1
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Mondal S, Karmakar T. Insights into the mechanism of peptide fibril growth on gold surface. Biophys Chem 2024; 310:107237. [PMID: 38640598 DOI: 10.1016/j.bpc.2024.107237] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2024] [Revised: 03/24/2024] [Accepted: 04/10/2024] [Indexed: 04/21/2024]
Abstract
Understanding the formation of β-fibrils over the gold surface is of paramount interest in nano-bio-medicinal Chemistry. The intricate mechanism of self-assembly of neurofibrillogenic peptides and their growth over the gold surface remains elusive, as experiments are limited in unveiling the microscopic dynamic details, in particular, at the early stage of the peptide aggregation. In this work, we carried out equilibrium molecular dynamics and enhanced sampling simulations to elucidate the underlying mechanism of the growth of an amyloid-forming sequence of tau fragments over the gold surface. Our results disclose that the collective intermolecular interactions between the peptide chains and peptides with the gold surface facilitate the peptide adsorption, followed by integration, finally leading to the fibril formation.
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Affiliation(s)
- Soumya Mondal
- Department of Chemistry, Indian Institute of Technology, Delhi, New Delhi 110016, Delhi, India
| | - Tarak Karmakar
- Department of Chemistry, Indian Institute of Technology, Delhi, New Delhi 110016, Delhi, India.
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2
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Zhang R, Jalali S, Dias CL, Haataja MP. Growth kinetics of amyloid-like fibrils: An integrated atomistic simulation and continuum theory approach. PNAS NEXUS 2024; 3:pgae045. [PMID: 38725528 PMCID: PMC11079572 DOI: 10.1093/pnasnexus/pgae045] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Accepted: 01/19/2024] [Indexed: 05/12/2024]
Abstract
Amyloid fibrils have long been associated with many neurodegenerative diseases. The conventional picture of the formation and proliferation of fibrils from unfolded proteins comprises primary and secondary nucleation of oligomers followed by elongation and fragmentation thereof. In this work, we first employ extensive all-atom molecular dynamics (MD) simulations of short peptides to investigate the governing processes of fibril growth at the molecular scale. We observe that the peptides in the bulk solution can bind onto and subsequently diffuse along the fibril surface, which leads to fibril elongation via either bulk- or surface-mediated docking mechanisms. Then, to guide the quantitative interpretation of these observations and to provide a more comprehensive picture of the growth kinetics of single fibrils, a continuum model which incorporates the key processes observed in the MD simulations is formulated. The model is employed to investigate how relevant physical parameters affect the kinetics of fibril growth and identify distinct growth regimes. In particular, it is shown that fibrils which strongly bind peptides may undergo a transient exponential growth phase in which the entire fibril surface effectively acts as a sink for peptides. We also demonstrate how the relevant model parameters can be estimated from the MD trajectories. Our results provide compelling evidence that the overall fibril growth rates are determined by both bulk and surface peptide fluxes, thereby contributing to a more fundamental understanding of the growth kinetics of amyloid-like fibrils.
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Affiliation(s)
- Ruoyao Zhang
- Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA
| | - Sharareh Jalali
- Department of Physics, New Jersey Institute of Technology, Newark, NJ 07102, USA
| | - Cristiano Luis Dias
- Department of Physics, New Jersey Institute of Technology, Newark, NJ 07102, USA
| | - Mikko P Haataja
- Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA
- Princeton Materials Institute, Princeton University, Princeton, NJ 08544, USA
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3
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Yokoyama K, Barbour E, Hirschkind R, Martinez Hernandez B, Hausrath K, Lam T. Protein Corona Formation and Aggregation of Amyloid β 1-40-Coated Gold Nanocolloids. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:1728-1746. [PMID: 38194428 DOI: 10.1021/acs.langmuir.3c02923] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2024]
Abstract
Amyloid fibrillogenesis is a pathogenic protein aggregation process that occurs through a highly ordered process of protein-protein interactions. To better understand the protein-protein interactions involved in amyloid fibril formation, we formed nanogold colloid aggregates by stepwise additions of ∼2 nmol of amyloid β 1-40 peptide (Aβ1-40) at pH ∼3.7 and ∼25 °C. The processes of protein corona formation and building of gold colloid [diameters (d) of 20 and 80 nm] aggregates were confirmed by a red-shift of the surface plasmon resonance (SPR) band, λpeak, as the number of Aβ1-40 peptides [N(Aβ1-40)] increased. The normalized red-shift of λpeak, Δλ, was correlated with the degree of protein aggregation, and this process was approximated as the adsorption isotherm explained by the Langmuir-Freundlich model. As the coverage fraction (θ) was analyzed as a function of ϕ, which is the N(Aβ1-40) per total surface area of nanogold colloids available for adsorption, the parameters for explaining the Langmuir-Freundlich model were in good agreement for both 20 and 80 nm gold, indicating that ϕ could define the stage of the aggregation process. Surface-enhanced Raman scattering (SERS) imaging was conducted at designated values of ϕ and suggested that a protein-gold surface interaction during the initial adsorption stage may be dependent on the nanosize. The 20 nm gold case seems to prefer a relatively smaller contacting section, such as a -C-N or C═C bond, but a plane of the benzene ring may play a significant role for 80 nm gold. Regardless of the size of the particles, the β-sheet and random coil conformations were considered to be used to form gold colloid aggregates. The methodology developed in this study allows for new insights into protein-protein interactions at distinct stages of aggregation.
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Affiliation(s)
- Kazushige Yokoyama
- Department of Chemistry, The State University of New York Geneseo College, 1 College Circle, Geneseo, New York 14454, United States
| | - Eli Barbour
- Department of Chemistry, The State University of New York Geneseo College, 1 College Circle, Geneseo, New York 14454, United States
| | - Rachel Hirschkind
- Department of Chemistry, The State University of New York Geneseo College, 1 College Circle, Geneseo, New York 14454, United States
| | - Bryan Martinez Hernandez
- Department of Chemistry, The State University of New York Geneseo College, 1 College Circle, Geneseo, New York 14454, United States
| | - Kaylee Hausrath
- Department of Chemistry, The State University of New York Geneseo College, 1 College Circle, Geneseo, New York 14454, United States
| | - Theresa Lam
- Department of Chemistry, The State University of New York Geneseo College, 1 College Circle, Geneseo, New York 14454, United States
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4
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Huang G, Tang H, Liu Y, Zhang C, Ke PC, Sun Y, Ding F. Direct Observation of Seeded Conformational Conversion of hIAPP In Silico Reveals the Mechanisms for Morphological Dependence and Asymmetry of Fibril Growth. J Chem Inf Model 2023; 63:5863-5873. [PMID: 37651616 PMCID: PMC10529695 DOI: 10.1021/acs.jcim.3c00898] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
Abstract
Rapid growth of amyloid fibrils via a seeded conformational conversion of monomers is a critical step of fibrillization and important for disease transmission and progression. Amyloid fibrils often display diverse morphologies with distinct populations, and yet the molecular mechanisms of fibril elongation and their corresponding morphological dependence remain poorly understood. Here, we computationally investigated the single-molecular growth of two experimentally resolved human islet amyloid polypeptide fibrils of different morphologies. In both cases, the incorporation of monomers into preformed fibrils was observed. The conformational conversion dynamics was characterized by a small number of fibril growth intermediates. Fibril morphology affected monomer binding at fibril elongation and lateral surfaces as well as the seeded conformational conversion dynamics at the fibril ends, resulting in different fibril elongation rates and populations. We also observed an asymmetric fibril growth as in our prior experiments, attributing to differences of two fibril ends in terms of their local surface curvatures and exposed hydrogen-bond donors and acceptors. Together, our mechanistic findings afforded a theoretical basis for delineating different amyloid strains-entailed divergent disease progression.
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Affiliation(s)
- Gangtong Huang
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, United States
| | - Huayuan Tang
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, United States
| | - Yuying Liu
- School of Physical Science and Technology, Ningbo University, Ningbo 315211, China
| | - Chi Zhang
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, United States
| | - Pu Chun Ke
- The Nanomedicine Center, The Great Bay Area National Institute for Nanotechnology Innovation, 136 Kaiyuan Avenue, Guangzhou, 510700, China
- Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, 381 Royal Parade, Parkville, VIC 3052, Australia
| | - Yunxiang Sun
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, United States
- School of Physical Science and Technology, Ningbo University, Ningbo 315211, China
| | - Feng Ding
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, United States
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5
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Dey P, Biswas P. Exploring the aggregation of amyloid-β 42 through Monte Carlo simulations. Biophys Chem 2023; 297:107011. [PMID: 37037120 DOI: 10.1016/j.bpc.2023.107011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Revised: 03/25/2023] [Accepted: 03/26/2023] [Indexed: 04/09/2023]
Abstract
Coarse-grained Monte Carlo simulations are performed for a disordered protein, amyloid-β 42 to identify the interactions and understand the mechanism of its aggregation. A statistical potential is developed from a selected dataset of intrinsically disordered proteins, which accounts for the respective contributions of the bonded and non-bonded potentials. While, the bonded potential comprises the bond, bend, and dihedral constraints, the nonbonded interactions include van der Waals interactions, hydrogen bonds, and the two-body potential. The two-body potential captures the features of both hydrophobic and electrostatic interactions that brings the chains at a contact distance, while the repulsive van der Waals interactions prevent them from a collapse. Increased two-body hydrophobic interactions facilitate the formation of amorphous aggregates rather than the fibrillar ones. The formation of aggregates is validated from the interchain distances, and the total energy of the system. The aggregate is structurally characterized by the root-mean-square deviation, root-mean-square fluctuation and the radius of gyration. The aggregates are characterized by a decrease in SASA, an increase in the non-local interactions and a distinct free energy minimum relative to that of the monomeric state of amyloid-β 42. The hydrophobic residues help in nucleation, while the charged residues help in oligomerization and aggregation.
