1
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Saha J, Ford BJ, Wang X, Boyd S, Morgan SE, Rangachari V. Sugar distributions on gangliosides guide the formation and stability of amyloid-β oligomers. Biophys Chem 2023; 300:107073. [PMID: 37413816 PMCID: PMC10529042 DOI: 10.1016/j.bpc.2023.107073] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Revised: 06/25/2023] [Accepted: 06/27/2023] [Indexed: 07/08/2023]
Abstract
Aggregation of Aβ peptides is a key contributor to the etiology of Alzheimer's disease. Being intrinsically disordered, monomeric Aβ is susceptible to conformational excursions, especially in the presence of important interacting partners such as membrane lipids, to adopt specific aggregation pathways. Furthermore, components such as gangliosides in membranes and lipid rafts are known to play important roles in the adoption of pathways and the generation of discrete neurotoxic oligomers. Yet, what roles do carbohydrates on gangliosides play in this process remains unknown. Here, using GM1, GM3, and GD3 ganglioside micelles as models, we show that the sugar distributions and cationic amino acids within Aβ N-terminal region modulate oligomerization of Aβ temporally, and dictate the stability and maturation of oligomers. These results demonstrate the selectivity of sugar distributions on the membrane surface toward oligomerization of Aβ and thus implicate cell-selective enrichment of oligomers.
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Affiliation(s)
- Jhinuk Saha
- Department of Chemistry and Biochemistry, School of Mathematics and Natural Sciences, 118, College Dr Hattiesburg, MS 39402, USA
| | - Brea J Ford
- Department of Chemistry and Biochemistry, School of Mathematics and Natural Sciences, 118, College Dr Hattiesburg, MS 39402, USA
| | | | - Sydney Boyd
- Department of Chemistry and Biochemistry, School of Mathematics and Natural Sciences, 118, College Dr Hattiesburg, MS 39402, USA
| | | | - Vijayaraghavan Rangachari
- Department of Chemistry and Biochemistry, School of Mathematics and Natural Sciences, 118, College Dr Hattiesburg, MS 39402, USA; Center for Molecular and Cellular Biosciences, University of Southern Mississippi, Hattiesburg, MS 39406, USA.
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2
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Viles JH. Imaging Amyloid-β Membrane Interactions: Ion-Channel Pores and Lipid-Bilayer Permeability in Alzheimer's Disease. ANGEWANDTE CHEMIE (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2023; 135:e202215785. [PMID: 38515735 PMCID: PMC10952214 DOI: 10.1002/ange.202215785] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Indexed: 03/08/2023]
Abstract
The accumulation of the amyloid-β peptides (Aβ) is central to the development of Alzheimer's disease. The mechanism by which Aβ triggers a cascade of events that leads to dementia is a topic of intense investigation. Aβ self-associates into a series of complex assemblies with different structural and biophysical properties. It is the interaction of these oligomeric, protofibril and fibrillar assemblies with lipid membranes, or with membrane receptors, that results in membrane permeability and loss of cellular homeostasis, a key event in Alzheimer's disease pathology. Aβ can have an array of impacts on lipid membranes, reports have included: a carpeting effect; a detergent effect; and Aβ ion-channel pore formation. Recent advances imaging these interactions are providing a clearer picture of Aβ induced membrane disruption. Understanding the relationship between different Aβ structures and membrane permeability will inform therapeutics targeting Aβ cytotoxicity.
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Affiliation(s)
- John H. Viles
- Department of Biochemistry, SBBS, Queen MaryUniversity of LondonUK
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3
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Viles JH. Imaging Amyloid-β Membrane Interactions: Ion-Channel Pores and Lipid-Bilayer Permeability in Alzheimer's Disease. Angew Chem Int Ed Engl 2023; 62:e202215785. [PMID: 36876912 PMCID: PMC10953358 DOI: 10.1002/anie.202215785] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 03/02/2023] [Accepted: 03/03/2023] [Indexed: 03/07/2023]
Abstract
The accumulation of the amyloid-β peptides (Aβ) is central to the development of Alzheimer's disease. The mechanism by which Aβ triggers a cascade of events that leads to dementia is a topic of intense investigation. Aβ self-associates into a series of complex assemblies with different structural and biophysical properties. It is the interaction of these oligomeric, protofibril and fibrillar assemblies with lipid membranes, or with membrane receptors, that results in membrane permeability and loss of cellular homeostasis, a key event in Alzheimer's disease pathology. Aβ can have an array of impacts on lipid membranes, reports have included: a carpeting effect; a detergent effect; and Aβ ion-channel pore formation. Recent advances imaging these interactions are providing a clearer picture of Aβ induced membrane disruption. Understanding the relationship between different Aβ structures and membrane permeability will inform therapeutics targeting Aβ cytotoxicity.
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Affiliation(s)
- John H. Viles
- Department of Biochemistry, SBBS, Queen MaryUniversity of LondonUK
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4
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Saha J, Ford BJ, Boyd S, Rangachari V. Sugar distributions on gangliosides guide the formation and stability of amyloid-β oligomers. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.09.540003. [PMID: 37214891 PMCID: PMC10197704 DOI: 10.1101/2023.05.09.540003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Aggregation of Aβ peptides has been known as a key contributor to the etiology of Alzheimer's disease. Being intrinsically disordered, the monomeric Aβ is susceptible to conformational excursions, especially in the presence of key interacting partners such as membrane lipids, to adopt specific aggregation pathways. Furthermore, key components such as gangliosides in membranes and lipid rafts are known to play important roles in the adoption of pathways and the generation of discrete neurotoxic oligomers. Yet, what roles the carbohydrates on gangliosides play in this process remains unknown. Here, using GM1, GM3, and GD3 ganglioside micelles as models, we show that the sugar distributions and cationic amino acids within Aβ N-terminal region modulate oligomerization of Aβ temporally, and dictate the stability and maturation of oligomers.
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5
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Yi Y, Lim MH. Current understanding of metal-dependent amyloid-β aggregation and toxicity. RSC Chem Biol 2023; 4:121-131. [PMID: 36794021 PMCID: PMC9906324 DOI: 10.1039/d2cb00208f] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Accepted: 11/22/2022] [Indexed: 11/23/2022] Open
Abstract
The discovery of effective therapeutics targeting amyloid-β (Aβ) aggregates for Alzheimer's disease (AD) has been very challenging, which suggests its complicated etiology associated with multiple pathogenic elements. In AD-affected brains, highly concentrated metals, such as copper and zinc, are found in senile plaques mainly composed of Aβ aggregates. These metal ions are coordinated to Aβ and affect its aggregation and toxicity profiles. In this review, we illustrate the current view on molecular insights into the assembly of Aβ peptides in the absence and presence of metal ions as well as the effect of metal ions on their toxicity.
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Affiliation(s)
- Yelim Yi
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea
| | - Mi Hee Lim
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea
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6
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Taylor AP, Davis PJ, Aubrey LD, White JBR, Parton ZN, Staniforth RA. Simple, Reliable Protocol for High-Yield Solubilization of Seedless Amyloid-β Monomer. ACS Chem Neurosci 2022; 14:53-71. [PMID: 36512740 PMCID: PMC9817077 DOI: 10.1021/acschemneuro.2c00411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Self-assembly of the amyloid-β (Aβ) peptide to form toxic oligomers and fibrils is a key causal event in the onset of Alzheimer's disease, and Aβ is the focus of intense research in neuroscience, biophysics, and structural biology aimed at therapeutic development. Due to its rapid self-assembly and extreme sensitivity to aggregation conditions, preparation of seedless, reproducible Aβ solutions is highly challenging, and there are serious ongoing issues with consistency in the literature. In this paper, we use a liquid-phase separation technique, asymmetric flow field-flow fractionation with multiangle light scattering (AF4-MALS), to develop and validate a simple, effective, economical method for re-solubilization and quality control of purified, lyophilized Aβ samples. Our findings were obtained with recombinant peptide but are physicochemical in nature and thus highly relevant to synthetic peptide. We show that much of the variability in the literature stems from the inability of overly mild solvent treatments to produce consistently monomeric preparations and is rectified by a protocol involving high-pH (>12) dissolution, sonication, and rapid freezing to prevent modification. Aβ treated in this manner is chemically stable, can be stored over long timescales at -80 °C, and exhibits remarkably consistent self-assembly behavior when returned to near-neutral pH. These preparations are highly monomeric, seedless, and do not require additional rounds of size exclusion, eliminating the need for this costly procedure and increasing the flexibility of use. We propose that our improved protocol is the simplest, fastest, and most effective way to solubilize Aβ from diverse sources for sensitive self-assembly and toxicity assays.
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7
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Saha J, Bose P, Dhakal S, Ghosh P, Rangachari V. Ganglioside-Enriched Phospholipid Vesicles Induce Cooperative Aβ Oligomerization and Membrane Disruption. Biochemistry 2022; 61:2206-2220. [PMID: 36173882 PMCID: PMC9840156 DOI: 10.1021/acs.biochem.2c00495] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
A major hallmark of Alzheimer's disease (AD) is the accumulation of extracellular aggregates of amyloid-β (Aβ). Structural polymorphism observed among Aβ fibrils in AD brains seem to correlate with the clinical subtypes suggesting a link between fibril polymorphism and pathology. Since fibrils emerge from a templated growth of low-molecular-weight oligomers, understanding the factors affecting oligomer generation is important. Membrane lipids are key factors to influence early stages of Aβ aggregation and oligomer generation, which cause membrane disruption. We have previously demonstrated that conformationally discrete Aβ oligomers can be generated by modulating the charge, composition, and chain length of lipids and surfactants. Here, we extend our studies into liposomal models by investigating Aβ oligomerization on large unilamellar vesicles (LUVs) of total brain extracts (TBE), reconstituted lipid rafts (LRs), or 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). Varying the vesicle composition by specifically increasing the amount of GM1 gangliosides as a constituent, we found that only GM1-enriched liposomes induce the formation of toxic, low-molecular-weight oligomers. Furthermore, we found that the aggregation on liposome surface and membrane disruption are highly cooperative and sensitive to membrane surface characteristics. Numerical simulations confirm such a cooperativity and reveal that GM1-enriched liposomes form twice as many pores as those formed in the absence GM1. Overall, this study uncovers mechanisms of cooperativity between oligomerization and membrane disruption under controlled lipid compositional bias, and refocuses the significance of the early stages of Aβ aggregation in polymorphism, propagation, and toxicity in AD.
