1
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Ham S, Wang X, Nair AKN, Sun S, Lattimer B, Qiao R. Transport of Heptane Molecules across Water-Vapor Interfaces Laden with Surfactants. J Phys Chem B 2023. [PMID: 37410979 DOI: 10.1021/acs.jpcb.3c02618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/08/2023]
Abstract
Molecular transport across liquid-vapor interfaces covered by surfactant monolayers plays a key role in applications such as fire suppression by foams. The molecular understanding of such transport, however, remains incomplete. This work uses molecular dynamics simulations to investigate the heptane transport across water-vapor interfaces populated with sodium dodecyl sulfate (SDS) surfactants. Heptane molecules' potential of mean force (PMF) and local diffusivity profiles across SDS monolayers with different SDS densities are calculated to obtain heptane's transport resistance. We show that a heptane molecule experiences a finite resistance as it crosses water-vapor interfaces covered by SDS. Such interfacial transport resistance is contributed significantly by heptane molecules' high PMF in the SDS headgroup region and their slow diffusion there. This resistance increases linearly as the SDS density rises from zero but jumps as the density approaches saturation when its value is equivalent to that afforded by a 5 nm thick layer of bulk water. These results are understood by analyzing the micro-environment experienced by a heptane molecule crossing SDS monolayers and the local perturbation it brings to the monolayers. The implications of these findings for the design of surfactants to suppress heptane transport through water-vapor interfaces are discussed.
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Affiliation(s)
- Seokgyun Ham
- Department of Mechanical Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Xin Wang
- Department of Mechanical Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Arun Kumar Narayanan Nair
- Department of Earth Science and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
| | - Shuyu Sun
- Department of Earth Science and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
| | - Brian Lattimer
- Department of Mechanical Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Rui Qiao
- Department of Mechanical Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States
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2
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Feroz H, Chennamsetty N, Byers S, Holstein M, Li ZJ, Ghose S. Assessing detergent-mediated virus inactivation, protein stability, and impurity clearance in biologics downstream processes. Biotechnol Bioeng 2022; 119:1091-1104. [PMID: 35023152 DOI: 10.1002/bit.28034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Revised: 12/13/2021] [Accepted: 01/04/2022] [Indexed: 11/12/2022]
Abstract
Detergent-mediated virus inactivation (VI) provides a valuable orthogonal strategy for viral clearance in mammalian processes, in particular for next-generation continuous manufacturing. Furthermore, there exists an industry-wide need to replace the conventionally employed detergent Triton X-100 with eco-friendly alternatives. However, given Triton X-100 has been the gold standard for VI due its minimal impact on protein stability and high inactivation efficacy, inactivation by other eco-friendly detergents and its impact on protein stability is not well understood. In this study, the sugar-based detergent commonly used in membrane protein purification, n-dodecyl-β- d-maltoside was found to be a promising alternative for VI. We investigated a panel of detergents to compare the relative VI efficacy, impact on therapeutic quality attributes, and clearance of the VI agent and other impurities through subsequent chromatographic steps. Detergent-mediated inactivation and protein stability showed comparable trends to low pH inactivation. Using experimental and modeling data, we found detergent-mediated product aggregation and its kinetics to be driven by extrinsic factors such as detergent and protein concentration. Detergent-mediated aggregation was also impacted by an initial aggregation level as well as intrinsic factors such as the protein sequence and detergent hydrophobicity, and critical micelle concentration. Knowledge gained here on factors driving product stability and VI provides valuable insight to design, standardize, and optimize conditions (concentration and duration of inactivation) for screening of detergent-mediated VI.
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Affiliation(s)
- Hasin Feroz
- Biologics Process Development, Global Product Development and Supply, Bristol Myers Squibb, Co., Devens, Massachusetts, USA
| | - Naresh Chennamsetty
- Analytical Development and Attribute Sciences, Biologics Development, Bristol Myers Squibb Company, New Brunswick, New Jersey, USA
| | - Sara Byers
- Analytical Development and Attribute Sciences, Biologics Development, Bristol Myers Squibb Co., Devens, Massachusetts, USA
| | - Melissa Holstein
- Biologics Process Development, Global Product Development and Supply, Bristol Myers Squibb, Co., Devens, Massachusetts, USA
| | - Zheng J Li
- Biologics Process Development, Global Product Development and Supply, Bristol Myers Squibb, Co., Devens, Massachusetts, USA
| | - Sanchayita Ghose
- Biologics Process Development, Global Product Development and Supply, Bristol Myers Squibb, Co., Devens, Massachusetts, USA
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3
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Feroz H, Cetnar D, Hewlett R, Sharma S, Holstein M, Ghose S, Li ZJ. Surrogate model to screen for inactivation-based clearance of enveloped viruses during biotherapeutics process development. Biotechnol J 2021; 16:e2100176. [PMID: 34506679 DOI: 10.1002/biot.202100176] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Revised: 09/03/2021] [Accepted: 09/07/2021] [Indexed: 11/07/2022]
Abstract
Viral surrogates to screen for virus inactivation (VI) can be a faster, cheaper and safer alternative to third-party testing of pathogenic BSL2 (Biosafety level 2) model viruses. Although the bacteriophage surrogate, Ø6, has been used to assess low pH BSL2 VI, it has not been used for evaluation of detergent-mediated VI. Furthermore, Ø6 is typically assayed through host cell infectivity which introduces the risk of cross-contaminating other cell lines in the facility. To circumvent contamination, we developed an in-house RT-qPCR (Reverse transcriptase quantitative polymerase chain reaction) assay for selective detection of active Ø6 from a population of live and dead phage. The RT-qPCR assay was used to evaluate Ø6 inactivation in cell culture fluid of monoclonal antibody and fusion protein. Complementary Ø6 infectivity was also conducted at a third-party testing facility. The Ø6 RT-qPCR and infectivity data was modeled against VI of three BSL2 viruses, X- MuLV, A- MuLV and HSV-1 in corresponding therapeutics. Both Ø6 methods demonstrate that any VI agent showing Ø6 clearance of a minimum of 2.5 logs would demonstrate complete BSL2 VI of ≥ 4.0 logs. Compared to BSL2 virus testing, this in-house Ø6 RT-qPCR tool can screen VI agents at 5% the cost and a turnaround time of 2 to 3 days vs. 4 to 7 months.
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Affiliation(s)
- Hasin Feroz
- Biologics Development, Bristol Myers Squibb, Devens, Massachusetts, USA
| | - Daniel Cetnar
- Biologics Development, Bristol Myers Squibb, Devens, Massachusetts, USA
| | - Robert Hewlett
- Biologics Development, Bristol Myers Squibb, Devens, Massachusetts, USA
| | - Satish Sharma
- Biologics Development, Bristol Myers Squibb, Devens, Massachusetts, USA
| | - Melissa Holstein
- Biologics Development, Bristol Myers Squibb, Devens, Massachusetts, USA
| | - Sanchayita Ghose
- Biologics Development, Bristol Myers Squibb, Devens, Massachusetts, USA
| | - Zheng Jian Li
- Biologics Development, Bristol Myers Squibb, Devens, Massachusetts, USA
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4
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Patel SJ, Van Lehn RC. Analysis of Charged Peptide Loop-Flipping across a Lipid Bilayer Using the String Method with Swarms of Trajectories. J Phys Chem B 2021; 125:5862-5873. [PMID: 34033491 DOI: 10.1021/acs.jpcb.1c02810] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The hydrophobic core of the lipid bilayer is conventionally considered a barrier to the translocation of charged species such that the translocation of even single ions occurs on long time scales. In contrast, experiments have revealed that some materials, including peptides, proteins, and nanoparticles, can translocate multiple charged moieties across the bilayer on experimentally relevant time scales. Understanding the molecular mechanisms underlying this behavior is challenging because resolving corresponding free-energy landscapes with molecular simulation techniques is computationally expensive. To address this challenge, we use atomistic molecular dynamics simulations with the swarms-of-trajectories (SOT) string method to analyze charge translocation pathways across single-component lipid bilayers as a function of multiple collective variables. We first demonstrate that the SOT string method can reproduce the free-energy barrier for the translocation of a charged lysine amino acid analogue in good agreement with the literature. We then obtain minimum free-energy pathways for the translocation, or flipping, of charged peptide loops across the lipid bilayer by utilizing trajectories from prior temperature-accelerated molecular dynamics (TAMD) simulations as initial configurations. The corresponding potential of mean force calculations reveal that the protonation of a central membrane-exposed aspartate residue substantially reduces the free-energy barrier for flipping charged loops by modulating the water content of the bilayer. These results provide new insight into the thermodynamics underlying loop-flipping processes and highlight how the combination of TAMD and the SOT string method can be used to understand complex charge translocation mechanisms.
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Affiliation(s)
- Samarthaben J Patel
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Reid C Van Lehn
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
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5
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Meingast CL, Joshi PU, Turpeinen DG, Xu X, Holstein M, Feroz H, Ranjan S, Ghose S, Li ZJ, Heldt CL. Physiochemical properties of enveloped viruses and arginine dictate inactivation. Biotechnol J 2021; 16:e2000342. [PMID: 33877739 DOI: 10.1002/biot.202000342] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 03/28/2021] [Accepted: 03/30/2021] [Indexed: 11/06/2022]
Abstract
BACKGROUND Therapeutic protein manufacturing would benefit by having an arsenal of ways to inactivate viruses. There have been many publications on the virus inactivation ability of arginine at pH 4.0, but the mechanism of this inactivation is unknown. This study explored how virus structure and solution conditions enhance virus inactivation by arginine and leads to a better understanding of the mechanism of virus inactivation by arginine. RESULTS Large diameter viruses from the Herpesviridae family (SuHV-1, HSV-1) with loosely packed lipids were highly inactivated by arginine, whereas small diameter, enveloped viruses (equine arteritis virus (EAV) and bovine viral diarrhea virus (BVDV)) with tightly packed lipids were negligibly inactivated by arginine. To increase the inactivation of viruses resistant to arginine, arginine-derivatives and arginine peptides were tested. Derivates and peptides demonstrated that a greater capacity for clustering and added hydrophobicity enhanced virus inactivation. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) detected increases in virus size after arginine exposure, supporting the mechanism of lipid expansion. CONCLUSIONS Arginine most likely interacts with the lipid membrane to cause inactivation. This is shown by larger viruses being more sensitive to inactivation and expansion of the viral size. The enhancement of arginine inactivation when increased hydrophobic molecules are present or arginine is clustered demonstrates a potential mechanism of how arginine interacts with the lipid membrane.