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6
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Arsiccio A, Liu X, Ganguly P, Buratto SK, Bowers MT, Shea JE. Effect of Cosolutes on the Aggregation of a Tau Fragment: A Combined Experimental and Simulation Approach. J Phys Chem B 2023; 127:4022-4031. [PMID: 37129599 DOI: 10.1021/acs.jpcb.3c00433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The intrinsically disordered protein Tau represents the main component of neurofibrillary tangles that are a hallmark of Alzheimer's disease. A small fragment of Tau, known as paired helical filament 6 (PHF6), is considered to be important for the formation of the β-structure core of the fibrils. Here we study the aggregation of this fragment in the presence of different cosolutes, including urea, TMAO, sucrose and 2-hydroxypropyl-β-cyclodextrin (2-HPβCD), using both experiments and molecular dynamics simulations. A novel implicit solvation approach (MIST - Model with Implicit Solvation Thermodynamics) is used, where an energetic contribution based on the concept of transfer free energies describes the effect of the cosolutes. The simulation predictions are compared to thioflavin-T and atomic force microscopy results, and the good agreement observed confirms the predictive ability of the computational approach herein proposed. Both simulations and experiments indicate that PHF6 aggregation is inhibited in the presence of urea and 2-HPβCD, while TMAO and sucrose stabilize associated conformations. The remarkable ability of HPβCD to inhibit aggregation represents an extremely promising result for future applications, especially considering the widespread use of this molecule as a drug carrier to the brain and as a solubilizer/excipient in pharmaceutical formulations.
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Affiliation(s)
- Andrea Arsiccio
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - Xikun Liu
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - Pritam Ganguly
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - Steven K Buratto
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - Michael T Bowers
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - Joan-Emma Shea
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
- Department of Physics, University of California, Santa Barbara, California 93106, United States
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7
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Mondal S, Ghanta KP, Bandyopadhyay S. Microscopic Understanding of the Conformational Stability of the Aggregated Nonamyloid β Components of α-Synuclein. J Chem Inf Model 2023; 63:1542-1555. [PMID: 36866721 DOI: 10.1021/acs.jcim.2c01540] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/04/2023]
Abstract
Self-association of α-synuclein peptides into oligomeric species and ordered amyloid fibrils is associated with Parkinson's disease, a progressive neurodegenerative disorder. In particular, the peptide domain formed between the residues Glu-61 (or E61) and Val-95 (or V95) of α-synuclein, typically termed the "nonamyloid β component" (NAC), is known to play critical roles in forming aggregated structures. In this work, we have employed molecular dynamics simulations to explore the conformational properties and relative stabilities of aggregated protofilaments of different orders, namely, tetramer (P(4)), hexamer (P(6)), octamer (P(8)), decamer (P(10)), dodecamer (P(12)), and tetradecamer (P(14)), formed by the NAC domains of α-synuclein. Besides, center-of-mass pulling and umbrella sampling simulation methods have also been employed to characterize the mechanistic pathway of peptide association/dissociation and the corresponding free energy profiles. Structural analysis showed that the disordered C-terminal loop and the central core regions of the peptide units lead to more flexible and distorted structures of the lower order protofilaments (P(4) and P(6)) as compared to the higher order ones. Interestingly, our calculation shows the presence of multiple distinctly populated conformational states for the lower order protofilament P(4), which may drive the oligomerization process along multiple pathways to form different polymorphic α-synuclein fibrillar structures. It is further observed that the nonpolar interaction between the peptides and the corresponding nonpolar solvation free energy play a dominant role in stabilizing the aggregated protofilaments. Importantly, our result showed that reduced cooperativity during the binding of a peptide unit beyond a critical size of the protofilament (P(12)) leads to less favorable binding free energy of a peptide.
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Affiliation(s)
- Souvik Mondal
- Molecular Modeling Laboratory, Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India
| | - Krishna Prasad Ghanta
- Molecular Modeling Laboratory, Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India
| | - Sanjoy Bandyopadhyay
- Molecular Modeling Laboratory, Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India
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8
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Qu W, Zhang L, Liang X, Yu Z, Huang H, Zhao J, Guo Y, Zhou X, Xu S, Luo H, Luo X. Elevated Plasma Oligomeric Amyloid β-42 Is Associated with Cognitive Impairments in Cerebral Small Vessel Disease. BIOSENSORS 2023; 13:bios13010110. [PMID: 36671945 PMCID: PMC9855662 DOI: 10.3390/bios13010110] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 01/02/2023] [Accepted: 01/03/2023] [Indexed: 05/31/2023]
Abstract
Due to the heterogeneity of amyloid β-42 (Aβ42) species, the potential correlation between plasma oligomeric Aβ42 (oAβ42) and cognitive impairments in cerebral small vessel disease (CSVD) remains unclear. Herein, a sandwich ELISA for the specific detection of Aβ42 oligomers (oAβ42) and total Aβ42 (tAβ42) was developed based on sequence- and conformation-specific antibody pairs for the evaluation of plasma samples from a Chinese CSVD community cohort. After age and gender matching, 3-Tesla magnetic resonance imaging and multidimensional cognitive assessment were conducted in 134 CSVD patients and equal controls. The results showed that plasma tAβ42 and oAβ42 levels were significantly elevated in CSVD patients. By regression analysis, these elevations were correlated with the presence of CSVD and its imaging markers (i.e., white matter hyperintensities). Plasma Aβ42 tests further strengthened the predictive power of vascular risk factors for the presence of CSVD. Relative to tAβ42, oAβ42 showed a closer correlation with memory domains evaluated by neuropsychological tests. In conclusion, this sensitive ELISA protocol facilitated the detection of plasma Aβ42; Aβ42, especially its oligomeric form, can serve as a biosensor for the presence of CSVD and associated cognitive impairments represented by memory domains.
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Affiliation(s)
- Wensheng Qu
- Neurological Department, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
- Hubei Key Laboratory of Neural Injury and Functional Reconstruction, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Liding Zhang
- Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430070, China
- MoE Key Laboratory for Biomedical Photonics, School of Engineering Sciences, Huazhong University of Science and Technology, Wuhan 430070, China
| | - Xiaohan Liang
- Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430070, China
- MoE Key Laboratory for Biomedical Photonics, School of Engineering Sciences, Huazhong University of Science and Technology, Wuhan 430070, China
| | - Zhiyuan Yu
- Neurological Department, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
- Hubei Key Laboratory of Neural Injury and Functional Reconstruction, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Hao Huang
- Neurological Department, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
- Hubei Key Laboratory of Neural Injury and Functional Reconstruction, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Jing Zhao
- Neurological Department, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Yinping Guo
- Neurological Department, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Xirui Zhou
- Neurological Department, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Shabei Xu
- Neurological Department, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
- Hubei Key Laboratory of Neural Injury and Functional Reconstruction, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Haiming Luo
- Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430070, China
- MoE Key Laboratory for Biomedical Photonics, School of Engineering Sciences, Huazhong University of Science and Technology, Wuhan 430070, China
| | - Xiang Luo
- Neurological Department, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
- Hubei Key Laboratory of Neural Injury and Functional Reconstruction, Huazhong University of Science and Technology, Wuhan 430030, China
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9
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Abstract
It is known that oligomers of amyloid-β (Aβ) peptide are associated with Alzheimer's disease. Aβ has two isoforms: Aβ40 and Aβ42. Although the difference between Aβ40 and Aβ42 is only two additional C-terminal residues, Aβ42 aggregates much faster than Aβ40. It is unknown what role the C-terminal two residues play in accelerating aggregation. Since Aβ42 is more toxic than Aβ40, its oligomerization process needs to be clarified. Moreover, clarifying the differences between the oligomerization processes of Aβ40 and Aβ42 is essential to elucidate the key factors of oligomerization. Therefore, to investigate the dimerization process, which is the early oligomerization process, Hamiltonian replica-permutation molecular dynamics simulations were performed for Aβ40 and Aβ42. We identified a key residue, Arg5, for the Aβ42 dimerization. The two additional residues in Aβ42 allow the C-terminus to form contact with Arg5 because of the electrostatic attraction between them, and this contact stabilizes the β-hairpin. This β-hairpin promotes dimer formation through the intermolecular β-bridges. Thus, we examined the effects of amino acid substitutions of Arg5, thereby confirming that the mutations remarkably suppressed the aggregation of Aβ42. Moreover, the mutations of Arg5 suppressed the Aβ40 aggregation. It was found by analyzing the simulations that Arg5 is important for Aβ40 to form intermolecular contacts. Thus, it was clarified that the role of Arg5 in the oligomerization process varies due to the two additional C-terminal residues.
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Affiliation(s)
- Satoru
G. Itoh
- Institute
for Molecular Science, National Institutes
of Natural Sciences, Okazaki, Aichi 444-8787, Japan,Exploratory
Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan,Department
of Structural Molecular Science, SOKENDAI
(The Graduate University for Advanced Studies), Okazaki, Aichi 444-8787, Japan
| | - Maho Yagi-Utsumi
- Institute
for Molecular Science, National Institutes
of Natural Sciences, Okazaki, Aichi 444-8787, Japan,Exploratory
Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan,Department
of Functional Molecular Science, SOKENDAI
(The Graduate University for Advanced Studies), Okazaki, Aichi 444-8787, Japan,Graduate
School of Pharmaceutical Sciences, Nagoya
City University, Nagoya, Aichi 465-8603, Japan
| | - Koichi Kato
- Institute
for Molecular Science, National Institutes
of Natural Sciences, Okazaki, Aichi 444-8787, Japan,Exploratory
Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan,Department
of Functional Molecular Science, SOKENDAI
(The Graduate University for Advanced Studies), Okazaki, Aichi 444-8787, Japan,Graduate
School of Pharmaceutical Sciences, Nagoya
City University, Nagoya, Aichi 465-8603, Japan
| | - Hisashi Okumura
- Institute
for Molecular Science, National Institutes
of Natural Sciences, Okazaki, Aichi 444-8787, Japan,Exploratory
Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan,Department
of Structural Molecular Science, SOKENDAI
(The Graduate University for Advanced Studies), Okazaki, Aichi 444-8787, Japan,
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10
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Kumar H, Udgaonkar JB. Elongation of Fibrils Formed by a Tau Fragment is Inhibited by a Transient Dimeric Intermediate. J Phys Chem B 2022; 126:3385-3397. [PMID: 35503811 DOI: 10.1021/acs.jpcb.1c10752] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The formation and propagation of aggregates of the tau protein in the brain are associated with the tauopathy group of neurodegenerative diseases. Different tauopathies have been shown to be associated with structurally distinct aggregates of tau. However, the mechanism by which different structural folds arise remains poorly understood. In this study of fibril formation by the fragment tau-K18 of tau, it is shown that the Lys 280 → Glu mutation in the variant tau-K18 K280E forms fibrils that are morphologically distinct from those formed by wild-type (wt) tau-K18. The mutant fibrils appear to have two protofilaments twisted around each other, whereas the wt fibrils are straight and appear to have a single protofilament. Modeling the kinetics of seeded aggregation, using a simple Michaelis-Menten-like mechanism, reveals that the two morphologically distinct fibrils are elongated with different catalytic efficiencies. Surprisingly, when the elongation of monomeric tau-K18 is seeded with tau-K18 K280E fibrils, it is seen to be inhibited at high monomer concentrations. Such inhibition is not seen when elongation is seeded with tau-K18 fibrils. The mechanism of inhibition is shown to be describable as uncompetitive inhibition, in which a transient dimeric form of tau-K18 acts as an uncompetitive inhibitor. Importantly, a dimeric form of tau-K18 is seen to be populated to a detectable extent early during aggregation. A covalently linked tau dimer, with an inter-molecular disulphide linkage, is shown to be capable of acting as an inhibitor. In summary, a quantitative kinetic approach has provided an understanding of how the formation of distinct structural folds of tau fibrils can be modulated by mutation and how the elongation of one fibril type, but not the other, is inhibited by a transiently formed dimer.