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Affiliation(s)
- Jhinuk Saha
- Department of Chemistry and Biochemistry, School of Mathematics and Natural Sciences, University of Southern Mississippi, Hattiesburg, Mississippi 39406, United States
| | - Priyankar Bose
- Department of Computer Science, Virginia Commonwealth University, Richmond, Virginia 23220, United States
| | - Shailendra Dhakal
- Center for Molecular and Cellular Biosciences, University of Southern Mississippi, Hattiesburg, Mississippi 39406, United States
| | - Preetam Ghosh
- Department of Computer Science, Virginia Commonwealth University, Richmond, Virginia 23220, United States
| | - Vijayaraghavan Rangachari
- Department of Chemistry and Biochemistry, School of Mathematics and Natural Sciences, University of Southern Mississippi, Hattiesburg, Mississippi 39406, United States; Center for Molecular and Cellular Biosciences, University of Southern Mississippi, Hattiesburg, Mississippi 39406, United States
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8
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McKnelly KJ, Kreutzer AG, Howitz WJ, Haduong K, Yoo S, Hart C, Nowick JS. Effects of Familial Alzheimer's Disease Mutations on the Assembly of a β-Hairpin Peptide Derived from Aβ 16-36. Biochemistry 2022; 61:446-454. [PMID: 35213141 PMCID: PMC9042424 DOI: 10.1021/acs.biochem.1c00664] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Familial Alzheimer's disease (FAD) is associated with mutations in the β-amyloid peptide (Aβ) or the amyloid precursor protein (APP). FAD mutations of Aβ were incorporated into a macrocyclic peptide that mimics a β-hairpin to study FAD point mutations K16N, A21G, E22Δ, E22G, E22Q, E22K, and L34V and their effect on assembly, membrane destabilization, and cytotoxicity. The X-ray crystallographic structures of the four E22 mutant peptides reveal that the peptides assemble to form the same compact hexamer. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) experiments reveal that the mutant FAD peptides assemble as trimers or hexamers, with peptides that have greater positive charge assembling as more stable hexamers. Mutations that increase the positive charge also increase the cytotoxicity of the peptides and their propensity to destabilize lipid membranes.
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Affiliation(s)
- Kate J McKnelly
- Department of Chemistry, University of California Irvine, Irvine, California 92697, United States
| | - Adam G Kreutzer
- Department of Chemistry, University of California Irvine, Irvine, California 92697, United States
| | - William J Howitz
- Department of Chemistry, University of California Irvine, Irvine, California 92697, United States
| | - Katelyn Haduong
- Department of Chemistry, University of California Irvine, Irvine, California 92697, United States
| | - Stan Yoo
- Department of Chemistry, University of California Irvine, Irvine, California 92697, United States
| | - Candace Hart
- Department of Chemistry, University of California Irvine, Irvine, California 92697, United States
| | - James S Nowick
- Department of Chemistry, University of California Irvine, Irvine, California 92697, United States.,Department of Pharmaceutical Sciences, University of California Irvine, Irvine, California 92697, United States
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9
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Mrdenovic D, Pieta IS, Nowakowski R, Kutner W, Lipkowski J, Pieta P. Amyloid β interaction with model cell membranes - What are the toxicity-defining properties of amyloid β? Int J Biol Macromol 2022; 200:520-531. [PMID: 35074328 DOI: 10.1016/j.ijbiomac.2022.01.117] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Revised: 01/10/2022] [Accepted: 01/18/2022] [Indexed: 01/26/2023]
Abstract
Disruption of the neuronal membrane by toxic amyloid β oligomers is hypothesized to be the major event associated with Alzheimer's disease's neurotoxicity. Misfolding of amyloid β is followed by aggregation via different pathways in which structurally different amyloid β oligomers can be formed. The respective toxic actions of these structurally diverse oligomers can vary significantly. Linking a particular toxic action to a structurally unique kind of amyloid β oligomers and resolving their toxicity-determining feature remains challenging because of their transient stability and heterogeneity. Moreover, the lipids that make up the membrane affect amyloid β oligomers' behavior, thus adding to the problem's complexity. The present review compares and analyzes the latest results to improve understanding of amyloid β oligomers' interaction with lipid bilayers.
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Affiliation(s)
- Dusan Mrdenovic
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland; Department of Chemistry, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada
| | - Izabela S Pieta
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Robert Nowakowski
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Wlodzimierz Kutner
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland; Faculty of Mathematics and Natural Sciences, School of Sciences, Cardinal Stefan Wyszynski University in Warsaw, Wóycickiego 1/3, 01-815 Warsaw, Poland
| | - Jacek Lipkowski
- Department of Chemistry, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada
| | - Piotr Pieta
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
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10
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Press-Sandler O, Miller Y. Molecular insights into the primary nucleation of polymorphic amyloid β dimers in DOPC lipid bilayer membrane. Protein Sci 2022; 31:e4283. [PMID: 35129859 PMCID: PMC8994488 DOI: 10.1002/pro.4283] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 02/01/2022] [Accepted: 02/03/2022] [Indexed: 11/29/2022]
Abstract
Alzheimer's disease (AD) pathology is characterized by loss of memory cognitive and behavioral deterioration. One of the hallmarks of AD is amyloid β (Aβ) plaques in the brain that consists of Aβ oligomers and fibrils. It is accepted that oligomers, particularly dimers, are toxic species that are produced extracellularly and intracellularly in membranes. It is believed that the disruption of membranes by polymorphic Aβ oligomers is the key for the pathology of AD. This is a first study that investigate the effect of polymorphic “α‐helix/random coil” and “fibril‐like” Aβ dimers on 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) membrane. It has been found that the DOPC membrane promotes Aβ1–42 “fibril‐like” dimers and impedes Aβ1–42 “α‐helix/random coil” dimers. The N‐termini domains within Aβ1–42 dimers play a role in Aβ aggregation in membrane milieus. In addition, the aromatic π–π interactions (involving residues F19 and F20 in Aβ1–42) are the driving forces for the hydrophobic interactions that initiate the primary nucleation of polymorphic Aβ1–42 dimers within DOPC membrane. Finally, the DOPC bilayer membrane thickness is locally decreased, and it is disrupted by an embedded distinct Aβ1–42 dimer, due to relatively large contacts between Aβ1–42 monomers and the DOPC membrane. This study reveals insights into the molecular mechanisms by which polymorphic early‐stage Aβ1–42 dimers have distinct impacts on DOPC membrane.
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Affiliation(s)
- Olga Press-Sandler
- Department of Chemistry, Ben-Gurion University of the Negev, P.O. Box 653, Be'er Sheva, Israel.,Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beér-Sheva, Israel
| | - Yifat Miller
- Department of Chemistry, Ben-Gurion University of the Negev, P.O. Box 653, Be'er Sheva, Israel.,Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beér-Sheva, Israel
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11
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Zaretsky DV, Zaretskaia MV, Molkov YI. Membrane channel hypothesis of lysosomal permeabilization by beta-amyloid. Neurosci Lett 2021; 770:136338. [PMID: 34767924 DOI: 10.1016/j.neulet.2021.136338] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Revised: 09/29/2021] [Accepted: 11/03/2021] [Indexed: 11/16/2022]
Abstract
Alzheimer's disease (AD) is the most common cause of dementia affecting millions of people. Neuronal death in AD is initiated by oligomeric amyloid-β (Aβ) peptides. Recently, we proposed the amyloid degradation toxicity hypothesis, which explains multiple major observations associated with AD including autophagy failure and a decreased metabolism. According to the hypothesis, the key event in the cellular toxicity of amyloid is the formation of non-selective membrane channels in lysosomal membranes by amyloid fragments that are produced by the digestion of Aβ previously absorbed by endocytosis. Electrophysiological data suggest that amyloid-formed channels have different sizes, which can be explained by the fact that channel creating barrel-shaped amyloid aggregates can consist of different number of monomers. To estimate the ability of channels to leak molecules of various molecular weights, we modeled the channels as saline-filled cylinders in non-conductive membranes that pass spheres with a density of average globular proteins. As a basis, we used the conductance distribution taken from the previously published experimental dataset, in which single channels with electrical conductance of up to one nanosiemens were registered. Our calculations show that channels with such a giant conductance can allow for passing macromolecules such as large as lysosomal cathepsins implicated in the activation of apoptosis. The formation of giant channels is disproportionally promoted in an acidic environment. Also, amyloid fragments leaking from permeabilized lysosomes can reach the internal leaflet of the plasma membrane and permeabilize it. We conclude that while dissipation of the proton gradient by any (even smallest) amyloid channels readily explains lysosomal failure, the relatively rare events of lysosomal permeabilization to large macromolecules can be an additional mechanism of cellular death induced by exposure to Aβ.
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Affiliation(s)
| | | | - Yaroslav I Molkov
- Department of Mathematics and Statistics and Neuroscience Institute, Georgia State University, Atlanta, GA 30303, United States
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12
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Zaretsky DV, Zaretskaia MV. Intracellular ion changes induced by the exposure to beta-amyloid can be explained by the formation of channels in the lysosomal membranes. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2021; 1869:119145. [PMID: 34606794 DOI: 10.1016/j.bbamcr.2021.119145] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2021] [Revised: 08/29/2021] [Accepted: 09/05/2021] [Indexed: 10/20/2022]
Abstract
In this manuscript, we reassess the data on beta-amyloid-induced changes of intracellular ions concentrations published previously by Abramov et al. (2003, 2004). Their observations made using high-resolution confocal microscopy with fast temporal resolution of images formed by fluorescent ion-sensitive fluorescent probes in living cells represent an unequivocal support for the amyloid channel theory. However, closer look reveals multiple facts which cannot be explained by channel formation in plasma membrane. Recently proposed amyloid degradation toxicity hypothesis provides the interpretation to these facts by considering that channels are formed in the lysosomal membranes.
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Zhao H, Huang X, Tong Z. Formaldehyde-Crosslinked Nontoxic Aβ Monomers to Form Toxic Aβ Dimers and Aggregates: Pathogenicity and Therapeutic Perspectives. ChemMedChem 2021; 16:3376-3390. [PMID: 34396700 DOI: 10.1002/cmdc.202100428] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Revised: 08/14/2021] [Indexed: 01/02/2023]
Abstract
Alzheimer's disease (AD) is characterized by the presence of senile plaques in the brain. However, medicines targeting amyloid-beta (Aβ) have not achieved the expected clinical effects. This review focuses on the formation mechanism of the Aβ dimer (the basic unit of oligomers and fibrils) and its tremendous potential as a drug target. Recently, age-associated formaldehyde and Aβ-derived formaldehyde have been found to crosslink the nontoxic Aβ monomer to form the toxic dimers, oligomers and fibrils. Particularly, Aβ-induced formaldehyde accumulation and formaldehyde-promoted Aβ aggregation form a vicious cycle. Subsequently, formaldehyde initiates Aβ toxicity in both the early-and late-onset AD. These facts also explain why AD drugs targeting only Aβ do not have the desired therapeutic effects. Development of the nanoparticle-based medicines targeting both formaldehyde and Aβ dimer is a promising strategy for improving the drug efficacy by penetrating blood-brain barrier and extracellular space into the cortical neurons in AD patients.