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Affiliation(s)
- Christa L Meingast
- Department of Environmental Engineering, Michigan Technological University, Houghton, Michigan, USA.,Health Research Institute, Michigan Technological University, Houghton, Michigan, USA
| | - Pratik U Joshi
- Health Research Institute, Michigan Technological University, Houghton, Michigan, USA.,Department of Chemical Engineering, Michigan Technological University, Houghton, Michigan, USA
| | - Dylan G Turpeinen
- Health Research Institute, Michigan Technological University, Houghton, Michigan, USA.,Department of Chemical Engineering, Michigan Technological University, Houghton, Michigan, USA
| | - Xuankuo Xu
- Biologics Process Development, Global Product Development and Supply, Bristol Myers Squibb, Devens, Massachusetts, USA
| | - Melissa Holstein
- Biologics Process Development, Global Product Development and Supply, Bristol Myers Squibb, Devens, Massachusetts, USA
| | - Hasin Feroz
- Biologics Process Development, Global Product Development and Supply, Bristol Myers Squibb, Devens, Massachusetts, USA
| | - Swarnim Ranjan
- Biologics Process Development, Global Product Development and Supply, Bristol Myers Squibb, Devens, Massachusetts, USA
| | - Sanchayita Ghose
- Biologics Process Development, Global Product Development and Supply, Bristol Myers Squibb, Devens, Massachusetts, USA
| | - Zheng Jian Li
- Biologics Process Development, Global Product Development and Supply, Bristol Myers Squibb, Devens, Massachusetts, USA
| | - Caryn L Heldt
- Health Research Institute, Michigan Technological University, Houghton, Michigan, USA.,Department of Chemical Engineering, Michigan Technological University, Houghton, Michigan, USA
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6
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Chen P, Vorobyov I, Roux B, Allen TW. Molecular Dynamics Simulations Based on Polarizable Models Show that Ion Permeation Interconverts between Different Mechanisms as a Function of Membrane Thickness. J Phys Chem B 2021; 125:1020-1035. [PMID: 33493394 DOI: 10.1021/acs.jpcb.0c08613] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Different mechanisms have been proposed to explain the permeation of charged compounds through lipid membranes. Overall, it is expected that an ion-induced defect permeation mechanism, where substantial membrane deformations accompany ion movement, should be dominant in thin membranes but that a solubility-diffusion mechanism, where ions partition into the membrane core with large associated dehydration energy costs, becomes dominant in thicker membranes. However, while this physical picture is intuitively reasonable, capturing the interconversion between these two permeation mechanisms in molecular dynamics (MD) simulations based on atomic models is challenging. In particular, simulations relying on nonpolarizable force fields are artificially unfavorable to the solubility-diffusion mechanism, as induced polarization of the nonpolar hydrocarbon is ignored, causing overestimated free energy costs for charged molecules to enter into this region of the membrane. In this study, all-atom MD simulations based on nonpolarizable and polarizable force fields are used to quantitatively characterize the permeation process for the arginine side chain analog methyl-guanidinium through bilayer membranes of mono-unsaturated phosphatidylcholine lipids with and without cholesterol, resulting in thicknesses spanning from ∼24 to ∼42 Å. With simulations based on a nonpolarizable force field, ion translocation can take place solely through an ion-induced defect mechanism, with free energy barriers increasing linearly from 14 to 40 kcal/mol, depending on the thickness. However, with simulations based on a polarizable force field, ion translocation is predominantly dominated by an ion-induced defect mechanism in thin membranes, which progressively converts to a solubility-diffusion mechanism as the membranes get thicker. The transition between the two mechanisms occurs at a thickness of ∼29 Å, with lipid tails of 22 or more carbon atoms. This situation appears to represent the upper limit for ion-induced defect permeation within the current polarizable models. Beyond this thickness, it becomes energetically preferable for the ion to dehydrate and partition into the membrane core-a phenomenon that cannot be captured using the nonpolarizable models. Induced electronic polarizability therefore leads not just to a shift in permeation energetics but to an interconversion between two strikingly different physical mechanisms. The result highlights the importance of induced polarizability in modeling lipid membranes.
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Affiliation(s)
- Peiran Chen
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Igor Vorobyov
- Department of Physiology & Membrane Biology, Department of Pharmacology, University of California, Davis, California 95616, United States
| | - Benoît Roux
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - Toby W Allen
- School of Science, RMIT University, Melbourne 3001, Australia
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7
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Apostolopoulos V, Bojarska J, Chai TT, Elnagdy S, Kaczmarek K, Matsoukas J, New R, Parang K, Lopez OP, Parhiz H, Perera CO, Pickholz M, Remko M, Saviano M, Skwarczynski M, Tang Y, Wolf WM, Yoshiya T, Zabrocki J, Zielenkiewicz P, AlKhazindar M, Barriga V, Kelaidonis K, Sarasia EM, Toth I. A Global Review on Short Peptides: Frontiers and Perspectives. Molecules 2021; 26:E430. [PMID: 33467522 PMCID: PMC7830668 DOI: 10.3390/molecules26020430] [Citation(s) in RCA: 153] [Impact Index Per Article: 51.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Revised: 12/23/2020] [Accepted: 01/09/2021] [Indexed: 12/13/2022] Open
Abstract
Peptides are fragments of proteins that carry out biological functions. They act as signaling entities via all domains of life and interfere with protein-protein interactions, which are indispensable in bio-processes. Short peptides include fundamental molecular information for a prelude to the symphony of life. They have aroused considerable interest due to their unique features and great promise in innovative bio-therapies. This work focusing on the current state-of-the-art short peptide-based therapeutical developments is the first global review written by researchers from all continents, as a celebration of 100 years of peptide therapeutics since the commencement of insulin therapy in the 1920s. Peptide "drugs" initially played only the role of hormone analogs to balance disorders. Nowadays, they achieve numerous biomedical tasks, can cross membranes, or reach intracellular targets. The role of peptides in bio-processes can hardly be mimicked by other chemical substances. The article is divided into independent sections, which are related to either the progress in short peptide-based theranostics or the problems posing challenge to bio-medicine. In particular, the SWOT analysis of short peptides, their relevance in therapies of diverse diseases, improvements in (bio)synthesis platforms, advanced nano-supramolecular technologies, aptamers, altered peptide ligands and in silico methodologies to overcome peptide limitations, modern smart bio-functional materials, vaccines, and drug/gene-targeted delivery systems are discussed.
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Affiliation(s)
- Vasso Apostolopoulos
- Institute for Health and Sport, Victoria University, Melbourne, VIC 3030, Australia; (V.A.); (J.M.); (V.B.)
| | - Joanna Bojarska
- Institute of General and Ecological Chemistry, Faculty of Chemistry, Lodz University of Technology, Żeromskiego 116, 90-924 Lodz, Poland
| | - Tsun-Thai Chai
- Department of Chemical Science, Faculty of Science, Universiti Tunku Abdul Rahman, Kampar 31900, Malaysia;
| | - Sherif Elnagdy
- Botany and Microbiology Department, Faculty of Science, Cairo University, Gamaa St., Giza 12613, Egypt; (S.E.); (M.A.)
| | - Krzysztof Kaczmarek
- Institute of Organic Chemistry, Faculty of Chemistry, Lodz University of Technology, Żeromskiego 116, 90-924 Lodz, Poland; (K.K.); (J.Z.)
| | - John Matsoukas
- Institute for Health and Sport, Victoria University, Melbourne, VIC 3030, Australia; (V.A.); (J.M.); (V.B.)
- NewDrug, Patras Science Park, 26500 Patras, Greece;
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, AB T2N 4N1, Canada
| | - Roger New
- Vaxcine (UK) Ltd., c/o London Bioscience Innovation Centre, London NW1 0NH, UK;
- Faculty of Science & Technology, Middlesex University, The Burroughs, London NW4 4BT, UK;
| | - Keykavous Parang
- Center for Targeted Drug Delivery, Department of Biomedical and Pharmaceutical Sciences, Chapman University School of Pharmacy, Harry and Diane Rinker Health Science Campus, Irvine, CA 92618, USA;
| | - Octavio Paredes Lopez
- Centro de Investigación y de Estudios Avanzados del IPN, Departamento de Biotecnología y Bioquímica, Irapuato 36824, Guanajuato, Mexico;
| | - Hamideh Parhiz
- Infectious Disease Division, Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6073, USA;
| | - Conrad O. Perera
- School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand;
| | - Monica Pickholz
- Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires 1428, Argentina;
- Instituto de Física de Buenos Aires (IFIBA, UBA-CONICET), Argentina, Buenos Aires 1428, Argentina
| | - Milan Remko
- Remedika, Luzna 9, 85104 Bratislava, Slovakia;
| | - Michele Saviano
- Institute of Crystallography (CNR), Via Amendola 122/o, 70126 Bari, Italy;
| | - Mariusz Skwarczynski
- School of Chemistry & Molecular Biosciences, The University of Queensland, St Lucia, QLD 4072, Australia; (M.S.); (I.T.)
| | - Yefeng Tang
- Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology (MOE), School of Pharma Ceutical Sciences, Tsinghua University, Beijing 100084, China;
| | - Wojciech M. Wolf
- Institute of General and Ecological Chemistry, Faculty of Chemistry, Lodz University of Technology, Żeromskiego 116, 90-924 Lodz, Poland
| | | | - Janusz Zabrocki
- Institute of Organic Chemistry, Faculty of Chemistry, Lodz University of Technology, Żeromskiego 116, 90-924 Lodz, Poland; (K.K.); (J.Z.)
| | - Piotr Zielenkiewicz
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland;
- Department of Systems Biology, Institute of Experimental Plant Biology and Biotechnology, University of Warsaw, Miecznikowa 1, 02-096 Warsaw, Poland
| | - Maha AlKhazindar
- Botany and Microbiology Department, Faculty of Science, Cairo University, Gamaa St., Giza 12613, Egypt; (S.E.); (M.A.)
| | - Vanessa Barriga
- Institute for Health and Sport, Victoria University, Melbourne, VIC 3030, Australia; (V.A.); (J.M.); (V.B.)
| | | | | | - Istvan Toth
- School of Chemistry & Molecular Biosciences, The University of Queensland, St Lucia, QLD 4072, Australia; (M.S.); (I.T.)
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD 4072, Australia
- School of Pharmacy, The University of Queensland, Woolloongabba, QLD 4102, Australia
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8
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Eslami H, Das S, Zhou T, Müller-Plathe F. How Alcoholic Disinfectants Affect Coronavirus Model Membranes: Membrane Fluidity, Permeability, and Disintegration. J Phys Chem B 2020; 124:10374-10385. [PMID: 33172260 PMCID: PMC7670823 DOI: 10.1021/acs.jpcb.0c08296] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 10/28/2020] [Indexed: 01/17/2023]
Abstract
Atomistic molecular dynamics simulations have been carried out with a view to investigating the stability of the SARS-CoV-2 exterior membrane with respect to two common disinfectants, namely, aqueous solutions of ethanol and n-propanol. We used dipalmitoylphosphatidylcholine (DPPC) as a model membrane material and did simulations on both gel and liquid crystalline phases of membrane surrounded by aqueous solutions of varying alcohol concentrations (up to 17.5 mol %). While a moderate effect of alcohol on the gel phase of membrane is observed, its liquid crystalline phase is shown to be influenced dramatically by either alcohol. Our results show that aqueous solutions of only 5 and 10 mol % alcohol already have significant weakening effects on the membrane. The effects of n-propanol are always stronger than those of ethanol. The membrane changes its structure, when exposed to disinfectant solutions; uptake of alcohol causes it to swell laterally but to shrink vertically. At the same time, the orientational order of lipid tails decreases significantly. Metadynamics and grand-canonical ensemble simulations were done to calculate the free-energy profiles for permeation of alcohol and alcohol/water solubility in the DPPC. We found that the free-energy barrier to permeation of the DPPC liquid crystalline phase by all permeants is significantly lowered by alcohol uptake. At a disinfectant concentration of 10 mol %, it becomes insignificant enough to allow almost free passage of the disinfectant to the inside of the virus to cause damage there. It should be noted that the disinfectant also causes the barrier for water permeation to drop. Furthermore, the shrinking of the membrane thickness shortens the gap needed to be crossed by penetrants from outside the virus into its core. The lateral swelling also increases the average distance between head groups, which is a secondary barrier to membrane penetration, and hence further increases the penetration by disinfectants. At alcohol concentrations in the disinfectant solution above 15 mol %, we reliably observe disintegration of the DPPC membrane in its liquid crystalline phase.