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Affiliation(s)
- Harish Kumar
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560065, India
| | - Jayant B Udgaonkar
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560065, India.,Indian Institute of Science Education and Research, Pune 411008, India
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11
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Molecular Dynamics Simulation Studies on the Aggregation of Amyloid-β Peptides and Their Disaggregation by Ultrasonic Wave and Infrared Laser Irradiation. Molecules 2022; 27:molecules27082483. [PMID: 35458686 PMCID: PMC9030874 DOI: 10.3390/molecules27082483] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Revised: 03/29/2022] [Accepted: 04/07/2022] [Indexed: 01/02/2023] Open
Abstract
Alzheimer’s disease is understood to be caused by amyloid fibrils and oligomers formed by aggregated amyloid-β (Aβ) peptides. This review article presents molecular dynamics (MD) simulation studies of Aβ peptides and Aβ fragments on their aggregation, aggregation inhibition, amyloid fibril conformations in equilibrium, and disruption of the amyloid fibril by ultrasonic wave and infrared laser irradiation. In the aggregation of Aβ, a β-hairpin structure promotes the formation of intermolecular β-sheet structures. Aβ peptides tend to exist at hydrophilic/hydrophobic interfaces and form more β-hairpin structures than in bulk water. These facts are the reasons why the aggregation is accelerated at the interface. We also explain how polyphenols, which are attracting attention as aggregation inhibitors of Aβ peptides, interact with Aβ. An MD simulation study of the Aβ amyloid fibrils in equilibrium is also presented: the Aβ amyloid fibril has a different structure at one end from that at the other end. The amyloid fibrils can be destroyed by ultrasonic wave and infrared laser irradiation. The molecular mechanisms of these amyloid fibril disruptions are also explained, particularly focusing on the function of water molecules. Finally, we discuss the prospects for developing treatments for Alzheimer’s disease using MD simulations.
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12
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Xie H, Rojas A, Maisuradze GG, Khelashvili G. Mechanistic Kinetic Model Reveals How Amyloidogenic Hydrophobic Patches Facilitate the Amyloid-β Fibril Elongation. ACS Chem Neurosci 2022; 13:987-1001. [PMID: 35258946 PMCID: PMC8986627 DOI: 10.1021/acschemneuro.1c00801] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Abnormal aggregation of amyloid β (Aβ) peptides into fibrils plays a critical role in the development of Alzheimer's disease. A two-stage "dock-lock" model has been proposed for the Aβ fibril elongation process. However, the mechanisms of the Aβ monomer-fibril binding process have not been elucidated with the necessary molecular-level precision, so it remains unclear how the lock phase dynamics leads to the overall in-register binding of the Aβ monomer onto the fibril. To gain mechanistic insights into this critical step during the fibril elongation process, we used molecular dynamics (MD) simulations with a physics-based coarse-grained UNited-RESidue (UNRES) force field and sampled extensively the dynamics of the lock phase process, in which a fibril-bound Aβ(9-40) peptide rearranged to establish the native docking conformation. Analysis of the MD trajectories with Markov state models was used to quantify the kinetics of the rearrangement process and the most probable pathways leading to the overall native docking conformation of the incoming peptide. These revealed a key intermediate state in which an intra-monomer hairpin is formed between the central core amyloidogenic patch 18VFFA21 and the C-terminal hydrophobic patch 34LMVG37. This hairpin structure is highly favored as a transition state during the lock phase of the fibril elongation. We propose a molecular mechanism for facilitation of the Aβ fibril elongation by amyloidogenic hydrophobic patches.
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Affiliation(s)
- Hengyi Xie
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, New York 10065, United States
| | - Ana Rojas
- Schrödinger, Inc., 1540 Broadway, 24th Floor, New York, New York 10036, United States
| | - Gia G. Maisuradze
- Baker Laboratory of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, New York 10065, United States
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13
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Sakae Y, Kawasaki T, Okamoto Y. Distribution and Structure Analysis of Fibril-Forming Peptides Focusing on Concentration Dependency. ACS OMEGA 2022; 7:10012-10021. [PMID: 35382341 PMCID: PMC8975544 DOI: 10.1021/acsomega.1c04960] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Accepted: 02/09/2022] [Indexed: 06/14/2023]
Abstract
We focus on the concentration dependency of fibril-forming peptides, which have the potential of aggregation by themselves. In this study, we performed replica-exchange molecular dynamics simulations of Lys-Phe-Phe-Glu (KFFE) fragments, which are known to form fibrils in experiments under different concentration environments. The analysis by static structure factors suggested that the density fluctuation of the KFFE fragments becomes large as the concentration increases. It was also found that the number of β-structures and oligomers also increases under a high concentration environment. Hence, a high concentration environment of fibril-forming peptides is likely to cause protein aggregation.
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Affiliation(s)
- Yoshitake Sakae
- Research
Organization for Information Science and Technology, Tokyo 105-0013, Japan
- Department
of Physics, Graduate School of Science, Nagoya University, Nagoya, Aichi 464-8602, Japan
| | - Takeshi Kawasaki
- Department
of Physics, Graduate School of Science, Nagoya University, Nagoya, Aichi 464-8602, Japan
| | - Yuko Okamoto
- Department
of Physics, Graduate School of Science, Nagoya University, Nagoya, Aichi 464-8602, Japan
- Information
Technology Center, Nagoya University, Nagoya, Aichi 464-8601, Japan
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14
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Watanabe-Nakayama T, Ono K. Single-molecule Observation of Self-Propagating Amyloid Fibrils. Microscopy (Oxf) 2022; 71:133-141. [DOI: 10.1093/jmicro/dfac011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 03/02/2022] [Accepted: 03/05/2022] [Indexed: 11/14/2022] Open
Abstract
Abstract
The assembly of misfolded proteins into amyloid fibrils is associated with amyloidosis, including neurodegenerative diseases, such as Alzheimer’s, Parkinson’s, and prion diseases. The self-propagation of amyloid fibrils is widely observed in the aggregation pathways of numerous amyloidogenic proteins. This propensity with plasticity in primary nucleation allows amyloid fibril polymorphism, which is correlated with the pathology/phenotypes of patients. Because the interference with the nucleation and replication processes of amyloid fibrils can alter the amyloid structure and the outcome of the disease, these processes can be a target for developing clinical drugs. Single-molecule observation of amyloid fibril replication can be an experimental system to provide the kinetic parameters for simulation studies and confirm the effect of clinical drugs. Here, we review single-molecule observation of the amyloid fibril replication process using fluorescence microscopy and time-lapse atomic force microscopy, including high-speed atomic force microscopy. We discussed the amyloid fibril replication process and combined single-molecule observation results with molecular dynamics simulations.
Mini Abstract Structural dynamics in amyloid aggregation is related with various Alzheimer’s and Parkinson’s disease symptoms. Single-molecule observation using high-speed atomic force microscopy can directly visualize the structural dynamics of individual amyloid aggregate assemblies. Here, we review historical and recent studies of single-molecule observation of amyloid aggregation with supportive molecular dynamics simulation.
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Affiliation(s)
| | - Kenjiro Ono
- Department of Neurology and Neurobiology of Aging, Kanazawa University Graduate School of Medical Sciences, Kanazawa University, 13-1, Takara-machi, Kanazawa 920-8640, Japan
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15
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Rojas AV, Maisuradze GG, Scheraga HA, Liwo A. Probing Protein Aggregation Using the Coarse-Grained UNRES Force Field. Methods Mol Biol 2022; 2340:79-104. [PMID: 35167071 DOI: 10.1007/978-1-0716-1546-1_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Protein aggregation is the cause of many, often lethal, diseases, including the Alzheimer's, Parkinson's, and Huntington's diseases, and familial amyloidosis. Theoretical investigation of the mechanism of this process, including the structures of the oligomeric intermediates which are the most toxic, is difficult because of long time scale of aggregation. Coarse-grained models, which enable us to extend the simulation time scale by three or more orders of magnitude, are, therefore, of great advantage in such studies. In this chapter, we describe the application of the physics-based UNited RESidue (UNRES) force field developed in our laboratory to study protein aggregation, in both free simulations and simulations of aggregation propagation from an existing template (seed), and illustrate it with the examples of Aβ-peptide aggregation and Aβ-peptide-assisted aggregation of the peptides derived from the repeat domains of tau (TauRD).