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Affiliation(s)
- Hang Zhao
- Institute of Aging, Key Laboratory of Alzheimer's Disease of Zhejiang Province, School of Mental Health, Wenzhou Medical University, Wenzhou, 325035, China
| | - Xuerong Huang
- Wenzhou Medical University Affiliated Hospital 3, Department of Neurology, Wenzhou, 325200, China
| | - Zhiqian Tong
- Institute of Aging, Key Laboratory of Alzheimer's Disease of Zhejiang Province, School of Mental Health, Wenzhou Medical University, Wenzhou, 325035, China
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14
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Zaretsky DV, Zaretskaia MV. Mini-review: Amyloid degradation toxicity hypothesis of Alzheimer's disease. Neurosci Lett 2021; 756:135959. [PMID: 34000347 DOI: 10.1016/j.neulet.2021.135959] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2021] [Revised: 04/28/2021] [Accepted: 05/10/2021] [Indexed: 12/21/2022]
Abstract
Alzheimer's disease (AD) is the most common cause of dementia affecting millions of people. Neuronal death in AD is initiated by oligomeric amyloid-β (Aβ) peptides. The amyloid channel hypothesis readily explains the primary molecular damage but does not address major observations associated with AD such as autophagy failure and decreased metabolism. The amyloid degradation toxicity hypothesis provides the interpretation as a sequence of molecular events. Aβ enters a cell by endocytosis, and the endocytic vesicle is merged with a lysosome. Lysosomal peptidases degrade the peptide. Fragments form membrane channels in lysosomal membranes that have a significant negative charge due to the presence of acidic phospholipids. Amyloid channels can transfer various ions (including protons) and even relatively large compounds, which explains lysosomal permeabilization. The neutralization of lysosomal content inactivates degradation enzymes, results in an accumulation of undigested amyloid, and stalls autophagy. Inadequate quality control of mitochondria is associated with an increased production of reactive oxygen species and decreased energy production. Also, the passage of lysosomal proteases through rare extremely large channels results in cell death. Proposed hypothesis identifies biochemical pathways involved in the initiation and progression of cellular damage induced by beta-amyloid and provides new potential pharmacological targets to treat Alzheimer's disease.
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15
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Zaretsky DV, Zaretskaia M. Degradation Products of Amyloid Protein: Are They The Culprits? Curr Alzheimer Res 2021; 17:869-880. [DOI: 10.2174/1567205017666201203142103] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 10/13/2020] [Accepted: 11/06/2020] [Indexed: 11/22/2022]
Abstract
Objectives:
Beta-amyloid (Aβ) peptides are most toxic to cells in oligomeric form. It is commonly accepted that
oligomers can form ion channels in cell membranes and allow calcium and other ions to enter cells. The activation of other
mechanisms, such as apoptosis or lipid peroxidation, aggravates the toxicity, but it itself can result from the same initial
point, that is, ion disturbance due to an increased permeability of membranes. However, experimental studies of membrane
channels created by Aβ are surprisingly limited. Methods: Here, we report a novel flow cytometry technique which can be
used to detect increased permeability of membranes to calcium induced by the exposure to amyloid peptides. Calcium entry
into the liposome is monitored using calcium-sensitive fluorescent probe. Undamaged lipid membranes are not permeable to
calcium. Liposomes that are prepared in a calcium-free medium become able to accumulate calcium in a calcium-containing
medium only after the formation of channels. Using this technique, we demonstrated that the addition of short amyloid
fragment Aβ, which is known for its extreme toxicity on cultured neurons, readily increased membrane permeability to
calcium. However, neither similarly sized peptide Ab22-35 nor full-length peptide Ab1-42 were producing channels. The
formation of channels was observed in the membranes made of phosphatidylserine, a negatively charged lipid, but not in
membranes made of the neutral phosphatidylcholine.
Methods:
Here, we report a novel flow cytometry technique which can be
used to detect increased permeability of membranes to calcium induced by the exposure to amyloid peptides. Calcium entry
into the liposome is monitored using calcium-sensitive fluorescent probe. Undamaged lipid membranes are not permeable to
calcium. Liposomes that are prepared in a calcium-free medium become able to accumulate calcium in a calcium-containing
medium only after the formation of channels. Using this technique, we demonstrated that the addition of short amyloid
fragment Aβ, which is known for its extreme toxicity on cultured neurons, readily increased membrane permeability to
calcium. However, neither similarly sized peptide Ab22-35 nor full-length peptide Ab1-42 were producing channels. The
formation of channels was observed in the membranes made of phosphatidylserine, a negatively charged lipid, but not in
membranes made of the neutral phosphatidylcholine.
Results:
In the Discussion section, we have analyzed several issues which could be critical for understanding the
pathogenesis of Alzheimer’s disease, specifically 1) the need for a negatively charged membrane to produce the ion channel;
2) the potential role of the aggregated form in cellular toxicity of Ab peptides; 3) channel-forming ability of multiple
degradation products of amyloid; 4) non-specificity of ion channels formed by amyloid peptides. Potential targets of
channel-forming oligomers appear to be intracellular and are organelles well-known for dysfunction in Alzheimer’s disease
(mitochondria and lysosomes). In fact, lysosomes can also be the producers of degraded amyloid. Provided speculations
support the hypothesis that neuronal toxicity can be caused by the degradation products of beta-amyloid.
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16
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Zaretsky DV, Zaretskaia MV. Flow cytometry method to quantify the formation of beta-amyloid membrane ion channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1863:183506. [PMID: 33171157 DOI: 10.1016/j.bbamem.2020.183506] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 08/29/2020] [Revised: 10/31/2020] [Accepted: 11/05/2020] [Indexed: 11/17/2022]
Abstract
It is accepted that the cytotoxicity of beta-amyloid is mediated by its oligomers. Amyloid peptides can form ion channels in cell membranes and allow calcium and other ions to enter cells. In this project, we developed a technique to quantify the appearance of calcium in liposomes and applied this technique to study the effect of amyloid peptides on the permeability of membranes. Calcium influx was monitored in liposomes made of phosphatidylcholine (PC) or phosphatidylserine (PS) with an addition of a lipid-soluble dye DiD and containing fluorescent calcium-sensitive probe Fluo-3. The intensity of fluorescence of individual liposomes was measured using a flow cytometer. Calcium ionophore ionomycin served as a positive control. The addition of micromolar concentrations of short fragments of amyloid-beta (Aβ25-35) permeabilized a significant number of PS liposomes. This effect was not observed in PC liposomes. Our data supports the hypothesis that the ion channel formation by amyloid peptide is dependent on electrostatic interactions. High concentrations of Aβ25-35 (above 20 μM) increased signal intensity in a recording channel corresponding to the calcium-sensing probe. However, this phenomenon was also observed in Ca2+-free conditions and even in liposomes without Fluo-3, so we interpreted it as an artifact. Using the described technique, we were not able to detect the formation of calcium channels by several other amyloid peptides. Considering that liposomes appeared resistant to reasonable concentrations of solvents, we expect that described flowmetric technique can be used in high-throughput screening applications.
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Ke PC, Zhou R, Serpell LC, Riek R, Knowles TPJ, Lashuel HA, Gazit E, Hamley IW, Davis TP, Fändrich M, Otzen DE, Chapman MR, Dobson CM, Eisenberg DS, Mezzenga R. Half a century of amyloids: past, present and future. Chem Soc Rev 2020; 49:5473-5509. [PMID: 32632432 PMCID: PMC7445747 DOI: 10.1039/c9cs00199a] [Citation(s) in RCA: 304] [Impact Index Per Article: 76.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Amyloid diseases are global epidemics with profound health, social and economic implications and yet remain without a cure. This dire situation calls for research into the origin and pathological manifestations of amyloidosis to stimulate continued development of new therapeutics. In basic science and engineering, the cross-β architecture has been a constant thread underlying the structural characteristics of pathological and functional amyloids, and realizing that amyloid structures can be both pathological and functional in nature has fuelled innovations in artificial amyloids, whose use today ranges from water purification to 3D printing. At the conclusion of a half century since Eanes and Glenner's seminal study of amyloids in humans, this review commemorates the occasion by documenting the major milestones in amyloid research to date, from the perspectives of structural biology, biophysics, medicine, microbiology, engineering and nanotechnology. We also discuss new challenges and opportunities to drive this interdisciplinary field moving forward.