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Affiliation(s)
- Hossein Eslami
- Eduard-Zintl-Institut
für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, Darmstadt 64287, Germany
- Department
of Chemistry, College of Sciences, Persian
Gulf University, Boushehr 75168, Iran
| | - Shubhadip Das
- Eduard-Zintl-Institut
für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, Darmstadt 64287, Germany
| | - Tianhang Zhou
- Eduard-Zintl-Institut
für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, Darmstadt 64287, Germany
| | - Florian Müller-Plathe
- Eduard-Zintl-Institut
für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, Darmstadt 64287, Germany
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9
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Lee BL, Kuczera K, Lee KH, Childs EW, Jas GS. Unassisted N-acetyl-phenylalanine-amide transport across membrane with varying lipid size and composition: kinetic measurements and atomistic molecular dynamics simulation. J Biomol Struct Dyn 2020; 40:1445-1460. [PMID: 33034537 DOI: 10.1080/07391102.2020.1827037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Biological membranes are essential to preserve structural integrity and regulate functional properties through the permeability of nutrients, pharmaceutical drugs, and neurotransmitters of a living cell. The movement of acetylated and amidated phenylalanine (NAFA) across 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membrane bilayers is investigated to probe physical transport. The rate of transport is measured experimentally applying parallel artificial membrane permeation assay (PAMPA). At the physiological temperature, 310 K, the measured time constants in the neutral pH were ∼6 h in DOPC and ∼3 h in POPC, while in a more acidic condition, at a pH 4.8, the time constants were ∼8 h in both lipids. Computationally, we have expanded our transport study of three aromatic dipeptides across a bilayer composed of DOPC18. In this study, we have examined the effects of lipid composition and bilayer size on the passive transport of NAFA by simulating the dipeptide in three different bilayers, with 50 DOPC lipids, 50 POPC lipids, and 40 POPC molecules. Specifically, atomistic molecular dynamics simulations with umbrella sampling were used to calculate the potential of mean force for the passive permeation of NAFA across the bilayers. Diffusion constants were then calculated by numerically solving the Smoluchowski equation. Permeability coefficients and mean first passage times were then calculated. Structural properties - Ramachandran plots, sidechain torsions, peptide insertion angles, radial distribution functions, and proximal peptide water molecules - were also examined to determine the effect of system size and lipid type. In terms of systems size, we observed a small decrease in the highest barrier of the potential of mean force and fewer sampled sidechain dihedral angle conformations with 40 versus 50 POPC lipids due to weaker membrane deformations within a smaller lipid bilayer. In terms of lipid type, DOPC contains two monounsaturated acyl chains compared to only one such acyl chain in POPC; therefore, DOPC bilayers are less ordered and more easily deformed, as seen by a much broader potential of mean force profile. The NAFA in DOPC lipid also transitioned to an internally hydrogen-bonded backbone conformation at lower membrane depths than in POPC. Similarly, as for other aromatic dipeptides, NAFA tends to insert into the membrane sidechain-first, remains mostly desolvated in the membrane center, and exhibits slow reorientations within the bilayer in both DOPC and POPC. With a joint experimental and computational study we have gained a new insight into the rate of transport and the underlying microscopic mechanism in different lipid bilayer conditions of the simplest hydrophobic aromatic dipeptide.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Brent L Lee
- Department of Chemistry, The University of Kansas, Lawrence, KS, USA
| | - Krzysztof Kuczera
- Department of Chemistry, The University of Kansas, Lawrence, KS, USA.,Department of Molecular Biosciences, The University of Kansas, Lawrence, KS, USA
| | - Kyung-Hoon Lee
- Department of Biology, Chowan University, Murfreesboro, NC, USA
| | - Ed W Childs
- Department of Surgery, Morehouse School of Medicine, Atlanta, GA, USA
| | - Gouri S Jas
- Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence, KS, USA
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10
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Cao Z, Liu L, Hu G, Bian Y, Li H, Wang J, Zhou Y. Interplay of hydrophobic and hydrophilic interactions in sequence-dependent cell penetration of spontaneous membrane-translocating peptides revealed by bias-exchange metadynamics simulations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183402. [PMID: 32569587 DOI: 10.1016/j.bbamem.2020.183402] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2019] [Revised: 06/14/2020] [Accepted: 06/16/2020] [Indexed: 12/29/2022]
Abstract
Spontaneous Membrane Translocating Peptides (SMTPs) can translocate silently across the bilayer and, thus, have the best potential to improve the delivery of therapeutic molecules to cells without toxicity. However, how their translocation mechanisms are affected by a specific peptide sequence remains poorly understood. Here, bias-exchange metadynamics simulations were employed to investigate the translocation mechanisms of five SMTPs with the same composition of amino acids (LLRLR, LRLLR, LLLRR, RLLLR, and LRLRL). Simulation results yield sequence-dependent free energy barrier using the FESs along the z-directional distance. An in-depth analysis of sequence-dependent interactions in different regions of the bilayers indicates that the free-energy barrier height of a specific sequence is resulted from the accessibility balance of isolated or clustered hydrophobic residues (L) and hydrophilic residues (R) that leads to different levels of resistance for moving of a peptide into the hydrophobic center of the membrane. At the maximal of the free-energy barrier, all peptides have a conformation parallel to the membrane surface with the barrier height determined by their affinity to the hydrophobic region. The appropriate bilayer perturbation and GDM+ pairing are beneficial for peptide translocation. These results provide an improved microscopic understanding of how peptide sequence influences the translocation efficiency and mechanism.
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Affiliation(s)
- Zanxia Cao
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China.
| | - Lei Liu
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China; College of Information Management, Dezhou University, Dezhou 253023, China.
| | - Guodong Hu
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China.
| | - Yunqiang Bian
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China.
| | - Haiyan Li
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China; College of Physics and Electronic Information, Dezhou University, Dezhou 253023, China.
| | - Jihua Wang
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China.
| | - Yaoqi Zhou
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China; Institute for Glycomics, School of Information and Communication Technology, Griffith University, Parklands Dr, Southport, QLD 4222, Australia.
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11
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Meingast C, Heldt CL. Arginine‐enveloped virus inactivation and potential mechanisms. Biotechnol Prog 2019; 36:e2931. [DOI: 10.1002/btpr.2931] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Revised: 10/09/2019] [Accepted: 10/14/2019] [Indexed: 11/06/2022]
Affiliation(s)
- Christa Meingast
- Department of Civil and Environmental Engineering Michigan Technological University Houghton Michigan
| | - Caryn L. Heldt
- Department of Chemical Engineering Michigan Technological University Houghton Michigan
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12
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Pandey P, Aytenfisu AH, MacKerell AD, Mallajosyula SS. Drude Polarizable Force Field Parametrization of Carboxylate and N-Acetyl Amine Carbohydrate Derivatives. J Chem Theory Comput 2019; 15:4982-5000. [PMID: 31411469 PMCID: PMC6852669 DOI: 10.1021/acs.jctc.9b00327] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
In this work, we report the development of Drude polarizable force field parameters for the carboxylate and N-acetyl amine derivatives, extending the functionality of the existing Drude polarizable carbohydrate force field. The force field parameters have been developed in a hierarchical manner, reproducing the quantum mechanical gas-phase properties of small model compounds representing the key functional group in the carbohydrate derivatives, including optimization of the electrostatic and bonded parameters. The optimized parameters were then used to generate the models for carboxylate and N-acetyl amine carbohydrate derivatives. The transferred parameters were further tested and optimized to reproduce crystal geometries and J-coupling data from nuclear magnetic resonance experiments. The parameter development resulted in the incorporation of d-glucuronate, l-iduronate, N-acetyl-d-glucosamine (GlcNAc), and N-acetyl-d-galactosamine (GalNAc) sugars into the Drude polarizable force field. The parameters developed in this study were then applied to study the conformational properties of glycosaminoglycan polymer hyaluronan, composed of d-glucuronate and N-acetyl-d-glucosamine, in aqueous solution. Upon comparing the results from the additive and polarizable simulations, it was found that the inclusion of polarization improved the description of the electrostatic interactions observed in hyaluronan, resulting in enhanced conformational flexibility. The developed Drude polarizable force field parameters in conjunction with the remainder of the Drude polarizable force field parameters can be used for future studies involving carbohydrates and their conjugates in complex, heterogeneous systems.
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Affiliation(s)
| | - Asaminew H Aytenfisu
- Department of Pharmaceutical Sciences , University of Maryland School of Pharmacy , 20 Penn Street , Baltimore , Maryland 21201 , United States
| | - Alexander D MacKerell
- Department of Pharmaceutical Sciences , University of Maryland School of Pharmacy , 20 Penn Street , Baltimore , Maryland 21201 , United States
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13
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Paloncýová M, Ameloot M, Knippenberg S. Orientational distribution of DPH in lipid membranes: a comparison of molecular dynamics calculations and experimental time-resolved anisotropy experiments. Phys Chem Chem Phys 2019; 21:7594-7604. [DOI: 10.1039/c8cp07754a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The behavior of the fluorescent probe diphenylhexatriene (DPH) in different lipid phases is investigated. The rotational autocorrelation functions are calculated in order to model the time-resolved fluorescence anisotropy decay. The role of the order parameters is discussed.
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Affiliation(s)
- Markéta Paloncýová
- Department of Theoretical Chemistry and Biology
- School of Engineering Sciences in Chemistry
- Biotechnology and Health
- Royal Institute of Technology
- Stockholm
| | - Marcel Ameloot
- Biomedical Research Institute, Hasselt University
- 3590 Diepenbeek
- Belgium
| | - Stefan Knippenberg
- Department of Theoretical Chemistry and Biology
- School of Engineering Sciences in Chemistry
- Biotechnology and Health
- Royal Institute of Technology
- Stockholm
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14
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Abstract
Molecular dynamics (MD) simulations have been widely applied to computer-aided drug design (CADD). While MD has been used in a variety of applications such as free energy perturbation and long-time simulations, the accuracy of the results from those methods depends strongly on the force field used. Force fields for small molecules are crucial, as they not only serve as building blocks for developing force fields for larger biomolecules but also act as model compounds that will be transferred to ligands used in CADD. Currently, a wide range of small molecule force fields based on additive or nonpolarizable models have been developed. While these nonpolarizable force fields can produce reasonable estimations of physical properties and have shown success in a variety of systems, there is still room for improvements due to inherent limitations in these models including the lack of an electronic polarization response. For this reason, incorporating polarization effects into the energy function underlying a force field is believed to be an important step forward, giving rise to the development of polarizable force fields. Recent simulations of biological systems have indicated that polarizable force fields are able to provide a better physical representation of intermolecular interactions and, in many cases, better agreement with experimental properties than nonpolarizable, additive force fields. Therefore, this chapter focuses on the development of small molecule force fields with emphasis on polarizable models. It begins with a brief introduction on the importance of small molecule force fields and their evolution from additive to polarizable force fields. Emphasis is placed on the additive CHARMM General Force Field and the polarizable force field based on the classical Drude oscillator. The theory for the Drude polarizable force field and results for small molecules are presented showing their improvements over the additive model. The potential importance of polarization for their application in a wide range of biological systems including CADD is then discussed.
