1
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Interplay of Hydropathy and Heterogeneous Diffusion in the Molecular Transport within Lamellar Lipid Mesophases. Pharmaceutics 2023; 15:pharmaceutics15020573. [PMID: 36839895 PMCID: PMC9959094 DOI: 10.3390/pharmaceutics15020573] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Revised: 01/18/2023] [Accepted: 02/03/2023] [Indexed: 02/11/2023] Open
Abstract
Lipid mesophases are being intensively studied as potential candidates for drug-delivery purposes. Extensive experimental characterization has unveiled a wide palette of release features depending on the nature of the host lipids and of the guest molecule, as well as on the environmental conditions. However, only a few simulation works have addressed the matter, which hampers a solid rationalization of the richness of outcomes observed in experiments. Particularly, to date, there are no theoretical works addressing the impact of hydropathy on the transport of a molecule within lipid mesophases, despite the significant fraction of hydrophobic molecules among currently-available drugs. Similarly, the high heterogeneity of water mobility in the nanoscopic channels within lipid mesophases has also been neglected. To fill this gap, we introduce here a minimal model to account for these features in a lamellar geometry, and systematically study the role played by hydropathy and water-mobility heterogeneity by Brownian-dynamics simulations. We unveil a fine interplay between the presence of free-energy barriers, the affinity of the drug for the lipids, and the reduced mobility of water in determining the net molecular transport. More in general, our work is an instance of how multiscale simulations can be fruitfully employed to assist experiments in release systems based on lipid mesophases.
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2
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Korn V, Pluhackova K. Not sorcery after all: Roles of multiple charged residues in membrane insertion of gasdermin-A3. Front Cell Dev Biol 2022; 10:958957. [PMID: 36120563 PMCID: PMC9479151 DOI: 10.3389/fcell.2022.958957] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Accepted: 07/26/2022] [Indexed: 11/16/2022] Open
Abstract
Gasdermins execute programmatory cell death, known as pyroptosis, by forming medium-sized membrane pores. Recently, the molecular structure of those pores as well as the diversity in their shape and size have been revealed by cryoTEM and atomic force microscopy, respectively. Even though a growth of smaller to larger oligomers and reshaping from slits to rings could be documented, the initiation of the gasdermin pore formation remains a mystery. In one hypothesis, gasdermin monomers insert into membranes before associating into oligomeric pores. In the other hypothesis, gasdermin oligomers preassemble on the membrane surface prior to membrane insertion. Here, by studying the behavior of monomeric membrane-inserted gasdermin-A3 (GSDMA3), we unveil that a monomeric gasdermin prefers the membrane-adsorbed over the membrane-inserted state. Our results thus support the hypothesis of oligomers preassembling on the membrane surface before membrane penetration. At the same time, our simulations of small membrane-inserted arcs of GSDMA3 suggest that the inserting oligomer can be small and does not have to comprise a full ring of approximately 26-30 subunits. Moreover, our simulations have revealed an astonishingly large impact of salt-bridge formation and protein surroundings on the transmembrane passage of charged residues, reducing the energetic cost by up to 53% as compared to their free forms. The here observed free energy barrier of mere 5.6 kcal/mol for the membrane insertion of monomeric GSDMA3 explains the surprising ability of gasdermins to spontaneously self-insert into cellular membranes.
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Affiliation(s)
| | - Kristyna Pluhackova
- Stuttgart Center for Simulation Science, Cluster of Excellence EXC 2075, University of Stuttgart, Stuttgart, Germany
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3
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Yue Z, Li C, Voth GA, Swanson JMJ. Dynamic Protonation Dramatically Affects the Membrane Permeability of Drug-like Molecules. J Am Chem Soc 2019; 141:13421-13433. [PMID: 31382734 DOI: 10.1021/jacs.9b04387] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Permeability (Pm) across biological membranes is of fundamental importance and a key factor in drug absorption, distribution, and development. Although the majority of drugs will be charged at some point during oral delivery, our understanding of membrane permeation by charged species is limited. The canonical model assumes that only neutral molecules partition into and passively permeate across membranes, but there is mounting evidence that these processes are also facile for certain charged species. However, it is unknown whether such ionizable permeants dynamically neutralize at the membrane surface or permeate in their charged form. To probe protonation-coupled permeation in atomic detail, we herein apply continuous constant-pH molecular dynamics along with free energy sampling to study the permeation of a weak base propranolol (PPL), and evaluate the impact of including dynamic protonation on Pm. The simulations reveal that PPL dynamically neutralizes at the lipid-tail interface, which dramatically influences the permeation free energy landscape and explains why the conventional model overestimates the assigned intrinsic permeability. We demonstrate how fixed-charge-state simulations can account for this effect, and propose a revised model that better describes pH-coupled partitioning and permeation. Our results demonstrate how dynamic changes in protonation state may play a critical role in the permeation of ionizable molecules, including pharmaceuticals and drug-like molecules, thus requiring a revision of the standard picture.
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Affiliation(s)
- Zhi Yue
- Department of Chemistry, James Frank Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Chenghan Li
- Department of Chemistry, James Frank Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Gregory A Voth
- Department of Chemistry, James Frank Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Jessica M J Swanson
- Department of Chemistry, James Frank Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
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4
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Bueno Franco Salla G, Bracht L, Valderrama Parizotto A, Comar JF, Peralta RM, Bracht F, Bracht A. Kinetics of the metabolic effects, distribution spaces and lipid-bilayer affinities of the organo-chlorinated herbicides 2,4-D and picloram in the liver. Toxicol Lett 2019; 313:137-149. [PMID: 31254607 DOI: 10.1016/j.toxlet.2019.06.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Revised: 05/24/2019] [Accepted: 06/25/2019] [Indexed: 10/26/2022]
Abstract
Tordon® is the commercial name of a mixture of two organo-chlorinated herbicides, 2,4-D and picloram. Both compounds affect energy transduction in isolated mitochondria and the present study aimed at characterizing the actions of these two compounds on liver metabolism and their cellular distribution in the isolated perfused rat liver. 2,4-D, but not picloram, increased glycolysis in the range from 10 to 400 μM. The redox potential of the cytosolic NAD+-NADH couple was also increased by 2,4-D. Both compounds inhibited lactate gluconeogenesis. Inhibitions by 2,4-D and picloram were incomplete, reaching maximally 46% and 23%, respectively. Both compounds diminished the cellular ATP levels. No synergism between the actions of 2,4-D and picloram was detected. Biotransformations of 2,4-D and picloram were slow, but their distributions occurred at high rates and were concentrative. Molecular dynamics simulations revealed that 2,4-D presented low affinity for the hydrophobic lipid bilayers, the opposite occurring with picloram. Inhibition of energy metabolism is possibly a relevant component of the toxicity of 2,4-D and of the commercial product Tordon®. Furthermore, the interactions of 2,4-D with the membrane lipid bilayer can be highly destructive and might equally be related to its cellular toxicity at high concentrations.