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Affiliation(s)
- Ana V Rojas
- Schrodinger Inc., 120 West 45th Street New York, New York, 10036, NY, USA
| | - Gia G Maisuradze
- Baker Laboratory of Chemistry and Chemical Biology, Cornell University, Ithaca, 14853-1301, NY, USA
| | - Harold A Scheraga
- Baker Laboratory of Chemistry and Chemical Biology, Cornell University, Ithaca, 14853-1301, NY, USA
| | - Adam Liwo
- Faculty of Chemistry, University of Gdańsk, Wita Stwosza 63, Gdańsk, 80-308, Poland.
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16
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Tachi Y, Itoh SG, Okumura H. Molecular dynamics simulations of amyloid-β peptides in heterogeneous environments. Biophys Physicobiol 2022; 19:1-18. [PMID: 35666692 PMCID: PMC9135617 DOI: 10.2142/biophysico.bppb-v19.0010] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2021] [Accepted: 03/31/2022] [Indexed: 12/01/2022] Open
Affiliation(s)
- Yuhei Tachi
- Department of Physics, Graduate school of Science, Nagoya University
| | - Satoru G. Itoh
- Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences
| | - Hisashi Okumura
- Institute for Molecular Science, National Institutes of Natural Sciences
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17
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de Oliveira OV, Gonçalves ADS, Almeida NECD. Insights into β-amyloid transition prevention by cucurbit[7]uril from molecular modeling. J Biomol Struct Dyn 2022; 40:9602-9612. [PMID: 34042019 DOI: 10.1080/07391102.2021.1932600] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
In this study, comparable molecular dynamic (MD) simulations of 1.2 microseconds were performed to clarify the prevention of the β-amyloid peptide (Aβ1-42) aggregation by cucurbit[7]uril (CB[7]). The accumulation of this peptide in the brain is one of the most harmful in Alzheimer's disease. The inhibition mechanism of Aβ1-42 aggregation by different molecules is attributed to preventing of Aβ1-42 conformational transition from α-helix to the β-sheet structure. However, our structural analysis shows that the pure water and aqueous solution of the CB[7] denature the native Aβ1-42 α-helix structure forming different compactness and unfolded conformations, not in β-sheet form. On the other hand, in the three CB[7]@Aβ1-42 complexes, it was observed the encapsulation of N-terminal (Asp1), Lys16, and Val36 by CB[7] along the MD trajectory, and not with aromatic residues as suggested by the literature. Only in one CB[7]@Aβ1-42 complex was observed stable Asp23-Lys28 salt bridge with an average distance of 0.36 nm. All CB[7]@Aβ1-42 complexes are very stable with binding free energy lowest than ∼-50 kcal/mol between the CB[7] and Aβ1-42 monomer from MM/PBSA calculation. Therefore, herein we show that the mechanism of the prevention of elongation protofibril by CB[7] is due to the disruption of the Asp23-Lys28 salt bridge and steric effects of CB[7]@Aβ1-42 complex with the fibril lattice, and not due to the transition from α-helix to β-sheet following the dock-lock mechanism.Communicated by Ramaswamy H. Sarma.
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18
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Aggregation and structure of amyloid β-protein. Neurochem Int 2021; 151:105208. [PMID: 34655726 DOI: 10.1016/j.neuint.2021.105208] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2021] [Revised: 10/07/2021] [Accepted: 10/10/2021] [Indexed: 01/21/2023]
Abstract
Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder and is characterized by major pathological hallmarks in the brain, including plaques composed of amyloid β-protein (Aβ) and neurofibrillary tangles of tau protein. Genetic studies, biochemical data, and animal models have suggested that Aβ is a critical species in the pathogenesis of AD. Aβ molecules aggregate to form oligomers, protofibrils (PFs), and mature fibrils. Because of their instability and structural heterogeneity, the misfolding and aggregation of Aβ is a highly complex process, leading to a variety of aggregates with different structures and morphologies. However, the elucidation of Aβ molecules is essential because they are believed to play an important role in AD pathogenesis. Recent combination studies using nuclear magnetic resonance (NMR) and cryo-electron microscopy (cryo-EM) have primarily revealed more detailed information about their aggregation process, including fibril extension and secondary nucleation, and the structural polymorphism of the fibrils under a variety of some conditions, including the actual brain. This review attempts to summarize the existing information on the major properties of the structure and aggregation of Aβ.
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19
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Multiscale Models for Fibril Formation: Rare Events Methods, Microkinetic Models, and Population Balances. Life (Basel) 2021; 11:life11060570. [PMID: 34204410 PMCID: PMC8234428 DOI: 10.3390/life11060570] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 05/30/2021] [Accepted: 06/09/2021] [Indexed: 11/17/2022] Open
Abstract
Amyloid fibrils are thought to grow by a two-step dock-lock mechanism. However, previous simulations of fibril formation (i) overlook the bi-molecular nature of the docking step and obtain rates with first-order units, or (ii) superimpose the docked and locked states when computing the potential of mean force for association and thereby muddle the docking and locking steps. Here, we developed a simple microkinetic model with separate locking and docking steps and with the appropriate concentration dependences for each step. We constructed a simple model comprised of chiral dumbbells that retains qualitative aspects of fibril formation. We used rare events methods to predict separate docking and locking rate constants for the model. The rate constants were embedded in the microkinetic model, with the microkinetic model embedded in a population balance model for “bottom-up” multiscale fibril growth rate predictions. These were compared to “top-down” results using simulation data with the same model and multiscale framework to obtain maximum likelihood estimates of the separate lock and dock rate constants. We used the same procedures to extract separate docking and locking rate constants from experimental fibril growth data. Our multiscale strategy, embedding rate theories, and kinetic models in conservation laws should help to extract docking and locking rate constants from experimental data or long molecular simulations with correct units and without compromising the molecular description.
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20
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Okumura H, Itoh SG. Molecular dynamics simulations of amyloid-β(16-22) peptide aggregation at air-water interfaces. J Chem Phys 2021; 152:095101. [PMID: 33480728 DOI: 10.1063/1.5131848] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Oligomers of amyloid-β (Aβ) peptides are known to be related to Alzheimer's disease, and their formation is accelerated at hydrophilic-hydrophobic interfaces, such as the cell membrane surface and air-water interface. Here, we report molecular dynamics simulations of aggregation of Aβ(16-22) peptides at air-water interfaces. First, 100 randomly distributed Aβ(16-22) peptides moved to the interface. The high concentration of peptides then accelerated their aggregation and formation of antiparallel β-sheets. Two layers of oligomers were observed near the interface. In the first layer from the interface, the oligomer with less β-bridges exposed the hydrophobic residues to the air. The second layer consisted of oligomers with more β-bridges that protruded into water. They are more soluble in water because the hydrophobic residues are covered by N- and C-terminal hydrophilic residues that are aligned well along the oligomer edge. These results indicate that amyloid protofibril formation mainly occurs in the second layer.
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Affiliation(s)
- Hisashi Okumura
- Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan
| | - Satoru G Itoh
- Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan
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21
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Okumura H, Itoh SG, Nakamura K, Kawasaki T. Role of Water Molecules and Helix Structure Stabilization in the Laser-Induced Disruption of Amyloid Fibrils Observed by Nonequilibrium Molecular Dynamics Simulations. J Phys Chem B 2021; 125:4964-4976. [PMID: 33961416 DOI: 10.1021/acs.jpcb.0c11491] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Water plays a crucial role in the formation and destruction of biomolecular structures. The mechanism for destroying biomolecular structures was thought to be an active breaking of hydrogen bonds by water molecules. However, using nonequilibrium molecular dynamics simulations, in which an amyloid-β amyloid fibril was destroyed via infrared free-electron laser (IR-FEL) irradiation, we discovered a new mechanism, in which water molecules disrupt protein aggregates. The intermolecular hydrogen bonds formed by C═O and N-H in the fibril are broken at each pulse of laser irradiation. These bonds spontaneously re-form after the irradiation in many cases. However, when a water molecule happens to enter the gap between C═O and N-H, it inhibits the re-formation of the hydrogen bonds. Such sites become defects in the regularly aligned hydrogen bonds, from which all hydrogen bonds in the intermolecular β-sheet are broken as the fraying spreads. This role of water molecules is entirely different from other known mechanisms. This new mechanism can explain the recent experiments showing that the amyloid fibrils are not destroyed by laser irradiation under dry conditions. Additionally, we found that helix structures form more after the amyloid disruption; this is because the resonance frequency is different in a helix structure. Our findings provide a theoretical basis for the application of IR-FEL to the future treatment of amyloidosis.
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Affiliation(s)
- Hisashi Okumura
- Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan.,Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan.,Department of Structural Molecular Science, SOKENDAI (The Graduate University for Advanced Studies), Okazaki, Aichi 444-8787, Japan
| | - Satoru G Itoh
- Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan.,Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan.,Department of Structural Molecular Science, SOKENDAI (The Graduate University for Advanced Studies), Okazaki, Aichi 444-8787, Japan
| | - Kazuhiro Nakamura
- Department of Laboratory Sciences, Graduate School of Health Sciences, Gunma University, Maebashi, Gunma 371-8514, Japan
| | - Takayasu Kawasaki
- IR Free Electron Laser Research Center, Research Institute for Science and Technology, Organization for Research Advancement, Tokyo University of Science, Noda, Chiba 278-8510, Japan
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22
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Promotion and Inhibition of Amyloid-β Peptide Aggregation: Molecular Dynamics Studies. Int J Mol Sci 2021; 22:ijms22041859. [PMID: 33668406 PMCID: PMC7918115 DOI: 10.3390/ijms22041859] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2021] [Revised: 02/10/2021] [Accepted: 02/11/2021] [Indexed: 01/06/2023] Open
Abstract
Aggregates of amyloid-β (Aβ) peptides are known to be related to Alzheimer’s disease. Their aggregation is enhanced at hydrophilic–hydrophobic interfaces, such as a cell membrane surface and air-water interface, and is inhibited by polyphenols, such as myricetin and rosmarinic acid. We review molecular dynamics (MD) simulation approaches of a full-length Aβ peptide, Aβ40, and Aβ(16–22) fragments in these environments. Since these peptides have both hydrophilic and hydrophobic amino acid residues, they tend to exist at the interfaces. The high concentration of the peptides accelerates the aggregation there. In addition, Aβ40 forms a β-hairpin structure, and this structure accelerates the aggregation. We also describe the inhibition mechanism of the Aβ(16–22) aggregation by polyphenols. The aggregation of Aβ(16–22) fragments is caused mainly by the electrostatic attraction between charged amino acid residues known as Lys16 and Glu22. Since polyphenols form hydrogen bonds between their hydroxy and carboxyl groups and these charged amino acid residues, they inhibit the aggregation.