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Affiliation(s)
- Fang-Yu Lin
- Department of Pharmaceutical Sciences, Computer-Aided Drug Design Center, School of Pharmacy, University of Maryland, Baltimore, MD, USA
| | - Alexander D MacKerell
- Department of Pharmaceutical Sciences, Computer-Aided Drug Design Center, School of Pharmacy, University of Maryland, Baltimore, MD, USA.
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15
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Patel SJ, Van Lehn RC. Characterizing the Molecular Mechanisms for Flipping Charged Peptide Flanking Loops across a Lipid Bilayer. J Phys Chem B 2018; 122:10337-10348. [PMID: 30376710 DOI: 10.1021/acs.jpcb.8b06613] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The cell membrane largely prevents the passive diffusion of charged molecules due to the large free energy barrier associated with translocating charged groups across the hydrophobic lipid bilayer core. Despite this barrier, some peptides can interconvert between transmembrane and surface-adsorbed states by "flipping" charged flanking loops across the bilayer on a surprisingly rapid second-minute time scale. The transmembrane helices of some multispanning membrane proteins undergo similar reorientation processes, suggesting that loop-flipping may be a mechanism for regulating membrane protein topology; however, the molecular mechanisms underlying this behavior remain unknown. In this work, we study the loop-flipping behavior exhibited by a peptide with a hydrophobic transmembrane helix, charged flanking loops, and a central, membrane-exposed aspartate residue of varying protonation state. We utilize all-atom temperature accelerated molecular dynamics simulations to predict the likelihood of loop-flipping without predefining specific loop-flipping pathways. We demonstrate that this approach can identify multiple possible flipping pathways, with the prevalence of each pathway depending on the protonation state of the central residue. In particular, we find that a charged central residue facilitates loop-flipping by stabilizing membrane water defects, enabling the "self-catalysis" of charge translocation. These findings provide detailed molecular-level insights into charged loop-flipping pathways that may generalize to other charge translocation processes, such as lipid flip-flop or the large-scale conformational rearrangements of multispanning membrane proteins.
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Affiliation(s)
- Samarthaben J Patel
- Department of Chemical and Biological Engineering , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Reid C Van Lehn
- Department of Chemical and Biological Engineering , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
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16
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Cao Z, Bian Y, Hu G, Zhao L, Kong Z, Yang Y, Wang J, Zhou Y. Bias-Exchange Metadynamics Simulation of Membrane Permeation of 20 Amino Acids. Int J Mol Sci 2018; 19:E885. [PMID: 29547563 PMCID: PMC5877746 DOI: 10.3390/ijms19030885] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2018] [Revised: 03/11/2018] [Accepted: 03/12/2018] [Indexed: 11/16/2022] Open
Abstract
Thermodynamics of the permeation of amino acids from water to lipid bilayers is an important first step for understanding the mechanism of cell-permeating peptides and the thermodynamics of membrane protein structure and stability. In this work, we employed bias-exchange metadynamics simulations to simulate the membrane permeation of all 20 amino acids from water to the center of a dipalmitoylphosphatidylcholine (DPPC) membrane (consists of 256 lipids) by using both directional and torsion angles for conformational sampling. The overall accuracy for the free energy profiles obtained is supported by significant correlation coefficients (correlation coefficient at 0.5-0.6) between our results and previous experimental or computational studies. The free energy profiles indicated that (1) polar amino acids have larger free energy barriers than nonpolar amino acids; (2) negatively charged amino acids are the most difficult to enter into the membrane; and (3) conformational transitions for many amino acids during membrane crossing is the key for reduced free energy barriers. These results represent the first set of simulated free energy profiles of membrane crossing for all 20 amino acids.
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Affiliation(s)
- Zanxia Cao
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China.
- College of Physics and Electronic Information, Dezhou University, Dezhou 253023, China.
| | - Yunqiang Bian
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China.
| | - Guodong Hu
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China.
- College of Physics and Electronic Information, Dezhou University, Dezhou 253023, China.
| | - Liling Zhao
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China.
- College of Physics and Electronic Information, Dezhou University, Dezhou 253023, China.
| | - Zhenzhen Kong
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China.
- College of Life Science, Shandong Normal University, Jinan 250014, China.
| | - Yuedong Yang
- Institute for Glycomics and School of Information and Communication Technology, Griffith University, Parklands Dr, Southport, QLD 4222, Australia.
- School of Data and Computer Science, Sun Yat-sen University, Guangzhou 510275, China.
| | - Jihua Wang
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China.
- College of Physics and Electronic Information, Dezhou University, Dezhou 253023, China.
| | - Yaoqi Zhou
- Shandong Provincial Key Laboratory of Biophysics, Institute of Biophysics, Dezhou University, Dezhou 253023, China.
- Institute for Glycomics and School of Information and Communication Technology, Griffith University, Parklands Dr, Southport, QLD 4222, Australia.
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17
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Zhang J, Yang W, Tan J, Ye S. In situ examination of a charged amino acid-induced structural change in lipid bilayers by sum frequency generation vibrational spectroscopy. Phys Chem Chem Phys 2018; 20:5657-5665. [PMID: 29412195 DOI: 10.1039/c7cp07389e] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The interactions between amino acids (AAs) and membranes represent various short-range and long-range interactions for biological phenomena; however, they are still poorly understood. In this study, we used cationic lysine and arginine as AA models, and systematically investigated the interactions between charged AAs and lipid bilayers using sum frequency generation vibrational spectroscopy (SFG-VS) in situ and in real time. The AA-induced dynamic structural changes of the lipid bilayer were experimentally monitored using the spectral features of CD2, CD3, the lipid head phosphate, and carbonyl groups in real time. Time-dependent SFG changes in the structure of the lipid bilayer provide direct evidence for the different interactions of lysine and arginine with the membrane. It was found that the discrepancy between lysine and arginine in binding with the lipid bilayer is due to the nature of the terminal functional groups. Arginine exhibits a more drastic impact on the membrane than lysine. SFG responses of the acyl chains, phosphate groups, and carbonyl groups provide evidence that the interaction between AAs and the membrane most likely follows an electrostatics and hydrogen bond-induced defect model. This work presents an exemplary method for comprehensive investigations of interactions between membranes and other functionally significant substances.
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Affiliation(s)
- Jiahui Zhang
- Hefei National Laboratory for Physical Sciences at the Microscale, and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
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18
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Huang M, Dissanayake T, Kuechler E, Radak BK, Lee TS, Giese TJ, York DM. A Multidimensional B-Spline Correction for Accurate Modeling Sugar Puckering in QM/MM Simulations. J Chem Theory Comput 2017; 13:3975-3984. [PMID: 28768099 PMCID: PMC5839098 DOI: 10.1021/acs.jctc.7b00161] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The computational efficiency of approximate quantum mechanical methods allows their use for the construction of multidimensional reaction free energy profiles. It has recently been demonstrated that quantum models based on the neglect of diatomic differential overlap (NNDO) approximation have difficulty modeling deoxyribose and ribose sugar ring puckers and thus limit their predictive value in the study of RNA and DNA systems. A method has been introduced in our previous work to improve the description of the sugar puckering conformational landscape that uses a multidimensional B-spline correction map (BMAP correction) for systems involving intrinsically coupled torsion angles. This method greatly improved the adiabatic potential energy surface profiles of DNA and RNA sugar rings relative to high-level ab initio methods even for highly problematic NDDO-based models. In the present work, a BMAP correction is developed, implemented, and tested in molecular dynamics simulations using the AM1/d-PhoT semiempirical Hamiltonian for biological phosphoryl transfer reactions. Results are presented for gas-phase adiabatic potential energy surfaces of RNA transesterification model reactions and condensed-phase QM/MM free energy surfaces for nonenzymatic and RNase A-catalyzed transesterification reactions. The results show that the BMAP correction is stable, efficient, and leads to improvement in both the potential energy and free energy profiles for the reactions studied, as compared with ab initio and experimental reference data. Exploration of the effect of the size of the quantum mechanical region indicates the best agreement with experimental reaction barriers occurs when the full CpA dinucleotide substrate is treated quantum mechanically with the sugar pucker correction.
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Affiliation(s)
- Ming Huang
- Center for Integrative Proteomics Research, Laboratory for Biomolecular Simulation Research and Department of Chemistry and Chemical Biology, Rutgers University, 174 Frelinghuysen Road, Piscataway, New Jersey 08854, United States
| | - Thakshila Dissanayake
- Center for Integrative Proteomics Research, Laboratory for Biomolecular Simulation Research and Department of Chemistry and Chemical Biology, Rutgers University, 174 Frelinghuysen Road, Piscataway, New Jersey 08854, United States
| | - Erich Kuechler
- Center for Integrative Proteomics Research, Laboratory for Biomolecular Simulation Research and Department of Chemistry and Chemical Biology, Rutgers University, 174 Frelinghuysen Road, Piscataway, New Jersey 08854, United States
| | - Brian K. Radak
- Center for Integrative Proteomics Research, Laboratory for Biomolecular Simulation Research and Department of Chemistry and Chemical Biology, Rutgers University, 174 Frelinghuysen Road, Piscataway, New Jersey 08854, United States
| | - Tai-Sung Lee
- Center for Integrative Proteomics Research, Laboratory for Biomolecular Simulation Research and Department of Chemistry and Chemical Biology, Rutgers University, 174 Frelinghuysen Road, Piscataway, New Jersey 08854, United States
| | - Timothy J. Giese
- Center for Integrative Proteomics Research, Laboratory for Biomolecular Simulation Research and Department of Chemistry and Chemical Biology, Rutgers University, 174 Frelinghuysen Road, Piscataway, New Jersey 08854, United States
| | - Darrin M. York
- Center for Integrative Proteomics Research, Laboratory for Biomolecular Simulation Research and Department of Chemistry and Chemical Biology, Rutgers University, 174 Frelinghuysen Road, Piscataway, New Jersey 08854, United States
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19
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Argudo D, Bethel NP, Marcoline FV, Wolgemuth CW, Grabe M. New Continuum Approaches for Determining Protein-Induced Membrane Deformations. Biophys J 2017; 112:2159-2172. [PMID: 28538153 DOI: 10.1016/j.bpj.2017.03.040] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Revised: 03/16/2017] [Accepted: 03/27/2017] [Indexed: 01/21/2023] Open
Abstract
The influence of the membrane on transmembrane proteins is central to a number of biological phenomena, notably the gating of stretch activated ion channels. Conversely, membrane proteins can influence the bilayer, leading to the stabilization of particular membrane shapes, topological changes that occur during vesicle fission and fusion, and shape-dependent protein aggregation. Continuum elastic models of the membrane have been widely used to study protein-membrane interactions. These mathematical approaches produce physically interpretable membrane shapes, energy estimates for the cost of deformation, and a snapshot of the equilibrium configuration. Moreover, elastic models are much less computationally demanding than fully atomistic and coarse-grained simulation methodologies; however, it has been argued that continuum models cannot reproduce the distortions observed in fully atomistic molecular dynamics simulations. We suggest that this failure can be overcome by using chemically and geometrically accurate representations of the protein. Here, we present a fast and reliable hybrid continuum-atomistic model that couples the protein to the membrane. We show that the model is in excellent agreement with fully atomistic simulations of the ion channel gramicidin embedded in a POPC membrane. Our continuum calculations not only reproduce the membrane distortions produced by the channel but also accurately determine the channel's orientation. Finally, we use our method to investigate the role of membrane bending around the charged voltage sensors of the transient receptor potential cation channel TRPV1. We find that membrane deformation significantly stabilizes the energy of insertion of TRPV1 by exposing charged residues on the S4 segment to solution.
