1
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Ashrafuzzaman M, Koeppe RE, Andersen OS. Intrinsic Lipid Curvature and Bilayer Elasticity as Regulators of Channel Function: A Comparative Single-Molecule Study. Int J Mol Sci 2024; 25:2758. [PMID: 38474005 PMCID: PMC10931550 DOI: 10.3390/ijms25052758] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2024] [Revised: 02/13/2024] [Accepted: 02/21/2024] [Indexed: 03/14/2024] Open
Abstract
Perturbations in bilayer material properties (thickness, lipid intrinsic curvature and elastic moduli) modulate the free energy difference between different membrane protein conformations, thereby leading to changes in the conformational preferences of bilayer-spanning proteins. To further explore the relative importance of curvature and elasticity in determining the changes in bilayer properties that underlie the modulation of channel function, we investigated how the micelle-forming amphiphiles Triton X-100, reduced Triton X-100 and the HII lipid phase promoter capsaicin modulate the function of alamethicin and gramicidin channels. Whether the amphiphile-induced changes in intrinsic curvature were negative or positive, amphiphile addition increased gramicidin channel appearance rates and lifetimes and stabilized the higher conductance states in alamethicin channels. When the intrinsic curvature was modulated by altering phospholipid head group interactions, however, maneuvers that promote a negative-going curvature stabilized the higher conductance states in alamethicin channels but destabilized gramicidin channels. Using gramicidin channels of different lengths to probe for changes in bilayer elasticity, we found that amphiphile adsorption increases bilayer elasticity, whereas altering head group interactions does not. We draw the following conclusions: first, confirming previous studies, both alamethicin and gramicidin channels are modulated by changes in lipid bilayer material properties, the changes occurring in parallel yet differing dependent on the property that is being changed; second, isolated, negative-going changes in curvature stabilize the higher current levels in alamethicin channels and destabilize gramicidin channels; third, increases in bilayer elasticity stabilize the higher current levels in alamethicin channels and stabilize gramicidin channels; and fourth, the energetic consequences of changes in elasticity tend to dominate over changes in curvature.
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Affiliation(s)
- Mohammad Ashrafuzzaman
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065, USA;
| | - Roger E. Koeppe
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA;
| | - Olaf S. Andersen
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065, USA;
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2
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Peyear TA, Andersen OS. Screening for bilayer-active and likely cytotoxic molecules reveals bilayer-mediated regulation of cell function. J Gen Physiol 2023; 155:e202213247. [PMID: 36763053 PMCID: PMC9948646 DOI: 10.1085/jgp.202213247] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Revised: 12/06/2022] [Accepted: 01/13/2023] [Indexed: 02/11/2023] Open
Abstract
A perennial problem encountered when using small molecules (drugs) to manipulate cell or protein function is to assess whether observed changes in function result from specific interactions with a desired target or from less specific off-target mechanisms. This is important in laboratory research as well as in drug development, where the goal is to identify molecules that are unlikely to be successful therapeutics early in the process, thereby avoiding costly mistakes. We pursued this challenge from the perspective that many bioactive molecules (drugs) are amphiphiles that alter lipid bilayer elastic properties, which may cause indiscriminate changes in membrane protein (and cell) function and, in turn, cytotoxicity. Such drug-induced changes in bilayer properties can be quantified as changes in the monomer↔dimer equilibrium for bilayer-spanning gramicidin channels. Using this approach, we tested whether molecules in the Pathogen Box (a library of 400 drugs and drug-like molecules with confirmed activity against tropical diseases released by Medicines for Malaria Venture to encourage the development of therapies for neglected tropical diseases) are bilayer modifiers. 32% of the molecules in the Pathogen Box were bilayer modifiers, defined as molecules that at 10 µM shifted the monomer↔dimer equilibrium toward the conducting dimers by at least 50%. Correlation analysis of the molecules' reported HepG2 cell cytotoxicity to bilayer-modifying potency, quantified as the shift in the gramicidin monomer↔dimer equilibrium, revealed that molecules producing <25% change in the equilibrium had significantly lower probability of being cytotoxic than molecules producing >50% change. Neither cytotoxicity nor bilayer-modifying potency (quantified as the shift in the gramicidin monomer↔dimer equilibrium) was well predicted by conventional physico-chemical descriptors (hydrophobicity, polar surface area, etc.). We conclude that drug-induced changes in lipid bilayer properties are robust predictors of the likelihood of membrane-mediated off-target effects, including cytotoxicity.
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Affiliation(s)
- Thasin A. Peyear
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY, USA
- Graduate Program in Physiology, Biophysics and Systems Biology, Weill Cornell Graduate School of Medical Sciences. New York, NY, USA
| | - Olaf S. Andersen
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY, USA
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3
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Ning Y, Han P, Ma J, Liu Y, Fu Y, Wang Z, Jia Y. Characterization of brevilaterins, multiple antimicrobial peptides simultaneously produced by Brevibacillus laterosporus S62-9, and their application in real food system. FOOD BIOSCI 2021. [DOI: 10.1016/j.fbio.2021.101091] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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4
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Dyett BP, Yu H, Lakic B, De Silva N, Dahdah A, Bao L, Blanch EW, Drummond CJ, Conn CE. Delivery of antimicrobial peptides to model membranes by cubosome nanocarriers. J Colloid Interface Sci 2021; 600:14-22. [PMID: 34000474 DOI: 10.1016/j.jcis.2021.03.161] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2020] [Revised: 03/21/2021] [Accepted: 03/28/2021] [Indexed: 11/16/2022]
Abstract
Antimicrobial peptides (AMPs), which typically disrupt the bacterial wall prompting leakage or lysis of the cell, form a growing contingent in the arsenal against antibiotic resistant bacteria. The effectiveness of AMPs is, however, hampered by their low solubility, general chemical and physical instability, and short half-life in vivo. Lipid nanocarriers such as cubosomes are effective at encapsulating and protecting proteins while simultaneously showing promise in delivery applications. Here, the efficacy of cubosome mediated delivery of AMPs is evaluated by the in-situ surface characterization of model membranes with varying composition. The cubosomes were observed to initially fuse with the membranes, with subsequent membrane disruption observed after approximately 20 - 60 min. The time for the disruption was sensitive to the charge of the cubosome as well as the composition of the bilayer. More physiologically relevant bilayers including lipids with phospho-(1'-rac-glycerol) (PG) or phosphoethanolamine (PE) headgroups were more vulnerable than those of neat phosphocholine (PC). Notably, disruption to the bilayer occurred an order of magnitude faster for encapsulated AMP compared to free AMP.
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Affiliation(s)
- Brendan P Dyett
- School of Science, STEM College, RMIT University, Victoria, Australia
| | - Haitao Yu
- School of Science, STEM College, RMIT University, Victoria, Australia
| | - Biserka Lakic
- School of Science, STEM College, RMIT University, Victoria, Australia
| | - Nilamuni De Silva
- School of Science, STEM College, RMIT University, Victoria, Australia
| | - Anthony Dahdah
- School of Science, STEM College, RMIT University, Victoria, Australia
| | - Lei Bao
- School of Engineering, STEM College, RMIT University, Victoria, Australia
| | - Ewan W Blanch
- School of Science, STEM College, RMIT University, Victoria, Australia
| | - Calum J Drummond
- School of Science, STEM College, RMIT University, Victoria, Australia.
| | - Charlotte E Conn
- School of Science, STEM College, RMIT University, Victoria, Australia.