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Affiliation(s)
| | - Lívia Bracht
- Department of Biochemistry, University of Maringá, 87020900 Maringá, Brazil
| | | | | | | | - Fabrício Bracht
- Department of Biochemistry, University of Maringá, 87020900 Maringá, Brazil
| | - Adelar Bracht
- Department of Biochemistry, University of Maringá, 87020900 Maringá, Brazil.
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5
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Enkavi G, Javanainen M, Kulig W, Róg T, Vattulainen I. Multiscale Simulations of Biological Membranes: The Challenge To Understand Biological Phenomena in a Living Substance. Chem Rev 2019; 119:5607-5774. [PMID: 30859819 PMCID: PMC6727218 DOI: 10.1021/acs.chemrev.8b00538] [Citation(s) in RCA: 184] [Impact Index Per Article: 36.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Indexed: 12/23/2022]
Abstract
Biological membranes are tricky to investigate. They are complex in terms of molecular composition and structure, functional over a wide range of time scales, and characterized by nonequilibrium conditions. Because of all of these features, simulations are a great technique to study biomembrane behavior. A significant part of the functional processes in biological membranes takes place at the molecular level; thus computer simulations are the method of choice to explore how their properties emerge from specific molecular features and how the interplay among the numerous molecules gives rise to function over spatial and time scales larger than the molecular ones. In this review, we focus on this broad theme. We discuss the current state-of-the-art of biomembrane simulations that, until now, have largely focused on a rather narrow picture of the complexity of the membranes. Given this, we also discuss the challenges that we should unravel in the foreseeable future. Numerous features such as the actin-cytoskeleton network, the glycocalyx network, and nonequilibrium transport under ATP-driven conditions have so far received very little attention; however, the potential of simulations to solve them would be exceptionally high. A major milestone for this research would be that one day we could say that computer simulations genuinely research biological membranes, not just lipid bilayers.
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Affiliation(s)
- Giray Enkavi
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
| | - Matti Javanainen
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Institute
of Organic Chemistry and Biochemistry of the Czech Academy
of Sciences, Flemingovo naḿesti 542/2, 16610 Prague, Czech Republic
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
| | - Waldemar Kulig
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
| | - Tomasz Róg
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
| | - Ilpo Vattulainen
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
- MEMPHYS-Center
for Biomembrane Physics
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6
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Ulmschneider JP, Smith JC, White SH, Ulmschneider MB. The importance of the membrane interface as the reference state for membrane protein stability. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:2539-2548. [PMID: 30293965 DOI: 10.1016/j.bbamem.2018.09.012] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2018] [Revised: 09/14/2018] [Accepted: 09/16/2018] [Indexed: 11/26/2022]
Abstract
The insertion of nascent polypeptide chains into lipid bilayer membranes and the stability of membrane proteins crucially depend on the equilibrium partitioning of polypeptides. For this, the transfer of full sequences of amino-acid residues into the bilayer, rather than individual amino acids, must be understood. Earlier studies have revealed that the most likely reference state for partitioning very hydrophobic sequences is the membrane interface. We have used μs-scale simulations to calculate the interface-to-transmembrane partitioning free energies ΔGS→TM for two hydrophobic carrier sequences in order to estimate the insertion free energy for all 20 amino acid residues when bonded to the center of a partitioning hydrophobic peptide. Our results show that prior single-residue scales likely overestimate the partitioning free energies of polypeptides. The correlation of ΔGS→TM with experimental full-peptide translocon insertion data is high, suggesting an important role for the membrane interface in translocon-based insertion. The choice of carrier sequence greatly modulates the contribution of each single-residue mutation to the overall partitioning free energy. Our results demonstrate the importance of quantifying the observed full-peptide partitioning equilibrium, which is between membrane interface and transmembrane inserted, rather than combining individual water-to-membrane amino acid transfer free energies.
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Affiliation(s)
- Jakob P Ulmschneider
- School of Physics and Astronomy and the Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai, China.