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Affiliation(s)
- Pu Chun Ke
- ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, Monash Institute of Pharmaceutical Sciences, Monash University, 381 Royal Parade, Parkville, VIC 3052, Australia
- Zhongshan Hospital, Fudan University, 111 Yixueyuan Rd, Xuhui District, Shanghai, China
| | - Ruhong Zhou
- Institute of Quantitative Biology, Zhejiang University, Hangzhou 310058, China; Department of Chemistry, Columbia University, New York, New York, 10027, USA
| | - Louise C. Serpell
- School of Life Sciences, University of Sussex, Falmer, East Sussex BN1 9QG, UK
| | - Roland Riek
- Laboratory of Physical Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Wolfgang-Pauli-Str. 10, 8093 Zurich, Switzerland
| | - Tuomas P. J. Knowles
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK
- Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, CB3 0HE, Cambridge, UK
| | - Hilal A. Lashuel
- Laboratory of Molecular Neurobiology and Neuroproteomics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Ehud Gazit
- Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences; Department of Materials Science and Engineering, Iby and Aladar Fleischman Faculty of Engineering, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Ian W. Hamley
- School of Chemistry, Food Biosciences and Pharmacy, University of Reading, Whiteknights, Reading RG6 6AD, UK
| | - Thomas P. Davis
- ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, Monash Institute of Pharmaceutical Sciences, Monash University, 381 Royal Parade, Parkville, VIC 3052, Australia
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane Qld 4072, Australia
| | - Marcus Fändrich
- Institute of Protein Biochemistry, Ulm University, 89081, Ulm, Germany
| | - Daniel Erik Otzen
- Department of Molecular Biology, Center for Insoluble Protein Structures (inSPIN), Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark
| | - Matthew R. Chapman
- Department of Molecular, Cellular and Developmental Biology, Centre for Microbial Research, University of Michigan, Ann Arbor, MI 48109-1048, USA
| | - Christopher M. Dobson
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK
| | - David S. Eisenberg
- Departments of Chemistry and Biochemistry and Biological Chemistry, UCLA-DOE Institute and Howard Hughes Medical Institute, UCLA, Los Angeles, CA, USA
| | - Raffaele Mezzenga
- Department of Health Science & Technology, ETH Zurich, Schmelzbergstrasse 9, LFO, E23, 8092 Zurich, Switzerland
- Department of Materials, ETH Zurich, Wolfgang Pauli Strasse 10, 8093 Zurich, Switzerland
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18
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W. Pilkington IV A, Legleiter J. Challenges in understanding the structure/activity relationship of Aβ oligomers. AIMS BIOPHYSICS 2019. [DOI: 10.3934/biophy.2019.1.1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
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19
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Gao Q, Fang Y, Zhang S, Li HW, Yung KKL, Lai KWC. Biophysical Characteristics of Human Neuroblastoma Cell in Oligomeric $\beta $ -Amyloid (1–40) Cytotoxicity. IEEE Trans Nanobioscience 2018; 17:70-77. [DOI: 10.1109/tnb.2018.2800723] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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20
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Zolghadr AR, Heydari Dokoohaki M. How Does the P7C3-Series of Neuroprotective Small Molecules Prevent Membrane Disruption? J Chem Inf Model 2017; 57:2009-2019. [PMID: 28691805 DOI: 10.1021/acs.jcim.7b00151] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Molecular dynamics (MD) simulations are conducted to suggest a mechanism of action for the aminopropyl dibromocarbazole derivative (P7C3) small molecule, which protects neurons from apoptotic cell death. At first, the influence of embedded Aβ42 stacks on the structure of membrane is studied. Then, the effect of P7C3 molecules on the Aβ42 fibril enriched membrane and Aβ42 fibril depleted membrane (when Aβ42 fibrils are originally dissolved in the aqueous phase) are evaluated. Also, the formation of an amyloid ion channel in the Aβ42 enriched membrane is examined by calculating deuterium order parameter, density profile, and surface thickness. For Aβ42 in the fully inserted state, ion channel-like structures are formed. The presence of P7C3 molecules in this case just postpones membrane destruction but could not prevent pore formation. In contrast, when both Aβ42 and P7C3 molecules are embedded in the aqueous solution, the P7C3 molecules are self-assembled at membrane/ionic aqueous solution interface and prevent the precipitation and deposition of Aβ42 fibrils into the membrane.
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21
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Bode DC, Baker MD, Viles JH. Ion Channel Formation by Amyloid-β42 Oligomers but Not Amyloid-β40 in Cellular Membranes. J Biol Chem 2016; 292:1404-1413. [PMID: 27927987 DOI: 10.1074/jbc.m116.762526] [Citation(s) in RCA: 148] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Revised: 11/24/2016] [Indexed: 12/23/2022] Open
Abstract
A central hallmark of Alzheimer's disease is the presence of extracellular amyloid plaques chiefly consisting of amyloid-β (Aβ) peptides in the brain interstitium. Aβ largely exists in two isoforms, 40 and 42 amino acids long, but a large body of evidence points to Aβ(1-42) rather than Aβ(1-40) as the cytotoxic form. One proposed mechanism by which Aβ exerts toxicity is the formation of ion channel pores that disrupt intracellular Ca2+ homeostasis. However, previous studies using membrane mimetics have not identified any notable difference in the channel forming properties between Aβ(1-40) and Aβ(1-42). Here, we tested whether a more physiological environment, membranes excised from HEK293 cells of neuronal origin, would reveal differences in the relative channel forming ability of monomeric, oligomeric, and fibrillar forms of both Aβ(1-40) and Aβ(1-42). Aβ preparations were characterized with transmission electron microscopy and thioflavin T fluorescence. Aβ was then exposed to the extracellular face of excised membranes, and transmembrane currents were monitored using patch clamp. Our data indicated that Aβ(1-42) assemblies in oligomeric preparations form voltage-independent, non-selective ion channels. In contrast, Aβ(1-40) oligomers, fibers, and monomers did not form channels. Ion channel conductance results suggested that Aβ(1-42) oligomers, but not monomers and fibers, formed three distinct pore structures with 1.7-, 2.1-, and 2.4-nm pore diameters. Our findings demonstrate that only Aβ(1-42) contains unique structural features that facilitate membrane insertion and channel formation, now aligning ion channel formation with the differential neurotoxic effect of Aβ(1-40) and Aβ(1-42) in Alzheimer's disease.
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Affiliation(s)
- David C Bode
- From the School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, United Kingdom and
| | - Mark D Baker
- the Blizard Institute, Centre for Neuroscience and Trauma, Barts and The London School of Medicine and Dentistry, Queen Mary, University of London, 4 Newark Street, London E1 2AT, United Kingdom
| | - John H Viles
- From the School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, United Kingdom and
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22
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Salinas DG. Flux theory for Poisson distributed pores with Gaussian permeability. Channels (Austin) 2015; 10:111-8. [PMID: 26488853 DOI: 10.1080/19336950.2015.1100778] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
The mean of the solute flux through membrane pores depends on the random distribution and permeability of the pores. Mathematical models including such randomness factors make it possible to obtain statistical parameters for pore characterization. Here, assuming that pores follow a Poisson distribution in the lipid phase and that their permeabilities follow a Gaussian distribution, a mathematical model for solute dynamics is obtained by applying a general result from a previous work regarding any number of different kinds of randomly distributed pores. The new proposed theory is studied using experimental parameters obtained elsewhere, and a method for finding the mean single pore flux rate from liposome flux assays is suggested. This method is useful for pores without requiring studies by patch-clamp in single cells or single-channel recordings. However, it does not apply in the case of ion-selective channels, in which a more complex flux law combining the concentration and electrical gradient is required.
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Affiliation(s)
- Dino G Salinas
- a Centro de Investigación Biomédica, Facultad de Medicina , Universidad Diego Portales , Santiago , Chile
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23
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24
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Berhanu WM, Hansmann UHE. Stability of amyloid oligomers. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2014; 96:113-41. [PMID: 25443956 DOI: 10.1016/bs.apcsb.2014.06.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/12/2023]
Abstract
Molecular simulations are now commonly used to complement experimental techniques in investigating amyloids and their role in human diseases. In this chapter, we will summarize techniques and approaches often used in amyloid simulations and will present recent success stories. Our examples will be focused on lessons learned from molecular dynamics simulations in aqueous environments that start from preformed aggregates. These studies explore the limitations that arise from the choice of force field, the role of mutations in the growth of amyloid aggregates, segmental polymorphism, and the importance of cross-seeding. Furthermore, they give evidence for potential toxicity mechanisms. We finally discuss the role of molecular simulations in the search for aggregation inhibitors.
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Affiliation(s)
- Workalemahu M Berhanu
- Department of Chemistry & Biochemistry, University of Oklahoma, Norman, Oklahoma, USA
| | - Ulrich H E Hansmann
- Department of Chemistry & Biochemistry, University of Oklahoma, Norman, Oklahoma, USA.
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25
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Walsh P, Vanderlee G, Yau J, Campeau J, Sim VL, Yip CM, Sharpe S. The mechanism of membrane disruption by cytotoxic amyloid oligomers formed by prion protein(106-126) is dependent on bilayer composition. J Biol Chem 2014; 289:10419-10430. [PMID: 24554723 PMCID: PMC4036164 DOI: 10.1074/jbc.m113.515866] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2013] [Revised: 02/01/2014] [Indexed: 11/06/2022] Open
Abstract
The formation of fibrillar aggregates has long been associated with neurodegenerative disorders such as Alzheimer and Parkinson diseases. Although fibrils are still considered important to the pathology of these disorders, it is now widely understood that smaller amyloid oligomers are the toxic entities along the misfolding pathway. One characteristic shared by the majority of amyloid oligomers is the ability to disrupt membranes, a commonality proposed to be responsible for their toxicity, although the mechanisms linking this to cell death are poorly understood. Here, we describe the physical basis for the cytotoxicity of oligomers formed by the prion protein (PrP)-derived amyloid peptide PrP(106-126). We show that oligomers of this peptide kill several mammalian cells lines, as well as mouse cerebellar organotypic cultures, and we also show that they exhibit antimicrobial activity. Physical perturbation of model membranes mimicking bacterial or mammalian cells was investigated using atomic force microscopy, polarized total internal reflection fluorescence microscopy, and NMR spectroscopy. Disruption of anionic membranes proceeds through a carpet or detergent model as proposed for other antimicrobial peptides. By contrast, when added to zwitterionic membranes containing cholesterol-rich ordered domains, PrP(106-126) oligomers induce a loss of domain separation and decreased membrane disorder. Loss of raft-like domains may lead to activation of apoptotic pathways, resulting in cell death. This work sheds new light on the physical mechanisms of amyloid cytotoxicity and is the first to clearly show membrane type-specific modes of action for a cytotoxic peptide.
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Affiliation(s)
- Patrick Walsh
- Molecular Structure and Function Program, The Hospital for Sick Children, Toronto, Ontario M5G 1X8; Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8
| | - Gillian Vanderlee
- Institute of Biomaterials and Biomedical Engineering, Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario M5S 3E1
| | - Jason Yau
- Molecular Structure and Function Program, The Hospital for Sick Children, Toronto, Ontario M5G 1X8; Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8
| | - Jody Campeau
- Department of Medicine, Division of Neurology, University of Alberta, Edmonton, Alberta T6G 2G3, Canada
| | - Valerie L Sim
- Department of Medicine, Division of Neurology, University of Alberta, Edmonton, Alberta T6G 2G3, Canada
| | - Christopher M Yip
- Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8; Institute of Biomaterials and Biomedical Engineering, Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario M5S 3E1
| | - Simon Sharpe
- Molecular Structure and Function Program, The Hospital for Sick Children, Toronto, Ontario M5G 1X8; Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8.
