Aβ42 assembles into specific β-barrel pore-forming oligomers in membrane-mimicking environments

Abstract

The formation of amyloid-β peptide (Aβ) oligomers at the cellular membrane is considered to be a crucial process underlying neurotoxicity in Alzheimer’s disease (AD). Therefore, it is critical to characterize the oligomers that form within a membrane environment. To contribute to this characterization, we have applied strategies widely used to examine the structure of membrane proteins to study the two major Aβ variants, Aβ40 and Aβ42. Accordingly, various types of detergent micelles were extensively screened to identify one that preserved the properties of Aβ in lipid environments—namely the formation of oligomers that function as pores. Remarkably, under the optimized detergent micelle conditions, Aβ40 and Aβ42 showed different behavior. Aβ40 aggregated into amyloid fibrils, whereas Aβ42 assembled into oligomers that inserted into lipid bilayers as well-defined pores and adopted a specific structure with characteristics of a β-barrel arrangement that we named β-barrel pore-forming Aβ42 oligomers (βPFOsAβ42). Because Aβ42, relative to Aβ40, has a more prominent role in AD, the higher propensity of Aβ42 to form βPFOs constitutes an indication of their relevance in AD. Moreover, because βPFOsAβ42 adopt a specific structure, this property offers an unprecedented opportunity for testing a hypothesis regarding the involvement of βPFOs and, more generally, membrane-associated Aβ oligomers in AD.

β‐Amyloid aggregation and heterogeneous nucleation

“…In addition, Aβ peptide aggregation is fostered by certain “membrane‐mimetic” solvents such as 2,2,2‐trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP) . In such environments as lipid or detergent micelles, and membrane‐mimetic solvents, Aβ peptides may assemble into soluble oligomers that can function as pores . There is, however, a great deal of still partially understood complexity in the interaction between Aβ peptides and lipids.…”

Nanoscopic Characterisation of Individual Endogenous Protein Aggregates in Human Neuronal Cells

“…The permeabilisation of membranes has been suggested to be the most ubiquitous toxic mechanism associated with protein aggregates 31, 32, 33, 34, 35. We have developed a method to characterise the ability of protein aggregates to permeabilise lipid membranes8 (details are given in the Supporting Information) and applied it in this study.…”

Ultrasensitive Measurement of Ca2+ Influx into Lipid Vesicles Induced by Protein Aggregates

“…The aggregation process that results in the formation of oligomers may contribute to cellular damage 12, 13, 14, 15. Some of these mechanisms are thought to involve specific binding to receptors on the cell membrane1, 5, 9 while others appear to be the consequence of non‐specific membrane disruption 1, 3, 5, 9, 16. A body of data suggests that small soluble aggregates, often called oligomers, rather than mature fibrils, are able to cause the membrane to become permeable to Ca 2+ resulting in Ca 2+ influx and the disruption of Ca 2+ homeostasis 2, 3, 5, 9, 17, 18.…”

“…Therefore, it is important to quantify and characterize these species within aggregation mixtures in vitro as well as to be able to perform measurements in biological samples, such as cerebrospinal fluid (CSF) 19. However, these oligomers are known to be present at low abundance and to be highly heterogeneous in nature, in terms of both their size and structure 1, 2, 3, 4, 9, 10, 16…”