| | - Jeremy C Smith
- Center for Molecular Biophysics, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Department of Biochemistry & Cellular Molecular Biology, University of Tennessee, Knoxville, TN, USA
| | - Stephen H White
- Department of Physiology & Biophysics, University of California at Irvine, Irvine, CA, USA
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7
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Zhang L, Wang J, Wang H, Wang W, Li Z, Liu J, Yang X, Ji X, Luo Y, Hu C, Hou Y, He Q, Fang J, Wang J, Liu Q, Li G, Lu Q, Zhang X. Moderate and strong static magnetic fields directly affect EGFR kinase domain orientation to inhibit cancer cell proliferation. Oncotarget 2018; 7:41527-41539. [PMID: 27223425 PMCID: PMC5173076 DOI: 10.18632/oncotarget.9479] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Accepted: 04/27/2016] [Indexed: 01/23/2023] Open
Abstract
Static magnetic fields (SMFs) can affect cell proliferation in a cell-type and intensity-dependent way but the mechanism remains unclear. At the same time, although the diamagnetic anisotropy of proteins has been proposed decades ago, the behavior of isolated proteins in magnetic fields has not been directly observed. Here we show that SMFs can affect isolated proteins at the single molecular level in an intensity-dependent manner. We found that Epidermal Growth Factor Receptor (EGFR), a protein that is overexpressed and highly activated in multiple cancers, can be directly inhibited by SMFs. Using Liquid-phase Scanning Tunneling Microscopy (STM) to examine pure EGFR kinase domain proteins at the single molecule level in solution, we observed orientation changes of these proteins in response to SMFs. This may interrupt inter-molecular interactions between EGFR monomers, which are critical for their activation. In molecular dynamics (MD) simulations, 1-9T SMFs caused increased probability of EGFR in parallel with the magnetic field direction in an intensity-dependent manner. A superconducting ultrastrong 9T magnet reduced proliferation of CHO-EGFR cells (Chinese Hamster Ovary cells with EGFR overexpression) and EGFR-expressing cancer cell lines by ~35%, but minimally affected CHO cells. We predict that similar effects of magnetic fields can also be applied to some other proteins such as ion channels. Our paper will help clarify some dilemmas in this field and encourage further investigations in order to achieve a better understanding of the biological effects of SMFs.
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Affiliation(s)
- Lei Zhang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Jihao Wang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China.,Hefei National Laboratory for Physical Sciences at The Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - HongLei Wang
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
| | - Wenchao Wang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Zhiyuan Li
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Juanjuan Liu
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Xingxing Yang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Xinmiao Ji
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Yan Luo
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Chen Hu
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Yubin Hou
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Qianqian He
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Jun Fang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Junfeng Wang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Qingsong Liu
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Guohui Li
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
| | - Qingyou Lu
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China.,Hefei National Laboratory for Physical Sciences at The Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China.,Collaborative Innovation Center of Advanced Microstructure, Nanjing University, Nanjing, Jiangsu 210093, China
| | - Xin Zhang
- High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026, China
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8
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Bonhenry D, Dehez F, Tarek M. Effects of hydration on the protonation state of a lysine analog crossing a phospholipid bilayer – insights from molecular dynamics and free-energy calculations. Phys Chem Chem Phys 2018; 20:9101-9107. [DOI: 10.1039/c8cp00312b] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Protonation states of amino acids crossing lipid bilayers from multidimensional free energy surfaces.
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Affiliation(s)
| | | | - Mounir Tarek
- Université de Lorraine
- CNRS
- LPCT
- F-54000 Nancy
- France
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9
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Transmembrane helices containing a charged arginine are thermodynamically stable. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2017; 46:627-637. [PMID: 28409218 DOI: 10.1007/s00249-017-1206-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Revised: 03/25/2017] [Accepted: 03/30/2017] [Indexed: 10/19/2022]
Abstract
Hydrophobic amino acids are abundant in transmembrane (TM) helices of membrane proteins. Charged residues are sparse, apparently due to the unfavorable energetic cost of partitioning charges into nonpolar phases. Nevertheless, conserved arginine residues within TM helices regulate vital functions, such as ion channel voltage gating and integrin receptor inactivation. The energetic cost of arginine in various positions along hydrophobic helices has been controversial. Potential of mean force (PMF) calculations from atomistic molecular dynamics simulations predict very large energetic penalties, while in vitro experiments with Sec61 translocons indicate much smaller penalties, even for arginine in the center of hydrophobic TM helices. Resolution of this conflict has proved difficult, because the in vitro assay utilizes the complex Sec61 translocon, while the PMF calculations rely on the choice of simulation system and reaction coordinate. Here we present the results of computational and experimental studies that permit direct comparison with the Sec61 translocon results. We find that the Sec61 translocon mediates less efficient membrane insertion of Arg-containing TM helices compared with our computational and experimental bilayer-insertion results. In the simulations, a combination of arginine snorkeling, bilayer deformation, and peptide tilting is sufficient to lower the penalty of Arg insertion to an extent such that a hydrophobic TM helix with a central Arg residue readily inserts into a model membrane. Less favorable insertion by the translocon may be due to the decreased fluidity of the endoplasmic reticulum (ER) membrane compared with pure palmitoyloleoyl-phosphocholine (POPC). Nevertheless, our results provide an explanation for the differences between PMF- and experiment-based penalties for Arg burial.
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10
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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: 75] [Impact Index Per Article: 9.4] [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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11
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Vorobyov I, Kim I, Chu ZT, Warshel A. Refining the treatment of membrane proteins by coarse-grained models. Proteins 2015; 84:92-117. [PMID: 26531155 DOI: 10.1002/prot.24958] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Revised: 10/19/2015] [Accepted: 10/23/2015] [Indexed: 01/19/2023]
Abstract
Obtaining a quantitative description of the membrane proteins stability is crucial for understanding many biological processes. However the advance in this direction has remained a major challenge for both experimental studies and molecular modeling. One of the possible directions is the use of coarse-grained models but such models must be carefully calibrated and validated. Here we use a recent progress in benchmark studies on the energetics of amino acid residue and peptide membrane insertion and membrane protein stability in refining our previously developed coarse-grained model (Vicatos et al., Proteins 2014;82:1168). Our refined model parameters were fitted and/or tested to reproduce water/membrane partitioning energetics of amino acid side chains and a couple of model peptides. This new model provides a reasonable agreement with experiment for absolute folding free energies of several β-barrel membrane proteins as well as effects of point mutations on a relative stability for one of those proteins, OmpLA. The consideration and ranking of different rotameric states for a mutated residue was found to be essential to achieve satisfactory agreement with the reference data.
