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Rodriguez-Larrea D. Single-aminoacid discrimination in proteins with homogeneous nanopore sensors and neural networks. Biosens Bioelectron 2021; 180:113108. [PMID: 33690101 DOI: 10.1016/j.bios.2021.113108] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Revised: 02/08/2021] [Accepted: 02/19/2021] [Indexed: 12/18/2022]
Abstract
A technology capable of sequencing individual protein molecules would revolutionize our understanding of biological processes. Nanopore technology can analyze single heteropolymer molecules such as DNA by measuring the ionic current flowing through a single nanometer hole made in an electrically insulating membrane. This current is sensitive to the monomer sequence. However, proteins are remarkably complex and identifying a single residue change in a protein remains a challenge. In this work, I show that simple neural networks can be trained to recognize protein mutants. Although these networks are quickly and efficiently trained, their ability to generalize in an independent experiment is poor. Using a thermal annealing protocol on the nanopore sample, and examining many mutants with the same nanopore sensor are measures aimed at reducing training data variability which produce an increase in the generalizability of the trained neural network. Using this approach, we obtain a 100% correct assignment among 9 mutants in >50% of the experiments. Interestingly, the neural network performance, compared to a random guess, improves as more mutants are included in the dataset for discrimination. Engineered nanopores prepared with high homogeneity coupled with state-of-the-art analysis of the ionic current signals may enable single-molecule protein sequencing.
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Affiliation(s)
- David Rodriguez-Larrea
- Biofisika Institute (CSIC, UPV/EHU) and Department of Biochemistry and Molecular Biology (UPV/EHU), Barrio Sarriena S/n, Leioa, 48940, Spain.
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2
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Zheng S, Sajib MSJ, Wei Y, Wei T. Discontinuous Molecular Dynamics Simulations of Biomolecule Interfacial Behavior: Study of Ovispirin-1 Adsorption on a Graphene Surface. J Chem Theory Comput 2021; 17:1874-1882. [PMID: 33586958 DOI: 10.1021/acs.jctc.0c01172] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Fundamental understanding of biomolecular interfacial behavior, such as protein adsorption at the microscopic scale, is critical to broad applications in biomaterials, nanomedicine, and nanoparticle-based biosensing techniques. The goal of achieving both computational efficiency and accuracy presents a major challenge for simulation studies at both atomistic and molecular scales. In this work, we developed a unique, accurate, high-throughput simulation method which, by integrating discontinuous molecular dynamics (DMD) simulations with the Go-like protein-surface interaction model, not only solves the dynamics efficiently, but also describes precisely the protein intramolecular and intermolecular interactions at the atomistic scale and the protein-surface interactions at the coarse-grained scale. Using our simulation method and in-house developed software, we performed a systematic study of α-helical ovispirin-1 peptide adsorption on a graphene surface, and our study focused on the effect of surface hydrophobic interactions and π-π stacking on protein adsorption. Our DMD simulations were consistent with full-atom molecular dynamics simulations and showed that a single ovispirin-1 peptide lay down on the flat graphene surface with randomized secondary structure due to strong protein-surface interactions. Peptide aggregates were formed with an internal hydrophobic core driven by strong interactions of hydrophobic residues in the bulk environment. However, upon adsorption, the hydrophobic graphene surface can break the hydrophobic core by denaturing individual peptide structures, leading to disassembling the aggregate structure and further randomizing the ovispirin-1 peptide's secondary structures.