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23
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Yang J, Agnihotri MV, Huseby CJ, Kuret J, Singer SJ. A theoretical study of polymorphism in VQIVYK fibrils. Biophys J 2021; 120:1396-1416. [PMID: 33571490 DOI: 10.1016/j.bpj.2021.01.032] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 01/07/2021] [Accepted: 01/11/2021] [Indexed: 02/06/2023] Open
Abstract
The VQIVYK fragment from the Tau protein, also known as PHF6, is essential for aggregation of Tau into neurofibrillary lesions associated with neurodegenerative diseases. VQIVYK itself forms amyloid fibrils composed of paired β-sheets. Therefore, the full Tau protein and VQIVYK fibrils have been intensively investigated. A central issue in these studies is polymorphism, the ability of a protein to fold into more than one structure. Using all-atom molecular simulations, we generate five stable polymorphs of VQIVYK fibrils, establish their relative free energy with umbrella sampling methods, and identify the side chain interactions that provide stability. The two most stable polymorphs, which have nearly equal free energy, are formed by interdigitation of the mostly hydrophobic VIY "face" sides of the β-sheets. Another stable polymorph is formed by interdigitation of the QVK "back" sides. When we turn to examine structures from cryo-electron microscopy experiments on Tau filaments taken from diseased patients or generated in vitro, we find that the pattern of side chain interactions found in the two most stable face-to-face as well as the back-to-back polymorphs are recapitulated in amyloid structures of the full protein. Thus, our studies suggest that the interactions stabilizing PHF6 fibrils explain the amyloidogenicity of the VQIVYK motif within the full Tau protein and provide justification for the use of VQIVYK fibrils as a test bed for the design of molecules that identify or inhibit amyloid structures.
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Affiliation(s)
- Jaehoon Yang
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio
| | - Mithila V Agnihotri
- Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio
| | - Carol J Huseby
- Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio
| | - Jeff Kuret
- Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio; Department of Biological Chemistry and Pharmacology, The Ohio State University, Columbus, Ohio.
| | - Sherwin J Singer
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio; Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, Ohio.
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24
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Abstract
Self-assembly of proteins and peptides into the amyloid fold is a widespread phenomenon in the natural world. The structural hallmark of self-assembly into amyloid fibrillar assemblies is the cross-beta motif, which conveys distinct morphological and mechanical properties. The amyloid fibril formation has contrasting results depending on the organism, in the sense that it can bestow an organism with the advantages of mechanical strength and improved functionality or, on the contrary, could give rise to pathological states. In this chapter we review the existing information on amyloid-like peptide aggregates, which could either be derived from protein sequences, but also could be rationally or de novo designed in order to self-assemble into amyloid fibrils under physiological conditions. Moreover, the development of self-assembled fibrillar biomaterials that are tailored for the desired properties towards applications in biomedical or environmental areas is extensively analyzed. We also review computational studies predicting the amyloid propensity of the natural amino acid sequences and the structure of amyloids, as well as designing novel functional amyloid materials.
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Affiliation(s)
- C. Kokotidou
- University of Crete, Department of Materials Science and Technology Voutes Campus GR-70013 Heraklion Crete Greece
- FORTH, Institute for Electronic Structure and Laser N. Plastira 100 GR 70013 Heraklion Greece
| | - P. Tamamis
- Texas A&M University, Artie McFerrin Department of Chemical Engineering College Station Texas 77843-3122 USA
| | - A. Mitraki
- University of Crete, Department of Materials Science and Technology Voutes Campus GR-70013 Heraklion Crete Greece
- FORTH, Institute for Electronic Structure and Laser N. Plastira 100 GR 70013 Heraklion Greece
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25
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Noda K, Tachi Y, Okamoto Y. Structural Characteristics of Monomeric Aβ42 on Fibril in the Early Stage of Secondary Nucleation Process. ACS Chem Neurosci 2020; 11:2989-2998. [PMID: 32794732 DOI: 10.1021/acschemneuro.0c00163] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Amyloid-β (Aβ) aggregates are believed to be one of the main causes of Alzheimer's disease. Aβ peptides form fibrils having cross β-sheet structures mainly through primary nucleation, secondary nucleation, and elongation. In particular, self-catalyzed secondary nucleation is of great interest. Here, we investigate the adsorption of Aβ42 peptides to the Aβ42 fibril to reveal a role of adsorption as a part of secondary nucleation. We performed extensive molecular dynamics simulations based on replica exchange with solute tempering 2 (REST2) to two systems: a monomeric Aβ42 in solution and a complex of an Aβ42 peptide and Aβ42 fibril. Results of our simulations show that the Aβ42 monomer is extended on the fibril. Furthermore, we find that the hairpin structure of the Aβ42 monomer decreases but the helix structure increases by adsorption to the fibril surface. These structural changes are preferable for forming fibril-like aggregates, suggesting that the fibril surface serves as a catalyst in the secondary nucleation process. In addition, the stabilization of the helix structure of the Aβ42 monomer on the fibril indicates that the strategy of a secondary nucleation inhibitor design for Aβ40 can also be used for Aβ42.
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Affiliation(s)
- Kohei Noda
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Aichi 464-8602, Japan
| | - Yuhei Tachi
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Aichi 464-8602, Japan
| | - Yuko Okamoto
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Aichi 464-8602, Japan
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26
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Cholko T, Barnum J, Chang CEA. Amyloid-β (Aβ42) Peptide Aggregation Rate and Mechanism on Surfaces with Widely Varied Properties: Insights from Brownian Dynamics Simulations. J Phys Chem B 2020; 124:5549-5558. [PMID: 32525673 DOI: 10.1021/acs.jpcb.0c02926] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Amyloid-β (Aβ) plaques, which form by aggregation of harmless Aβ peptide monomers into larger fibrils, are characteristic of neurodegenerative disorders such as Alzheimer's disease. Efforts to treat Alzheimer's disease focus on stopping or reversing the aggregation process that leads to fibril formation. However, effective treatments are elusive due to certain unknown aspects of the process. Many hypotheses point to disruption of cell membranes by adsorbed Aβ monomers or oligomers, but how Aβ behaves and aggregates on surfaces of widely varying properties, such as those present in a cell, is unclear. Elucidating the effects of various surfaces on the dynamics of Aβ and the kinetics of the aggregation process from bulk solution to a surface-adsorbed multimer can help identify what drives aggregation, leading to new methods of intervention by inhibitory drugs or other means. In this work, we used all-atom Brownian dynamics simulations to study the association of two distinct Aβ42 monomer conformations with a surface-adsorbed or free-floating Aβ42 dimer. We calculated the association time, surface interaction energy, surface diffusion coefficient, surface residence time, and the mechanism of association on four different surfaces and two different bulk solution scenarios. In the presence of a surface, the majority of monomers underwent a two-dimensional surface-mediated association that depended primarily on an Aβ42 electrostatic interaction with the self-assembled monolayer (SAM) surfaces. Moreover, aggregation could be inhibited greatly by surfaces with high affinity for Aβ42 and heterogeneous charge distribution. Our results can be used to identify new opportunities for disrupting or reversing the Aβ42 aggregation process.
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Affiliation(s)
- Timothy Cholko
- Department of Chemistry, University of California, Riverside, Riverside, California 92521, United States
| | - Joseph Barnum
- Department of Chemistry, University of California, Riverside, Riverside, California 92521, United States
| | - Chia-En A Chang
- Department of Chemistry, University of California, Riverside, Riverside, California 92521, United States
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27
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Amyloid assembly is dominated by misregistered kinetic traps on an unbiased energy landscape. Proc Natl Acad Sci U S A 2020; 117:10322-10328. [PMID: 32345723 DOI: 10.1073/pnas.1911153117] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Atomistic description of protein fibril formation has been elusive due to the complexity and long time scales of the conformational search. Here, we develop a multiscale approach combining numerous atomistic simulations in explicit solvent to construct Markov State Models (MSMs) of fibril growth. The search for the in-register fully bound fibril state is modeled as a random walk on a rugged two-dimensional energy landscape defined by β-sheet alignment and hydrogen-bonding states, whereas transitions involving states without hydrogen bonds are derived from kinetic clustering. The reversible association/dissociation of an incoming peptide and overall growth kinetics are then computed from MSM simulations. This approach is applied to derive a parameter-free, comprehensive description of fibril elongation of Aβ16-22 and how it is modulated by phenylalanine-to-cyclohexylalanine (CHA) mutations. The trajectories show an aggregation mechanism in which the peptide spends most of its time trapped in misregistered β-sheet states connected by weakly bound states twith short lifetimes. Our results recapitulate the experimental observation that mutants CHA19 and CHA1920 accelerate fibril elongation but have a relatively minor effect on the critical concentration for fibril growth. Importantly, the kinetic consequences of mutations arise from cumulative effects of perturbing the network of productive and nonproductive pathways of fibril growth. This is consistent with the expectation that nonfunctional states will not have evolved efficient folding pathways and, therefore, will require a random search of configuration space. This study highlights the importance of describing the complete energy landscape when studying the elongation mechanism and kinetics of protein fibrils.