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26
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Ávila CL, Torres-Bugeau CM, Barbosa LRS, Sales EM, Ouidja MO, Socías SB, Celej MS, Raisman-Vozari R, Papy-Garcia D, Itri R, Chehín RN. Structural characterization of heparin-induced glyceraldehyde-3-phosphate dehydrogenase protofibrils preventing α-synuclein oligomeric species toxicity. J Biol Chem 2014; 289:13838-50. [PMID: 24671416 DOI: 10.1074/jbc.m113.544288] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional enzyme that has been associated with neurodegenerative diseases. GAPDH colocalizes with α-synuclein in amyloid aggregates in post-mortem tissue of patients with sporadic Parkinson disease and promotes the formation of Lewy body-like inclusions in cell culture. In a previous work, we showed that glycosaminoglycan-induced GAPDH prefibrillar species accelerate the conversion of α-synuclein to fibrils. However, it remains to be determined whether the interplay among glycosaminoglycans, GAPDH, and α-synuclein has a role in pathological states. Here, we demonstrate that the toxic effect exerted by α-synuclein oligomers in dopaminergic cell culture is abolished in the presence of GAPDH prefibrillar species. Structural analysis of prefibrillar GAPDH performed by small angle x-ray scattering showed a particle compatible with a protofibril. This protofibril is shaped as a cylinder 22 nm long and a cross-section diameter of 12 nm. Using biocomputational techniques, we obtained the first all-atom model of the GAPDH protofibril, which was validated by cross-linking coupled to mass spectrometry experiments. Because GAPDH can be secreted outside the cell where glycosaminoglycans are present, it seems plausible that GAPDH protofibrils could be assembled in the extracellular space kidnapping α-synuclein toxic oligomers. Thus, the role of GAPDH protofibrils in neuronal proteostasis must be considered. The data reported here could open alternative ways in the development of therapeutic strategies against synucleinopathies like Parkinson disease.
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Affiliation(s)
- César L Ávila
- From the Instituto Superior de Investigaciones Biológicas (INSIBIO), CONICET-UNT, and Instituto de Química Biológica "Dr. Bernabé Bloj," FBQF-UNT, Chacabuco 461, T4000ILI Tucumán, Argentina
| | - Clarisa M Torres-Bugeau
- From the Instituto Superior de Investigaciones Biológicas (INSIBIO), CONICET-UNT, and Instituto de Química Biológica "Dr. Bernabé Bloj," FBQF-UNT, Chacabuco 461, T4000ILI Tucumán, Argentina
| | - Leandro R S Barbosa
- the Instituto de Física da Universidade de São Paulo, Rua do Matão, Travessa R, 187, São Paulo, Brazil
| | - Elisa Morandé Sales
- the Instituto de Física da Universidade de São Paulo, Rua do Matão, Travessa R, 187, São Paulo, Brazil
| | - Mohand O Ouidja
- INSERM U1127, CNRS UMR 7225, Institut de Cerveau et de la Moelle Epinière, Paris, France, the Laboratoire Croissance, Réparation et Régénération Tissulaires, CNRS EAC 7149, Université Paris Est Créteil, Université Paris Est, F-94000, Créteil, France, and
| | - Sergio B Socías
- INSERM U1127, CNRS UMR 7225, Institut de Cerveau et de la Moelle Epinière, Paris, France
| | - M Soledad Celej
- the Departamento de Química Biológica, Centro de Investigaciones en Química Biológica de Córdoba, CONICET, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, X5000HUA Córdoba, Argentina
| | - Rita Raisman-Vozari
- INSERM U1127, CNRS UMR 7225, Institut de Cerveau et de la Moelle Epinière, Paris, France
| | - Dulce Papy-Garcia
- the Laboratoire Croissance, Réparation et Régénération Tissulaires, CNRS EAC 7149, Université Paris Est Créteil, Université Paris Est, F-94000, Créteil, France, and
| | - Rosangela Itri
- the Instituto de Física da Universidade de São Paulo, Rua do Matão, Travessa R, 187, São Paulo, Brazil
| | - Rosana N Chehín
- From the Instituto Superior de Investigaciones Biológicas (INSIBIO), CONICET-UNT, and Instituto de Química Biológica "Dr. Bernabé Bloj," FBQF-UNT, Chacabuco 461, T4000ILI Tucumán, Argentina,
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27
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Tinker-Mill C, Mayes J, Allsop D, Kolosov OV. Ultrasonic force microscopy for nanomechanical characterization of early and late-stage amyloid-β peptide aggregation. Sci Rep 2014; 4:4004. [PMID: 24500006 PMCID: PMC3915309 DOI: 10.1038/srep04004] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Accepted: 01/20/2014] [Indexed: 11/09/2022] Open
Abstract
The aggregation of amyloid-β peptides into protein fibres is one of the main neuropathological features of Alzheimer's disease (AD). While imaging of amyloid-β aggregate morphology in vitro is extremely important for understanding AD pathology and in the development of aggregation inhibitors, unfortunately, potentially highly toxic, early aggregates are difficult to observe by current electron microscopy and atomic force microscopy (AFM) methods, due to low contrast and variability of peptide attachment to the substrate. Here, we use a poly-L-Lysine (PLL) surface that captures all protein components from monomers to fully formed fibres, followed by nanomechanical mapping via ultrasonic force microscopy (UFM), which marries high spatial resolution and nanomechanical contrast with the non-destructive nature of tapping mode AFM. For the main putative AD pathogenic component, Aβ1-42, the PLL-UFM approach reveals the morphology of oligomers, protofibrils and mature fibres, and finds that a fraction of small oligomers is still present at later stages of fibril assembly.
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Affiliation(s)
| | - Jennifer Mayes
- Division of Biomedical and Life Sciences, Lancaster University, Lancaster, LA1 4YB, UK
| | - David Allsop
- Division of Biomedical and Life Sciences, Lancaster University, Lancaster, LA1 4YB, UK
| | - Oleg V. Kolosov
- Physics Department, Lancaster University, Lancaster, LA1 4YB, UK
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28
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Poojari C, Strodel B. Stability of transmembrane amyloid β-peptide and membrane integrity tested by molecular modeling of site-specific Aβ42 mutations. PLoS One 2013; 8:e78399. [PMID: 24244308 PMCID: PMC3820573 DOI: 10.1371/journal.pone.0078399] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Accepted: 09/11/2013] [Indexed: 11/20/2022] Open
Abstract
Interactions of the amyloid β-protein (Aβ) with neuronal cell membranes, leading to the disruption of membrane integrity, are considered to play a key role in the development of Alzheimer’s disease. Natural mutations in Aβ42, such as the Arctic mutation (E22G) have been shown to increase Aβ42 aggregation and neurotoxicity, leading to the early-onset of Alzheimer’s disease. A correlation between the propensity of Aβ42 to form protofibrils and its effect on neuronal dysfunction and degeneration has been established. Using rational mutagenesis of the Aβ42 peptide it was further revealed that the aggregation of different Aβ42 mutants in lipid membranes results in a variety of polymorphic aggregates in a mutation dependent manner. The mutant peptides also have a variable ability to disrupt bilayer integrity. To further test the connection between Aβ42 mutation and peptide–membrane interactions, we perform molecular dynamics simulations of membrane-inserted Aβ42 variants (wild-type and E22G, D23G, E22G/D23G, K16M/K28M and K16M/E22G/D23G/K28M mutants) as β-sheet monomers and tetramers. The effects of charged residues on transmembrane Aβ42 stability and membrane integrity are analyzed at atomistic level. We observe an increased stability for the E22G Aβ42 peptide and a decreased stability for D23G compared to wild-type Aβ42, while D23G has the largest membrane-disruptive effect. These results support the experimental observation that the altered toxicity arising from mutations in Aβ is not only a result of the altered aggregation propensity, but also originates from modified Aβ interactions with neuronal membranes.
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Affiliation(s)
- Chetan Poojari
- Institute of Complex Systems: Structural Biochemistry, Forschungszentrum Jülich GmbH, Jülich, Germany
| | - Birgit Strodel
- Institute of Complex Systems: Structural Biochemistry, Forschungszentrum Jülich GmbH, Jülich, Germany
- Institute of Theoretical and Computational Chemistry, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
- * E-mail:
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29
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Cataldi M. The changing landscape of voltage-gated calcium channels in neurovascular disorders and in neurodegenerative diseases. Curr Neuropharmacol 2013; 11:276-97. [PMID: 24179464 PMCID: PMC3648780 DOI: 10.2174/1570159x11311030004] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Revised: 02/02/2013] [Accepted: 02/14/2013] [Indexed: 12/12/2022] Open
Abstract
It is a common belief that voltage-gated calcium channels (VGCC) cannot carry toxic amounts of Ca2+ in neurons. Also, some of them as L-type channels are essential for Ca2+-dependent regulation of prosurvival gene-programs. However, a wealth of data show a beneficial effect of drugs acting on VGCCs in several neurodegenerative and neurovascular diseases. In the present review, we explore several mechanisms by which the “harmless” VGCCs may become “toxic” for neurons. These mechanisms could explain how, though usually required for neuronal survival, VGCCs may take part in neurodegeneration. We will present evidence showing that VGCCs can carry toxic Ca2+ when: a) their density or activity increases because of aging, chronic hypoxia or exposure to β-amyloid peptides or b) Ca2+-dependent action potentials carry high Ca2+ loads in pacemaker neurons. Besides, we will examine conditions in which VGCCs promote neuronal cell death without carrying excess Ca2+. This can happen, for instance, when they carry metal ions into the neuronal cytoplasm or when a pathological decrease in their activity weakens Ca2+-dependent prosurvival gene programs. Finally, we will explore the role of VGCCs in the control of nonneuronal cells that take part to neurodegeneration like those of the neurovascular unit or of microglia.
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Affiliation(s)
- Mauro Cataldi
- Division of Pharmacology, Department of Neuroscience, Reproductive and Odontostomatological Sciences, Federico II University of Naples, Italy
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30
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Macdonald CL, Silva GA. A positive feedback cell signaling nucleation model of astrocyte dynamics. FRONTIERS IN NEUROENGINEERING 2013; 6:4. [PMID: 23847529 PMCID: PMC3706728 DOI: 10.3389/fneng.2013.00004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Accepted: 06/10/2013] [Indexed: 11/13/2022]
Abstract
We constructed a model of calcium signaling in astrocyte neural glial cells that incorporates a positive feedback nucleation mechanism, whereby small microdomain increases in local calcium can stochastically produce global cellular and intercellular network scale dynamics. The model is able to simultaneously capture dynamic spatial and temporal heterogeneities associated with intracellular calcium transients in individual cells and intercellular calcium waves (ICW) in spatially realistic networks of astrocytes, i.e., networks where the positions of cells were taken from real in vitro experimental data of spontaneously forming sparse networks, as opposed to artificially constructed grid networks or other non-realistic geometries. This is the first work we are aware of where an intracellular model of calcium signaling that reproduces intracellular dynamics inherently accounts for intercellular network dynamics. These results suggest that a nucleation type mechanism should be further investigated experimentally in order to test its contribution to calcium signaling in astrocytes and in other cells more broadly. It may also be of interest in engineered neuromimetic network systems that attempt to emulate biological signaling and information processing properties in synthetic hardwired neuromorphometric circuits or coded algorithms.
