Abstract
Amyloid proteins are widespread in nature both as pathological species involved in several diseases and as functional entities that can provide protection and storage for the organism. Lipids have been found in amyloid deposits from various amyloid diseases and have been shown to strongly affect the formation and structure of both pathological and functional amyloid proteins. Here, we investigate how fibrillation of the functional amyloid FapC from Pseudomonas is affected by two lysolipids, the zwitterionic lipid 1-myristoyl-2-hydroxy-sn-glycero-3-phosphocholine and the anionic lipid 1-myristoyl-2-hydroxy-sn-glycero-3-phospho-(1′-rac-glycerol) (LPG). Small-angle X-ray scattering, circular dichroism, dynamic light scattering, and thioflavin T fluorescence measurements were performed simultaneously on the same sample to ensure reproducibility and allow a multimethod integrated analysis. We found that LPG strongly induces fibrillation around its critical micelle concentration (cmc) by promoting formation of large structures, which mature via accumulation of intermediate fibril structures with a large cross section. At concentrations above its cmc, LPG strongly inhibits fibrillation by locking FapC in a core–shell complex. In contrast, lipid 1-myristoyl-2-hydroxy-sn-glycero-3-phosphocholine induces fibrillation at concentrations above its cmc, not via strong interactions with FapC but by being incorporated during fibrillation and likely stabilizing the fibrillation nucleus to reduce the lag phase. Finally, we show that LPG is not incorporated into the fibril during assembly but rather can coat the final fibril. We conclude that lipids affect both the mechanism and outcome of fibrillation of functional amyloid, highlighting a role for lipid concentration and composition in the onset and mechanism of fibrillation in vivo.
Highlights
Amyloid proteins are involved in various diseases such as Alzheimer’s disease (Aβ [1] and tau [2]), Parkinson’s disease (α-synuclein [3]) and type II diabetes mellitus (islet amyloid polypeptide (IAPP) [4])
Creating an overview of the fibrillation mechanisms We report a detailed study of how FapC’s initial state, final state, and overall fibrillation mechanism are affected by the addition of LPG and LPC using circular dichroism (CD), small-angle X-ray scattering (SAXS), thioflavin T (ThT) fluorescence, dynamic light scattering (DLS), isothermal titration calorimetry (ITC), transmission electron microscopy (TEM), and a lipid quantification assay
Since the subsequent phases are sensitive to the absolute concentrations of LPG and LPC, we need to determine which concentrations of lipids we are to use in the subsequent analyses
Summary
Amyloid proteins are involved in various diseases such as Alzheimer’s disease (Aβ [1] and tau [2]), Parkinson’s disease (α-synuclein [3]) and type II diabetes mellitus (islet amyloid polypeptide (IAPP) [4]). No stable oligomeric form of FapC has been isolated, which is the case for a number of functional amyloids [14] This suggests that there is not the same buildup of oligomeric species as seen for pathogenic amyloids, where these species often show the highest toxicity compared to monomers/fibrils [15]. This lack of oligomeric species in functional amyloids is generally attributed to the tight control from cooperation proteins, but other components from the extracellular matrix such as lipids could affect the amount and kind of intermediate species. The negative charge of the LPG head group strongly promotes aggregation of other
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