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5
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Ngo V, Li H, MacKerell AD, Allen TW, Roux B, Noskov S. Polarization Effects in Water-Mediated Selective Cation Transport across a Narrow Transmembrane Channel. J Chem Theory Comput 2021; 17:1726-1741. [PMID: 33539082 DOI: 10.1021/acs.jctc.0c00968] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Despite the progress in modeling complex molecular systems of ever-increasing complexity, a quantitatively accurate computational treatment of ion permeation through narrow membrane channels remains challenging. An important factor to reach this goal is induced electronic polarization, which is likely to impact the permeation rate of small ions through narrow molecular pores. In this work, we extended the recently developed polarizable force field based on the classical Drude oscillators to assess the role of induced polarization effects on the energetics of sodium and potassium ion transport across the gramicidin A (gA) ion channel. The inclusion of induced polarization lowers barriers present in 1D potential of mean force (PMF) for cation permeation by ∼50% compared to those obtained with the additive force field. Conductance properties calculated with 1D PMFs from Drude simulations are in better agreement with experimental results. Polarization of single-file water molecules and protein atoms forming the narrow pore has a direct impact on the free-energy barriers and cation-specific solid-state NMR chemical shifts. Sensitivity analysis indicates that small changes to water-channel interactions can alter the free energy barrier for ion permeation. These results, illustrating polarization effects present in the complex electrostatic environment of the gA channel, have broad implications for revising proposed mechanisms of ion permeation and selectivity in a variety of ion channels.
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Affiliation(s)
- Van Ngo
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N1N4, Canada.,Center for Nonlinear Studies, Los Alamos National Lab, Los Alamos, New Mexico 87544, United States
| | - Hui Li
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, United States
| | - Alexander D MacKerell
- Computer-Aided Drug Design Center, Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, Maryland 21201, United States
| | - Toby W Allen
- School of Science, RMIT University, Melbourne, VIC 3001, Australia
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, United States
| | - Sergei Noskov
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N1N4, Canada
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6
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Sun D, He S, Bennett WFD, Bilodeau CL, Andersen OS, Lightstone FC, Ingólfsson HI. Atomistic Characterization of Gramicidin Channel Formation. J Chem Theory Comput 2021; 17:7-12. [PMID: 33378617 PMCID: PMC7808174 DOI: 10.1021/acs.jctc.0c00989] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2020] [Indexed: 01/09/2023]
Abstract
We investigated gramicidin A (gA) subunit dimerization in lipid bilayers using microsecond-long replica-exchange umbrella sampling simulations, millisecond-long unbiased molecular dynamics simulations, and machine learning. Our simulations led to a dimer structure that is indistinguishable from the experimentally determined gA channel structures, with the two gA subunits joined by six hydrogen bonds (6HB). The simulations also uncovered two additional dimer structures, with different gA-gA stacking orientations that were stabilized by four or two hydrogen bonds (4HB or 2HB). When examining the temporal evolution of the dimerization, we found that two bilayer-inserted gA subunits can form the 6HB dimer directly, with no discernible intermediate states, as well as through paths that involve the 2HB and 4HB dimers.
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Affiliation(s)
- Delin Sun
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore
National Laboratory, 7000 East Avenue, Livermore, California 94550, United States
| | - Stewart He
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore
National Laboratory, 7000 East Avenue, Livermore, California 94550, United States
| | - W. F. Drew Bennett
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore
National Laboratory, 7000 East Avenue, Livermore, California 94550, United States
| | - Camille L. Bilodeau
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore
National Laboratory, 7000 East Avenue, Livermore, California 94550, United States
- Howard
P. Isermann Department of Chemical and Biological Engineering and
Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
| | - Olaf S. Andersen
- Department
of Physiology and Biophysics, Weill Cornell
Medicine, New York, New York 10065, United States
| | - Felice C. Lightstone
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore
National Laboratory, 7000 East Avenue, Livermore, California 94550, United States
| | - Helgi I. Ingólfsson
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore
National Laboratory, 7000 East Avenue, Livermore, California 94550, United States
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7
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Abel S, Marchi M. Deciphering the Structure of the Gramicidin A Channel in the Presence of AOT Reverse Micelles in Pentane Using Molecular Dynamics Simulations. J Phys Chem B 2020; 124:11802-11818. [PMID: 33346653 DOI: 10.1021/acs.jpcb.0c08902] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Structural studies of proteins and, in particular, integral membrane proteins (IMPs) using solution NMR spectroscopy approaches are challenging due to not only their inherent structural complexities but also the fact that they need to be solubilized in biomimetic environments (such as micelles), which enhances the slow molecular reorientation. To deal with these difficulties and increase the effective rate of molecular reorientation, the encapsulation of IMPs in the aqueous core of the reverse micelle (RM) dissolved in a low-viscosity solvent has been proven to be a viable approach. However, the effect of the reverse micelle (RM) environment on the IMP structure and function is little known. To gain insight into these aspects, this article presents a series of atomistic unconstrained molecular dynamics (MD) of a model ion channel (gramicidin A, gA) with RMs formed with anionic surfactant diacyl chain bis(2-ethylhexyl) sodium succinate (AOT) in pentane at a water-to-surfactant molar ratio (W0) of 6. The simulations were carried out with different protocols and starting conditions for a total of 2.4 μs and were compared with other MDs used with the gA channel inserted in models of the SDS micelle or the DMPC membrane. We show here that in the presence of AOT RMs the gA dimer did not look like the "dumbbell-like" model anticipated by experiments, where the C-terminal parts of the gA are capped with two RMs and the rest of the dimer is protected from the oil solvent by the AOT acyl chains. In contrast, the MD simulations reveal that the AOT, Na+, and water formed two well-defined and elongated RMs attached to the C-terminal ends of the gA dimer, while the rest is in direct contact with the pentane. The initial β6.3 secondary structure of the gA is well conserved and filled with 6-9 waters, as in SDS micelles or the DMPC membrane. Finally, the water movement inside the gA is strongly affected by the presence of RMs at each extremity, and no passage of water molecules through the gA channel is observed even after a long simulation period, whereas the opposite was found for gA in SDS and DMPC.
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Affiliation(s)
- Stéphane Abel
- CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Université Paris-Saclay, 91198 Gif-sur-Yvette, France
| | - Massimo Marchi
- CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Université Paris-Saclay, 91198 Gif-sur-Yvette, France
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8
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Foreman-Ortiz IU, Liang D, Laudadio ED, Calderin JD, Wu M, Keshri P, Zhang X, Schwartz MP, Hamers RJ, Rotello VM, Murphy CJ, Cui Q, Pedersen JA. Anionic nanoparticle-induced perturbation to phospholipid membranes affects ion channel function. Proc Natl Acad Sci U S A 2020; 117:27854-27861. [PMID: 33106430 PMCID: PMC7668003 DOI: 10.1073/pnas.2004736117] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Understanding the mechanisms of nanoparticle interaction with cell membranes is essential for designing materials for applications such as bioimaging and drug delivery, as well as for assessing engineered nanomaterial safety. Much attention has focused on nanoparticles that bind strongly to biological membranes or induce membrane damage, leading to adverse impacts on cells. More subtle effects on membrane function mediated via changes in biophysical properties of the phospholipid bilayer have received little study. Here, we combine electrophysiology measurements, infrared spectroscopy, and molecular dynamics simulations to obtain insight into a mode of nanoparticle-mediated modulation of membrane protein function that was previously only hinted at in prior work. Electrophysiology measurements on gramicidin A (gA) ion channels embedded in planar suspended lipid bilayers demonstrate that anionic gold nanoparticles (AuNPs) reduce channel activity and extend channel lifetimes without disrupting membrane integrity, in a manner consistent with changes in membrane mechanical properties. Vibrational spectroscopy indicates that AuNP interaction with the bilayer does not perturb the conformation of membrane-embedded gA. Molecular dynamics simulations reinforce the experimental findings, showing that anionic AuNPs do not directly interact with embedded gA channels but perturb the local properties of lipid bilayers. Our results are most consistent with a mechanism in which anionic AuNPs disrupt ion channel function in an indirect manner by altering the mechanical properties of the surrounding bilayer. Alteration of membrane mechanical properties represents a potentially important mechanism by which nanoparticles induce biological effects, as the function of many embedded membrane proteins depends on phospholipid bilayer biophysical properties.