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Affiliation(s)
- Size Zheng
- College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu, Sichuan 610059, P. R. China
| | - Md Symon Jahan Sajib
- Chemical Engineering Department, Howard University, Washington, D.C. 20059, United States
| | - Yong Wei
- Department of Computer Science and Information Systems, University of North Georgia, Dahlonega, Georgia 30597, United States
| | - Tao Wei
- Chemical Engineering Department, Howard University, Washington, D.C. 20059, United States
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Zheng S, Sahimi A, Shing KS, Sahimi M. Molecular Dynamics Study of Structure, Folding, and Aggregation of Poly-PR and Poly-GR Proteins. Biophys J 2021; 120:64-72. [PMID: 33253636 PMCID: PMC7820734 DOI: 10.1016/j.bpj.2020.11.2258] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Revised: 10/30/2020] [Accepted: 11/17/2020] [Indexed: 11/25/2022] Open
Abstract
Poly-proline-arginine (poly-PR) and poly-glycine-arginine (poly-GR) proteins are believed to be the most toxic dipeptide repeat (DPR) proteins that are expressed by the hexanucleotide repeat expansion mutation in C9ORF72, which are associated with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) diseases. Their structural information and mechanisms of toxicity remain incomplete, however. Using molecular dynamics simulation and all-atom model of proteins, we study folding and aggregation of both poly-PR and poly-GR. The results indicate formation of double-helix structure during the aggregation of poly-PR into dimers, whereas no stable aggregate is formed during the aggregation of poly-GR; the latter only folds into α-helix and double-helix structures that are similar to those formed in the folding of poly-glycine-alanine (poly-GA) protein. Our findings are consistent with the experimental data indicating that poly-PR and poly-GR are less likely to aggregate because of the hydrophilic arginine residues within their structures. Such characteristics could, however, in some respect facilitate migration of the DPR proteins between and within cells and, at the same time, give proline residues the benefits of activating the receptors that regulate ionotropic effect in neurons, resulting in death or malfunction of neurons because of the abnormal increase or decrease of the ion transmission. This may explain the neurotoxicities of poly-PR and poly-GR associated with many neurodegenerative diseases. To our knowledge, this is the first molecular dynamics simulation of the phenomena involving poly-PR and poly-GR proteins.
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Affiliation(s)
- Size Zheng
- College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu, Sichuan, People's Republic of China.
| | - Ali Sahimi
- Department of Stem Cell Biology and Regenerative Medicine, University of Southern California, Los Angeles, California
| | - Katherine S Shing
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California
| | - Muhammad Sahimi
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California
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Bergamasco L, Alberghini M, Fasano M. Nano-metering of Solvated Biomolecules Or Nanoparticles from Water Self-Diffusivity in Bio-inspired Nanopores. NANOSCALE RESEARCH LETTERS 2019; 14:336. [PMID: 31659492 PMCID: PMC6816642 DOI: 10.1186/s11671-019-3178-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Accepted: 10/04/2019] [Indexed: 06/10/2023]
Abstract
Taking inspiration from the structure of diatom algae frustules and motivated by the need for new detecting strategies for emerging nanopollutants in water, we analyze the potential of nanoporous silica tablets as metering devices for the concentration of biomolecules or nanoparticles in water. The concept relies on the different diffusion behavior that water molecules exhibit in bulk and nanoconfined conditions, e.g., in nanopores. In this latter situation, the self-diffusion coefficient of water reduces according to the geometry and surface properties of the pore and to the concentration of suspended biomolecules or nanoparticles in the pore, as extensively demonstrated in a previous study. Thus, for a given pore-liquid system, the self-diffusivity of water in nanopores filled with biomolecules or nanoparticles provides an indirect measure of their concentration. Using molecular dynamics and previous results from the literature, we demonstrate the correlation between the self-diffusion coefficient of water in silica nanopores and the concentration of proteins or nanoparticles contained therein. Finally, we estimate the time required for the nanoparticles to fill the nanopores, in order to assess the practical feasibility of the overall nano-metering protocol. Results show that the proposed approach may represent an alternative method for assessing the concentration of some classes of nanopollutants or biomolecules in water.