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28
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Frigori RB, Barroso da Silva FL, Carvalho PPD, Alves NA. Occurrence of Biased Conformations as Precursors of Assembly States in Fibril Elongation of Amyloid-β Fibril Variants: An In Silico Study. J Phys Chem B 2020; 124:2798-2805. [DOI: 10.1021/acs.jpcb.0c01360] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Rafael B. Frigori
- Universidade Tecnológica Federal do Paraná, Rua Cristo Rei 19, Toledo 85902-490, Paraná, Brazil
| | - Fernando L. Barroso da Silva
- Departamento de Ciências Biomoleculares, FCFRP, Universidade de São Paulo, Avenida do Café, s/no, Ribeirão Preto 14040-903, São Paulo, Brazil
| | - Patrícia P. D. Carvalho
- Departamento de Fı́sica, FFCLRP, Universidade de São Paulo, Avenida Bandeirantes, 3900, Ribeirão Preto 14040-901, São Paulo, Brazil
| | - Nelson A. Alves
- Departamento de Fı́sica, FFCLRP, Universidade de São Paulo, Avenida Bandeirantes, 3900, Ribeirão Preto 14040-901, São Paulo, Brazil
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29
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Cosolvent effects on the growth of amyloid fibrils. Curr Opin Struct Biol 2020; 60:101-109. [DOI: 10.1016/j.sbi.2019.12.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2019] [Revised: 12/08/2019] [Accepted: 12/16/2019] [Indexed: 02/05/2023]
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30
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Computational studies of protein aggregation mediated by amyloid: Fibril elongation and secondary nucleation. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2020; 170:461-504. [DOI: 10.1016/bs.pmbts.2019.12.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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31
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Vettore N, Buell AK. Thermodynamics of amyloid fibril formation from chemical depolymerization. Phys Chem Chem Phys 2019; 21:26184-26194. [PMID: 31755512 DOI: 10.1039/c9cp04524d] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Amyloid fibrils are homo-molecular protein polymers that play an important role in disease and biological function. While much is known about their kinetics and mechanisms of formation, the origin and magnitude of their thermodynamic stability has received significantly less attention. This is despite the fact that the thermodynamic stability of amyloid fibrils is an important determinant of their lifetimes and processing in vivo. Here we use depolymerization by chemical denaturants of amyloid fibrils of two different proteins (PI3K-SH3 and glucagon) at different concentrations and show that the previously applied isodesmic linear polymerization model is an oversimplification that does not capture the concentration dependence of chemical depolymerization of amyloid fibrils. We show that cooperative polymerization, which is compatible with the picture of amyloid formation as a nucleated polymerization process, is able to quantitatively describe the thermodynamic data. We use this combined experimental and conceptual framework in order to probe the ionic strength dependence of amyloid fibril stability. In combination with previously published data on the ionic strength dependence of amyloid fibril growth kinetics, our results provide strong evidence for the product-like nature of the transition state of amyloid fibril growth.
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Affiliation(s)
- Nicola Vettore
- Institut for Physical Biology, Heinrich-Heine-Universitaet Duesseldorf, Universitaetstrasse 1, Duesseldorf, Germany
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32
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Mahmoudinobar F, Urban JM, Su Z, Nilsson BL, Dias CL. Thermodynamic Stability of Polar and Nonpolar Amyloid Fibrils. J Chem Theory Comput 2019; 15:3868-3874. [DOI: 10.1021/acs.jctc.9b00145] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Farbod Mahmoudinobar
- Department of Physics, New Jersey Institute of Technology, Newark, New Jersey 07102, United States
| | - Jennifer M. Urban
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
| | - Zhaoqian Su
- Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, New York 10461, United States
| | - Bradley L. Nilsson
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
| | - Cristiano L. Dias
- Department of Physics, New Jersey Institute of Technology, Newark, New Jersey 07102, United States
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33
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Ilie IM, Caflisch A. Simulation Studies of Amyloidogenic Polypeptides and Their Aggregates. Chem Rev 2019; 119:6956-6993. [DOI: 10.1021/acs.chemrev.8b00731] [Citation(s) in RCA: 93] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Ioana M. Ilie
- Department of Biochemistry, University of Zürich, Zürich CH-8057, Switzerland
| | - Amedeo Caflisch
- Department of Biochemistry, University of Zürich, Zürich CH-8057, Switzerland
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34
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Mondal B, Reddy G. Cosolvent Effects on the Growth of Protein Aggregates Formed by a Single Domain Globular Protein and an Intrinsically Disordered Protein. J Phys Chem B 2019; 123:1950-1960. [DOI: 10.1021/acs.jpcb.8b11128] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Balaka Mondal
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012, Karnataka, India
| | - Govardhan Reddy
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012, Karnataka, India
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35
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Nishikawa N, Sakae Y, Gouda T, Tsujimura Y, Okamoto Y. Structural Analysis of a Trimer of β 2-Microgloblin Fragment by Molecular Dynamics Simulations. Biophys J 2019; 116:781-790. [PMID: 30771855 DOI: 10.1016/j.bpj.2018.11.3143] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2017] [Revised: 06/08/2018] [Accepted: 11/06/2018] [Indexed: 01/22/2023] Open
Abstract
A peptide β2-m21-31, which is a fragment from residue 21 to residue 31 of β2-microgloblin, is experimentally known to self-assemble and form amyloid fibrils. In order to understand the mechanism of amyloid fibril formations, we applied the replica-exchange molecular dynamics method to the system consisting of three fragments of β2-m21-31. From the analyses on the temperature dependence, we found that there is a clear phase transition temperature in which the peptides aggregate with each other. Moreover, we found by the free energy analyses that there are two major stable states: One of them is like amyloid fibrils and the other is amorphous aggregates.
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Affiliation(s)
- Naohiro Nishikawa
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Aichi, Japan; Department of Theoretical and Computational Molecular Science, Institute for Molecular Science, Okazaki, Aichi, Japan
| | - Yoshitake Sakae
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Aichi, Japan
| | - Takuya Gouda
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Aichi, Japan
| | - Yuichiro Tsujimura
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Aichi, Japan
| | - Yuko Okamoto
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Aichi, Japan; Structural Biology Research Center, Graduate School of Science, Nagoya University, Nagoya, Aichi, Japan; Center for Computational Science, Graduate School of Engineering, Nagoya University, Nagoya, Aichi, Japan; Information Technology Center, Nagoya University, Nagoya, Aichi, Japan; JST-CREST, Nagoya, Aichi, Japan.
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36
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Recent Advances by In Silico and In Vitro Studies of Amyloid-β 1-42 Fibril Depicted a S-Shape Conformation. Int J Mol Sci 2018; 19:ijms19082415. [PMID: 30115846 PMCID: PMC6121414 DOI: 10.3390/ijms19082415] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2018] [Revised: 08/09/2018] [Accepted: 08/10/2018] [Indexed: 12/19/2022] Open
Abstract
The amyloid-β 1-42 (Aβ1-42) peptide is produced by proteolytic cleavage of the amyloid precursor protein (APP) by sequential reactions that are catalyzed by γ and β secretases. Aβ1-42, together with the Tau protein are two principal hallmarks of Alzheimer's disease (AD) that are related to disease genesis and progression. Aβ1-42 possesses a higher aggregation propensity, and it is able to form fibrils via nucleated fibril formation. To date, there are compounds available that prevent Aβ1-42 aggregation, but none have been successful in clinical trials, possibly because the Aβ1-42 structure and aggregation mechanisms are not thoroughly understood. New molecules have been designed, employing knowledge of the Aβ1-42 structure and are based on preventing or breaking the ionic interactions that have been proposed for formation of the Aβ1-42 fibril U-shaped structure. Recently, a new Aβ1-42 fibril S-shaped structure was reported that, together with its aggregation and catalytic properties, could be helpful in the design of new inhibitor molecules. Therefore, in silico and in vitro methods have been employed to analyze the Aβ1-42 fibril S-shaped structure and its aggregation to obtain more accurate Aβ1-42 oligomerization data for the design and evaluation of new molecules that can prevent the fibrillation process.
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37
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Kar RK, Brender JR, Ghosh A, Bhunia A. Nonproductive Binding Modes as a Prominent Feature of Aβ 40 Fiber Elongation: Insights from Molecular Dynamics Simulation. J Chem Inf Model 2018; 58:1576-1586. [PMID: 30047732 DOI: 10.1021/acs.jcim.8b00169] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The formation of amyloid fibers has been implicated in a number of neurodegenerative diseases. The growth of amyloid fibers is strongly thermodynamically favorable, but kinetic traps exist where the incoming monomer binds in an incompatible conformation that blocks further elongation. Unfortunately, this process is difficult to follow experimentally at the atomic level. It is also too complex to simulate in full detail and to date has been explored either through coarse-grained simulations, which may miss many important interactions, or full atomic simulations, in which the incoming peptide is constrained to be near the ideal fiber geometry. Here we use an alternate approach starting from a docked complex in which the monomer is from an experimental NMR structure of one of the major conformations in the unbound ensemble, a largely unstructured peptide with the central hydrophobic region in a 310 helix. A 1000 ns full atomic simulation in explicit solvent shows the formation of a metastable intermediate by sequential, concerted movements of both the fiber and the monomer. A Markov state model shows that the unfolded monomer is trapped at the end of the fiber in a set of interconverting antiparallel β-hairpin conformations. The simulation here may serve as a model for the binding of other non-β-sheet conformations to amyloid fibers.
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Affiliation(s)
- Rajiv K Kar
- Department of Biophysics , Bose Institute , P-1/12 CIT Scheme VII (M) , Kolkata 700054 , India
| | - Jeffrey R Brender
- Radiation Biology Branch , National Institutes of Health , Bethesda , Maryland 20814 , United States
| | - Anirban Ghosh
- Department of Biophysics , Bose Institute , P-1/12 CIT Scheme VII (M) , Kolkata 700054 , India
| | - Anirban Bhunia
- Department of Biophysics , Bose Institute , P-1/12 CIT Scheme VII (M) , Kolkata 700054 , India
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38
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Ilie IM, den Otter WK, Briels WJ. The attachment of α-synuclein to a fiber: A coarse-grain approach. J Chem Phys 2018; 146:115102. [PMID: 28330339 DOI: 10.1063/1.4978297] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
We present simulations of the amyloidogenic core of α-synuclein, the protein causing Parkinson's disease, as a short chain of coarse-grain patchy particles. Each particle represents a sequence of about a dozen amino acids. The fluctuating secondary structure of this intrinsically disordered protein is modelled by dynamic variations of the shape and interaction characteristics of the patchy particles, ranging from spherical with weak isotropic attractions for the disordered state to spherocylindrical with strong directional interactions for a β-sheet. Flexible linkers between the particles enable sampling of the tertiary structure. This novel model is applied here to study the growth of an amyloid fibril, by calculating the free energy profile of a protein attaching to the end of a fibril. The simulation results suggest that the attaching protein readily becomes trapped in a mis-folded state, thereby inhibiting further growth of the fibril until the protein has readjusted to conform to the fibril structure, in line with experimental findings and previous simulations on small fragments of other proteins.