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Affiliation(s)
| | - Dongyue Liang
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706
- Department of Chemistry, Boston University, Boston, MA 02215
| | | | - Jorge D Calderin
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706
| | - Meng Wu
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801
| | - Puspam Keshri
- Department of Chemistry, University of Massachusetts, Amherst, MA 01003
| | - Xianzhi Zhang
- Department of Chemistry, University of Massachusetts, Amherst, MA 01003
| | - Michael P Schwartz
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706
| | - Robert J Hamers
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706
| | - Vincent M Rotello
- Department of Chemistry, University of Massachusetts, Amherst, MA 01003
| | - Catherine J Murphy
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801
| | - Qiang Cui
- Department of Chemistry, Boston University, Boston, MA 02215
- Department of Physics, Boston University, Boston, MA 02215
- Department of Biomedical Engineering, Boston University, Boston, MA 02215
| | - Joel A Pedersen
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706;
- Department of Soil Science, University of Wisconsin-Madison, Madison, WI 53706
- Department of Civil & Environmental Engineering, University of Wisconsin-Madison, Madison, WI 53706
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9
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Sun D, Peyear TA, Bennett WFD, Holcomb M, He S, Zhu F, Lightstone FC, Andersen OS, Ingólfsson HI. Assessing the Perturbing Effects of Drugs on Lipid Bilayers Using Gramicidin Channel-Based In Silico and In Vitro Assays. J Med Chem 2020; 63:11809-11818. [PMID: 32945672 PMCID: PMC7586341 DOI: 10.1021/acs.jmedchem.0c00958] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Indexed: 01/07/2023]
Abstract
Partitioning of bioactive molecules, including drugs, into cell membranes may produce indiscriminate changes in membrane protein function. As a guide to safe drug development, it therefore becomes important to be able to predict the bilayer-perturbing potency of hydrophobic/amphiphilic drugs candidates. Toward this end, we exploited gramicidin channels as molecular force probes and developed in silico and in vitro assays to measure drugs' bilayer-modifying potency. We examined eight drug-like molecules that were found to enhance or suppress gramicidin channel function in a thick 1,2-dierucoyl-sn-glycero-3-phosphocholine (DC22:1PC) but not in thin 1,2-dioleoyl-sn-glycero-3-phosphocholine (DC18:1PC) lipid bilayer. The mechanism underlying this difference was attributable to the changes in gramicidin dimerization free energy by drug-induced perturbations of lipid bilayer physical properties and bilayer-gramicidin interactions. The combined in silico and in vitro approaches, which allow for predicting the perturbing effects of drug candidates on membrane protein function, have implications for preclinical drug safety assessment.
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Affiliation(s)
- Delin Sun
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Thasin A. Peyear
- Department
of Physiology and Biophysics, Weill Cornell
Medicine, New York, New York 10065, United States
| | - W. F. Drew Bennett
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Matthew Holcomb
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Stewart He
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Fangqiang Zhu
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Felice C. Lightstone
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Olaf S. Andersen
- Department
of Physiology and Biophysics, Weill Cornell
Medicine, New York, New York 10065, United States
| | - Helgi I. Ingólfsson
- Biosciences
and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
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10
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Abstract
Despite the well-characterized structural symmetry of the dimeric transmembrane antibiotic gramicidin A, we show that the symmetry is broken by selective hydrogen bonding between eight waters comprising a transmembrane water wire and a specific subset of the 26 pore-lining carbonyl oxygens of the gramicidin A channel. The 17O NMR spectroscopic resolution of the carbonyl resonances from the two subunits required the use of a world record high field magnet (35.2 T; 1,500 MHz for 1H). Uniquely, this result documented the millisecond timescale stability of the water wire orientation within the gramicidin A pore that had been reported to have only subnanosecond stability. These 17O spectroscopic results portend wide applications in molecular biophysics and beyond. Water wires are critical for the functioning of many membrane proteins, as in channels that conduct water, protons, and other ions. Here, in liquid crystalline lipid bilayers under symmetric environmental conditions, the selective hydrogen bonding interactions between eight waters comprising a water wire and a subset of 26 carbonyl oxygens lining the antiparallel dimeric gramicidin A channel are characterized by 17O NMR spectroscopy at 35.2 T (or 1,500 MHz for 1H) and computational studies. While backbone 15N spectra clearly indicate structural symmetry between the two subunits, single site 17O labels of the pore-lining carbonyls report two resonances, implying a break in dimer symmetry caused by the selective interactions with the water wire. The 17O shifts document selective water hydrogen bonding with carbonyl oxygens that are stable on the millisecond timescale. Such interactions are supported by density functional theory calculations on snapshots taken from molecular dynamics simulations. Water hydrogen bonding in the pore is restricted to just three simultaneous interactions, unlike bulk water environs. The stability of the water wire orientation and its electric dipole leads to opposite charge-dipole interactions for K+ ions bound at the two ends of the pore, thereby providing a simple explanation for an ∼20-fold difference in K+ affinity between two binding sites that are ∼24 Å apart. The 17O NMR spectroscopy reported here represents a breakthrough in high field NMR technology that will have applications throughout molecular biophysics, because of the acute sensitivity of the 17O nucleus to its chemical environment.
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11
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Lin FY, Huang J, Pandey P, Rupakheti C, Li J, Roux B, MacKerell AD. Further Optimization and Validation of the Classical Drude Polarizable Protein Force Field. J Chem Theory Comput 2020; 16:3221-3239. [PMID: 32282198 PMCID: PMC7306265 DOI: 10.1021/acs.jctc.0c00057] [Citation(s) in RCA: 49] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The CHARMM Drude-2013 polarizable force field (FF) was developed to include the explicit treatment of induced electronic polarizability, resulting in a more accurate description of the electrostatic interactions in molecular dynamics (MD) simulations. While the Drude-2013 protein FF has shown success in improving the folding properties of α-helical peptides and to reproduce experimental observables in simulations up to 1 μs, some limitations were noted regarding the stability of β-sheet structures in simulations longer than 100 ns as well as larger deviations from crystal structures in simulations of a number of proteins compared to the additive CHARMM36 protein FF. The origin of the instability has been identified and appears to be primarily due to overestimated atomic polarizabilities and induced dipole-dipole interactions on the Cβ, Cγ, and Cδ side chain atoms. To resolve this and other issues, a number of aspects of the model were revisited, resulting in Drude-2019 protein FF. Backbone parameters were optimized targeting the conformational properties of the (Ala)5 peptide in solution along with gas phase properties of the alanine dipeptide. Dipeptides that contain N-acetylated and N'-methylamidated termini, excluding Gly, Pro, and Ala, were used as models to optimize the atomic polarizabilities and Thole screening factors on selected Cβ, Cγ, and Cδ carbons by targeting quantum mechanical (QM) dipole moments and molecular polarizabilities. In addition, to obtain better conformational properties, side chain χ1 and χ2 dihedral parameters were optimized targeting QM data for the respective side chain dipeptide conformations as well as Protein Data Bank survey data based on the χ1, χ2 sampling from Hamiltonian replica-exchange MD simulations of (Ala)4-X-(Ala)4 in solution, where X is the amino acid of interest. Further improvements include optimizing nonbonded interactions between charged residues to reproduce QM interaction energies of the charged-protein model compounds and experimental osmotic pressures. Validation of the optimized Drude protein FF includes MD simulations of a collection of peptides and proteins including β-sheet structures, as well as transmembrane ion channels. Results showed that the updated Drude-2019 protein FF yields smaller overall root-mean-square differences of proteins as compared to the additive CHARMM36m and Drude-2013 FFs as well as similar or improved agreement with experimental NMR properties, allowing for long time scale simulation studies of proteins and more complex biomolecular systems in conjunction with the remainder of the Drude polarizable FF.