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Affiliation(s)
- David Argudo
- Cardiovascular Research Institute, Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California
| | - Neville P Bethel
- Cardiovascular Research Institute, Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California
| | - Frank V Marcoline
- Cardiovascular Research Institute, Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California
| | - Charles W Wolgemuth
- Departments of Molecular and Cellular Biology and Physics, University of Arizona, Tucson, Arizona
| | - Michael Grabe
- Cardiovascular Research Institute, Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California.
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20
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Hub JS, Awasthi N. Probing a Continuous Polar Defect: A Reaction Coordinate for Pore Formation in Lipid Membranes. J Chem Theory Comput 2017; 13:2352-2366. [PMID: 28376619 DOI: 10.1021/acs.jctc.7b00106] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Various biophysical processes involve the formation of aqueous pores over lipid membranes, including processes of membrane fusion, antimicrobial peptide activity, lipid flip-flop, and membrane permeation. Reliable and efficient free-energy calculations of pore formation using molecular dynamics simulations remained challenging due to the lack of good reaction coordinates (RCs) for pore formation. We present a new RC for pore formation that probes the formation and rupture of a continuous polar defect over the membrane. Potential of mean force (PMF) calculations along the new RC rapidly converge and exhibit no hysteresis between pore-opening and pore-closing pathways, in contrast to calculations based on previous RCs. We show that restraints along the new RC may restrain the system tightly to the transition state of pore formation, rationalizing the absence of hysteresis. We observe that the PMF of pore formation in a tension-free membrane of dimyristoylphosphatidylcholine (DMPC) reveals a free-energy barrier for pore nucleation, confirming a long-hypothesized metastable prepore state. We test the influence of the lipid force field, the cutoff distance used for Lennard-Jones interactions, and the lateral membrane size on the free energies of pore formation. In contrast to PMF calculations based on previous RCs, we find that such parameters have a relatively small influence on the free energies of pore nucleation. However, the metastability of the open pore in DMPC may depend on such parameters. The RC has been implemented into an extension of the GROMACS simulation software. The new RC allows for reliable and computationally efficient free-energy calculations of pore formation in lipid membranes.
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Affiliation(s)
- Jochen S Hub
- Institute for Microbiology and Genetics, University of Göttingen , Justus-von-Liebig Weg 11, 37077 Goettingen, Germany
| | - Neha Awasthi
- Institute for Microbiology and Genetics, University of Göttingen , Justus-von-Liebig Weg 11, 37077 Goettingen, Germany
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21
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Zhang Y, Wang H, Xu W, Meng F. Structural effects and translocation of spontaneous membrane-translocating peptides with POPC bilayer. JOURNAL OF THEORETICAL & COMPUTATIONAL CHEMISTRY 2017. [DOI: 10.1142/s021963361750002x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Martini coarse-grained force field simulations have been carried out to estimate the free energy profiles of the spontaneous membrane-translocating peptide TP2 and one negative control peptide ONEG with POPC as the model bilayer. The results show that the free energy minimum of TP2 is [Formula: see text]20[Formula: see text]kJ/mol lower than that of ONEG. In addition, the minimum of TP2 shifts slightly to the bilayer center compared with ONEG. The translocation barrier height for TP2 and ONEG are 119.0[Formula: see text]kJ/mol and 155.7[Formula: see text]kJ/mol, respectively. The lower central energy barrier of TP2 facilitates the transition between two leaflets of POPC. Both translocating peptides induce the formation of funnel-shaped structures at the bilayer center, but TP2 has a more compact structure and brings less perturbation compared with ONEG. Subsequently all atom molecular simulations testify the findings. It is indicated that compared with its negative control ONEG, TP2 binds better with lipid and penetrates deeper into bilayer with less perturbation to the bilayer structure. Our findings may shed light on the design and virtual screening of spontaneous membrane-translocating peptides.
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Affiliation(s)
- Yuan Zhang
- Tianjin University of Traditional Chinese Medicine, Tianjin 300193, P. R. China
| | - Huanjie Wang
- Tianjin Key Laboratory of Molecular Design and Drug Discovery, Tianjin Institute of Pharmaceutical, Research, Tianjin 300193, P. R. China
| | - Weiren Xu
- Tianjin Key Laboratory of Molecular Design and Drug Discovery, Tianjin Institute of Pharmaceutical, Research, Tianjin 300193, P. R. China
| | - Fancui Meng
- Tianjin Key Laboratory of Molecular Design and Drug Discovery, Tianjin Institute of Pharmaceutical, Research, Tianjin 300193, P. R. China
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22
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Thukral L, Sengupta D, Ramkumar A, Murthy D, Agrawal N, Gokhale RS. The Molecular Mechanism Underlying Recruitment and Insertion of Lipid-Anchored LC3 Protein into Membranes. Biophys J 2016; 109:2067-78. [PMID: 26588566 DOI: 10.1016/j.bpj.2015.09.022] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Revised: 09/03/2015] [Accepted: 09/18/2015] [Indexed: 11/16/2022] Open
Abstract
Lipid modification of cytoplasmic proteins initiates membrane engagement that triggers diverse cellular processes. Despite the abundance of lipidated proteins in the human proteome, the key determinants underlying membrane recognition and insertion are poorly understood. Here, we define the course of spontaneous membrane insertion of LC3 protein modified with phosphatidylethanolamine using multiple coarse-grain simulations. The partitioning of the lipid anchor chains proceeds through a concerted process, with its two acyl chains inserting one after the other. Concurrently, a conformational rearrangement involving the α-helix III of LC3, especially in the three basic residues Lys65, Arg68, and Arg69, ensures stable insertion of the phosphatidylethanolamine anchor into membranes. Mutational studies validate the crucial role of these residues, and further live-cell imaging analysis shows a substantial reduction in the formation of autophagic vesicles for the mutant proteins. Our study captures the process of water-favored LC3 protein recruitment to the membrane and thus opens, to our knowledge, new avenues to explore the cellular dynamics underlying vesicular trafficking.
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Affiliation(s)
- Lipi Thukral
- CSIR-Institute of Genomics and Integrative Biology (IGIB), New Delhi, India.
| | | | - Amrita Ramkumar
- CSIR-Institute of Genomics and Integrative Biology (IGIB), New Delhi, India
| | - Divya Murthy
- CSIR-Institute of Genomics and Integrative Biology (IGIB), New Delhi, India
| | - Nikhil Agrawal
- CSIR-Institute of Genomics and Integrative Biology (IGIB), New Delhi, India
| | - Rajesh S Gokhale
- CSIR-Institute of Genomics and Integrative Biology (IGIB), New Delhi, India.
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23
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Hu Y, Patel S. Thermodynamics of cell-penetrating HIV1 TAT peptide insertion into PC/PS/CHOL model bilayers through transmembrane pores: the roles of cholesterol and anionic lipids. SOFT MATTER 2016; 12:6716-6727. [PMID: 27435187 DOI: 10.1039/c5sm01696g] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Efficient delivery of pharmaceutically active molecules across cellular membranes using cell penetrating peptides (CPPs), such as the cationic human immunodeficiency virus-1 trans-acting activator of transcription peptide (HIV-1 TAT), continues to attract scientific attention in drug design and disease treatment. Experimental results show that the TAT peptide is not only capable of directly penetrating the biological membrane in a passive manner, but also forming physical, membrane-spanning pores that may facilitate transport. Experiments further show that anionic lipids accelerate peptide permeation within a range of mole percentage composition. In this work, we explored the structures and translocation thermodynamics of the cationic TAT peptide across a series of DPPC/DPPS model membranes with the presence of 0-30 mol% cholesterol. We computed the potentials of the mean force by using umbrella sampling molecular dynamics simulations coupled to the Martini coarse-grained force field. We systematically investigated the roles of cholesterol and anionic lipids (membrane surface charge) in TAT peptide translocation. In qualitative agreement with experimental findings, the barrier heights were significantly reduced in the presence of anionic lipids. A toroidal hydrophilic pore was strongly suggested by membrane structure analysis. Cholesterol stabilizes the liquid-ordered (Lo) phase of membranes and increases the elastic stiffness of bilayers. Consequently, it hinders transmembrane pore formation and thus modulates solute permeability, since the liquid-ordered phase suppresses reorientation of the lipid molecules on simulation time scales. Though cholesterol contributes marginally to the total free energy associated with peptide permeation, the coordination of cholesterol to the peptide weakens more favorable peptide-lipid interactions. The addition of the anionic lipid DPPS to the neutral DPPC bilayer leads to the emergence and further enhancement of an interfacially stable state of the peptide due to the favorable peptide-anionic lipid interactions. Translocation free energy barriers decrease in lockstep with increasing DPPS composition in the model bilayers simulated. Finally, we investigated the size of hydrophilic pores emerging in our simulations, as well as the qualitative mobility of the peptide on the membrane surface.
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Affiliation(s)
- Yuan Hu
- Merck Research Laboratories, 2015 Galloping Hill Road, Kenilworth, New Jersey 07033, USA
| | - Sandeep Patel
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA.
