The structural underpinnings for the higher toxicity of the oligomeric intermediates of amyloidogenic peptides, compared to the mature fibrils, remain unknown at present. The transient nature and heterogeneity of the oligomers make it difficult to follow their structure. Here, using vibrational and solid-state nuclear magnetic resonance spectroscopy, and molecular dynamics simulations, we show that freely aggregating Aβ oligomers in physiological solutions have an intramolecular antiparallel configuration that is distinct from the intermolecular parallel β-sheet structure observed in mature fibrils. The intramolecular hydrogen-bonding network flips nearly 90°, and the two β-strands of each monomeric unit move apart, to give rise to the well-known intermolecular in-register parallel β-sheet structure in the mature fibrils. Solid-state nuclear magnetic resonance distance measurements capture the interstrand separation within monomer units during the transition from the oligomer to the fibril form. We further find that the D23-K28 salt-bridge, a major feature of the Aβ fibrils and a focal point of mutations linked to early onset Alzheimer's disease, is not detectable in the small oligomers. Molecular dynamics simulations capture the correlation between changes in the D23-K28 distance and the flipping of the monomer secondary structure between antiparallel and parallel β-sheet architectures. Overall, we propose interstrand separation and salt-bridge formation as key reaction coordinates describing the structural transition of the small Aβ oligomers to fibrils.
Serotonin, an importants ignalingm olecule in humans, has an unexpectedly high lipid membrane affinity. The significance of this finding has evokedc onsiderable speculation. Here we show that membrane binding by serotonin can directly modulate membrane properties and cellular function, providing an activity pathway completelyi ndependent of serotonin receptors. Atomic force microscopy shows that serotonin makes artificial lipid bilayers softer,a nd inducesn ucleation of liquid disordered domains inside the raft-likel iquid-ordered domains. Solid-state NMR spectrosco-py corroborates this data at the atomic level,r evealing ah omogeneous decrease in the order parameter of the lipid chainsi nt he presence of serotonin. In the RN46A immortalized serotonergicn euronal cell line, extracellular serotonin enhances transferrin receptor endocytosis, even in the presence of broad-spectrum serotonin receptor and transporter inhibitors. Similarly,i ti ncreases the membrane binding and internalizationo fo ligomeric peptides. Our resultsu ncover a mode of serotonin-membrane interaction that can potentiate key cellular processes in ar eceptor-independent fashion.
While the roles of intrinsically disordered protein domains in driving many interactions are increasingly well‐appreciated, the mechanism of toxicity of disease‐causing disordered proteins remains poorly understood. A prime example is Alzheimer's disease (AD) associated amyloid beta (Aβ). Aβ oligomers are highly toxic partially structured peptide assemblies with a distinct ordered region (residues ~10–40) and a shorter disordered region (residues ~1–9). Here, we investigate the role of this disordered domain and its relation to the ordered domain in the manifestation of toxicity through a set of Aβ fragments and stereo‐isomers designed for this purpose. We have measured their effects on lipid membranes and cultured neurons, probing their toxicity, intracellular distributions, and specific molecular interactions using the techniques of confocal imaging, lattice light sheet imaging, fluorescence lifetime imaging, and fluorescence correlation spectroscopy (FCS). Remarkably, we find that neither part ‐ Aβ10–40 or Aβ1–9, is toxic by itself. The ordered part (Aβ10–40) is the major determinant of how Aβ attaches to lipid bilayers, enters neuronal cells, and localizes primarily in the late endosomal compartments. However, once Aβ enters the cell, it is the disordered part (only when it is connected to the rest of the peptide) which has a strong and stereospecific interaction with an unknown cellular component, as demonstrated by distinct changes in the fluorescence lifetime of a fluorophore attached to the N‐terminal. This interaction appears to commit Aβ to the toxic pathway. Our findings correlate well with Aβ sites of familial AD mutations, a significant fraction of which cluster in the disordered region. We conclude that while the ordered region dictates attachment and cellular entry, the key to toxicity lies in the ordered part presenting the disordered part for a specific cellular interaction. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.
Shape complementarity between close-packed residues plays a critical role in the amyloid aggregation process. Here, we probe such "steric zipper" interactions in amyloid-β (Aβ), whose aggregation is linked to Alzheimer's disease, by replacing natural residues by their stereoisomers. Such mutations are expected to specifically destabilize the shape sensitive "packing" interactions, which may potentially increase their solubility and change other properties. We study the stereomutants DF19 and DL34 and also the DA2/DF4/DH6/DS8 mutant of Aβ. F19-L34 is a critical contact in a tightly packed region of Aβ, while residues 1-9 are known to be disordered. While both DF19 and DL34 slow down the kinetics of aggregation and form amyloid fibrils efficiently, only DL34 increases the final solubility. DF19 gives rise to additional off-pathway aggregation which results in large, kinetically stable aggregates, and has lower net solubility. DA2/DF4/DH6/DS8 does not have an effect on the kinetics or the solubility. Notably, both DF19 and DL34 oligomers have a significantly lower level of interactions with lipid vesicles and live cells. We conclude that stereoisomers can cause complex site dependent changes in amyloid properties, and provide an effective tool to determine the role of individual residues in shaping the packed interiors of amyloid aggregates.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.