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Affiliation(s)
- Fang-Yu Lin
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, 20 Penn Street, Baltimore, MD 21201, USA
| | - Jing Huang
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, 20 Penn Street, Baltimore, MD 21201, USA
- Westlake University, 18 Shilongshan Road, Hangzhou 310024, Zhejiang, China
| | - Poonam Pandey
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, 20 Penn Street, Baltimore, MD 21201, USA
| | - Chetan Rupakheti
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, 60637, USA
| | - Jing Li
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, 60637, USA
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, 60637, USA
| | - Alexander D. MacKerell
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, 20 Penn Street, Baltimore, MD 21201, USA
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12
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Rostovtseva TK, Queralt-Martín M, Rosencrans WM, Bezrukov SM. Targeting the Multiple Physiologic Roles of VDAC With Steroids and Hydrophobic Drugs. Front Physiol 2020; 11:446. [PMID: 32457654 PMCID: PMC7221028 DOI: 10.3389/fphys.2020.00446] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 04/09/2020] [Indexed: 12/12/2022] Open
Abstract
There is accumulating evidence that endogenous steroids and non-polar drugs are involved in the regulation of mitochondrial physiology. Many of these hydrophobic compounds interact with the Voltage Dependent Anion Channel (VDAC). This major metabolite channel in the mitochondrial outer membrane (MOM) regulates the exchange of ions and water-soluble metabolites, such as ATP and ADP, across the MOM, thus governing mitochondrial respiration. Proteomics and biochemical approaches together with molecular dynamics simulations have identified an impressively large number of non-polar compounds, including endogenous, able to bind to VDAC. These findings have sparked speculation that both natural steroids and synthetic hydrophobic drugs regulate mitochondrial physiology by directly affecting VDAC ion channel properties and modulating its metabolite permeability. Here we evaluate recent studies investigating the effect of identified VDAC-binding natural steroids and non-polar drugs on VDAC channel functioning. We argue that while many compounds are found to bind to the VDAC protein, they do not necessarily affect its channel functions in vitro. However, they may modify other aspects of VDAC physiology such as interaction with its cytosolic partner proteins or complex formation with other mitochondrial membrane proteins, thus altering mitochondrial function.
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Affiliation(s)
- Tatiana K Rostovtseva
- Section on Molecular Transport, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States
| | - María Queralt-Martín
- Section on Molecular Transport, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States
| | - William M Rosencrans
- Section on Molecular Transport, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States
| | - Sergey M Bezrukov
- Section on Molecular Transport, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States
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13
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Sun D, Peyear TA, Bennett WFD, Andersen OS, Lightstone FC, Ingólfsson HI. Molecular Mechanism for Gramicidin Dimerization and Dissociation in Bilayers of Different Thickness. Biophys J 2019; 117:1831-1844. [PMID: 31676135 PMCID: PMC7018991 DOI: 10.1016/j.bpj.2019.09.044] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 09/01/2019] [Accepted: 09/04/2019] [Indexed: 01/01/2023] Open
Abstract
Membrane protein functions can be altered by subtle changes in the host lipid bilayer physical properties. Gramicidin channels have emerged as a powerful system for elucidating the underlying mechanisms of membrane protein function regulation through changes in bilayer properties, which are reflected in the thermodynamic equilibrium distribution between nonconducting gramicidin monomers and conducting bilayer-spanning dimers. To improve our understanding of how subtle changes in bilayer thickness alter the gramicidin monomer and dimer distributions, we performed extensive atomistic molecular dynamics simulations and fluorescence-quenching experiments on gramicidin A (gA). The free-energy calculations predicted a nonlinear coupling between the bilayer thickness and channel formation. The energetic barrier inhibiting gA channel formation was sharply increased in the thickest bilayer (1,2-dierucoyl-sn-glycero-3-phosphocholine). This prediction was corroborated by experimental results on gramicidin channel activity in bilayers of different thickness. To further explore the mechanism of channel formation, we performed extensive unbiased molecular dynamics simulations, which allowed us to observe spontaneous gA dimer formation in lipid bilayers. The simulations revealed structural rearrangements in the gA subunits and changes in lipid packing, as well as water reorganization, that occur during the dimerization process. Together, the simulations and experiments provide new, to our knowledge, insights into the process and mechanism of gramicidin channel formation, as a prototypical example of the bilayer regulation of membrane protein function.
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Affiliation(s)
- Delin Sun
- Biosciences and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California
| | - Thasin A Peyear
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, New York
| | - W F Drew Bennett
- Biosciences and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California
| | - Olaf S Andersen
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, New York
| | - Felice C Lightstone
- Biosciences and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California
| | - Helgi I Ingólfsson
- Biosciences and Biotechnology Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California.
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14
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Park S, Yeom MS, Andersen OS, Pastor RW, Im W. Quantitative Characterization of Protein-Lipid Interactions by Free Energy Simulation between Binary Bilayers. J Chem Theory Comput 2019; 15:6491-6503. [PMID: 31560853 PMCID: PMC7076909 DOI: 10.1021/acs.jctc.9b00815] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Using a recently developed binary bilayer system (BBS) consisting of two patches of laterally contacting bilayers, umbrella sampling molecular dynamics (MD) simulations were performed for quantitative characterization of protein-lipid interactions. The BBS is composed of 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) with an embedded model membrane protein, a gramicidin A (gA) channel. The calculated free energy difference for the transfer of a gA channel from DLPC (hydrophobic thickness ≈ 21.5 Å) to DMPC (hydrophobic thickness ≈ 25.5 Å) bilayers, ΔG(DLPC → DMPC), is -2.2 ± 0.7 kcal/mol. This value appears at odds with the traditional view that the hydrophobic length of the gA channel is ∼22 Å. To understand this discrepancy, we first note that recent MD simulations by different groups have shown that lipid bilayer thickness profiles in the vicinity of a gA channel differ qualitatively from the deformation profile predicted from continuum elastic bilayer models. Our MD simulations at low and high gA:lipid molar ratios and different membrane compositions indicate that the gA channel's effective hydrophobic length is ∼26 Å. Using this effective hydrophobic length, ΔG(DLPC → DMPC) determined here is in excellent agreement with predictions based on continuum elastic models (-3.0 to -2.2 kcal/mol) where the bilayer deformation energy is approximated as a harmonic function of the mismatch between the channel's effective hydrophobic length and the hydrophobic thickness of the bilayer. The free energy profile for gA in the BBS includes a barrier at the interface between the two bilayers which can be attributed to the line tension at the interface between two bilayers with different hydrophobic thicknesses. This observation implies that translation of a peptide between two different regions of a cell membrane (such as between the liquid ordered and disordered phases) may include effects of a barrier at the interface in addition to the relative free energies of the species far from the interface. The BBS allows for direct transfer free energy calculations between bilayers without a need of a reference medium, such as bulk water, and thus provides an efficient simulation protocol for the quantitative characterization of protein-lipid interactions at all-atom resolution.
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Affiliation(s)
- Soohyung Park
- Departments of Biological Sciences and Bioengineering , Lehigh University , Bethlehem , Pennsylvania 18015 , United States
| | - Min Sun Yeom
- Korean Institute of Science and Technology Information , Daejeon , Korea
| | - Olaf S Andersen
- Department of Physiology and Biophysics , Weill Cornell Medicine , New York , New York 10065 , United States
| | - Richard W Pastor
- Laboratory of Computational Biology, National Heart, Lung and Blood Institute , National Institutes of Health , Bethesda , Maryland 20892 , United States
| | - Wonpil Im
- Departments of Biological Sciences and Bioengineering , Lehigh University , Bethlehem , Pennsylvania 18015 , United States.,School of Computational Sciences , Korea Institute for Advanced Study , Seoul 02455 , Republic of Korea
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15
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Barreto-Santamaría A, Patarroyo ME, Curtidor H. Designing and optimizing new antimicrobial peptides: all targets are not the same. Crit Rev Clin Lab Sci 2019; 56:351-373. [DOI: 10.1080/10408363.2019.1631249] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Adriana Barreto-Santamaría
- Fundación Instituto de Inmunología de Colombia - FIDIC, Receptor-Ligand Department, Bogotá D.C, Colombia
- Universidad del Rosario, School of Medicine and Health Sciences, Bogotá D.C., Colombia
| | - Manuel E. Patarroyo
- Fundación Instituto de Inmunología de Colombia - FIDIC, Receptor-Ligand Department, Bogotá D.C, Colombia
- Universidad Nacional de Colombia - Bogotá, Faculty of Medicine, Bogotá D.C., Colombia
| | - Hernando Curtidor
- Fundación Instituto de Inmunología de Colombia - FIDIC, Receptor-Ligand Department, Bogotá D.C, Colombia
- Universidad del Rosario, School of Medicine and Health Sciences, Bogotá D.C., Colombia
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16
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17
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Reimer JM, Harb I, Ovchinnikova OG, Jiang J, Whitfield C, Schmeing TM. Structural Insight into a Novel Formyltransferase and Evolution to a Nonribosomal Peptide Synthetase Tailoring Domain. ACS Chem Biol 2018; 13:3161-3172. [PMID: 30346688 DOI: 10.1021/acschembio.8b00739] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Nonribosomal peptide synthetases (NRPSs) increase the chemical diversity of their products by acquiring tailoring domains. Linear gramicidin synthetase starts with a tailoring formylation (F) domain, which likely originated from a sugar formyltransferase (FT) gene. Here, we present studies on an Anoxybacillus kamchatkensis sugar FT representative of the prehorizontal gene transfer FT. Gene cluster analysis reveals that this FT acts on a UDP-sugar in a novel pathway for synthesis of a 7-formamido derivative of CMP-pseudaminic acid. We recapitulate the pathway up to and including the formylation step in vitro, experimentally demonstrating the role of the FT. We also present X-ray crystal structures of the FT alone and with ligands, which unveil contrasts with other structurally characterized sugar FTs and show close structural similarity with the F domain. The structures reveal insights into the adaptations that were needed to co-opt and evolve a sugar FT into a functional and useful NRPS domain.