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31
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Burke KA, Yates EA, Legleiter J. Biophysical insights into how surfaces, including lipid membranes, modulate protein aggregation related to neurodegeneration. Front Neurol 2013; 4:17. [PMID: 23459674 PMCID: PMC3585431 DOI: 10.3389/fneur.2013.00017] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Accepted: 02/09/2013] [Indexed: 11/13/2022] Open
Abstract
There are a vast number of neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD), and Huntington’s disease (HD), associated with the rearrangement of specific proteins to non-native conformations that promotes aggregation and deposition within tissues and/or cellular compartments. These diseases are commonly classified as protein-misfolding or amyloid diseases. The interaction of these proteins with liquid/surface interfaces is a fundamental phenomenon with potential implications for protein-misfolding diseases. Kinetic and thermodynamic studies indicate that significant conformational changes can be induced in proteins encountering surfaces, which can play a critical role in nucleating aggregate formation or stabilizing specific aggregation states. Surfaces of particular interest in neurodegenerative diseases are cellular and subcellular membranes that are predominately comprised of lipid components. The two-dimensional liquid environments provided by lipid bilayers can profoundly alter protein structure and dynamics by both specific and non-specific interactions. Importantly for misfolding diseases, these bilayer properties can not only modulate protein conformation, but also exert influence on aggregation state. A detailed understanding of the influence of (sub)cellular surfaces in driving protein aggregation and/or stabilizing specific aggregate forms could provide new insights into toxic mechanisms associated with these diseases. Here, we review the influence of surfaces in driving and stabilizing protein aggregation with a specific emphasis on lipid membranes.
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Affiliation(s)
- Kathleen A Burke
- C. Eugene Bennett Department of Chemistry, West Virginia University Morgantown, WV, USA
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Poojari C, Kukol A, Strodel B. How the amyloid-β peptide and membranes affect each other: An extensive simulation study. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:327-39. [DOI: 10.1016/j.bbamem.2012.09.001] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2012] [Revised: 09/03/2012] [Accepted: 09/04/2012] [Indexed: 11/24/2022]
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Two-step mechanism of membrane disruption by Aβ through membrane fragmentation and pore formation. Biophys J 2013; 103:702-10. [PMID: 22947931 DOI: 10.1016/j.bpj.2012.06.045] [Citation(s) in RCA: 309] [Impact Index Per Article: 28.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2012] [Revised: 06/11/2012] [Accepted: 06/18/2012] [Indexed: 12/25/2022] Open
Abstract
Disruption of cell membranes by Aβ is believed to be one of the key components of Aβ toxicity. However, the mechanism by which this occurs is not fully understood. Here, we demonstrate that membrane disruption by Aβ occurs by a two-step process, with the initial formation of ion-selective pores followed by nonspecific fragmentation of the lipid membrane during amyloid fiber formation. Immediately after the addition of freshly dissolved Aβ(1-40), defects form on the membrane that share many of the properties of Aβ channels originally reported from single-channel electrical recording, such as cation selectivity and the ability to be blockaded by zinc. By contrast, subsequent amyloid fiber formation on the surface of the membrane fragments the membrane in a way that is not cation selective and cannot be stopped by zinc ions. Moreover, we observed that the presence of ganglioside enhances both the initial pore formation and the fiber-dependent membrane fragmentation process. Whereas pore formation by freshly dissolved Aβ(1-40) is weakly observed in the absence of gangliosides, fiber-dependent membrane fragmentation can only be observed in their presence. These results provide insights into the toxicity of Aβ and may aid in the design of specific compounds to alleviate the neurodegeneration of Alzheimer's disease.
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Robertson JWF, Kasianowicz JJ, Banerjee S. Analytical Approaches for Studying Transporters, Channels and Porins. Chem Rev 2012; 112:6227-49. [DOI: 10.1021/cr300317z] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Joseph W. F. Robertson
- Physical Measurement Laboratory,
National Institute of Standards and Technology, Gaithersburg, Maryland
20899, United States
| | - John J. Kasianowicz
- Physical Measurement Laboratory,
National Institute of Standards and Technology, Gaithersburg, Maryland
20899, United States
| | - Soojay Banerjee
- National
Institute of Neurological
Disorders and Stroke, Bethesda, Maryland 20824, United States
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Norlin N, Hellberg M, Filippov A, Sousa AA, Gröbner G, Leapman RD, Almqvist N, Antzutkin ON. Aggregation and fibril morphology of the Arctic mutation of Alzheimer's Aβ peptide by CD, TEM, STEM and in situ AFM. J Struct Biol 2012; 180:174-89. [PMID: 22750418 PMCID: PMC3466396 DOI: 10.1016/j.jsb.2012.06.010] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2012] [Revised: 06/10/2012] [Accepted: 06/14/2012] [Indexed: 10/28/2022]
Abstract
Morphology of aggregation intermediates, polymorphism of amyloid fibrils and aggregation kinetics of the "Arctic" mutant of the Alzheimer's amyloid β-peptide, Aβ((1-40))(E22G), in a physiologically relevant Tris buffer (pH 7.4) were thoroughly explored in comparison with the human wild type Alzheimer's amyloid peptide, wt-Aβ((1-40)), using both in situ atomic force and electron microscopy, circular dichroism and thioflavin T fluorescence assays. For arc-Aβ((1-40)) at the end of the 'lag'-period of fibrillization an abrupt appearance of ≈ 3 nm size 'spherical aggregates' with a homogeneous morphology, was identified. Then, the aggregation proceeds with a rapid growth of amyloid fibrils with a variety of morphologies, while the spherical aggregates eventually disappeared during in situ measurements. Arc-Aβ((1-40)) was also shown to form fibrils at much lower concentrations than wt-Aβ((1-40)): ≤ 2.5 μM and 12.5 μM, respectively. Moreover, at the same concentration, 50 μM, the aggregation process proceeds more rapidly for arc-Aβ((1-40)): the first amyloid fibrils were observed after c.a. 72 h from the onset of incubation as compared to approximately 7 days for wt-Aβ((1-40)). Amyloid fibrils of arc-Aβ((1-40)) exhibit a large variety of polymorphs, at least five, both coiled and non-coiled distinct fibril structures were recognized by AFM, while at least four types of arc-Aβ((1-40)) fibrils were identified by TEM and STEM and their mass-per-length statistics were collected suggesting supramolecular structures with two, four and six β-sheet laminae. Our results suggest a pathway of fibrillogenesis for full-length Alzheimer's peptides with small and structurally ordered transient spherical aggregates as on-pathway immediate precursors of amyloid fibrils.
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Affiliation(s)
- Nils Norlin
- Chemistry of Interfaces, Luleå University of Technology, SE-971 87 Luleå, Sweden
| | - Magnus Hellberg
- Division of Physics, Luleå University of Technology, SE-971 87 Luleå, Sweden
| | - Andrei Filippov
- Chemistry of Interfaces, Luleå University of Technology, SE-971 87 Luleå, Sweden
- Department of Physics, Kazan State University, 420008, Kazan, Russia
| | - Alioscka A. Sousa
- Laboratory of Bioengineering and Physical Science, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892-5766, USA
| | - Gerhard Gröbner
- Department of Biological Chemistry, Institute of Chemistry, Umeå University, SE-90187, Umeå, Sweden
| | - Richard D. Leapman
- Laboratory of Bioengineering and Physical Science, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892-5766, USA
| | - Nils Almqvist
- Division of Physics, Luleå University of Technology, SE-971 87 Luleå, Sweden
| | - Oleg N. Antzutkin
- Chemistry of Interfaces, Luleå University of Technology, SE-971 87 Luleå, Sweden
- Department of Physics, Warwick University, Coventry, CV4 7AL, United Kingdom
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Zhao LN, Long H, Mu Y, Chew LY. The toxicity of amyloid β oligomers. Int J Mol Sci 2012; 13:7303-7327. [PMID: 22837695 PMCID: PMC3397527 DOI: 10.3390/ijms13067303] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Revised: 06/01/2012] [Accepted: 06/08/2012] [Indexed: 12/13/2022] Open
Abstract
In this review, we elucidate the mechanisms of Aβ oligomer toxicity which may contribute to Alzheimer's disease (AD). In particular, we discuss on the interaction of Aβ oligomers with the membrane through the process of adsorption and insertion. Such interaction gives rises to phase transitions in the sub-structures of the Aβ peptide from α-helical to β-sheet structure. By means of a coarse-grained model, we exhibit the tendency of β-sheet structures to aggregate, thus providing further insights to the process of membrane induced aggregation. We show that the aggregated oligomer causes membrane invagination, which is a precursor to the formation of pore structures and ion channels. Other pathological progressions to AD due to Aβ oligomers are also covered, such as their interaction with the membrane receptors, and their direct versus indirect effects on oxidative stress and intraneuronal accumulation. We further illustrate that the molecule curcumin is a potential Aβ toxicity inhibitor as a β-sheet breaker by having a high propensity to interact with certain Aβ residues without binding to them. The comprehensive understanding gained from these current researches on the various toxicity mechanisms show promises in the provision of better therapeutics and treatment strategies in the near future.
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Affiliation(s)
- Li Na Zhao
- School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, 637731, Singapore; E-Mails: (L.N.Z.); (H.W.L.)
| | - HonWai Long
- School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, 637731, Singapore; E-Mails: (L.N.Z.); (H.W.L.)
- High Performance Computing Centre, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore
| | - Yuguang Mu
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, 637551, Singapore
| | - Lock Yue Chew
- School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, 637731, Singapore; E-Mails: (L.N.Z.); (H.W.L.)