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Affiliation(s)
- Igor Vorobyov
- Department of Chemistry, University of Southern California, Los Angeles, California, 90089-1062
| | - Ilsoo Kim
- Department of Chemistry, University of Southern California, Los Angeles, California, 90089-1062
| | - Zhen T Chu
- Department of Chemistry, University of Southern California, Los Angeles, California, 90089-1062
| | - Arieh Warshel
- Department of Chemistry, University of Southern California, Los Angeles, California, 90089-1062
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12
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Spontaneous transmembrane helix insertion thermodynamically mimics translocon-guided insertion. Nat Commun 2014; 5:4863. [PMID: 25204588 PMCID: PMC4161982 DOI: 10.1038/ncomms5863] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Accepted: 07/30/2014] [Indexed: 01/01/2023] Open
Abstract
The favorable transfer free energy for a transmembrane (TM) α-helix between the aqueous phase and lipid bilayer underlies the stability of membrane proteins. However, the connection between the energetics and process of membrane protein assembly by the Sec61/SecY translocon complex in vivo is not clear. Here, we directly determine the partitioning free energies of a family of designed peptides using three independent approaches: an experimental microsomal Sec61 translocon assay, a biophysical (spectroscopic) characterization of peptide insertion into hydrated planar lipid bilayer arrays, and an unbiased atomic-detail equilibrium folding-partitioning molecular dynamics simulation. Remarkably, the measured free energies of insertion are quantitatively similar for all three approaches. The molecular dynamics simulations show that TM helix insertion involves equilibrium with the membrane interface, suggesting that the interface may play a role in translocon-guided insertion.
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13
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Lazaridis T, Leveritt JM, PeBenito L. Implicit membrane treatment of buried charged groups: application to peptide translocation across lipid bilayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:2149-59. [PMID: 24525075 DOI: 10.1016/j.bbamem.2014.01.015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2013] [Accepted: 01/10/2014] [Indexed: 01/06/2023]
Abstract
The energetic cost of burying charged groups in the hydrophobic core of lipid bilayers has been controversial, with simulations giving higher estimates than certain experiments. Implicit membrane approaches are usually deemed too simplistic for this problem. Here we challenge this view. The free energy of transfer of amino acid side chains from water to the membrane center predicted by IMM1 is reasonably close to all-atom free energy calculations. The shape of the free energy profile, however, for the charged side chains needs to be modified to reflect the all-atom simulation findings (IMM1-LF). Membrane thinning is treated by combining simulations at different membrane widths with an estimate of membrane deformation free energy from elasticity theory. This approach is first tested on the voltage sensor and the isolated S4 helix of potassium channels. The voltage sensor is stably inserted in a transmembrane orientation for both the original and the modified model. The transmembrane orientation of the isolated S4 helix is unstable in the original model, but a stable local minimum in IMM1-LF, slightly higher in energy than the interfacial orientation. Peptide translocation is addressed by mapping the effective energy of the peptide as a function of vertical position and tilt angle, which allows identification of minimum energy pathways and transition states. The barriers computed for the S4 helix and other experimentally studied peptides are low enough for an observable rate. Thus, computational results and experimental studies on the membrane burial of peptide charged groups appear to be consistent. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.
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Affiliation(s)
- Themis Lazaridis
- Department of Chemistry, City College of New York, 160 Convent Avenue, New York, NY 10031, USA.
| | - John M Leveritt
- Department of Chemistry, City College of New York, 160 Convent Avenue, New York, NY 10031, USA
| | - Leo PeBenito
- Department of Chemistry, City College of New York, 160 Convent Avenue, New York, NY 10031, USA
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14
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Bonhenry D, Tarek M, Dehez F. Effects of Phospholipid Composition on the Transfer of a Small Cationic Peptide Across a Model Biological Membrane. J Chem Theory Comput 2013; 9:5675-84. [PMID: 26592298 DOI: 10.1021/ct400576e] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The transfer of a lysine amino acid analogue across phospholipid membrane models was investigated using molecular-dynamics simulations. The evolution of the protonation state of this small peptide as a function of its position inside the membrane was studied by determining the local pKa by means of free-energy calculations. Permeability and mean-first-passage time were evaluated and showed that the transfer occurs on the submillisecond time scale. Comparative studies were conducted to evaluate changes in the pKa arising from differences in the phospholipid chemical structure. We compared, hence, the effect of an ether vs an ester linkage of the lipid headgroup as well as linear vs branched lipid tails. The study reveals that protonated lysine residues can be buried further inside an ether lipid membrane than an ester lipid membrane, while branched lipids are found to stabilize less the charged form compared to their unbranched lipid chain counterparts.