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Affiliation(s)
- Janice M. Reimer
- Department of Biochemistry, McGill University, Montréal, Québec H3G 0B1, Canada
| | - Ingrid Harb
- Department of Biochemistry, McGill University, Montréal, Québec H3G 0B1, Canada
| | - Olga G. Ovchinnikova
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Jessie Jiang
- Department of Biochemistry, McGill University, Montréal, Québec H3G 0B1, Canada
| | - Chris Whitfield
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - T. Martin Schmeing
- Department of Biochemistry, McGill University, Montréal, Québec H3G 0B1, Canada
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18
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Ganesan P, Ramalingam R. Investigation of structural stability and functionality of homodimeric gramicidin towards peptide‐based drug: a molecular simulation approach. J Cell Biochem 2018; 120:4903-4911. [DOI: 10.1002/jcb.27765] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2018] [Accepted: 09/06/2018] [Indexed: 12/17/2022]
Affiliation(s)
- Pavithrra Ganesan
- Bioinformatics Lab, Department of Biotechnology, School of Biosciences and Technology Vellore Institute of Technology (VIT) Vellore India
| | - Rajasekaran Ramalingam
- Bioinformatics Lab, Department of Biotechnology, School of Biosciences and Technology Vellore Institute of Technology (VIT) Vellore India
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19
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Identification of Effective Dimeric Gramicidin-D Peptide as Antimicrobial Therapeutics over Drug Resistance: In-Silico Approach. Interdiscip Sci 2018; 11:575-583. [PMID: 30182355 DOI: 10.1007/s12539-018-0304-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2018] [Revised: 07/25/2018] [Accepted: 08/28/2018] [Indexed: 10/28/2022]
Abstract
Discovering and developing the antimicrobial peptides are recently focused on pharmaceutical firm, since they serve as complementary to antibiotics in prevailing over drug resistance by eliciting the disruption of microbial membrane. Still, there are lots of challenges to bring up the structurally stable and functionally efficient antimicrobial peptides. It is well known that gramicidin D is the prominent antimicrobial peptide that exists as g-AB, g-BC, and g-AC. This study analyzes the structural stability and the functional activity of hetero-dimeric double-stranded gramicidin-D peptides, thereby demonstrating its potent antimicrobial activity against antibiotic-resistant micro-organisms. To investigate the structural stability and functionality of gramicidin D, we performed static and dynamic analysis. Initially, we observed a maximum number of intermolecular interactions and membrane penetration in g-AB as compared to g-BC and g-AC. To substantiate further, the geometrical and thermodynamic parameters revealed the retention of maximum stability in g-AB than g-AC and g-BC. Thus, the conformational free energy and the binding free energy showed the variation among gramicidin-D peptides for the prediction of increased stability and functionality. In conclusion, g-AB peptide has definitely demonstrated adequate structural stability and functionality and this work will need to be considered in peptide-based drug discovery.
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20
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Azar E, Constantin D, Warschawski DE. The effect of gramicidin inclusions on the local order of membrane components. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2018; 41:44. [PMID: 29582214 PMCID: PMC7088371 DOI: 10.1140/epje/i2018-11644-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Accepted: 03/07/2018] [Indexed: 06/08/2023]
Abstract
We study the local effect of the antimicrobial peptide Gramicidin A on bilayers composed of lipids or surfactants using nuclear magnetic resonance spectroscopy and wide-angle X-ray scattering, techniques that probe the orientational and positional order of the alkyl chains, respectively. The two types of order vary with temperature and peptide concentration in complex ways which depend on the membrane composition, highlighting the subtlety of the interaction between inclusions and the host bilayer. The amplitude of the variation is relatively low, indicating that the macroscopic constants used to describe the elasticity of the bilayer are unlikely to change with the addition of peptide.
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Affiliation(s)
- Elise Azar
- Laboratoire de Physique des Solides, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405, Orsay Cedex, France
| | - Doru Constantin
- Laboratoire de Physique des Solides, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405, Orsay Cedex, France.
| | - Dror E Warschawski
- UMR 7099, CNRS-Université Paris Diderot, Institut de Biologie Physico-Chimique, Paris, France
- Département de Chimie, Université du Québec à Montréal, Downtown Station, P.O. Box 8888, H3C 3P8, Montreal, Canada
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21
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Lum K, Ingólfsson HI, Koeppe RE, Andersen OS. Exchange of Gramicidin between Lipid Bilayers: Implications for the Mechanism of Channel Formation. Biophys J 2017; 113:1757-1767. [PMID: 29045870 DOI: 10.1016/j.bpj.2017.08.049] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2017] [Revised: 08/25/2017] [Accepted: 08/30/2017] [Indexed: 11/30/2022] Open
Abstract
The canonical mechanism of gramicidin (gA) channel formation is transmembrane dimerization of nonconducting subunits that reside in opposite bilayer leaflets. The channels do not open and close; they appear and disappear due to subunit association and dissociation. Many different types of experiments support this monomer ↔ dimer mechanism. Recently, however, this mechanism was challenged, based on experiments with lipid vesicle-incorporated gA under conditions where vesicle fusion could be controlled. In these experiments, sustained channel activity was observed long after fusion had been terminated, which led to the proposal that gA single-channel current transitions result from closed-open transitions in long-lived bilayer-spanning dimers. This proposal is at odds with 40 years of experiments, but involves the key assumption that gA monomers do not exchange between bilayers. We tested the possibility of peptide exchange between bilayers using three different types of experiments. First, we demonstrated the exchange of gA between 1,2-dierucoyl-sn-glycero-3-phosphocholine (DC22:1PC) or 1,2-dioleoyl-sn-glycero-3-phosphocholine (DC18:1PC) lipid vesicles using a fluorescence assay for gA channel activity. Second, we added gA-free DC22:1PC vesicles to both sides of planar DC18:1PC bilayers preincubated with gA, which reduced channel activity up to 10-fold. Third, we added gA-containing DC22:1PC vesicles to one or both sides of DC18:1PC planar bilayers, which produced much higher channel activity when the gA-containing vesicles were added to both sides of the bilayer, as compared to one side only. All three types of experiments show that gA subunits can exchange between lipid bilayers. The exchange of subunits between bilayers thus is firmly established, which becomes a crucial consideration with respect to the mechanism of channel formation.
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Affiliation(s)
- Kevin Lum
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Helgi I Ingólfsson
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Roger E Koeppe
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas
| | - Olaf S Andersen
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York.