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Affiliation(s)
- Luca Bergamasco
- Department of Energy, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, 10129 Italy
| | - Matteo Alberghini
- Department of Energy, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, 10129 Italy
- Clean Water Center, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, 10129 Italy
| | - Matteo Fasano
- Department of Energy, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, 10129 Italy
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Haridasan N, Kannam SK, Mogurampelly S, Sathian SP. Rotational Diffusion of Proteins in Nanochannels. J Phys Chem B 2019; 123:4825-4832. [DOI: 10.1021/acs.jpcb.9b00895] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Navaneeth Haridasan
- Micro and Nanoscale Transport Lab, Applied Mechanics Department, Indian Institute of Technology Madras, Chennai 600036, India
| | - Sridhar Kumar Kannam
- Department of Mathematics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Melbourne, Victoria 3122, Australia
- School of Sciences, RMIT University, Melbourne, Victoria 3001, Australia
| | - Santosh Mogurampelly
- Institute for Computational Molecular Science, Temple University, Philadelphia 19122, United States
- Department of Physics, Indian Institute of Technology Jodhpur, Rajasthan 342037, India
| | - Sarith P Sathian
- Micro and Nanoscale Transport Lab, Applied Mechanics Department, Indian Institute of Technology Madras, Chennai 600036, India
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Zheng S, Sahimi A, Shing KS, Sahimi M. Molecular dynamics study of structure, folding, and aggregation of poly-glycine-alanine (Poly-GA). J Chem Phys 2019; 150:144307. [PMID: 30981220 DOI: 10.1063/1.5081867] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Poly-glycine-alanine (poly-GA) proteins are widely believed to be one of the main toxic dipeptide repeat molecules associated with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia diseases. Using discontinuous molecular dynamics simulation and an all-atom model of the proteins, we study folding, stability, and aggregation of poly-GA. The results demonstrate that poly-GA is an aggregation-prone protein that, after a long enough time, forms β-sheet-rich aggregates that match recent experiment data and that two unique helical structures are formed very frequently, namely, β-helix and double-helix. The details of the two structures are analyzed. The analysis indicates that such helical structures are stable and share the characteristics of both α-helices and β-sheets. Molecular simulations indicate that identical phenomena also occur in the aggregation of poly-glycine-arginine (poly-GR). Therefore, we hypothesize that proteins of type (GX)n in which X may be any non-glycine amino acid and n is the repeat length may share the same folding structures of β-helix and double-helix and that it is the glycine in the repeat that contributes the most to this characteristic. Molecular dynamics simulation with continuous interaction potentials and explicit water molecules as the solvent supports the hypothesis. To our knowledge, this is the first molecular dynamics simulation of the phenomena involving poly-GA and poly-GR proteins.
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Affiliation(s)
- Size Zheng
- College of Materials and Chemistry and Chemical Engineering, Chengdu University of Technology, Chengdu, Sichuan 610059, People's Republic of China
| | - Ali Sahimi
- Department of Stem Cell Biology and Regenerative Medicine, University of Southern California, Los Angeles, California 90033-1425, USA
| | - Katherine S Shing
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA
| | - Muhammad Sahimi
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA
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Christoulaki A, Chennevière A, Dubois E, Jouault N. Duplex nanoporous alumina and polyelectrolyte adsorption: more insights from a combined neutron reflectivity and electron microscopy study. NANOSCALE 2019; 11:2148-2152. [PMID: 30667446 DOI: 10.1039/c8nr09018a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Neutron reflectivity (NR) is a powerful technique to investigate the incorporation of nanomaterials (polymers, nanoparticles, etc) into multilayer porous systems. Here we propose an experimental approach combining NR and scanning electron microscopy (SEM) to successfully characterize duplex nanoporous anodic aluminum oxides (nAAO) and to extract quantitative information about the entering and adsorption of polyelectrolytes (PEs) in nanopores. Duplex nAAO are promising systems to study the influence of geometrical constriction, i.e. the reduction of pore diameters along the pore channel, on the confinement of condensed matters.
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8
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Wang C, Piroozan N, Javidpour L, Sahimi M. Effect of the geometry of confining media on the stability and folding rate of α -helix proteins. J Chem Phys 2018; 148:194305. [PMID: 30307193 DOI: 10.1063/1.5020841] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Protein folding in confined media has attracted wide attention over the past 15 years due to its importance to both in vivo and in vitro applications. It is generally believed that protein stability increases by decreasing the size of the confining medium, if the medium's walls are repulsive, and that the maximum folding temperature in confinement is in a pore whose size D 0 is only slightly larger than the smallest dimension of a protein's folded state. Until recently, the stability of proteins in pores with a size very close to that of the folded state has not received the attention it deserves. In a previous paper [L. Javidpour and M. Sahimi, J. Chem. Phys. 135, 125101 (2011)], we showed that, contrary to the current theoretical predictions, the maximum folding temperature occurs in larger pores for smaller α-helices. Moreover, in very tight pores, the free energy surface becomes rough, giving rise to a new barrier for protein folding close to the unfolded state. In contrast to unbounded domains, in small nanopores proteins with an α-helical native state that contain the β structures are entropically stabilized implying that folding rates decrease notably and that the free energy surface becomes rougher. In view of the potential significance of such results to interpretation of many sets of experimental data that could not be explained by the current theories, particularly the reported anomalously low rates of folding and the importance of entropic effects on proteins' misfolded states in highly confined environments, we address the following question in the present paper: To what extent the geometry of a confined medium affects the stability and folding rates of proteins? Using millisecond-long molecular dynamics simulations, we study the problem in three types of confining media, namely, cylindrical and slit pores and spherical cavities. Most importantly, we find that the prediction of the previous theories that the dependence of the maximum folding temperature T f on the size D of a confined medium occurs in larger media for larger proteins is correct only in spherical geometry, whereas the opposite is true in the two other geometries that we study. Also studied is the effect of the strength of the interaction between the confined media's walls and the proteins. If the walls are only weakly or moderately attractive, a complex behavior emerges that depends on the size of the confining medium.