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Affiliation(s)
- Ioana M Ilie
- Computational Chemical Physics, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Wouter K den Otter
- Computational Chemical Physics, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Wim J Briels
- Computational Chemical Physics, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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39
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Wang Y, Hall CK. Seeding and cross-seeding fibrillation of N-terminal prion protein peptides PrP(120-144). Protein Sci 2018; 27:1304-1313. [PMID: 29637634 DOI: 10.1002/pro.3421] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Revised: 04/02/2018] [Accepted: 04/04/2018] [Indexed: 11/07/2022]
Abstract
Prion diseases are infectious neurodegenerative diseases that are capable of cross-species transmission, thus arousing public health concerns. Seed-templating propagation of prion protein is believed to underlie prion cross-species transmission pathology. Understanding the molecular fundamentals of prion propagation is key to unravelling the pathology of prion diseases. In this study, we use coarse-grained molecular dynamics to investigate the seeding and cross-seeding aggregation of three prion protein fragments PrP(120-144) originating from human (Hu), bank vole (BV), and Syrian hamster (SHa). We find that the seed accelerates the aggregation of the monomer peptides by eliminating the lag phase. The monomer aggregation kinetics are mainly determined by the structure of the seed. The stronger the hydrophobic residues on the seed associate with each other, the higher the probability that the seed recruits monomer peptides to its surface/interface. For cross-seeding aggregation, we show that Hu has a strong tendency to adopt the conformation of the BV seed and vice versa; the Hu and BV monomers have a weak tendency to adopt the conformation of the SHa seed. These two findings are consistent with Apostol et al.'s experimental findings on PrP(138-143) and partially consistent with Jones et al.'s finding on PrP(23-144). We also identify several conformational mismatches when SHa cross-seeds BV and Hu peptides, indicating the existence of a cross-seeding barrier between SHa and the other two sequences. This study sheds light on the molecular mechanism of seed-templating aggregation of prion protein fragments underlying the sequence-dependent transmission barrier in prion diseases.
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Affiliation(s)
- Yiming Wang
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, 27695-7905
| | - Carol K Hall
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, 27695-7905
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40
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Rodriguez RA, Chen LY, Plascencia-Villa G, Perry G. Thermodynamics of Amyloid-β Fibril Elongation: Atomistic Details of the Transition State. ACS Chem Neurosci 2018; 9:783-789. [PMID: 29239603 PMCID: PMC5911799 DOI: 10.1021/acschemneuro.7b00409] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
![]()
Amyloid-β
(Aβ) fibrils and plaques are one of the hallmarks
of Alzheimer’s disease. While the kinetics of fibrillar growth
of Aβ have been extensively studied, several vital questions
remain. In particular, the atomistic origins of the Arrhenius barrier
observed in experiments have not been elucidated. Employing the familiar
thermodynamic integration method, we have directly simulated the dissociation
of an Aβ(15–40) (D23N mutant) peptide from
the surface of a filament along its most probable path (MPP) using
all-atom molecular dynamics. This allows for a direct calculation
of the free energy profile along the MPP, revealing a multipeak energetic
barrier between the free peptide state and the aggregated state. By
definition of the MPP, this simulated unbinding process represents
the reverse of the physical elongation pathway, allowing us to draw
biophysically relevant conclusions from the simulation data. Analyzing
the detailed atomistic interactions along the MPP, we identify the
atomistic origins of these peaks as resulting from the dock-lock mechanism
of filament elongation. Careful analysis of the dynamics of filament
elongation could prove key to the development of novel therapeutic
strategies for amyloid-related diseases.
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Affiliation(s)
- Roberto A. Rodriguez
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas 78249, United States
| | - Liao Y. Chen
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas 78249, United States
| | - Germán Plascencia-Villa
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas 78249, United States
| | - George Perry
- Department of Biology and Neurosciences Institute, University of Texas at San Antonio, San Antonio, Texas 78249, United States
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41
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Abstract
The aggregation of the Aβ peptide (Aβ1-42) to form fibrils is a key feature of Alzheimer's disease. The mechanism is thought to be a nucleation stage followed by an elongation process. The elongation stage involves the consecutive addition of monomers to one end of the growing fibril. The aggregation process proceeds in a stop-and-go fashion and may involve off-pathway aggregates, complicating experimental and computational studies. Here we present exploration of a well-defined region in the free and potential energy landscapes for the Aβ17-42 pentamer. We find that the ideal aggregation process agrees with the previously reported dock-lock mechanism. We also analyze a large number of additional stable structures located on the multifunnel energy landscape, which constitute kinetic traps. The key contributors to the formation of such traps are misaligned strong interactions, for example the stacking of F19 and F20, as well as entropic contributions. Our results suggest that folding templates for aggregation are a necessity and that aggregation studies could employ such species to obtain a more detailed description of the process.
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Affiliation(s)
- Konstantin Röder
- Department of Chemistry , University of Cambridge , Lensfield Road , Cambridge , CB2 1EW , United Kingdom
| | - David J Wales
- Department of Chemistry , University of Cambridge , Lensfield Road , Cambridge , CB2 1EW , United Kingdom
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42
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Brotzakis ZF, Gehre M, Voets IK, Bolhuis PG. Stability and growth mechanism of self-assembling putative antifreeze cyclic peptides. Phys Chem Chem Phys 2018; 19:19032-19042. [PMID: 28702528 DOI: 10.1039/c7cp02465g] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Cyclic peptides (CPs) that self-assemble in nanotubes can be candidates for use as antifreeze proteins. Based on the cyclic peptide sequence cyclo-[(l-LYS-d-ALA-l-LEU-d-ALA)2], which can stack into nanotubes, we propose a putative antifreeze cyclic peptide (AFCP) sequence, cyclo-[(l-LYS-d-ALA)2-(l-THR-d-ALA)2], containing THR-ALA-THR ice binding motifs. Using molecular dynamics simulations we investigate the stability of these cyclic peptides and their growth mechanism. Both nanotube sequences get more stable as a function of size. The relative stability of the AFCP sequence CPNT increases at sizes greater than a dimer by forming intermolecular THR side chain H-bonds. We find that, like the naturally occurring AF protein from spruce budworm (Choristoneura fumiferana), the THR distances of the AFCP's ice binding motif match the ice prism plane O-O distances, thus making the AFCP a suitable AF candidate. In addition, we investigated the nanotube growth process, i.e. the association/dissociation of a single CP to an existing AFCP nanotube, by Transition Path Sampling. We found a general dock-lock mechanism, in which a single CP first docks loosely before locking into place. Moreover, we identified several qualitatively different mechanisms for association, involving different metastable intermediates, including a state in which the peptide was misfolded inside the hydrophobic core of the tube. Finally, we find evidence for a mechanism involving non-specific association followed by 1D diffusion. Under most conditions, this will be the dominant pathway. The results yield insights into the mechanisms of peptide assembly, and might lead to an improved design of self-assembling antifreeze proteins.
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Affiliation(s)
- Z Faidon Brotzakis
- Van't Hoff Institute for Molecular Sciences, Universiteit van Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
| | - Mascha Gehre
- Van't Hoff Institute for Molecular Sciences, Universiteit van Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
| | - Ilja K Voets
- Laboratory of Macromolecular and Organic Chemistry, Laboratory of Physical Chemistry, and Institute for Complex Molecular Systems, Eindhoven University of Technology, Post Office Box 513, 5600 MB, Eindhoven, The Netherlands
| | - Peter G Bolhuis
- Van't Hoff Institute for Molecular Sciences, Universiteit van Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
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43
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Young LJ, Kaminski Schierle GS, Kaminski CF. Imaging Aβ(1-42) fibril elongation reveals strongly polarised growth and growth incompetent states. Phys Chem Chem Phys 2017; 19:27987-27996. [PMID: 29026905 PMCID: PMC7612976 DOI: 10.1039/c7cp03412a] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The major hallmark of Alzheimer's disease is the deposition of plaques of amyloid fibrils formed from amyloid-β (Aβ) peptides. Kinetic studies have contributed significantly towards a mechanistic understanding of amyloid fibril self-assembly, however dynamic features of the aggregation process cannot be captured using ensemble methods. Here we present an assay for imaging Aβ42 aggregation dynamics at the single fibril level, allowing for the quantitative extraction of concentration and temperature dependent kinetic parameters. From direct observation of elongation using TIRF and super-resolution optical microscopy, we find that Aβ42 fibril growth is strongly polarized, with fast and slow growing ends arising from different elongation rates, but also from a growth incompetent state, which dominates the process at the slow growing end. Our findings reveal the surprising complexity of the Aβ42 fibril elongation reaction at the microscopic level.
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Affiliation(s)
- Laurence J Young
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, CB3 0AS, UK.
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44
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Khatua P, Sinha SK, Bandyopadhyay S. Size-Dependent Conformational Features of Aβ17–42 Protofilaments from Molecular Simulation Studies. J Chem Inf Model 2017; 57:2378-2392. [DOI: 10.1021/acs.jcim.7b00407] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Prabir Khatua
- Molecular
Modeling Laboratory, Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India
| | - Sudipta Kumar Sinha
- Department
of Chemistry, Indian Institute of Technology Ropar, Ropar 140001, India
| | - Sanjoy Bandyopadhyay
- Molecular
Modeling Laboratory, Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India
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45
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Structural Properties of Human IAPP Dimer in Membrane Environment Studied by All-Atom Molecular Dynamics Simulations. Sci Rep 2017; 7:7915. [PMID: 28801684 PMCID: PMC5554177 DOI: 10.1038/s41598-017-08504-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 07/12/2017] [Indexed: 12/27/2022] Open
Abstract
The aggregation of human islet amyloid polypeptide (hIAPP) can damage the membrane of the β-cells in the pancreatic islets and induce type 2 diabetes (T2D). Growing evidences indicated that the major toxic species are small oligomers of IAPP. Due to the fast aggregation nature, it is hard to characterize the structures of IAPP oligomers by experiments, especially in the complex membrane environment. On the other side, molecular dynamics simulation can provide atomic details of the structure and dynamics of the aggregation of IAPP. In this study, all-atom bias-exchange metadynamics (BE-Meta) and unbiased molecular dynamics simulations were employed to study the structural properties of IAPP dimer in the membranes environments. A number of intermediates, including α-helical states, β-sheet states, and fully disordered states, are identified. The formation of N-terminal β-sheet structure is prior to the C-terminal β-sheet structure towards the final fibril-like structures. The α-helical intermediates have lower propensity in the dimeric hIAPP and are off-pathway intermediates. The simulations also demonstrate that the β-sheet intermediates induce more perturbation on the membrane than the α-helical and disordered states and thus pose higher disruption ability.