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22
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Abstract
An important limitation of standard classical molecular dynamics simulations is the inability to make or break chemical bonds. This restricts severely our ability to study processes that involve even the simplest of chemical reactions, the transfer of a proton. Existing approaches for allowing proton transfer in the context of classical mechanics are rather cumbersome and have not achieved widespread use and routine status. Here we reconsider the combination of molecular dynamics with periodic stochastic proton hops. To ensure computational efficiency, we propose a non-Boltzmann acceptance criterion that is heuristically adjusted to maintain the correct or desirable thermodynamic equilibria between different protonation states and proton transfer rates. Parameters are proposed for hydronium, Asp, Glu, and His. The algorithm is implemented in the program CHARMM and tested on proton diffusion in bulk water and carbon nanotubes and on proton conductance in the gramicidin A channel. Using hopping parameters determined from proton diffusion in bulk water, the model reproduces the enhanced proton diffusivity in carbon nanotubes and gives a reasonable estimate of the proton conductance in gramicidin A.
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Affiliation(s)
- Themis Lazaridis
- Department of Chemistry, City College of New York/CUNY , 160 Convent Avenue, New York, New York 10031, United States.,Graduate Programs in Chemistry, Biochemistry & Physics, Graduate Center, City University of New York , 365 Fifth Ave, New York, New York 10016, United States
| | - Gerhard Hummer
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics , Max-von-Laue Strasse 3, 60438 Frankfurt am Main, Germany
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23
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Li J, Richards MR, Kitova EN, Klassen JS. Delivering Transmembrane Peptide Complexes to the Gas Phase Using Nanodiscs and Electrospray Ionization. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2017; 28:2054-2065. [PMID: 28681358 DOI: 10.1007/s13361-017-1735-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Revised: 05/25/2017] [Accepted: 06/01/2017] [Indexed: 06/07/2023]
Abstract
The gas-phase conformations of dimers of the channel-forming membrane peptide gramicidin A (GA), produced from isobutanol or aqueous solutions of GA-containing nanodiscs (NDs), are investigated using electrospray ionization-ion mobility separation-mass spectrometry (ESI-IMS-MS) and molecular dynamics (MD) simulations. The IMS arrival times measured for (2GA + 2Na)2+ ions from isobutanol reveal three different conformations, with collision cross-sections (Ω) of 683 Å2 (conformation 1, C1), 708 Å2 (C2), and 737 Å2 (C3). The addition of NH4CH3CO2 produced (2GA + 2Na)2+ and (2GA + H + Na)2+ ions, with Ω similar to those of C1, C2, and C3, as well as (2GA + 2H)2+, (2GA + 2NH4)2+, and (2GA + H + NH4)2+ ions, which adopt a single conformation with a Ω similar to that of C2. These results suggest that the nature of the charging agents, imparted by the ESI process, can influence dimer conformation in the gas phase. Notably, the POPC NDs produced exclusively (2GA + 2NH4)2+ dimer ions; the DMPC NDs produced both (2GA + 2H)2+ and (2GA + 2NH4)2+ dimer ions. While the Ω of (2GA + 2H)2+ is similar to that of C2, the (2GA + 2NH4)2+ ions from NDs adopt a more compact structure, with a Ω of 656 Å2. It is proposed that this compact structure corresponds to the ion conducting single stranded head-to-head helical GA dimer. These findings highlight the potential of NDs, combined with ESI, for transferring transmembrane peptide complexes directly from lipid bilayers to the gas phase. Graphical Abstract ᅟ.
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Affiliation(s)
- Jun Li
- Alberta Glycomics Centre and Department of Chemistry, University of Alberta, Edmonton, T6G 2G2, Alberta, Canada
| | - Michele R Richards
- Alberta Glycomics Centre and Department of Chemistry, University of Alberta, Edmonton, T6G 2G2, Alberta, Canada
| | - Elena N Kitova
- Alberta Glycomics Centre and Department of Chemistry, University of Alberta, Edmonton, T6G 2G2, Alberta, Canada
| | - John S Klassen
- Alberta Glycomics Centre and Department of Chemistry, University of Alberta, Edmonton, T6G 2G2, Alberta, Canada.
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24
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Time-resolved measurements of an ion channel conformational change driven by a membrane phase transition. Proc Natl Acad Sci U S A 2017; 114:10840-10845. [PMID: 28973859 DOI: 10.1073/pnas.1708070114] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Using temperature-jump infrared spectroscopy, we are able to trigger a gel-to-fluid phase transition in lipid vesicles and monitor in real time how a membrane protein responds to structural changes in the membrane. The melting of lipid domains in 1,2-dimyristoyl-sn-glycero-3-phosphocholine vesicles is observed to occur in as fast as 50 ns, with a temperature dependence characteristic of critical slowing. Gramicidin D (gD) added to the membrane responds primarily to the change in thickness of the membrane on a timescale coincident with the membrane melting. Using structure-based spectral modeling, we assign the conformational changes to compression and rotation of a partially dissociated gD dimer. Free energy calculations indicate that the high rate is a result of near-barrierless diffusion on a protein energy landscape that is radically reshaped by membrane thinning. The structural changes associated with the phase transition are similar to the fluctuation modes of fluid phase membranes, highlighting the importance of understanding the dynamic nature of the membrane environment around proteins.
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25
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Beaven AH, Sodt AJ, Pastor RW, Koeppe RE, Andersen OS, Im W. Characterizing Residue-Bilayer Interactions Using Gramicidin A as a Scaffold and Tryptophan Substitutions as Probes. J Chem Theory Comput 2017; 13:5054-5064. [PMID: 28870079 DOI: 10.1021/acs.jctc.7b00400] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Previous experiments have shown that the lifetime of a gramicidin A dimer channel (which forms from two nonconducting monomers) in a lipid bilayer is modulated by mutations of the tryptophan (Trp) residues at the bilayer-water interface. We explore this further using extensive molecular dynamics simulations of various gA dimer and monomer mutants at the Trp positions in phosphatidylcholine bilayers with different tail lengths. gA interactions with the surrounding bilayer are strongly modulated by mutating these Trp residues. There are three principal effects: eliminating residue hydrogen bonding ability (i.e., reducing the channel-monolayer coupling strength) reduces the extent of the bilayer deformation caused by the assembled dimeric channel; a residue's size and geometry affects its orientation, leading to different hydrogen bonding partners; and increasing a residue's hydrophobicity increases the depth of gA monomer insertion relative to the bilayer center, thereby increasing the lipid bending frustration.
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Affiliation(s)
- Andrew H Beaven
- Department of Chemistry, The University of Kansas , Lawrence, Kansas 66045, United States
| | | | | | - Roger E Koeppe
- Department of Chemistry and Biochemistry, University of Arkansas , Fayetteville, Arkansas 72701, United States
| | - Olaf S Andersen
- Department of Physiology and Biophysics, Weill Cornell Medical College , New York, New York 10065, United States
| | - Wonpil Im
- Departments of Biological Sciences and Bioengineering, Lehigh University , Bethlehem, Pennsylvania 18015, United States
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26
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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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27
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Sodt AJ, Beaven AH, Andersen OS, Im W, Pastor RW. Gramicidin A Channel Formation Induces Local Lipid Redistribution II: A 3D Continuum Elastic Model. Biophys J 2017; 112:1198-1213. [PMID: 28355547 DOI: 10.1016/j.bpj.2017.01.035] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Revised: 01/11/2017] [Accepted: 01/30/2017] [Indexed: 12/20/2022] Open
Abstract
To change conformation, a protein must deform the surrounding bilayer. In this work, a three-dimensional continuum elastic model for gramicidin A in a lipid bilayer is shown to describe the sensitivity to thickness, curvature stress, and the mechanical properties of the lipid bilayer. A method is demonstrated to extract the gramicidin-lipid boundary condition from all-atom simulations that can be used in the three-dimensional continuum model. The boundary condition affects the deformation dramatically, potentially much more than typical variations in the material stiffness do as lipid composition is changed. Moreover, it directly controls the sensitivity to curvature stress. The curvature stress and hydrophobic surfaces of the all-atom and continuum models are found to be in excellent agreement. The continuum model is applied to estimate the enrichment of hydrophobically matched lipids near the channel in a mixture, and the results agree with single-channel experiments and extended molecular dynamics simulations from the companion article by Beaven et al. in this issue of Biophysical Journal.
