critically depend on various environmental factors and especially on the presence of interfaces. Here, we show in detail how the presence of surfaces with different physicochemical properties influences the assembly dynamics and especially the aggregate morphology of hIAPP(20-29), an amyloidogenic fragment of the peptide hormone human islet amyloid polypeptide (hIAPP), which is involved in the development of type 2 diabetes. Time-lapse atomic force microscopy is employed to study the assembly dynamics of hIAPP(20-29) and the morphology of the resulting aggregates in bulk solution as well as at hydrophilic and hydrophobic model surfaces. We find that the presence of hydrophilic mica surfaces promotes fibrillation when compared with the assembly in bulk solution and results in a more pronounced polymorphism. Three fibrillar species are found to coexist on the mica surface, that is, straight, coiled, and ribbon-like fibrils, whereas only the straight and coiled fibrils are observed in bulk solution after comparable incubation times. In addition, the straight and coiled fibrils assembled at the mica surface have significantly different dimensions compared with those assembled in bulk solution. The three fibrillar species found on the mica surface most likely form independently by lateral association of arbitrary numbers of protofibrils with about 2 nm height. On hydrophobic hydrocarbon surfaces, fibrillation is retarded but not completely suppressed, in contrast to previous observations for full-length hIAPP(1-37). Our results show that peptide-surface interactions may induce diverse, peptide-specific alterations of amyloid assembly dynamics and fibrillar polymorphism. They may therefore contribute to a deeper understanding of the molecular processes that govern amyloid aggregation at different surfaces.

Effect of Terminal Modifications on the Adsorption and Assembly of hIAPP(20–29)

“…Furthermore, it was previously observed that purely electrostatic adsorption of native hIAPP(20–29) at a negatively charged mica surface results first in the adsorption of monomers in an upright conformation that is stabilized by intermolecular β-sheets and finally in enhanced fibrillization. 22 This is also observed in the AFM images shown in Figure S8, where few short protofibrils are visible for the native fragment (+|-).…”

“…At the same time, low monomer adsorption and high lateral mobility are generally considered a prerequisite for amyloid assembly at solid–liquid interfaces. 21,22,24,72,73 This is evident from Figure S8, which shows large prefibrillar aggregates and a few protofibrils for native hIAPP(20–29). PM-IRRAS (Figure 5) reveals significantly increased β-sheet contents for all fragments compared to the assembly in bulk solution (Figure 2b).…”

“…In contrast to the positively charged NH 2 SAM, electrostatic interactions seem to be less important for hIAPP(20–29) adsorption to the negatively charged COOH SAM. Most notably, we found that the often observed effect of negatively charged interfaces promoting hIAPP amyloid formation 21,22,74−76 depends on the molecular structure of the peptide termini. Although increased β-sheet formation was observed for all fragments, the increase in β-sheet content varied drastically from fragment to fragment.…”

“…In our previous study, we have observed that fibrillization of native hIAPP(20–29) is delayed in contact with a hydrophobic hydrocarbon surface, whereas adsorption to a negatively charged mica surface resulted in strongly enhanced fibrillization compared to assembly in bulk solution. 22 However, these experiments were performed at room temperature in water and not in PBS at 37 °C as the current experiments. Since amyloid assembly in general and aggregate polymorphism in particular are highly sensitive toward environmental conditions, 79 these experimental differences may provide an explanation for these unexpected results.…”

Dynamic membrane interactions of antibacterial and antifungal biomolecules, and amyloid peptides, revealed by solid-state NMR spectroscopy

“…To further probe the fiber-formation dependent “detergent-type” membrane disruption by human-IAPP, solid-state NMR experiments were performed on aligned lipid bilayers [128,129]. These NMR studies demonstrated that the C-terminal domain of human-IAPP plays a vital role in fiber formation [108], and thus human-IAPP-20–29 peptide fragment (SNNFGAILSS) which forms fibers [130], was used to demonstrate the membrane disruption process. 31 P NMR experiments on anode aluminum oxide (AAO) nanotubes revealed the fragmentation of aligned lipid bilayers in the presence of human IAPP-20–29 (Fig.…”