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Affiliation(s)
- Congyue Wang
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA
| | - Nariman Piroozan
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA
| | - Leili Javidpour
- Departments of Energy Engineering and Physics, Amirkabir University of Technology, Tehran 15875-4413, Iran
| | - Muhammad Sahimi
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA
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Zheng S, Shing KS, Sahimi M. Dynamics of proteins aggregation. II. Dynamic scaling in confined media. J Chem Phys 2018; 148:104305. [PMID: 29544316 DOI: 10.1063/1.5008543] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
In this paper, the second in a series devoted to molecular modeling of protein aggregation, a mesoscale model of proteins together with extensive discontinuous molecular dynamics simulation is used to study the phenomenon in a confined medium. The medium, as a model of a crowded cellular environment, is represented by a spherical cavity, as well as cylindrical tubes with two aspect ratios. The aggregation process leads to the formation of β sheets and eventually fibrils, whose deposition on biological tissues is believed to be a major factor contributing to many neuro-degenerative diseases, such as Alzheimer's, Parkinson's, and amyotrophic lateral sclerosis diseases. Several important properties of the aggregation process, including dynamic evolution of the total number of the aggregates, the mean aggregate size, and the number of peptides that contribute to the formation of the β sheets, have been computed. We show, similar to the unconfined media studied in Paper I [S. Zheng et al., J. Chem. Phys. 145, 134306 (2016)], that the computed properties follow dynamic scaling, characterized by power laws. The existence of such dynamic scaling in unconfined media was recently confirmed by experiments. The exponents that characterize the power-law dependence on time of the properties of the aggregation process in spherical cavities are shown to agree with those in unbounded fluids at the same protein density, while the exponents for aggregation in the cylindrical tubes exhibit sensitivity to the geometry of the system. The effects of the number of amino acids in the protein, as well as the size of the confined media, have also been studied. Similarities and differences between aggregation in confined and unconfined media are described, including the possibility of no fibril formation, if confinement is severe.
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Affiliation(s)
- Size Zheng
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA
| | - Katherine S Shing
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA
| | - Muhammad Sahimi
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA
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10
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Zheng S, Javidpour L, Shing KS, Sahimi M. Dynamics of proteins aggregation. I. Universal scaling in unbounded media. J Chem Phys 2017; 145:134306. [PMID: 27782447 DOI: 10.1063/1.4962837] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
It is well understood that in some cases proteins do not fold correctly and, depending on their environment, even properly-folded proteins change their conformation spontaneously, taking on a misfolded state that leads to protein aggregation and formation of large aggregates. An important factor that contributes to the aggregation is the interactions between the misfolded proteins. Depending on the aggregation environment, the aggregates may take on various shapes forming larger structures, such as protein plaques that are often toxic. Their deposition in tissues is a major contributing factor to many neuro-degenerative diseases, such as Alzheimer's, Parkinson's, amyotrophic lateral sclerosis, and prion. This paper represents the first part in a series devoted to molecular simulation of protein aggregation. We use the PRIME, a meso-scale model of proteins, together with extensive discontinuous molecular dynamics simulation to study the aggregation process in an unbounded fluid system, as the first step toward MD simulation of the same phenomenon in crowded cellular environments. Various properties of the aggregates have been computed, including dynamic evolution of aggregate-size distribution, mean aggregate size, number of peptides that contribute to the formation of β sheets, number of various types of hydrogen bonds formed in the system, radius of gyration of the aggregates, and the aggregates' diffusivity. We show that many of such quantities follow dynamic scaling, similar to those for aggregation of colloidal clusters. In particular, at long times the mean aggregate size S(t) grows with time as, S(t) ∼ tz, where z is the dynamic exponent. To our knowledge, this is the first time that the qualitative similarity between aggregation of proteins and colloidal aggregates has been pointed out.