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Affiliation(s)
- Alexander J Sodt
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland.
| | - Andrew H Beaven
- Department of Chemistry, The University of Kansas, Lawrence, Kansas
| | - Olaf S Andersen
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Wonpil Im
- Department of Biological Sciences and Bioengineering Program, Lehigh University, Bethlehem, Pennsylvania
| | - Richard W Pastor
- Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
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28
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Beaven AH, Maer AM, Sodt AJ, Rui H, Pastor RW, Andersen OS, Im W. Gramicidin A Channel Formation Induces Local Lipid Redistribution I: Experiment and Simulation. Biophys J 2017; 112:1185-1197. [PMID: 28355546 DOI: 10.1016/j.bpj.2017.01.028] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2016] [Revised: 01/11/2017] [Accepted: 01/30/2017] [Indexed: 10/19/2022] Open
Abstract
Integral membrane protein function can be modulated by the host bilayer. Because biological membranes are diverse and nonuniform, we explore the consequences of lipid diversity using gramicidin A channels embedded in phosphatidylcholine (PC) bilayers composed of equimolar mixtures of di-oleoyl-PC and di-erucoyl-PC (dC18:1+dC22:1, respectively), di-palmitoleoyl-PC and di-nervonoyl-PC (dC16:1+dC24:1, respectively), and di-eicosenoyl-PC (pure dC20:1), all of which have the same average bilayer chain length. Single-channel lifetime experiments, molecular dynamics simulations, and a simple lipid compression model are used in tandem to gain insight into lipid redistribution around the channel, which partially alleviates the bilayer deformation energy associated with channel formation. The average single-channel lifetimes in the two-component bilayers (95 ± 10 ms for dC18:1+dC22:1 and 195 ± 20 ms for dC16:1+dC24:1) were increased relative to the single-component dC20:1 control bilayer (65 ± 10 ms), implying lipid redistribution. Using a theoretical treatment of thickness-dependent changes in channel lifetimes, the effective local enrichment of lipids around the channel was estimated to be 58 ± 4% dC18:1 and 66 ± 2% dC16:1 in the dC18:1+dC22:1 and dC16:1+dC24:1 bilayers, respectively. 3.5-μs molecular dynamics simulations show 66 ± 2% dC16:1 in the first lipid shell around the channel in the dC16:1+dC24:1 bilayer, but no significant redistribution (50 ± 4% dC18:1) in the dC18:1+dC22:1 bilayer; these simulated values are within the 95% confidence intervals of the experimental averages. The strong preference for the better matching lipid (dC16:1) near the channel in the dC16:1+dC24:1 mixture and lesser redistribution in the dC18:1+dC22:1 mixture can be explained by the energetic cost associated with compressing the lipids to match the channel's hydrophobic length.
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Affiliation(s)
- Andrew H Beaven
- Department of Chemistry, The University of Kansas, Lawrence, Kansas
| | - Andreia M Maer
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Alexander J Sodt
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
| | - Huan Rui
- Department of Biological Sciences and Bioengineering Program, Lehigh University, Bethlehem, Pennsylvania
| | - Richard W Pastor
- Laboratory of Computational Biology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - Olaf S Andersen
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York.
| | - Wonpil Im
- Department of Biological Sciences and Bioengineering Program, Lehigh University, Bethlehem, Pennsylvania.
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Ageitos J, Sánchez-Pérez A, Calo-Mata P, Villa T. Antimicrobial peptides (AMPs): Ancient compounds that represent novel weapons in the fight against bacteria. Biochem Pharmacol 2017; 133:117-138. [DOI: 10.1016/j.bcp.2016.09.018] [Citation(s) in RCA: 328] [Impact Index Per Article: 46.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Accepted: 09/19/2016] [Indexed: 01/01/2023]
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Stevenson P, Tokmakoff A. Ultrafast Fluctuations of High Amplitude Electric Fields in Lipid Membranes. J Am Chem Soc 2017; 139:4743-4752. [DOI: 10.1021/jacs.6b12412] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Paul Stevenson
- Department
of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts
Ave., Cambridge, Massachusetts 02139, United States
- Department
of Chemistry, James Frank Institute, and The Institute
for Biophysical Dynamics, The University of Chicago, 929 E 57th Street, Chicago, Illinois 60637, United States
| | - Andrei Tokmakoff
- Department
of Chemistry, James Frank Institute, and The Institute
for Biophysical Dynamics, The University of Chicago, 929 E 57th Street, Chicago, Illinois 60637, United States
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31
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Venable RM, Ingólfsson HI, Lerner MG, Perrin BS, Camley BA, Marrink SJ, Brown FLH, Pastor RW. Lipid and Peptide Diffusion in Bilayers: The Saffman-Delbrück Model and Periodic Boundary Conditions. J Phys Chem B 2017; 121:3443-3457. [PMID: 27966982 DOI: 10.1021/acs.jpcb.6b09111] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The periodic Saffman-Delbrück (PSD) model, an extension of the Saffman-Delbrück model developed to describe the effects of periodic boundary conditions on the diffusion constants of lipids and proteins obtained from simulation, is tested using the coarse-grained Martini and all-atom CHARMM36 (C36) force fields. Simulations of pure Martini dipalmitoylphosphatidylcholine (DPPC) bilayers and those with one embedded gramicidin A (gA) dimer or one gA monomer with sizes ranging from 512 to 2048 lipids support the PSD model. Underestimates of D∞ (the value of the diffusion constant for an infinite system) from the 512-lipid system are 35% for DPPC, 45% for the gA monomer, and 70% for the gA dimer. Simulations of all-atom DPPC and dioleoylphosphatidylcholine (DOPC) bilayers yield diffusion constants not far from experiment. However, the PSD model predicts that diffusion constants at the sizes of the simulation should underestimate experiment by approximately a factor of 3 for DPPC and 2 for DOPC. This likely implies a deficiency in the C36 force field. A Bayesian method for extrapolating diffusion constants of lipids and proteins in membranes obtained from simulation to infinite system size is provided.
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Affiliation(s)
- Richard M Venable
- Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health , Bethesda, Maryland 20892, United States
| | - Helgi I Ingólfsson
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Michael G Lerner
- Department of Chemistry & Biochemistry and Department of Physics and Astronomy, Earlham College , Richmond, Indiana 47374, United States
| | - B Scott Perrin
- Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health , Bethesda, Maryland 20892, United States
| | - Brian A Camley
- Department of Physics, University of California , San Diego, California 92093, United States
| | - Siewert J Marrink
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Frank L H Brown
- Department of Chemistry & Biochemistry and Department of Physics, University of California , Santa Barbara, California 93106, United States
| | - Richard W Pastor
- Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health , Bethesda, Maryland 20892, United States
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32
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The importance of N-methylations for the stability of the $$\beta ^{6.3}$$ β 6.3 -helical conformation of polytheonamide B. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2016; 46:363-374. [DOI: 10.1007/s00249-016-1179-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Revised: 08/15/2016] [Accepted: 08/22/2016] [Indexed: 10/20/2022]
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33
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Manin N, da Silva MC, Zdravkovic I, Eliseeva O, Dyshin A, Yaşar O, Salahub DR, Kolker AM, Kiselev MG, Noskov SY. LiCl solvation in N-methyl-acetamide (NMA) as a model for understanding Li(+) binding to an amide plane. Phys Chem Chem Phys 2016; 18:4191-200. [PMID: 26784370 DOI: 10.1039/c5cp04847h] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The thermodynamics of ion solvation in non-aqueous solvents remains of great significance for understanding cellular transport and ion homeostasis for the design of novel ion-selective materials and applications in molecular pharmacology. Molecular simulations play pivotal roles in connecting experimental measurements to the microscopic structures of liquids. One of the most useful and versatile mimetic systems for understanding biological ion transport is N-methyl-acetamide (NMA). A plethora of theoretical studies for ion solvation in NMA have appeared recently, but further progress is limited by two factors. One is an apparent lack of experimental data on solubility and thermodynamics of solvation for a broad panel of 1 : 1 salts over an appropriate temperature and concentration range. The second concern is more substantial and has to do with the limitations hardwired in the additive (fixed charge) approximations used for most of the existing force-fields. In this submission, we report on the experimental evaluation of LiCl solvation in NMA over a broad range of concentrations and temperatures and compare the results with those of MD simulations with several additive and one polarizable force-field (Drude). By comparing our simulations and experimental results to density functional theory computations, we discuss the limiting factors in existing potential functions. To evaluate the possible implications of explicit and implicit polarizability treatments on ion permeation across biological channels, we performed potential of mean force (PMF) computations for Li(+) transport through a model narrow ion channel with additive and polarizable force-fields.