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Awasthi N, Hub JS. Simulations of Pore Formation in Lipid Membranes: Reaction Coordinates, Convergence, Hysteresis, and Finite-Size Effects. J Chem Theory Comput 2016; 12:3261-9. [DOI: 10.1021/acs.jctc.6b00369] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Neha Awasthi
- Institute for Microbiology
and Genetics, Georg-August-Universität, Justus-von-Liebig Weg 11, 37077 Göttingen, Germany
| | - Jochen S. Hub
- Institute for Microbiology
and Genetics, Georg-August-Universität, Justus-von-Liebig Weg 11, 37077 Göttingen, Germany
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25
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Molecular Basis of the Membrane Interaction of the β2e Subunit of Voltage-Gated Ca(2+) Channels. Biophys J 2016; 109:922-35. [PMID: 26331250 DOI: 10.1016/j.bpj.2015.07.040] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2015] [Revised: 07/27/2015] [Accepted: 07/28/2015] [Indexed: 12/30/2022] Open
Abstract
The auxiliary β subunit plays an important role in the regulation of voltage-gated calcium (CaV) channels. Recently, it was revealed that β2e associates with the plasma membrane through an electrostatic interaction between N-terminal basic residues and anionic phospholipids. However, a molecular-level understanding of β-subunit membrane recruitment in structural detail has remained elusive. In this study, using a combination of site-directed mutagenesis, liposome-binding assays, and multiscale molecular-dynamics (MD) simulation, we developed a physical model of how the β2e subunit is recruited electrostatically to the plasma membrane. In a fluorescence resonance energy transfer assay with liposomes, binding of the N-terminal peptide (23 residues) to liposome was significantly increased in the presence of phosphatidylserine (PS) and phosphatidylinositol 4,5-bisphosphate (PIP2). A mutagenesis analysis suggested that two basic residues proximal to Met-1, Lys-2 (K2) and Trp-5 (W5), are more important for membrane binding of the β2e subunit than distal residues from the N-terminus. Our MD simulations revealed that a stretched binding mode of the N-terminus to PS is required for stable membrane attachment through polar and nonpolar interactions. This mode obtained from MD simulations is consistent with experimental results showing that K2A, W5A, and K2A/W5A mutants failed to be targeted to the plasma membrane. We also investigated the effects of a mutated β2e subunit on inactivation kinetics and regulation of CaV channels by PIP2. In experiments with voltage-sensing phosphatase (VSP), a double mutation in the N-terminus of β2e (K2A/W5A) increased the PIP2 sensitivity of CaV2.2 and CaV1.3 channels by ∼3-fold compared with wild-type β2e subunit. Together, our results suggest that membrane targeting of the β2e subunit is initiated from the nonspecific electrostatic insertion of N-terminal K2 and W5 residues into the membrane. The PS-β2e interaction observed here provides a molecular insight into general principles for protein binding to the plasma membrane, as well as the regulatory roles of phospholipids in transporters and ion channels.
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26
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Lemkul J, Huang J, Roux B, MacKerell AD. An Empirical Polarizable Force Field Based on the Classical Drude Oscillator Model: Development History and Recent Applications. Chem Rev 2016; 116:4983-5013. [PMID: 26815602 PMCID: PMC4865892 DOI: 10.1021/acs.chemrev.5b00505] [Citation(s) in RCA: 379] [Impact Index Per Article: 47.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Indexed: 11/28/2022]
Abstract
Molecular mechanics force fields that explicitly account for induced polarization represent the next generation of physical models for molecular dynamics simulations. Several methods exist for modeling induced polarization, and here we review the classical Drude oscillator model, in which electronic degrees of freedom are modeled by charged particles attached to the nuclei of their core atoms by harmonic springs. We describe the latest developments in Drude force field parametrization and application, primarily in the last 15 years. Emphasis is placed on the Drude-2013 polarizable force field for proteins, DNA, lipids, and carbohydrates. We discuss its parametrization protocol, development history, and recent simulations of biologically interesting systems, highlighting specific studies in which induced polarization plays a critical role in reproducing experimental observables and understanding physical behavior. As the Drude oscillator model is computationally tractable and available in a wide range of simulation packages, it is anticipated that use of these more complex physical models will lead to new and important discoveries of the physical forces driving a range of chemical and biological phenomena.
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Affiliation(s)
- Justin
A. Lemkul
- Department
of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, Baltimore, Maryland 21201, United States
| | - Jing Huang
- Department
of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, Baltimore, Maryland 21201, United States
| | - Benoît Roux
- Department
of Biochemistry and Molecular Biology, University
of Chicago, Chicago, Illinois 60637, United
States
| | - Alexander D. MacKerell
- Department
of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, Baltimore, Maryland 21201, United States
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27
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Lee CT, Comer J, Herndon C, Leung N, Pavlova A, Swift RV, Tung C, Rowley CN, Amaro RE, Chipot C, Wang Y, Gumbart JC. Simulation-Based Approaches for Determining Membrane Permeability of Small Compounds. J Chem Inf Model 2016; 56:721-33. [PMID: 27043429 DOI: 10.1021/acs.jcim.6b00022] [Citation(s) in RCA: 150] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Predicting the rate of nonfacilitated permeation of solutes across lipid bilayers is important to drug design, toxicology, and signaling. These rates can be estimated using molecular dynamics simulations combined with the inhomogeneous solubility-diffusion model, which requires calculation of the potential of mean force and position-dependent diffusivity of the solute along the transmembrane axis. In this paper, we assess the efficiency and accuracy of several methods for the calculation of the permeability of a model DMPC bilayer to urea, benzoic acid, and codeine. We compare umbrella sampling, replica exchange umbrella sampling, adaptive biasing force, and multiple-walker adaptive biasing force for the calculation of the transmembrane PMF. No definitive advantage for any of these methods in their ability to predict the membrane permeability coefficient Pm was found, provided that a sufficiently long equilibration is performed. For diffusivities, a Bayesian inference method was compared to a generalized Langevin method, both being sensitive to chosen parameters and the slow relaxation of membrane defects. Agreement within 1.5 log units of the computed Pm with experiment is found for all permeants and methods. Remaining discrepancies can likely be attributed to limitations of the force field as well as slowly relaxing collective movements within the lipid environment. Numerical calculations based on model profiles show that Pm can be reliably estimated from only a few data points, leading to recommendations for calculating Pm from simulations.
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Affiliation(s)
- Christopher T Lee
- Department of Chemistry and Biochemistry, University of California, San Diego , 9500 Gilman Drive, La Jolla, California 92093-0340, United States
| | - Jeffrey Comer
- Nanotechnology Innovation Center of Kansas State, Institute of Computational Comparative Medicine, Department of Anatomy and Physiology, Kansas State University , P-213 Mosier Hall, Manhattan, Kansas 66506, United States
| | - Conner Herndon
- School of Physics, Georgia Institute of Technology , 837 State Street, Atlanta, Georgia 30332, United States
| | - Nelson Leung
- Department of Physics, The Chinese University of Hong Kong , Shatin, Hong Kong SAR, China
| | - Anna Pavlova
- School of Physics, Georgia Institute of Technology , 837 State Street, Atlanta, Georgia 30332, United States
| | - Robert V Swift
- Department of Chemistry and Biochemistry, University of California, San Diego , 9500 Gilman Drive, La Jolla, California 92093-0340, United States
| | - Chris Tung
- Department of Physics, The Chinese University of Hong Kong , Shatin, Hong Kong SAR, China
| | - Christopher N Rowley
- Department of Chemistry, Memorial University of Newfoundland , St. John's, NL A1B 3X7 Canada
| | - Rommie E Amaro
- Department of Chemistry and Biochemistry, University of California, San Diego , 9500 Gilman Drive, La Jolla, California 92093-0340, United States
| | - Christophe Chipot
- Laboratoire International Associé Centre National de la Recherche Scientifique and University of Illinois at Urbana-Champaign, UMR n° 7565, Université de Lorraine , B.P. 70239, 54506 Vandœuvre-lès-Nancy, France.,Beckman Institute for Advanced Science and Technology and Department of Physics, University of Illinois at Urbana-Champaign , 405 North Mathews, Urbana, Illinois 61801, United States
| | - Yi Wang
- Department of Physics, The Chinese University of Hong Kong , Shatin, Hong Kong SAR, China.,Shenzhen Research Institute, The Chinese University of Hong Kong , Shatin, Hong Kong SAR, China
| | - James C Gumbart
- School of Physics, Georgia Institute of Technology , 837 State Street, Atlanta, Georgia 30332, United States.,School of Chemistry and Biochemistry, Georgia Institute of Technology , 901 Atlantic Drive NW, Atlanta, Georgia 30332, United States
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28
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Neale C, Pomès R. Sampling errors in free energy simulations of small molecules in lipid bilayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2539-2548. [PMID: 26952019 DOI: 10.1016/j.bbamem.2016.03.006] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Revised: 03/01/2016] [Accepted: 03/02/2016] [Indexed: 12/14/2022]
Abstract
Free energy simulations are a powerful tool for evaluating the interactions of molecular solutes with lipid bilayers as mimetics of cellular membranes. However, these simulations are frequently hindered by systematic sampling errors. This review highlights recent progress in computing free energy profiles for inserting molecular solutes into lipid bilayers. Particular emphasis is placed on a systematic analysis of the free energy profiles, identifying the sources of sampling errors that reduce computational efficiency, and highlighting methodological advances that may alleviate sampling deficiencies. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.
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Affiliation(s)
- Chris Neale
- Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 8th St, Troy, New York 12180-3590, USA
| | - Régis Pomès
- Molecular Structure and Function, The Hospital for Sick Children, 686 Bay Street, Toronto, Ontario M5G 0A4, Canada; Department of Biochemistry, University of Toronto, 101 College Street, Toronto, Ontario M5G 1L7, Canada.
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29
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Maximally asymmetric transbilayer distribution of anionic lipids alters the structure and interaction with lipids of an amyloidogenic protein dimer bound to the membrane surface. Chem Phys Lipids 2016; 196:33-51. [PMID: 26827904 DOI: 10.1016/j.chemphyslip.2016.01.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2015] [Revised: 01/13/2016] [Accepted: 01/14/2016] [Indexed: 12/23/2022]
Abstract
We used molecular dynamics simulations to explore the effects of asymmetric transbilayer distribution of anionic phosphatidylserine (PS) lipids on the structure of a protein on the membrane surface and subsequent protein-lipid interactions. Our simulation systems consisted of an amyloidogenic, beta-sheet rich dimeric protein (D42) absorbed to the phosphatidylcholine (PC) leaflet, or protein-contact PC leaflet, of two membrane systems: a single-component PC bilayer and double PC/PS bilayers. The latter comprised of a stable but asymmetric transbilayer distribution of PS in the presence of counterions, with a 1-component PC leaflet coupled to a 1-component PS leaflet in each bilayer. The maximally asymmetric PC/PS bilayer had a non-zero transmembrane potential (TMP) difference and higher lipid order packing, whereas the symmetric PC bilayer had a zero TMP difference and lower lipid order packing under physiologically relevant conditions. Analysis of the adsorbed protein structures revealed weaker protein binding, more folding in the N-terminal domain, more aggregation of the N- and C-terminal domains and larger tilt angle of D42 on the PC leaflet surface of the PC/PS bilayer versus the PC bilayer. Also, analysis of protein-induced membrane structural disruption revealed more localized bilayer thinning in the PC/PS versus PC bilayer. Although the electric field profile in the non-protein-contact PS leaflet of the PC/PS bilayer differed significantly from that in the non-protein-contact PC leaflet of the PC bilayer, no significant difference in the electric field profile in the protein-contact PC leaflet of either bilayer was evident. We speculate that lipid packing has a larger effect on the surface adsorbed protein structure than the electric field for a maximally asymmetric PC/PS bilayer. Our results support the mechanism that the higher lipid packing in a lipid leaflet promotes stronger protein-protein but weaker protein-lipid interactions for a dimeric protein on membrane surfaces.