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Affiliation(s)
- Size Zheng
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA
| | - Leili Javidpour
- School of Physics, Institute for Research in Fundamental Sciences (IPM), Tehran 19395-5531, Iran
| | - Katherine S Shing
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA
| | - Muhammad Sahimi
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA
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Huber P. Soft matter in hard confinement: phase transition thermodynamics, structure, texture, diffusion and flow in nanoporous media. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:103102. [PMID: 25679044 DOI: 10.1088/0953-8984/27/10/103102] [Citation(s) in RCA: 130] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Spatial confinement in nanoporous media affects the structure, thermodynamics and mobility of molecular soft matter often markedly. This article reviews thermodynamic equilibrium phenomena, such as physisorption, capillary condensation, crystallisation, self-diffusion, and structural phase transitions as well as selected aspects of the emerging field of spatially confined, non-equilibrium physics, i.e. the rheology of liquids, capillarity-driven flow phenomena, and imbibition front broadening in nanoporous materials. The observations in the nanoscale systems are related to the corresponding bulk phenomenologies. The complexity of the confined molecular species is varied from simple building blocks, like noble gas atoms, normal alkanes and alcohols to liquid crystals, polymers, ionic liquids, proteins and water. Mostly, experiments with mesoporous solids of alumina, gold, carbon, silica, and silicon with pore diameters ranging from a few up to 50 nm are presented. The observed peculiarities of nanopore-confined condensed matter are also discussed with regard to applications. A particular emphasis is put on texture formation upon crystallisation in nanoporous media, a topic both of high fundamental interest and of increasing nanotechnological importance, e.g. for the synthesis of organic/inorganic hybrid materials by melt infiltration, the usage of nanoporous solids in crystal nucleation or in template-assisted electrochemical deposition of nano structures.
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Affiliation(s)
- Patrick Huber
- Hamburg University of Technology (TUHH), Institute of Materials Physics and Technology, Eißendorfer Str. 42, D-21073 Hamburg-Harburg (Germany
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Kannam SK, Kim SC, Rogers PR, Gunn N, Wagner J, Harrer S, Downton MT. Sensing of protein molecules through nanopores: a molecular dynamics study. NANOTECHNOLOGY 2014; 25:155502. [PMID: 24651263 DOI: 10.1088/0957-4484/25/15/155502] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Solid-state nanopores have been shown to be suitable for single molecule detection. While numerous modeling investigations exist for DNA within nanopores, there are few simulations of protein translocations. In this paper, we use atomistic molecular dynamics to investigate the translocation of proteins through a silicon nitride nanopore. The nanopore dimensions and profile are representative of experimental systems. We are able to calculate the change in blockade current and friction coefficient for different positions of the protein within the pore. The change in ionic current is found to be negligible until the protein is fully within the pore and the current is lowest when the protein is in the pore center. Using a simple theory that gives good quantitative agreement with the simulation results we are able to show that the variation in current with position is a function of the pore shape. In simulations that guide the protein through the nanopore we identify the effect that confinement has on the friction coefficient of the protein. This integrated view of translocation at the nanoscale provides useful insights that can be used to guide the design of future devices.