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Sheikh K, Giordani C, McManus JJ, Hovgaard MB, Jarvis SP. Differing modes of interaction between monomeric Aβ1–40 peptides and model lipid membranes: an AFM study. Chem Phys Lipids 2012; 165:142-50. [DOI: 10.1016/j.chemphyslip.2011.11.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2011] [Revised: 11/24/2011] [Accepted: 11/25/2011] [Indexed: 11/25/2022]
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Grasso G, Giuffrida ML, Rizzarelli E. Metallostasis and amyloid β-degrading enzymes. Metallomics 2012; 4:937-49. [DOI: 10.1039/c2mt20105d] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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39
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Kagan BL. Membrane pores in the pathogenesis of neurodegenerative disease. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2012; 107:295-325. [PMID: 22482454 DOI: 10.1016/b978-0-12-385883-2.00001-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The neurodegenerative diseases described in this volume, as well as many nonneurodegenerative diseases, are characterized by deposits known as amyloid. Amyloid has long been associated with these various diseases as a pathological marker and has been implicated directly in the molecular pathogenesis of disease. However, increasing evidence suggests that these proteinaceous Congo red staining deposits may not be toxic or destructive of tissue. Recent studies strongly implicate smaller aggregates of amyloid proteins as the toxic species underlying these neurodegenerative diseases. Despite the outward obvious differences among these clinical syndromes, there are some striking similarities in their molecular pathologies. These include dysregulation of intracellular calcium levels, impairment of mitochondrial function, and the ability of virtually all amyloid peptides to form ion-permeable pores in lipid membranes. Pore formation is enhanced by environmental factors that promote protein aggregation and is inhibited by agents, such as Congo red, which prevent aggregation. Remarkably, the pores formed by a variety of amyloid peptides from neurodegenerative and other diseases share a common set of physiologic properties. These include irreversible insertion of the pores in lipid membranes, formation of heterodisperse pore sizes, inhibition by Congo red of pore formation, blockade of pores by zinc, and a relative lack of ion selectivity and voltage dependence. Although there exists some information about the physical structure of these pores, molecular modeling suggests that 4-6-mer amyloid subunits may assemble into 24-mer pore-forming aggregates. The molecular structure of these pores may resemble the β-barrel structure of the toxics pore formed by bacterial toxins, such as staphylococcal α-hemolysin, anthrax toxin, and Clostridium perfringolysin.
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Affiliation(s)
- Bruce L Kagan
- Department of Psychiatry & Biobehavioral Sciences, David Geffen School of Medicine at UCLA, Semel Institute for Neuroscience and Human Behavior, Los Angeles, California, USA
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Mithu V, Sarkar B, Bhowmik D, Chandrakesan M, Maiti S, Madhu P. Zn(++) binding disrupts the Asp(23)-Lys(28) salt bridge without altering the hairpin-shaped cross-β Structure of Aβ(42) amyloid aggregates. Biophys J 2011; 101:2825-32. [PMID: 22261072 PMCID: PMC3297803 DOI: 10.1016/j.bpj.2011.10.023] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Revised: 10/06/2011] [Accepted: 10/12/2011] [Indexed: 11/16/2022] Open
Abstract
Observations like high Zn(2+) concentrations in senile plaques found in the brains of Alzheimer's patients and evidences emphasizing the role of Zn(2+) in amyloid-β (Aβ)-induced toxicity have triggered wide interest in understanding the nature of Zn(2+)-Aβ interaction. In vivo and in vitro studies have shown that aggregation kinetics, toxicity, and morphology of Aβ aggregates are perturbed in the presence of Zn(2+). Structural studies have revealed that Zn(2+) has a binding site in the N-terminal region of monomeric Aβ, but not much is precisely known about the nature of binding of Zn(2+) with aggregated forms of Aβ or its effect on the molecular structure of these aggregates. Here, we explore this aspect of the Zn(2+)-Aβ interaction using one- and two-dimensional (13)C and (15)N solid-state NMR. We find that Zn(2+) causes major structural changes in the N-terminal and the loop region connecting the two β-sheets. It breaks the salt bridge between the side chains of Asp(23) and Lys(28) by driving these residues into nonsalt-bridge-forming conformations. However, the cross-β structure of Aβ(42) aggregates remains unperturbed though the fibrillar morphology changes distinctly. We conclude that the salt bridge is not important for defining the characteristic molecular architecture of Aβ(42) but is significant for determining its fibrillar morphology and toxicity.
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Affiliation(s)
- Venus Singh Mithu
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai, India
| | - Bidyut Sarkar
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai, India
| | - Debanjan Bhowmik
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai, India
| | - Muralidharan Chandrakesan
- Department of Biochemistry, Seth Gordhandas Sunderdas Medical College and King Edward Memorial Hospital, Parel, Mumbai, India
| | - Sudipta Maiti
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai, India
| | - Perunthiruthy K. Madhu
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai, India
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Nag S, Chen J, Irudayaraj J, Maiti S. Measurement of the attachment and assembly of small amyloid-β oligomers on live cell membranes at physiological concentrations using single-molecule tools. Biophys J 2011; 99:1969-75. [PMID: 20858443 DOI: 10.1016/j.bpj.2010.07.020] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Revised: 06/22/2010] [Accepted: 07/09/2010] [Indexed: 01/11/2023] Open
Abstract
It is thought that the pathological cascade in Alzheimer's disease is initiated by the formation of amyloid-β (Aβ) peptide complexes on cell membranes. However, there is considerable debate about the nature of these complexes and the type of solution-phase Aβ aggregates that may contribute to their formation. Also, it is yet to be shown that Aβ attaches strongly to living cell membranes, and that this can happen at low, physiologically relevant Aβ concentrations. Here, we simultaneously measure the aggregate size and fluorescence lifetime of fluorescently labeled Aβ(1-40) on and above the membrane of cultured PC12 cells at near-physiological concentrations. We find that at 350 nM Aβ concentration, large (>>10 nm average hydrodynamic radius) assemblies of codiffusing, membrane-attached Aβ molecules appear on the cell membrane together with a near-monomeric species. When the extracellular concentration is 150 nM, the membrane contains only the smaller species, but with a similar degree of attachment. At both concentrations, the extracellular solution contains only small (∼2.3 nm average hydrodynamic radius) Aβ oligomers or monomers. We conclude that at near-physiological concentrations only the small oligomeric Aβ species are relevant, they are capable of attaching to the cell membrane, and they assemble in situ to form much larger complexes.
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Affiliation(s)
- Suman Nag
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai, India
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42
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Abstract
There has been a growing recognition of a wide variety of diseases commonly referred to as conformational diseases, which share the feature of specific disease-related proteins adopting nonnative conformation that promote their ordered aggregation and deposition on surfaces. Due to the nanoscale dimensions and the varied morphology of such aggregates, atomic force microscopy (AFM) has emerged as an ideal tool for distinguishing structural features of the numerous potential aggregate forms, ranging from small globular oligomers to large mature amyloid fibrils. Beyond the ability to morphologically distinguish aggregate forms, AFM also can dynamically track the aggregation process due to its unique ability to be operated not only in air (ex situ), but also in solution (in situ). This feature provides for tracking the fate of individual aggregates over time. This chapter describes the use of AFM in characterizing the aggregation of the amyloid-β peptide (Aβ), which is hypothesized to play a key role in Alzheimer's disease (AD), a late-onset neurodegenerative conformational disease.
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Affiliation(s)
- Justin Legleiter
- The C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, WV, USA
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Jang H, Arce FT, Ramachandran S, Capone R, Lal R, Nussinov R. β-Barrel topology of Alzheimer's β-amyloid ion channels. J Mol Biol 2010; 404:917-34. [PMID: 20970427 PMCID: PMC7291702 DOI: 10.1016/j.jmb.2010.10.025] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2010] [Revised: 10/06/2010] [Accepted: 10/15/2010] [Indexed: 11/19/2022]
Abstract
Emerging evidence supports the ion channel mechanism for Alzheimer's disease pathophysiology wherein small β-amyloid (Aβ) oligomers insert into the cell membrane, forming toxic ion channels and destabilizing the cellular ionic homeostasis. Solid-state NMR-based data of amyloid oligomers in solution indicate that they consist of a double-layered β-sheets where each monomer folds into β-strand-turn-β-strand and the monomers are stacked atop each other. In the membrane, Aβ peptides are proposed to be β-type structures. Experimental structural data available from atomic force microscopy (AFM) imaging of Aβ oligomers in membranes reveal heterogeneous channel morphologies. Previously, we modeled the channels in a non-tilted organization, parallel with the cross-membrane normal. Here, we modeled a β-barrel-like organization. β-Barrels are common in transmembrane toxin pores, typically consisting of a monomeric chain forming a pore, organized in a single-layered β-sheet with antiparallel β-strands and a right-handed twist. Our explicit solvent molecular dynamics simulations of a range of channel sizes and polymorphic turns and comparisons of these with AFM image dimensions support a β-barrel channel organization. Different from the transmembrane β-barrels where the monomers are folded into a circular β-sheet with antiparallel β-strands stabilized by the connecting loops, these Aβ barrels consist of multimeric chains forming double β-sheets with parallel β-strands, where the strands of each monomer are connected by a turn. Although the Aβ barrels adopt the right-handed β-sheet twist, the barrels still break into heterogeneous, loosely attached subunits, in good agreement with AFM images and previous modeling. The subunits appear mobile, allowing unregulated, hence toxic, ion flux.
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Affiliation(s)
- Hyunbum Jang
- Center for Cancer Research Nanobiology Program, SAIC-Frederick, Inc., National Cancer Institute-Frederick, Frederick, MD 21702, USA
| | - Fernando Teran Arce
- Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093, USA
- Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093, USA
| | - Srinivasan Ramachandran
- Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093, USA
- Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093, USA
| | - Ricardo Capone
- Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093, USA
- Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093, USA
| | - Ratnesh Lal
- Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093, USA
- Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093, USA
| | - Ruth Nussinov
- Center for Cancer Research Nanobiology Program, SAIC-Frederick, Inc., National Cancer Institute-Frederick, Frederick, MD 21702, USA
- Department of Human Molecular Genetics, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
- Department of Biochemistry, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
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Serem WK, Bett CK, Ngunjiri JN, Garno JC. Studies of the growth, evolution, and self-aggregation of β-amyloid fibrils using tapping-mode atomic force microscopy. Microsc Res Tech 2010; 74:699-708. [PMID: 21698718 DOI: 10.1002/jemt.20940] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2010] [Accepted: 08/22/2010] [Indexed: 11/08/2022]
Abstract
Amyloid peptide (Aβ) is the major protein component of plaques found in Alzheimer's disease, and the aggregation of Aβ into oligomeric and fibrillic assemblies has been shown to be an early event of the disease pathway. Visualization of the progressive evolution of nanoscale changes in the morphology of Aβ oligomeric assemblies and amyloid fibrils has been accomplished ex situ using atomic force microscopy (AFM) in ambient conditions. In this report, the size and the shape of amyloid β(1-40) fibrils, as well as the secondary organization into aggregate structures were monitored at different intervals over a period of 5 months. Characterizations with tapping-mode AFM serve to minimize the strong adhesive forces between the probe and the sample to prevent damage or displacement of fragile fibrils. The early stages of Aβ growth showed a predominance of spherical seed structures, oligomeric assemblies, and protofibrils; however the size and density of fibrils progressively increased with time. Within a few days of incubation, linear assemblies and fibrils became apparent. Over extended time scales of up to 5 months, the fibrils formed dense ensembles spanning lengths of several microns, which exhibit interesting changes due to self-organization of the fibrils into bundles or tangles. Detailed characterization of the Aβ assembly process at the nanoscale will help elucidate the role of Aβ in the pathology of Alzheimer's disease.