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Affiliation(s)
- Daniel Bonhenry
- Université de Lorraine, SRSMC, UMR 7565 , Vandoeuvre-lès-Nancy, F-54500, France.,CNRS, SRSMC, UMR 7565 , Vandoeuvre-lès-Nancy, F-54500, France
| | - Mounir Tarek
- Université de Lorraine, SRSMC, UMR 7565 , Vandoeuvre-lès-Nancy, F-54500, France.,CNRS, SRSMC, UMR 7565 , Vandoeuvre-lès-Nancy, F-54500, France
| | - François Dehez
- Université de Lorraine, SRSMC, UMR 7565 , Vandoeuvre-lès-Nancy, F-54500, France.,CNRS, SRSMC, UMR 7565 , Vandoeuvre-lès-Nancy, F-54500, France
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15
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Martins-Costa MTC, Ruiz-Lopez MF. Amino Acid Capture by Aqueous Interfaces. Implications for Biological Uptake. J Phys Chem B 2013; 117:12469-74. [DOI: 10.1021/jp4083689] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Marilia T. C. Martins-Costa
- SRSMC,
UMR 7565, University of Lorraine, BP 70239, 54506, Vandoeuvre-les-Nancy, France
- SRSMC, UMR 7565, CNRS, BP 70239, 54506, Vandoeuvre-les-Nancy, France
| | - Manuel F. Ruiz-Lopez
- SRSMC,
UMR 7565, University of Lorraine, BP 70239, 54506, Vandoeuvre-les-Nancy, France
- SRSMC, UMR 7565, CNRS, BP 70239, 54506, Vandoeuvre-les-Nancy, France
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16
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Li L, Vorobyov I, Allen TW. The different interactions of lysine and arginine side chains with lipid membranes. J Phys Chem B 2013; 117:11906-20. [PMID: 24007457 DOI: 10.1021/jp405418y] [Citation(s) in RCA: 224] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The basic amino acids lysine (Lys) and arginine (Arg) play important roles in membrane protein activity, the sensing of membrane voltages, and the actions of antimicrobial, toxin, and cell-penetrating peptides. These roles are thought to stem from the strong interactions and disruptive influences of these amino acids on lipid membranes. In this study, we employ fully atomistic molecular dynamics simulations to observe, quantify, and compare the interactions of Lys and Arg with saturated phosphatidylcholine membranes of different thickness. We make use of both charged (methylammonium and methylguanidinium) and neutral (methylamine and methylguanidine) analogue molecules, as well as Lys and Arg side chains on transmembrane helix models. We find that the free energy barrier experienced by a charged Lys crossing the membrane is strikingly similar to that of a charged Arg (to within 2 kcal/mol), despite the two having different chemistries, H-bonding capability, and hydration free energies that differ by ∼10 kcal/mol. In comparison, the barrier for neutral Arg is higher than that for neutral Lys by around 5 kcal/mol, being more selective than that for the charged species. This can be explained by the different transport mechanisms for charged or neutral amino acid side chains in the membrane, involving membrane deformations or simple dehydration, respectively. As a consequence, we demonstrate that Lys would be deprotonated in the membrane, whereas Arg would maintain its charge. Our simulations also reveal that Arg attracts more phosphate and water in the membrane, and can form extensive H-bonding with its five H-bond donors to stabilize Arg-phosphate clusters. This leads to enhanced interfacial binding and membrane perturbations, including the appearance of a trans-membrane pore in a thinner membrane. These results highlight the special role played by Arg as an amino acid to bind to, disrupt, and permeabilize lipid membranes, as well as to sense voltages for a range of peptide and protein activities in nature and in engineered bionanodevices.
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Affiliation(s)
- Libo Li
- Department of Chemistry, University of California, Davis , Davis, California 95616, United States
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17
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18
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Maffeo C, Bhattacharya S, Yoo J, Wells D, Aksimentiev A. Modeling and simulation of ion channels. Chem Rev 2012; 112:6250-84. [PMID: 23035940 PMCID: PMC3633640 DOI: 10.1021/cr3002609] [Citation(s) in RCA: 148] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Christopher Maffeo
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - Swati Bhattacharya
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - Jejoong Yoo
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - David Wells
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - Aleksei Aksimentiev
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
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19
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He J, Hristova K, Wimley WC. A Highly Charged Voltage-Sensor Helix Spontaneously Translocates across Membranes. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201202741] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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20
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He J, Hristova K, Wimley WC. A highly charged voltage-sensor helix spontaneously translocates across membranes. Angew Chem Int Ed Engl 2012; 51:7150-3. [PMID: 22696138 DOI: 10.1002/anie.201202741] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2012] [Indexed: 11/06/2022]
Abstract
Moving freely: A recent model for voltage gating of potassium channels proposed that the four arginine residues of the voltage-sensing S4 helix (left) are in direct contact with the membrane lipids and move into the hydrocarbon core of the membrane during gating. It is demonstrated that the physical properties of the isolated S4 sequence (right) are sufficient to allow it to freely translocate across synthetic membranes.
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Affiliation(s)
- Jing He
- Biochemistry, Tulane University School of Medicine, New Orleans, LA 70112, USA
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21
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Abstract
Of great interest to the academic and pharmaceutical research communities, helical transmembrane proteins are characterized by their ability to dissolve and fold in lipid bilayers—properties conferred by polypeptide spans termed transmembrane domains (TMDs). The apolar nature of TMDs necessitates the use of membrane-mimetic solvents for many structure and folding studies. This review examines the relationship between TMD structure and solvent environment, focusing on principles elucidated largely in membrane-mimetic environments with single-TMD protein and peptide models. Following a brief description of TMD sequence and conformational characteristics gleaned from the structural database, we present an overview of the conceptual models used to study folding in vitro. The impact of sequence and solvent context on the incorporation of TMDs into membranes, and its role in measurements of TMD self-assembly strengths, is then described. We conclude with a discussion of the nonspecific effects of membrane components on TMD stability.
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Affiliation(s)
- Arianna Rath
- Division of Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, M5G 1X8 Canada
| | - Charles M. Deber
- Division of Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, M5G 1X8 Canada
- Department of Biochemistry, University of Toronto, Toronto, Ontario, M5S 1A8 Canada
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22
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Yuzlenko O, Lazaridis T. Interactions between ionizable amino acid side chains at a lipid bilayer-water interface. J Phys Chem B 2011; 115:13674-84. [PMID: 21985663 DOI: 10.1021/jp2052213] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Potentials of mean force (PMF) between ionizable amino acid side chains (Arg, Lys, His, Glu) in the headgroup area of a palmitoyl oleoyl phosphatidylcholine lipid bilayer were obtained from all-atom molecular dynamics simulations and the adaptive biasing force method. Simulations in bulk water were also performed for comparison. Side chains were constrained in collinear, stacking, and orthogonal (T-shaped) orientations. The most structured and attractive PMFs were observed for hydrogen-bonded side chains. Contact minima occurred at a distance of 2.6-3.1 Å between selected atoms or centers of mass with the most attractive interaction (-9.6 kcal/mol) observed between Arg(+) and Glu(-). Hydrogen bonds play a significant role in stabilizing these interactions. Interactions between like charged side chains can also be very attractive if the charges are screened by surrounding molecules or groups (e.g., the PMF value at the contact minimum for Arg(+)···Arg(+) is -7.6 kcal/mol). Like charged side chains can have contact minima as close as 3.6 Å. The PMFs depend strongly on the relative orientation of the side chains. In agreement with experimental studies and other simulations, we found the stacking arrangement of like charged side chains to be the most favorable orientation. Interaction energies and Lennard-Jones energies between side chains, headgroups, and water molecules were analyzed in order to rationalize the observed PMFs and their dependence on orientation. In general, the results cannot be explained by simple dielectric arguments.