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46
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Prokopovich DV, Whittaker JW, Muthee MM, Ahmed A, Larini L. Impact of Phosphorylation and Pseudophosphorylation on the Early Stages of Aggregation of the Microtubule-Associated Protein Tau. J Phys Chem B 2017; 121:2095-2103. [PMID: 28218850 DOI: 10.1021/acs.jpcb.7b00194] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The microtubule-associated protein tau regulates the stability of microtubules within neurons in the central nervous system. In turn, microtubules are responsible for the remodeling of the cytoskeleton that ultimately leads to the formation or pruning of new connections among neurons. As a consequence, dysfunction of tau is associated with many forms of dementia as well as Alzheimer's disease. In the brain, tau activity is regulated by its phosphorylation state. Phosphorylation is a post-translational modification of proteins that adds a phosphate group to the side chain of an amino acid. Phosphorylation at key locations in the tau sequence leads to a higher or lower affinity for microtubules. In Alzheimer's disease, tau is present in an abnormal phosphorylation state. However, studying the effect of phosphorylation experimentally has been extremely challenging as there is no viable way of exactly selecting the location and the number of phosphorylated sites. For this reason, researchers have turned to pseudophosphorylation. In this technique, actual phosphorylation is mimicked by mutating the selected amino acid into glutamate or aspartate. Whether this methodology is equivalent to actual phosphorylation is still open to debate. In this study, we will show that phosphorylation and pseudophosphorylation are not exactly equivalent. Although for larger aggregates the two techniques lead to similar structures, the kinetics of the process may be altered. In addition, very little is known about the impact that this may have on the early stages of aggregation, such as nucleation and conformational rearrangement. In this study, we show that the two methods may produce a similar ensemble of conformations, even though the kinetic and chemical details that lead to it are quite different.
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Affiliation(s)
- Dmitriy V Prokopovich
- Department of Physics and ‡Center for Computational and Integrative Biology, Rutgers University-Camden , Camden, New Jersey 08102, United States
| | - John W Whittaker
- Department of Physics and ‡Center for Computational and Integrative Biology, Rutgers University-Camden , Camden, New Jersey 08102, United States
| | - Micaiah M Muthee
- Department of Physics and ‡Center for Computational and Integrative Biology, Rutgers University-Camden , Camden, New Jersey 08102, United States
| | - Azka Ahmed
- Department of Physics and ‡Center for Computational and Integrative Biology, Rutgers University-Camden , Camden, New Jersey 08102, United States
| | - Luca Larini
- Department of Physics and ‡Center for Computational and Integrative Biology, Rutgers University-Camden , Camden, New Jersey 08102, United States
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47
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Hu ZW, Ma MR, Chen YX, Zhao YF, Qiang W, Li YM. Phosphorylation at Ser 8 as an Intrinsic Regulatory Switch to Regulate the Morphologies and Structures of Alzheimer's 40-residue β-Amyloid (Aβ40) Fibrils. J Biol Chem 2017; 292:2611-2623. [PMID: 28031462 PMCID: PMC5314160 DOI: 10.1074/jbc.m116.757179] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Revised: 12/05/2016] [Indexed: 01/23/2023] Open
Abstract
Polymorphism of amyloid-β (Aβ) fibrils, implying different fibril structures, may play important pathological roles in Alzheimer's disease (AD). Morphologies of Aβ fibrils were found to be sensitive to fibrillation conditions. Herein, the Ser8-phosphorylated Aβ (pAβ), which is assumed to specially associate with symptomatic AD, is reported to modify the morphology, biophysical properties, cellular toxicity, and structures of Aβ fibrils. Under the same fibrillation conditions, pAβ favors the formation of fibrils (Fpβ), which are different from the wild-type Aβ fibrils (Fβ). Both Fβ and Fpβ fibrils show single predominant morphologies. Compared with Fβ, Fpβ exhibits higher propagation efficiency and higher neuronal cell toxicity. The residue-specific structural differences between the Fβ- and Fpβ-seeded Aβ fibrils were identified using magic angle spin NMR. Our results suggest a potential regulatory mechanism of phosphorylation on Aβ fibril formation in AD and imply that the post-translationally modified Aβ, especially the phosphorylated Aβ, may be an important target for the diagnosis or treatment of AD at specific stages.
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Affiliation(s)
- Zhi-Wen Hu
- From the Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China
| | - Meng-Rong Ma
- From the Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China
| | - Yong-Xiang Chen
- From the Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China
| | - Yu-Fen Zhao
- From the Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China
| | - Wei Qiang
- Department of Chemistry, Binghamton University, State University of New York, Binghamton, New York 13902, and
| | - Yan-Mei Li
- From the Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China,
- Beijing Institute for Brain Disorders, Beijing 100069, China
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48
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Rojas A, Maisuradze N, Kachlishvili K, Scheraga HA, Maisuradze GG. Elucidating Important Sites and the Mechanism for Amyloid Fibril Formation by Coarse-Grained Molecular Dynamics. ACS Chem Neurosci 2017; 8:201-209. [PMID: 28095675 DOI: 10.1021/acschemneuro.6b00331] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Fibrils formed by the β-amyloid (Aβ) peptide play a central role in the development of Alzheimer's disease. In this study, the principles governing their growth and stability are investigated by analyzing canonical and replica-exchange molecular dynamics trajectories of Aβ(9-40) fibrils. In particular, an unstructured monomer was allowed to interact freely with an Aβ fibril template. Trajectories were generated with the coarse-grained united-residue force field, and one- and two-dimensional free-energy landscapes (FELs) along the backbone virtual-bond angle θ and backbone virtual-bond-dihedral angle γ of each residue and principal components, respectively, were analyzed. Also, thermal unbinding (unfolding) of an Aβ peptide from the fibril template was investigated. These analyses enable us to illustrate the entire process of Aβ fibril elongation and to elucidate the key residues involved in it. Several different pathways were identified during the search for the fibril conformation by the monomer, which finally follows a dock-lock mechanism with two distinct locking stages. However, it was found that the correct binding, with native hydrogen bonds, of the free monomer to the fibril template at both stages is crucial for fibril elongation. In other words, if the monomer is incorrectly bound (with nonnative hydrogen bonds) to the fibril template during the first "docking" stage, it can remain attached to it for a long time before it dissociates and either attempts a different binding or allows another monomer to bind. This finding is consistent with an experimentally observed "stop-and-go" mechanism of fibril growth.
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Affiliation(s)
- Ana Rojas
- Baker Laboratory
of Chemistry
and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, United States
| | - Nika Maisuradze
- Baker Laboratory
of Chemistry
and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, United States
| | - Khatuna Kachlishvili
- Baker Laboratory
of Chemistry
and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, United States
| | - Harold A. Scheraga
- Baker Laboratory
of Chemistry
and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, United States
| | - Gia G. Maisuradze
- Baker Laboratory
of Chemistry
and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, United States
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49
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Levine ZA, Shea JE. Simulations of disordered proteins and systems with conformational heterogeneity. Curr Opin Struct Biol 2016; 43:95-103. [PMID: 27988422 DOI: 10.1016/j.sbi.2016.11.006] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Accepted: 11/07/2016] [Indexed: 12/29/2022]
Abstract
Intrinsically disordered proteins (IDPs) and protein regions can facilitate a wide variety of complex physiological processes such as binding, signaling, and formation of membraneless organelles. They can however also play pathological roles by aggregating into cytotoxic oligomers and fibrils. Characterizing the structure and function of disordered proteins is an onerous task, primarily because these proteins adopt transient structures, which are difficult to capture in experiments. Simulations have emerged as a powerful tool for interpreting and augmenting experimental measurements of IDPs. In this review we focus on computer simulations of disordered protein structures, functions, assemblies, and emerging questions that, taken together, give an overview of the field as it exists today.
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Affiliation(s)
- Zachary A Levine
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106, USA; Department of Physics, University of California Santa Barbara, Santa Barbara, CA 93106, USA
| | - Joan-Emma Shea
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106, USA; Department of Physics, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
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50
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Structural and fluctuational difference between two ends of Aβ amyloid fibril: MD simulations predict only one end has open conformations. Sci Rep 2016; 6:38422. [PMID: 27934893 PMCID: PMC5146922 DOI: 10.1038/srep38422] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Accepted: 11/08/2016] [Indexed: 02/02/2023] Open
Abstract
Aβ amyloid fibrils, which are related to Alzheimer’s disease, have a cross-β structure consisting of two β-sheets: β1 and β2. The Aβ peptides are thought to be serially arranged in the same molecular conformation along the fibril axis. However, to understand the amyloid extension mechanism, we must understand the amyloid fibril structure and fluctuation at the fibril end, which has not been revealed to date. Here, we reveal these features by all-atom molecular dynamics (MD) simulations of Aβ42 and Aβ40 fibrils in explicit water. The structure and fluctuation were observed to differ between the two ends. At the even end, the Aβ peptide always took a closed form wherein β1 and β2 were closely spaced. The Aβ peptide fluctuated more at the odd end and took an open form wherein the two β-sheets were well separated. The differences are attributed to the stronger β-sheet formation by the β1 exposed at the even end than the β2 exposed at the odd end. Along with the small fluctuations at the even end, these results explain why the fibril extends from one end only, as observed in experiments. Our MD results agree well with recent observations by high-speed atomic force microscopy.
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