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Affiliation(s)
- Wilson K Serem
- Chemistry Department, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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Effect of trehalose on the interaction of Alzheimer's Aβ-peptide and anionic lipid monolayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:26-33. [PMID: 20920466 DOI: 10.1016/j.bbamem.2010.09.024] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2009] [Revised: 09/26/2010] [Accepted: 09/29/2010] [Indexed: 01/07/2023]
Abstract
The interaction of amyloid β-peptide (Aβ) with cell membranes is believed to play a central role in the pathogenesis of Alzheimer's disease. In particular, recent experimental evidence indicates that bilayer and monolayer membranes accelerate the aggregation and amyloid fibril formation rate of Aβ. Understanding that interaction could help develop therapeutic strategies for treatment of the disease. Trehalose, a disaccharide of glucose, has been shown to be effective in preventing the aggregation of numerous proteins. It has also been shown to delay the onset of certain amyloid-related diseases in a mouse model. Using Langmuir monolayers and molecular simulations of the corresponding system, we study several thermodynamic and kinetic aspects of the insertion of Aβ peptide into DPPG monolayers in water and trehalose subphases. In the water subphase, the insertion of the Aβ peptide into the monolayer exhibits a lag time which decreases with increasing temperature of the subphase. In the presence of trehalose, the lag time is completely eliminated and peptide insertion is completed within a shorter time period compared to that observed in pure water. Molecular simulations show that more peptide is inserted into the monolayer in the water subphase, and that such insertion is deeper. The peptide at the monolayer interface orients itself parallel to the monolayer, while it inserts with an angle of 50° in the trehalose subphase. Simulations also show that trehalose reduces the conformational change that the peptide undergoes when it inserts into the monolayer. This observation helps explain the experimentally observed elimination of the lag time by trehalose and the temperature dependence of the lag time in the water subphase.
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46
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Jang H, Teran Arce F, Ramachandran S, Capone R, Lal R, Nussinov R. Structural convergence among diverse, toxic beta-sheet ion channels. J Phys Chem B 2010; 114:9445-51. [PMID: 20608696 PMCID: PMC2908347 DOI: 10.1021/jp104073k] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2010] [Revised: 06/22/2010] [Indexed: 12/11/2022]
Abstract
Recent studies show that an array of beta-sheet peptides, including N-terminally truncated Abeta peptides (Abeta(11-42/17-42)), K3 (a beta(2)-microglobulin fragment), and protegrin-1 (PG-1) peptides form ion channel-like structures and elicit single channel ion conductance when reconstituted in lipid bilayers and induce cell damage through cell calcium overload. Striking similarities are observed in the dimensions of these toxic channels irrespective of their amino acid sequences. However, the intriguing question of preferred channel sizes is still unresolved. Here, exploiting ssNMR-based, U-shaped, beta-strand-turn-beta-strand coordinates, we modeled truncated Abeta peptide (p3) channels with different sizes (12- to 36-mer). Molecular dynamics (MD) simulations show that optimal channel sizes of the ion channels presenting toxic ionic flux range between 16- and 24-mer. This observation is in good agreement with channel dimensions imaged by AFM for Abeta(9-42), K3 fragment, and PG-1 channels and highlights the bilayer-supported preferred toxic beta-channel sizes and organization, regardless of the peptide sequence.
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Affiliation(s)
| | | | | | | | - Ratnesh Lal
- Corresponding authors. (R.N.) Phone: 301-846-5579. Fax: 301-846-5598. E-mail: . (R.L.) E-mail:
| | - Ruth Nussinov
- Corresponding authors. (R.N.) Phone: 301-846-5579. Fax: 301-846-5598. E-mail: . (R.L.) E-mail:
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Murakami K, Masuda Y, Shirasawa T, Shimizu T, Irie K. The turn formation at positions 22 and 23 in the 42-mer amyloid β peptide: The emerging role in the pathogenesis of Alzheimer's disease. Geriatr Gerontol Int 2010; 10 Suppl 1:S169-79. [DOI: 10.1111/j.1447-0594.2010.00598.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Membrane biophysics and mechanics in Alzheimer's disease. Mol Neurobiol 2010; 41:138-48. [PMID: 20437210 DOI: 10.1007/s12035-010-8121-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2009] [Accepted: 03/17/2010] [Indexed: 12/12/2022]
Abstract
Alzheimer's disease is a chronic neurodegenerative disorder characterized by neuronal loss, cerebrovascular inflammation, and accumulation of senile plaques in the brain parenchyma and cerebral blood vessels. Amyloid-beta peptide (Abeta), a major component of senile plaques, has been shown to exert multiple toxic effects to neurons, astrocytes, glial cells, and brain endothelium. Oligomeric Abeta can disturb the structure and function of cell membranes and alter membrane mechanical properties, such as membrane fluidity and molecular order. Much of these effects are attributed to their capability to trigger oxidative stress and inflammation. In this review, we discuss the effects of Abeta on neuronal cells, astrocytes, and cerebral endothelial cells with special emphasis on cell membrane properties and cell functions.
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Jang H, Arce FT, Ramachandran S, Capone R, Azimova R, Kagan BL, Nussinov R, Lal R. Truncated beta-amyloid peptide channels provide an alternative mechanism for Alzheimer's Disease and Down syndrome. Proc Natl Acad Sci U S A 2010; 107:6538-43. [PMID: 20308552 PMCID: PMC2851998 DOI: 10.1073/pnas.0914251107] [Citation(s) in RCA: 186] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Full-length amyloid beta peptides (Abeta(1-40/42)) form neuritic amyloid plaques in Alzheimer's disease (AD) patients and are implicated in AD pathology. However, recent transgenic animal models cast doubt on their direct role in AD pathology. Nonamyloidogenic truncated amyloid-beta fragments (Abeta(11-42) and Abeta(17-42)) are also found in amyloid plaques of AD and in the preamyloid lesions of Down syndrome, a model system for early-onset AD study. Very little is known about the structure and activity of these smaller peptides, although they could be the primary AD and Down syndrome pathological agents. Using complementary techniques of molecular dynamics simulations, atomic force microscopy, channel conductance measurements, calcium imaging, neuritic degeneration, and cell death assays, we show that nonamyloidogenic Abeta(9-42) and Abeta(17-42) peptides form ion channels with loosely attached subunits and elicit single-channel conductances. The subunits appear mobile, suggesting insertion of small oligomers, followed by dynamic channel assembly and dissociation. These channels allow calcium uptake in amyloid precursor protein-deficient cells. The channel mediated calcium uptake induces neurite degeneration in human cortical neurons. Channel conductance, calcium uptake, and neurite degeneration are selectively inhibited by zinc, a blocker of amyloid ion channel activity. Thus, truncated Abeta fragments could account for undefined roles played by full length Abetas and provide a unique mechanism of AD and Down syndrome pathologies. The toxicity of nonamyloidogenic peptides via an ion channel mechanism necessitates a reevaluation of the current therapeutic approaches targeting the nonamyloidogenic pathway as avenue for AD treatment.
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Affiliation(s)
- Hyunbum Jang
- Center for Cancer Research Nanobiology Program, SAIC-Frederick, Inc., National Cancer Institute, Frederick, MD 21702
| | - Fernando Teran Arce
- Center for Nanomedicine and Department of Medicine, University of Chicago, Chicago, IL 60637
| | - Srinivasan Ramachandran
- Center for Nanomedicine and Department of Medicine, University of Chicago, Chicago, IL 60637
| | - Ricardo Capone
- Center for Nanomedicine and Department of Medicine, University of Chicago, Chicago, IL 60637
| | - Rushana Azimova
- Semel Neuropsychiatric Institute, The David Geffen School of Medicine, University of California at Los Angeles and Greater Los Angeles Veterans Administration Health System, Los Angeles, CA 90024; and
| | - Bruce L. Kagan
- Semel Neuropsychiatric Institute, The David Geffen School of Medicine, University of California at Los Angeles and Greater Los Angeles Veterans Administration Health System, Los Angeles, CA 90024; and
| | - Ruth Nussinov
- Center for Cancer Research Nanobiology Program, SAIC-Frederick, Inc., National Cancer Institute, Frederick, MD 21702
- Department of Human Molecular Genetics and Biochemistry, The Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
| | - Ratnesh Lal
- Center for Nanomedicine and Department of Medicine, University of Chicago, Chicago, IL 60637
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Jang H, Arce FT, Capone R, Ramachandran S, Lal R, Nussinov R. Misfolded amyloid ion channels present mobile beta-sheet subunits in contrast to conventional ion channels. Biophys J 2010; 97:3029-37. [PMID: 19948133 DOI: 10.1016/j.bpj.2009.09.014] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2009] [Revised: 08/31/2009] [Accepted: 09/10/2009] [Indexed: 02/05/2023] Open
Abstract
In Alzheimer's disease, calcium permeability through cellular membranes appears to underlie neuronal cell death. It is increasingly accepted that calcium permeability involves toxic ion channels. We modeled Alzheimer's disease ion channels of different sizes (12-mer to 36-mer) in the lipid bilayer using molecular dynamics simulations. Our Abeta channels consist of the solid-state NMR-based U-shaped beta-strand-turn-beta-strand motif. In the simulations we obtain ion-permeable channels whose subunit morphologies and shapes are consistent with electron microscopy/atomic force microscopy. In agreement with imaged channels, the simulations indicate that beta-sheet channels break into loosely associated mobile beta-sheet subunits. The preferred channel sizes (16- to 24-mer) are compatible with electron microscopy/atomic force microscopy-derived dimensions. Mobile subunits were also observed for beta-sheet channels formed by cytolytic PG-1 beta-hairpins. The emerging picture from our large-scale simulations is that toxic ion channels formed by beta-sheets spontaneously break into loosely interacting dynamic units that associate and dissociate leading to toxic ionic flux. This sharply contrasts intact conventional gated ion channels that consist of tightly interacting alpha-helices that robustly prevent ion leakage, rather than hydrogen-bonded beta-strands. The simulations suggest why conventional gated channels evolved to consist of interacting alpha-helices rather than hydrogen-bonded beta-strands that tend to break in fluidic bilayers. Nature designs folded channels but not misfolded toxic channels.
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Affiliation(s)
- Hyunbum Jang
- Center for Cancer Research Nanobiology Program, NCI-Frederick, SAIC-Frederick, Frederick, Maryland, USA.
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