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Affiliation(s)
- Olga Yuzlenko
- Department of Chemistry, City College of the City University of New York, 160 Convent Avenue, New York, New York 10031, USA
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23
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MacCallum JL, Bennett WFD, Tieleman DP. Transfer of arginine into lipid bilayers is nonadditive. Biophys J 2011; 101:110-7. [PMID: 21723820 DOI: 10.1016/j.bpj.2011.05.038] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2011] [Revised: 04/29/2011] [Accepted: 05/17/2011] [Indexed: 01/21/2023] Open
Abstract
Computer simulations suggest that the translocation of arginine through the hydrocarbon core of a lipid membrane proceeds by the formation of a water-filled defect that keeps the arginine molecule hydrated even at the center of the bilayer. We show here that adding additional arginine molecules into one of these water defects causes only a small change in free energy. The barrier for transferring multiple arginines through the membrane is approximately the same as for a single arginine and may even be lower depending on the exact geometry of the system. We discuss these results in the context of arginine-rich peptides such as antimicrobial and cell-penetrating peptides.
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Affiliation(s)
- Justin L MacCallum
- Department of Biological Sciences, Institute for Biocomplexity and Informatics, University of Calgary, Calgary, Alberta, Canada
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24
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Bennett WFD, Tieleman DP. Water Defect and Pore Formation in Atomistic and Coarse-Grained Lipid Membranes: Pushing the Limits of Coarse Graining. J Chem Theory Comput 2011; 7:2981-8. [PMID: 26605486 DOI: 10.1021/ct200291v] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Defects in lipid bilayers are important in a range of biological processes, including interactions between antimicrobial peptides and membranes, transport of polar molecules (including drugs) across membranes, and lipid flip-flop from one monolayer to the other. Passive lipid flip-flop and the translocation of polar molecules across lipid membranes occur on a slow time scale because of high-energy intermediates involving water defects and pores in the membrane. Such defects are an interesting test case for coarse-grained models because of their relatively small characteristic size at the level of water molecules and the complex environment of water and polar head groups in a low-dielectric membrane interior. Here we compare coarse-grained simulations with the MARTINI model with the standard MARTINI water and two recently developed coarse-grained polarizable water models to atomistic simulations. Although in several cases the MARTINI model reproduces the correct free energies, there are structural differences between the atomistic and coarse-grained models. The polarizable water model improves the free energies but only moderately improves the structures. Atomistic test simulations in which water molecules are artificially tethered to each other in groups of four, the resolution of MARTINI, suggest that the limiting factor is not the size of the coarse-grained particles but rather the simple interaction potential and/or the entropy lost in coarse graining the system. By increasing the attractive interaction between the lipids' headgroup and water, we did observe pore formation but at the expense of the correct equilibrium properties of the bilayers.
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Affiliation(s)
- W F Drew Bennett
- Department of Biological Sciences and Institute for Biocomplexity and Informatics, University of Calgary , 2500 University Drive N.W., Calgary, Alberta T2N 1N4, Canada
| | - D Peter Tieleman
- Department of Biological Sciences and Institute for Biocomplexity and Informatics, University of Calgary , 2500 University Drive N.W., Calgary, Alberta T2N 1N4, Canada
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25
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Fleming PJ, Freites JA, Moon CP, Tobias DJ, Fleming KG. Outer membrane phospholipase A in phospholipid bilayers: a model system for concerted computational and experimental investigations of amino acid side chain partitioning into lipid bilayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:126-34. [PMID: 21816133 DOI: 10.1016/j.bbamem.2011.07.016] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Revised: 07/07/2011] [Accepted: 07/09/2011] [Indexed: 12/21/2022]
Abstract
Understanding the forces that stabilize membrane proteins in their native states is one of the contemporary challenges of biophysics. To date, estimates of side chain partitioning free energies from water to the lipid environment show disparate values between experimental and computational measures. Resolving the disparities is particularly important for understanding the energetic contributions of polar and charged side chains to membrane protein function because of the roles these residue types play in many cellular functions. In general, computational free energy estimates of charged side chain partitioning into bilayers are much larger than experimental measurements. However, the lack of a protein-based experimental system that uses bilayers against which to vet these computational predictions has traditionally been a significant drawback. Moon & Fleming recently published a novel hydrophobicity scale that was derived experimentally by using a host-guest strategy to measure the side chain energetic perturbation due to mutation in the context of a native membrane protein inserted into a phospholipid bilayer. These values are still approximately an order of magnitude smaller than computational estimates derived from molecular dynamics calculations from several independent groups. Here we address this discrepancy by showing that the free energy differences between experiment and computation become much smaller if the appropriate comparisons are drawn, which suggests that the two fields may in fact be converging. In addition, we present an initial computational characterization of the Moon & Fleming experimental system used for the hydrophobicity scale: OmpLA in DLPC bilayers. The hydrophobicity scale used OmpLA position 210 as the guest site, and our preliminary results demonstrate that this position is buried in the center of the DLPC membrane, validating its usage in the experimental studies. We further showed that the introduction of charged Arg at position 210 is well tolerated in OmpLA and that the DLPC bilayers accommodate this perturbation by creating a water dimple that allows the Arg side chain to remain hydrated. Lipid head groups visit the dimple and can hydrogen bond with Arg, but these interactions are transient. Overall, our study demonstrates the unique advantages of this molecular system because it can be interrogated by both computational and experimental practitioners, and it sets the stage for free energy calculations in a system for which there is unambiguous experimental data. This article is part of a Special Issue entitled: Membrane protein structure and function.