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30
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Majhi AK, Kanchi S, Venkataraman V, Ayappa KG, Maiti PK. Estimation of activation energy for electroporation and pore growth rate in liquid crystalline and gel phases of lipid bilayers using molecular dynamics simulations. SOFT MATTER 2015; 11:8632-8640. [PMID: 26372335 DOI: 10.1039/c5sm02029h] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Molecular dynamics simulations of electroporation in POPC and DPPC lipid bilayers have been carried out at different temperatures ranging from 230 K to 350 K for varying electric fields. The dynamics of pore formation, including threshold field, pore initiation time, pore growth rate, and pore closure rate after the field is switched off, was studied in both the gel and liquid crystalline (Lα) phases of the bilayers. Using an Arrhenius model of pore initiation kinetics, the activation energy for pore opening was estimated to be 25.6 kJ mol(-1) and 32.6 kJ mol(-1) in the Lα phase of POPC and DPPC lipids respectively at a field strength of 0.32 V nm(-1). The activation energy decreases to 24.2 kJ mol(-1) and 23.7 kJ mol(-1) respectively at a higher field strength of 1.1 V nm(-1). At temperatures below the melting point, the activation energy in the gel phase of POPC and DPPC increases to 28.8 kJ mol(-1) and 34.4 kJ mol(-1) respectively at the same field of 1.1 V nm(-1). The pore closing time was found to be higher in the gel than in the Lα phase. The pore growth rate increases linearly with temperature and quadratically with field, consistent with viscosity limited growth models.
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Affiliation(s)
- Amit Kumar Majhi
- Department of Physics, Indian Institute of Science, Bangalore, India.
| | - Subbarao Kanchi
- Department of Physics, Indian Institute of Science, Bangalore, India.
| | - V Venkataraman
- Department of Physics, Indian Institute of Science, Bangalore, India.
| | - K G Ayappa
- Department of Chemical Engineering, Center for Biosystems Science and Engineering, Bangalore, India.
| | - Prabal K Maiti
- Department of Physics, Indian Institute of Science, Bangalore, India.
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31
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Hu Y, Sinha SK, Patel S. Investigating Hydrophilic Pores in Model Lipid Bilayers Using Molecular Simulations: Correlating Bilayer Properties with Pore-Formation Thermodynamics. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:6615-31. [PMID: 25614183 PMCID: PMC4934177 DOI: 10.1021/la504049q] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Cell-penetrating and antimicrobial peptides show a remarkable ability to translocate across physiological membranes. Along with factors such as electric-potential-induced perturbations of membrane structure and surface tension effects, experiments invoke porelike membrane configurations during the solute transfer process into vesicles and cells. The initiation and formation of pores are associated with a nontrivial free-energy cost, thus necessitating a consideration of the factors associated with pore formation and the attendant free energies. Because of experimental and modeling challenges related to the long time scales of the translocation process, we use umbrella sampling molecular dynamics simulations with a lipid-density-based order parameter to investigate membrane-pore-formation free energy employing Martini coarse-grained models. We investigate structure and thermodynamic features of the pore in 18 lipids spanning a range of headgroups, charge states, acyl chain lengths, and saturation. We probe the dependence of pore-formation barriers on the area per lipid, lipid bilayer thickness, and membrane bending rigidities in three different lipid classes. The pore-formation free energy in pure bilayers and peptide translocating scenarios are significantly coupled with bilayer thickness. Thicker bilayers require more reversible work to create pores. The pore-formation free energy is higher in peptide-lipid systems than in peptide-free lipid systems due to penalties to maintain the solvation of charged hydrophilic solutes within the membrane environment.
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Affiliation(s)
- Yuan Hu
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA
| | - Sudipta Kumar Sinha
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA
| | - Sandeep Patel
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA
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32
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Cardenas AE, Shrestha R, Webb LJ, Elber R. Membrane permeation of a peptide: it is better to be positive. J Phys Chem B 2015; 119:6412-20. [PMID: 25941740 DOI: 10.1021/acs.jpcb.5b02122] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A joint experimental and computational study investigates the translocation of a tryptophan molecule through a phospholipid membrane. Time dependent spectroscopy of the tryptophan side chain determines the rate of permeation into 150 nm phospholipid vesicles. Atomically detailed simulations are conducted to calculate the free energy profiles and the permeation coefficient. Different charging conditions of the peptide (positive, negative, or zwitterion) are considered. Both experiment and simulation reproduce the qualitative trend and suggest that the fastest permeation is when the tryptophan is positively charged. The permeation mechanism, which is revealed by molecular dynamics simulations, is of a translocation assisted by a local defect. The influence of long-range electrostatic interactions, such as the membrane dipole potential on the permeation process, is not significant.
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Affiliation(s)
- Alfredo E Cardenas
- †Institute for Computational Engineering and Sciences and ‡Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - Rebika Shrestha
- †Institute for Computational Engineering and Sciences and ‡Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - Lauren J Webb
- †Institute for Computational Engineering and Sciences and ‡Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - Ron Elber
- †Institute for Computational Engineering and Sciences and ‡Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
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33
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Sun D, Forsman J, Woodward CE. Evaluating Force Fields for the Computational Prediction of Ionized Arginine and Lysine Side-Chains Partitioning into Lipid Bilayers and Octanol. J Chem Theory Comput 2015; 11:1775-91. [PMID: 26574387 DOI: 10.1021/ct501063a] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Abundant peptides and proteins containing arginine (Arg) and lysine (Lys) amino acids can apparently permeate cell membranes with ease. However, the mechanisms by which these peptides and proteins succeed in traversing the free energy barrier imposed by cell membranes remain largely unestablished. Precise thermodynamic studies (both theoretical and experimental) on the interactions of Arg and Lys residues with model lipid bilayers can provide valuable clues to the efficacy of these cationic peptides and proteins. We have carried out molecular dynamics simulations to calculate the interactions of ionized Arg and Lys side-chains with the zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayer for 10 widely used lipid/protein force fields: CHARMM36/CHARMM36, SLIPID/AMBER99SB-ILDN, OPLS-AA/OPLS-AA, Berger/OPLS-AA, Berger/GROMOS87, Berger/GROMOS53A6, GROMOS53A6/GROMOS53A6, nonpolarizable MARTINI, polarizable MARTINI, and BMW MARTINI. We performed umbrella sampling simulations to obtain the potential of mean force for Arg and Lys side-chains partitioning from water to the bilayer interior. We found significant differences between the force fields, both for the interactions between side-chains and bilayer surface, as well as the free energy cost for placing the side-chain at the center of the bilayer. These simulation results were compared with the Wimley-White interfacial scale. We also calculated the free energy cost for transferring ionized Arg and Lys side-chains from water to both dry and wet octanol. Our simulations reveal rapid diffusion of water molecules into octanol whereby the equilibrium mole fraction of water in the wet octanol phase was ∼25%. Surprisingly, our free energy calculations found that the high water content in wet octanol lowered the water-to-octanol partitioning free energies for cationic residues by only 0.6 to 0.7 kcal/mol.
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Affiliation(s)
- Delin Sun
- School of Physical, Environmental and Mathematical Sciences, University of New South Wales , Canberra ACT 2600, Australia
| | - Jan Forsman
- Theoretical Chemistry, Chemical Centre, Lund University , P.O. Box 124, S-221 00 Lund, Sweden
| | - Clifford E Woodward
- School of Physical, Environmental and Mathematical Sciences, University of New South Wales , Canberra ACT 2600, Australia
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34
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Porasso RD, Ale NM, Ciocco Aloia F, Masone D, Del Pópolo MG, Ben Altabef A, Gomez-Zavaglia A, Diaz SB, Vila JA. Interaction of glycine, lysine, proline and histidine with dipalmitoylphosphatidylcholine lipid bilayers: a theoretical and experimental study. RSC Adv 2015. [DOI: 10.1039/c5ra03236a] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The interaction of unblocked glycine, lysine, proline and histidine with a DPPC bilayer was assessed using extensive atomistic molecular dynamics simulations.
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Affiliation(s)
- Rodolfo D. Porasso
- Instituto de Matemática Aplicada San Luis (IMASL)
- CONICET
- Universidad Nacional de San Luis
- Argentina
| | - Norma M. Ale
- Instituto de Química Física
- Facultad de Bioquímica, Química y Farmacia
- U. N. T
- San Lorenzo 456
- Argentina
| | - Facundo Ciocco Aloia
- CONICET
- Facultad de Ciencias Exactas y Naturales
- Universidad Nacional de Cuyo
- Mendoza
- Argentina
| | - Diego Masone
- CONICET
- Facultad de Ciencias Exactas y Naturales
- Universidad Nacional de Cuyo
- Mendoza
- Argentina
| | - Mario G. Del Pópolo
- CONICET
- Facultad de Ciencias Exactas y Naturales
- Universidad Nacional de Cuyo
- Mendoza
- Argentina
| | - Aida Ben Altabef
- Instituto de Química Física
- Facultad de Bioquímica, Química y Farmacia
- U. N. T
- San Lorenzo 456
- Argentina
| | - Andrea Gomez-Zavaglia
- Center for Research and Development in Food Cryotechnology (CIDCA, CCT-CONICET, La Plata)
- Argentina
| | - Sonia B. Diaz
- Instituto de Química Física
- Facultad de Bioquímica, Química y Farmacia
- U. N. T
- San Lorenzo 456
- Argentina
| | - Jorge A. Vila
- Instituto de Matemática Aplicada San Luis (IMASL)
- CONICET
- Universidad Nacional de San Luis
- Argentina
- Baker Laboratory of Chemistry and Chemical Biology
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35
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36
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Hu Y, Sinha SK, Patel S. Reconciling structural and thermodynamic predictions using all-atom and coarse-grain force fields: the case of charged oligo-arginine translocation into DMPC bilayers. J Phys Chem B 2014; 118:11973-92. [PMID: 25290376 PMCID: PMC4199542 DOI: 10.1021/jp504853t] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Using the translocation of short, charged cationic oligo-arginine peptides (mono-, di-, and triarginine) from bulk aqueous solution into model DMPC bilayers, we explore the question of the similarity of thermodynamic and structural predictions obtained from molecular dynamics simulations using all-atom and Martini coarse-grain force fields. Specifically, we estimate potentials of mean force associated with translocation using standard all-atom (CHARMM36 lipid) and polarizable and nonpolarizable Martini force fields, as well as a series of modified Martini-based parameter sets. We find that we are able to reproduce qualitative features of potentials of mean force of single amino acid side chain analogues into model bilayers. In particular, modifications of peptide-water and peptide-membrane interactions allow prediction of free energy minima at the bilayer-water interface as obtained with all-atom force fields. In the case of oligo-arginine peptides, the modified parameter sets predict interfacial free energy minima as well as free energy barriers in almost quantitative agreement with all-atom force field based simulations. Interfacial free energy minima predicted by a modified coarse-grained parameter set are -2.51, -4.28, and -5.42 for mono-, di-, and triarginine; corresponding values from all-atom simulations are -0.83, -3.33, and -3.29, respectively, all in units of kcal/mol. We found that a stronger interaction between oligo-arginine and the membrane components and a weaker interaction between oligo-arginine and water are crucial for producing such minima in PMFs using the polarizable CG model. The difference between bulk aqueous and bilayer center states predicted by the modified coarse-grain force field are 11.71, 14.14, and 16.53 kcal/mol, and those by the all-atom model are 6.94, 8.64, and 12.80 kcal/mol; those are of almost the same order of magnitude. Our simulations also demonstrate a remarkable similarity in the structural aspects of the ensemble of configurations generated using the all-atom and coarse-grain force fields. Both resolutions show that oligo-arginine peptides adopt preferential orientations as they translocate into the bilayer. The guiding theme centers on charged groups maintaining coordination with polar and charged bilayer components as well as local water. We also observe similar behaviors related with membrane deformations.