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Lee PH, Helms V, Geyer T. Coarse-grained Brownian dynamics simulations of protein translocation through nanopores. J Chem Phys 2012; 137:145105. [DOI: 10.1063/1.4757265] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
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Palmieri B, Safran SA. Diffusion in a soft confining environment: dynamic effects of thermal fluctuations. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 86:031111. [PMID: 23030870 DOI: 10.1103/physreve.86.031111] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2012] [Indexed: 06/01/2023]
Abstract
A dynamical model of a soft, thermally fluctuating two-dimensional tube is used to study the effect of thermal fluctuations of a confining environment on diffusive transport. The tube fluctuations in both space and time are driven by Brownian motion and suppressed by surface tension and the rigidity of the surrounding environment. The dynamical fluctuations modify the concentration profile boundary condition at the tube surface. They decrease the diffusive transport rate through the tube for two important cases: uniform tube fluctuations (wave vector, q=0 mode) for finite tube lengths and fluctuations of any wave vector for infinitely long tubes.
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Affiliation(s)
- Benoit Palmieri
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel
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15
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Shirvanyants D, Ding F, Tsao D, Ramachandran S, Dokholyan NV. Discrete molecular dynamics: an efficient and versatile simulation method for fine protein characterization. J Phys Chem B 2012; 116:8375-82. [PMID: 22280505 PMCID: PMC3406226 DOI: 10.1021/jp2114576] [Citation(s) in RCA: 166] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Until now it has been impractical to observe protein folding in silico for proteins larger than 50 residues. Limitations of both force field accuracy and computational efficiency make the folding problem very challenging. Here we employ discrete molecular dynamics (DMD) simulations with an all-atom force field to fold fast-folding proteins. We extend the DMD force field by introducing long-range electrostatic interactions to model salt-bridges and a sequence-dependent semiempirical potential accounting for natural tendencies of certain amino acid sequences to form specific secondary structures. We enhance the computational performance by parallelizing the DMD algorithm. Using a small number of commodity computers, we achieve sampling quality and folding accuracy comparable to the explicit-solvent simulations performed on high-end hardware. We demonstrate that DMD can be used to observe equilibrium folding of villin headpiece and WW domain, study two-state folding kinetics, and sample near-native states in ab initio folding of proteins of ∼100 residues.
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Affiliation(s)
- David Shirvanyants
- Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Feng Ding
- Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Douglas Tsao
- Department of Chemistry, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Srinivas Ramachandran
- Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Nikolay V. Dokholyan
- Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill, NC 27599, USA
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17
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Javidpour L, Sahimi M. Confinement in nanopores can destabilize α-helix folding proteins and stabilize the β structures. J Chem Phys 2012; 135:125101. [PMID: 21974560 DOI: 10.1063/1.3641482] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Protein folding in confined media has attracted wide attention over the past decade due to its importance in both in vivo and in vitro applications. Currently, it is generally believed that protein stability increases by decreasing the size of the confining medium, if its interaction with the confining walls is repulsive, and that the maximum folding temperature in confinement occurs for a pore size only slightly larger than the smallest dimension of the folded state of a protein. Protein stability in pore sizes, very close to the size of the folded state, has not however received the attention that it deserves. Using detailed, 0.3-ms-long molecular dynamics simulations, we show that proteins with an α-helix native state can have an optimal folding temperature in pore sizes that do not affect the folded-state structure. In contradiction to the current theoretical explanations, we find that the maximum folding temperature occurs in larger pores for smaller α-helices. In highly confined pores the free energy surface becomes rough, and a new barrier for protein folding may appear close to the unfolded state. In addition, in small nanopores the protein states that contain the β structures are entropically stabilized, in contrast to the bulk. As a consequence, folding rates decrease notably and the free energy surface becomes rougher. The results shed light on many recent experimental observations that cannot be explained by the current theories, and demonstrate the importance of entropic effects on proteins' misfolded states in highly confined environments. They also support the concept of passive effect of chaperonin GroEL on protein folding by preventing it from aggregation in crowded environment of biological cells, and provide deeper clues to the α → β conformational transition, believed to contribute to Alzheimer's and Parkinson's diseases. The strategy of protein and enzyme stabilization in confined media may also have to be revisited in the case of tight confinement. For in silico studies of protein folding in confined media, use of non-Go potentials may be more appropriate.
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Affiliation(s)
- Leili Javidpour
- School of Physics, Institute for Research in Fundamental Sciences, IPM, Tehran 19395-5531, Iran
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Peters MH. Langevin dynamics for the transport of flexible biological macromolecules in confined geometries. J Chem Phys 2011; 134:025105. [DOI: 10.1063/1.3525381] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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