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Affiliation(s)
- Patrick J Fleming
- T. C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
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26
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Martínez-Gil L, Saurí A, Marti-Renom MA, Mingarro I. Membrane protein integration into the endoplasmic reticulum. FEBS J 2011; 278:3846-58. [PMID: 21592307 DOI: 10.1111/j.1742-4658.2011.08185.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Most integral membrane proteins are targeted, inserted and assembled in the endoplasmic reticulum membrane. The sequential and potentially overlapping events necessary for membrane protein integration take place at sites termed translocons, which comprise a specific set of membrane proteins acting in concert with ribosomes and, probably, molecular chaperones to ensure the success of the whole process. In this minireview, we summarize our current understanding of helical membrane protein integration at the endoplasmic reticulum, and highlight specific characteristics that affect the biogenesis of multispanning membrane proteins.
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Affiliation(s)
- Luis Martínez-Gil
- Departament de Bioquímica i Biologia Molecular, Universitat de València, Burjassot, Spain
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27
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Vila Verde A, Campen RK. Disaccharide Topology Induces Slowdown in Local Water Dynamics. J Phys Chem B 2011; 115:7069-84. [DOI: 10.1021/jp112178c] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ana Vila Verde
- FOM Institute AMOLF, 104 Science Park, 1098 XG Amsterdam, The Netherlands
- Centro de Física, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal
| | - R. Kramer Campen
- FOM Institute AMOLF, 104 Science Park, 1098 XG Amsterdam, The Netherlands
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28
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Free-energy cost for translocon-assisted insertion of membrane proteins. Proc Natl Acad Sci U S A 2011; 108:3596-601. [PMID: 21317362 DOI: 10.1073/pnas.1012758108] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nascent membrane proteins typically insert in a sequential fashion into the membrane via a protein-conducting channel, the Sec translocon. How this process occurs is still unclear, although a thermodynamic partitioning between the channel and the membrane environment has been proposed. Experiment- and simulation-based scales for the insertion free energy of various amino acids are, however, at variance, the former appearing to lie in a narrower range than the latter. Membrane insertion of arginine, for instance, requires 14-17 kcal/mol according to molecular dynamics simulations, but only 2-3 kcal/mol according to experiment. We suggest that this disagreement is resolved by assuming a two-stage insertion process wherein the first step, the insertion into the translocon, is energized by protein synthesis and, therefore, has an effectively zero free-energy cost; the second step, the insertion into the membrane, invokes the translocon as an intermediary between the fully hydrated and the fully inserted locations. Using free-energy perturbation calculations, the effective transfer free energies from the translocon to the membrane have been determined for both arginine and leucine amino acids carried by a background polyleucine helix. Indeed, the insertion penalty for arginine as well as the insertion gain for leucine from the translocon to the membrane is found to be significantly reduced compared to direct insertion from water, resulting in the same compression as observed in the experiment-based scale.
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29
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Bonn M, Bakker HJ, Ghosh A, Yamamoto S, Sovago M, Campen RK. Structural inhomogeneity of interfacial water at lipid monolayers revealed by surface-specific vibrational pump-probe spectroscopy. J Am Chem Soc 2011; 132:14971-8. [PMID: 20882964 DOI: 10.1021/ja106194u] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We report vibrational lifetime measurements of the OH stretch vibration of interfacial water in contact with lipid monolayers, using time-resolved vibrational sum frequency (VSF) spectroscopy. The dynamics of water in contact with four different lipids are reported and are characterized by vibrational relaxation rates measured at 3200, 3300, 3400, and 3500 cm(-1). We observe that the water molecules with an OH frequency ranging from 3300 to 3500 cm(-1) all show vibrational relaxation with a time constant of T(1) = 180 ± 35 fs, similar to what is found for bulk water. Water molecules with OH groups near 3200 cm(-1) show distinctly faster relaxation dynamics, with T(1) < 80 fs. We successfully model the data by describing the interfacial water containing two distinct subensembles in which spectral diffusion is, respectively, rapid (3300-3500 cm(-1)) and absent (3200 cm(-1)). We discuss the potential biological implications of the presence of the strongly hydrogen-bonded, rapidly relaxing water molecules at 3200 cm(-1) that are decoupled from the bulk water system.
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Affiliation(s)
- Mischa Bonn
- FOM Institute AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands
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30
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Kyrychenko A, Sevriukov IY, Syzova ZA, Ladokhin AS, Doroshenko AO. Partitioning of 2,6-Bis(1H-Benzimidazol-2-yl)pyridine fluorophore into a phospholipid bilayer: complementary use of fluorescence quenching studies and molecular dynamics simulations. Biophys Chem 2011; 154:8-17. [PMID: 21211898 PMCID: PMC4167733 DOI: 10.1016/j.bpc.2010.12.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2010] [Revised: 12/04/2010] [Accepted: 12/05/2010] [Indexed: 10/18/2022]
Abstract
Successful use of fluorescence sensing in elucidating the biophysical properties of lipid membranes requires knowledge of the distribution and location of an emitting molecule in the bilayer. We report here that 2,6-bis(1H-benzimidazol-2-yl)pyridine (BBP), which is almost non-fluorescent in aqueous solutions, reveals a strong emission enhancement in a hydrophobic environment of a phospholipid bilayer, making it interesting for fluorescence probing of water content in a lipid membrane. Comparing the fluorescence behavior of BBP in a wide variety of solvents with those in phospholipid vesicles, we suggest that the hydrogen bonding interactions between a BBP fluorophore and water molecules play a crucial role in the observed "light switch effect". Therefore, the loss of water-induced fluorescence quenching inside a membrane are thought to be due to deep penetration of BBP into the hydrophobic, water-free region of a bilayer. Characterized by strong quenching by transition metal ions in solution, BBP also demonstrated significant shielding from the action of the quencher in the presence of phospholipid vesicles. We used the increase in fluorescence intensity, measured upon titration of probe molecules with lipid vesicles, to estimate the partition constant and the Gibbs free energy (ΔG) of transfer of BBP from aqueous buffer into a membrane. Partitioning BBP revealed strongly favorable ΔG, which depends only slightly on the lipid composition of a bilayer, varying in a range from -6.5 to -7.0kcal/mol. To elucidate the binding interactions of the probe with a membrane on the molecular level, a distribution and favorable location of BBP in a POPC bilayer were modeled via atomistic molecular dynamics (MD) simulations using two different approaches: (i) free, diffusion-driven partitioning of the probe molecules into a bilayer and (ii) constrained umbrella sampling of a penetration profile of the dye molecule across a bilayer. Both of these MD approaches agreed with regard to the preferred location of a BBP fluorophore within the interfacial region of a bilayer, located between the hydrocarbon acyl tails and the initial portion of the lipid headgroups. MD simulations also revealed restricted permeability of water molecules into this region of a POPC bilayer, determining the strong fluorescence enhancement observed experimentally for the membrane-partitioned form of BBP.