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Affiliation(s)
- Yuan Hu
- Department of Chemistry and Biochemistry, University of Delaware , Newark, Delaware 19716, United States
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37
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Huang J, Lopes PM, Roux B, MacKerell AD. Recent Advances in Polarizable Force Fields for Macromolecules: Microsecond Simulations of Proteins Using the Classical Drude Oscillator Model. J Phys Chem Lett 2014; 5:3144-3150. [PMID: 25247054 PMCID: PMC4167036 DOI: 10.1021/jz501315h] [Citation(s) in RCA: 105] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Accepted: 08/27/2014] [Indexed: 05/13/2023]
Abstract
In this Perspective, we summarize recent efforts to include the explicit treatment of induced electronic polarization in biomolecular force fields. Methods used to treat polarizability, including the induced dipole, fluctuating charge, and classical Drude oscillator models, are presented, including recent advances in force fields using those methods. This is followed by recent results obtained with the Drude model, including microsecond molecular dynamics (MD) simulations of multiple proteins in explicit solvent. Results show significant variability of backbone and side-chain dipole moments as a function of environment, including significant changes during individual simulations. Dipole moments of water in the vicinity of the proteins reveal small but systematic changes, with the direction of the changes dependent on the environment. Analyses of the full proteins show that the polarizable Drude model leads to larger values of the dielectric constant of the protein interior, especially in the case of hydrophobic regions. These results indicate that the inclusion of explicit electronic polarizability leads to significant differences in the physical forces affecting the structure and dynamics of proteins, which can be investigated in a computationally tractable fashion in the context of the Drude model.
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Affiliation(s)
- Jing Huang
- Department
of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, 20 Penn Street, Room 629, Baltimore, Maryland 21201, United States
| | - Pedro
E. M. Lopes
- Department
of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, 20 Penn Street, Room 629, Baltimore, Maryland 21201, United States
| | - Benoît Roux
- Department
of Biochemistry and Molecular Biology, University
of Chicago, Chicago, Illinois 60637, United
States
| | - Alexander D. MacKerell
- Department
of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, 20 Penn Street, Room 629, Baltimore, Maryland 21201, United States
- E-mail: . Phone: (410) 706-7442. Fax: (410) 706-5017
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Jakobtorweihen S, Zuniga AC, Ingram T, Gerlach T, Keil FJ, Smirnova I. Predicting solute partitioning in lipid bilayers: Free energies and partition coefficients from molecular dynamics simulations and COSMOmic. J Chem Phys 2014; 141:045102. [DOI: 10.1063/1.4890877] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
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Structural and Thermodynamic Insight into Spontaneous Membrane-Translocating Peptides Across Model PC/PG Lipid Bilayers. J Membr Biol 2014; 248:505-15. [PMID: 25008278 DOI: 10.1007/s00232-014-9702-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Accepted: 06/18/2014] [Indexed: 12/20/2022]
Abstract
We present results of Martini coarse-grained force field simulations to estimate the potentials of mean force for a series of recently screened spontaneous membrane-translocating peptides, SMTPs. We consider model bilayer composed of POPC and POPG, the latter providing the anionic component as used in experimental studies. We observe a significant barrier for translocation in the case of the canonical cationic cell-penetrating peptide nona-arginine, ARG9. In the case of the TP1, TP2, and TP3 peptides, potentials of mean force are systematically lower relative to the ARG9 case. Though the barriers predicted by the simulations, on the order of 20 kcal/mol, are still rather large to recapitulate the experimental kinetics of internalization, we emphasize that the qualitative trend of reduction of barrier heights is a significant result. Decomposition of the PMFs indicates that though there is a substantial entropic stability when the peptides reside at bilayer center, barriers as predicted from these force field-based studies are largely determined by enthalpic (potential energy) interactions. We note that the binding of the SMTPs is critically dependent on the mix of hydrophilic and hydrophobic residues that constitute the amino acid motif/sequence of these peptides. For the cationic ARG9 which only contains hydrophilic residues, there is no tight binding observed. The specific motif [Formula: see text] (where [Formula: see text] is a general residue) is a potential sequence in drug/peptide design. The SMTPs with this motif are able to translocate into membrane at a significantly lower free energy cost, compared to the negative control peptides. Finally, we compare the different membrane perturbations induced by the presence of the different peptides in the bilayer center. In some cases, hydrophilic pores are observed to form, thus conferring stability to the internalized state. In other cases, SMTPs are associated only with membrane defects such as induced membrane curvature. These latter observations suggest some influence of membrane rigidity as embodied in the full range of membrane undulatory modes in defining pore-forming propensities in bilayers.
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Cohen-Avrahami M, Shames AI, Ottaviani MF, Aserin A, Garti N. HIV-TAT Enhances the Transdermal Delivery of NSAID Drugs from Liquid Crystalline Mesophases. J Phys Chem B 2014; 118:6277-87. [DOI: 10.1021/jp412739p] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Marganit Cohen-Avrahami
- Casali
Institute of Applied Chemistry, The Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel
| | - Alexander I. Shames
- Department
of Physics, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel
| | - M. Francesca Ottaviani
- Department
of Earth, Life and Environment Sciences, University of Urbino, Località
Crocicchia, Urbino 61029, Italy
| | - Abraham Aserin
- Casali
Institute of Applied Chemistry, The Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel
| | - Nissim Garti
- Casali
Institute of Applied Chemistry, The Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel
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Latorraca NR, Callenberg KM, Boyle JP, Grabe M. Continuum approaches to understanding ion and peptide interactions with the membrane. J Membr Biol 2014; 247:395-408. [PMID: 24652510 PMCID: PMC4096575 DOI: 10.1007/s00232-014-9646-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2013] [Accepted: 02/22/2014] [Indexed: 12/22/2022]
Abstract
Experimental and computational studies have shown that cellular membranes deform to stabilize the inclusion of transmembrane (TM) proteins harboring charge. Recent analysis suggests that membrane bending helps to expose charged and polar residues to the aqueous environment and polar head groups. We previously used elasticity theory to identify membrane distortions that minimize the insertion of charged TM peptides into the membrane. Here, we extend our work by showing that it also provides a novel, computationally efficient method for exploring the energetics of ion and small peptide penetration into membranes. First, we show that the continuum method accurately reproduces energy profiles and membrane shapes generated from molecular simulations of bare ion permeation at a fraction of the computational cost. Next, we demonstrate that the dependence of the ion insertion energy on the membrane thickness arises primarily from the elastic properties of the membrane. Moreover, the continuum model readily provides a free energy decomposition into components not easily determined from molecular dynamics. Finally, we show that the energetics of membrane deformation strongly depend on membrane patch size both for ions and peptides. This dependence is particularly strong for peptides based on simulations of a known amphipathic, membrane binding peptide from the human pathogen Toxoplasma gondii. In total, we address shortcomings and advantages that arise from using a variety of computational methods in distinct biological contexts.
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Affiliation(s)
- Naomi R Latorraca
- Department of Biological Sciences, University of Pittsburgh, 4249 Fifth Avenue, Pittsburgh, PA, 15260, USA
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Hu Y, Liu X, Sinha SK, Patel S. Translocation thermodynamics of linear and cyclic nonaarginine into model DPPC bilayer via coarse-grained molecular dynamics simulation: implications of pore formation and nonadditivity. J Phys Chem B 2014; 118:2670-82. [PMID: 24506488 PMCID: PMC3983342 DOI: 10.1021/jp412600e] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
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Structural mechanisms
and underlying thermodynamic determinants
of efficient internalization of charged cationic peptides (cell-penetrating
peptides, CPPs) such as TAT, polyarginine, and their variants, into
cells, cellular constructs, and model membrane/lipid bilayers (large
and giant unilamellar or multilamelar vesicles) continue to garner
significant attention. Two widely held views on the translocation
mechanism center on endocytotic and nonendocytotic (diffusive) processes.
Espousing the view of a purely diffusive internalization process (supported
by recent experimental evidence, [Säälik, P.; et al. J. Controlled Release2011, 153, 117–125]), we consider the underlying free energetics of
the translocation of a nonaarginine peptide (Arg9) into
a model DPPC bilayer. In the case of the Arg9 cationic
peptide, recent experiments indicate a higher internalization efficiency
of the cyclic structure (cyclic Arg9) relative to the linear
conformer. Furthermore, recent all-atom resolution molecular dynamics
simulations of cyclic Arg9 [Huang, K.; et al. Biophys.
J., 2013, 104, 412–420]
suggested a critical stabilizing role of water- and lipid-constituted
pores that form within the bilayer as the charged Arg9 translocates
deep into the bilayer center. Herein, we use umbrella sampling molecular
dynamics simulations with coarse-grained Martini lipids, polarizable
coarse-grained water, and peptide to explore the dependence of translocation
free energetics on peptide structure and conformation via calculation
of potentials of mean force along preselected reaction paths allowing
and preventing membrane deformations that lead to pore formation.
Within the context of the coarse-grained force fields we employ, we
observe significant barriers for Arg9 translocation from
bulk aqueous solution to bilayer center. Moreover, we do not find
free-energy minima in the headgroup–water interfacial region,
as observed in simulations using all-atom force fields. The pore-forming
paths systematically predict lower free-energy barriers (ca. 90 kJ/mol
lower) than the non pore-forming paths, again consistent with all-atom
force field simulations. The current force field suggests no preference
for the more compact or covalently cyclic structures upon entering
the bilayer. Decomposition of the PMF into the system’s components
indicates that the dominant stabilizing contribution along the pore-forming
path originates from the membrane as both layers of it deformed due
to the formation of pore. Furthermore, our analysis revealed that
although there is significant entropic stabilization arising from
the enhanced configurational entropy exposing more states as the peptide
moves through the bilayer, the enthalpic loss (as predicted by the
interactions of this coarse-grained model) far outweighs any former
stabilization, thus leading to significant barrier to translocation.
Finally, we observe reduction in the translocation free-energy barrier
for a second Arg9 entering the bilayer in the presence
of an initial peptide restrained at the center, again, in qualitative
agreement with all-atom force fields.
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Affiliation(s)
- Yuan Hu
- Department of Chemistry and Biochemistry, University of Delaware , 238 Brown Laboratory, Newark, Delaware 19716, United States
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