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Affiliation(s)
- Alexander Kyrychenko
- Institute for Chemistry, V.N. Karazin Kharkiv National University, 4 Svobody Square, Kharkiv 61077, Ukraine
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas 66160-7421, United States
- Ukrainian-American Laboratory of Computational Chemistry, Kharkiv, Ukraine and Jackson, Mississippi, United States
| | - Igor Yu. Sevriukov
- Institute for Chemistry, V.N. Karazin Kharkiv National University, 4 Svobody Square, Kharkiv 61077, Ukraine
| | - Zoya A. Syzova
- Institute for Chemistry, V.N. Karazin Kharkiv National University, 4 Svobody Square, Kharkiv 61077, Ukraine
| | - Alexey S. Ladokhin
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas 66160-7421, United States
| | - Andrey O. Doroshenko
- Institute for Chemistry, V.N. Karazin Kharkiv National University, 4 Svobody Square, Kharkiv 61077, Ukraine
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31
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The energetics of transmembrane helix insertion into a lipid bilayer. Biophys J 2011; 99:2534-40. [PMID: 20959094 DOI: 10.1016/j.bpj.2010.08.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2010] [Revised: 07/30/2010] [Accepted: 08/02/2010] [Indexed: 11/22/2022] Open
Abstract
Free energy profiles for insertion of a hydrophobic transmembrane protein α-helix (M2 from CFTR) into a lipid bilayer have been calculated using coarse-grained molecular dynamics simulations and umbrella sampling to yield potentials of mean force along a reaction path corresponding to translation of a helix across a lipid bilayer. The calculated free energy of insertion is smaller when a bilayer with a thinner hydrophobic region is used. The free energies of insertion from the potentials of mean force are compared with those derived from a number of hydrophobicity scales and with those derived from translocon-mediated insertion. This comparison supports recent models of translocon-mediated insertion and in particular suggests that: 1), helices in an about-to-be-inserted state may be located in a hydrophobic region somewhat thinner than the core of a lipid bilayer; and/or 2), helices in a not-to-be-inserted state may experience an environment more akin (e.g., in polarity/hydrophobicity) to the bilayer/water interface than to bulk water.
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32
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Herce HD, Garcia AE, Litt J, Kane RS, Martin P, Enrique N, Rebolledo A, Milesi V. Arginine-rich peptides destabilize the plasma membrane, consistent with a pore formation translocation mechanism of cell-penetrating peptides. Biophys J 2009; 97:1917-25. [PMID: 19804722 DOI: 10.1016/j.bpj.2009.05.066] [Citation(s) in RCA: 208] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2009] [Revised: 05/22/2009] [Accepted: 05/29/2009] [Indexed: 10/20/2022] Open
Abstract
Recent molecular-dynamics simulations have suggested that the arginine-rich HIV Tat peptides translocate by destabilizing and inducing transient pores in phospholipid bilayers. In this pathway for peptide translocation, Arg residues play a fundamental role not only in the binding of the peptide to the surface of the membrane, but also in the destabilization and nucleation of transient pores across the bilayer. Here we present a molecular-dynamics simulation of a peptide composed of nine Args (Arg-9) that shows that this peptide follows the same translocation pathway previously found for the Tat peptide. We test experimentally the hypothesis that transient pores open by measuring ionic currents across phospholipid bilayers and cell membranes through the pores induced by Arg-9 peptides. We find that Arg-9 peptides, in the presence of an electrostatic potential gradient, induce ionic currents across planar phospholipid bilayers, as well as in cultured osteosarcoma cells and human smooth muscle cells. Our results suggest that the mechanism of action of Arg-9 peptides involves the creation of transient pores in lipid bilayers and cell membranes.
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Affiliation(s)
- H D Herce
- Department of Physics, Rensselaer Polytechnic Institute, Troy, New York, USA
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33
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Protein contents in biological membranes can explain abnormal solvation of charged and polar residues. Proc Natl Acad Sci U S A 2009; 106:15684-9. [PMID: 19805218 DOI: 10.1073/pnas.0905394106] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Transmembrane helices are generally believed to insert into membranes based on their hydrophobicity. Nevertheless, there are important exceptions where polar residues have great functional importance, for instance the S4 helix of voltage-gated ion channels. It has been shown experimentally that insertion can be accomplished by hydrophobic counterbalance, predicting an arginine insertion cost of only 2.5 kcal/mol, compared with 14.9 kcal/mol in cyclohexane. Previous simulations of pure bilayers have produced values close to the pure hydrocarbon, which has lead to spirited discussion about the experimental conditions. Here, we have performed computer simulations of models better mimicking biological membranes by explicitly including protein helices at mass fractions from 15% to 55%, as well as an actual translocon. This has a striking effect on the solvation free energy of arginine. With some polar residues present, the solvation cost comes close to experimental observation at approximately 30% mass fraction, and negligible at 40%. In the presence of a translocon in the membrane, the cost of inserting arginine next to the lateral gate can be as low as 3-5 kcal/mol. The effect is mainly due to the extra helices making it easier to retain hydration water. These results offer a possible explanation for the discrepancy between the in vivo hydrophobicity scale and computer simulations and highlight the importance of the high protein contents in membranes. Although many membrane proteins are stable in pure bilayers, such simplified models might not be sufficiently accurate for insertion of polar or charged residues in biological membranes.
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