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Affiliation(s)
- Nikolai Manin
- G.A. Krestov Institute for Solution Chemistry, Russian Academy of Sciences, Akademicheskaya str, 1, Ivanovo, 153045, Russia.
| | - Mauricio C da Silva
- Centre for Molecular Simulation, BI-447, University of Calgary, 2500 University Drive NW, Calgary, AB T3A 2T3, Canada. and Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada
| | - Igor Zdravkovic
- Centre for Molecular Simulation, BI-447, University of Calgary, 2500 University Drive NW, Calgary, AB T3A 2T3, Canada. and Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, AB T3A 2T3, Canada
| | - Olga Eliseeva
- G.A. Krestov Institute for Solution Chemistry, Russian Academy of Sciences, Akademicheskaya str, 1, Ivanovo, 153045, Russia.
| | - Alexey Dyshin
- G.A. Krestov Institute for Solution Chemistry, Russian Academy of Sciences, Akademicheskaya str, 1, Ivanovo, 153045, Russia.
| | - Orhan Yaşar
- Centre for Molecular Simulation, BI-447, University of Calgary, 2500 University Drive NW, Calgary, AB T3A 2T3, Canada. and Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, AB T3A 2T3, Canada
| | - Dennis R Salahub
- Centre for Molecular Simulation, BI-447, University of Calgary, 2500 University Drive NW, Calgary, AB T3A 2T3, Canada. and Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada
| | - Arkadiy M Kolker
- G.A. Krestov Institute for Solution Chemistry, Russian Academy of Sciences, Akademicheskaya str, 1, Ivanovo, 153045, Russia.
| | - Michael G Kiselev
- G.A. Krestov Institute for Solution Chemistry, Russian Academy of Sciences, Akademicheskaya str, 1, Ivanovo, 153045, Russia.
| | - Sergei Yu Noskov
- Centre for Molecular Simulation, BI-447, University of Calgary, 2500 University Drive NW, Calgary, AB T3A 2T3, Canada. and Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, AB T3A 2T3, Canada
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Setiadi J, Kuyucak S. Computational Investigation of the Effect of Lipid Membranes on Ion Permeation in Gramicidin A. MEMBRANES 2016; 6:membranes6010020. [PMID: 26999229 PMCID: PMC4812426 DOI: 10.3390/membranes6010020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/10/2016] [Revised: 03/08/2016] [Accepted: 03/08/2016] [Indexed: 06/05/2023]
Abstract
Membrane proteins are embedded in a lipid bilayer and interact with the lipid molecules in subtle ways. This can be studied experimentally by examining the effect of different lipid bilayers on the function of membrane proteins. Understanding the causes of the functional effects of lipids is difficult to dissect experimentally but more amenable to a computational approach. Here we perform molecular dynamics simulations and free energy calculations to study the effect of two lipid types (POPC and NODS) on the conductance of the gramicidin A (gA) channel. A larger energy barrier is found for the K⁺ potential of mean force in gA embedded in POPC compared to that in NODS, which is consistent with the enhanced experimental conductance of cations in gA embedded in NODS. Further analysis of the contributions to the potential energy of K⁺ reveals that gA and water molecules in gA make similar contributions in both bilayers but there are significant differences between the two bilayers when the lipid molecules and interfacial waters are considered. It is shown that the stronger dipole moments of the POPC head groups create a thicker layer of interfacial waters with better orientation, which ultimately is responsible for the larger energy barrier in the K⁺ PMF in POPC.
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Affiliation(s)
- Jeffry Setiadi
- School of Physics, University of Sydney, Sydney NSW 2006, Australia.
| | - Serdar Kuyucak
- School of Physics, University of Sydney, Sydney NSW 2006, Australia.
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35
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Zerfas BL, Joo Y, Gao J. Gramicidin A Mutants with Antibiotic Activity against Both Gram-Positive and Gram-Negative Bacteria. ChemMedChem 2016; 11:629-36. [PMID: 26918268 DOI: 10.1002/cmdc.201500602] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2015] [Indexed: 01/01/2023]
Abstract
Antimicrobial peptides (AMPs) have shown potential as alternatives to traditional antibiotics for fighting infections caused by antibiotic-resistant bacteria. One promising example of this is gramicidin A (gA). In its wild-type sequence, gA is active by permeating the plasma membrane of Gram-positive bacteria. However, gA is toxic to human red blood cells at similar concentrations to those required for it to exert its antimicrobial effects. Installing cationic side chains into gA has been shown to lower its hemolytic activity while maintaining the antimicrobial potency. In this study, we present the synthesis and the antibiotic activity of a new series of gA mutants that display cationic side chains. Specifically, by synthesizing alkylated lysine derivatives through reductive amination, we were able to create a broad selection of structures with varied activities towards Staphylococcus aureus and methicillin-resistant S. aureus (MRSA). Importantly, some of the new mutants were observed to have an unprecedented activity towards important Gram-negative pathogens, including Escherichia coli, Klebsiella pneumoniae and Psuedomonas aeruginosa.
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Affiliation(s)
- Breanna L Zerfas
- Department of Chemistry, Merkert Chemisty Center, Boston College, 2609 Beacon St., Chestnut Hill, MA, 02461, USA
| | - Yechaan Joo
- Department of Chemistry, Merkert Chemisty Center, Boston College, 2609 Beacon St., Chestnut Hill, MA, 02461, USA
| | - Jianmin Gao
- Department of Chemistry, Merkert Chemisty Center, Boston College, 2609 Beacon St., Chestnut Hill, MA, 02461, USA.
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36
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Lee H, Kim SM, Jeon TJ. Effects of imidazolium-based ionic liquids on the stability and dynamics of gramicidin A and lipid bilayers at different salt concentrations. J Mol Graph Model 2015; 61:53-60. [DOI: 10.1016/j.jmgm.2015.06.016] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2015] [Revised: 05/19/2015] [Accepted: 06/29/2015] [Indexed: 10/23/2022]
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37
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Stevenson P, Tokmakoff A. Distinguishing gramicidin D conformers through two-dimensional infrared spectroscopy of vibrational excitons. J Chem Phys 2015; 142:212424. [PMID: 26049444 PMCID: PMC4401804 DOI: 10.1063/1.4917321] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2015] [Accepted: 03/31/2015] [Indexed: 11/14/2022] Open
Abstract
Gramicidin D is a short peptide which dimerizes to form helical pores, adopting one of two conformations in the process. These conformations differ primarily in number of residues per turn and the hydrogen-bond registry between rungs of the helix. Using amide I 2D infrared (IR) and FTIR, we have demonstrated that it is possible to distinguish between the different conformers of gramicidin D in solution. We show that the spectra observed for this helical peptide bear no resemblance to the spectra of α- or 310-helices and that while the FTIR spectra appear similar to spectra of β-sheets, 2D IR reveals that the observed resonances arise from vibrational modes unlike those observed in β-sheets. We also present an idealized model which reproduces the experimental data with high fidelity. This model is able to explain the polarization-dependence of the experimental 2D IR data. Using this model, we show the coupling between the rungs of the helix dominates the spectra, and as a consequence of this, the number of residues per turn can greatly influence the amide I spectra of gramicidin D.
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Affiliation(s)
- Paul Stevenson
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139, USA
| | - Andrei Tokmakoff
- Department of Chemistry, James Frank Institute, and The Institute for Biophysical Dynamics, The University of Chicago, 929 E 57th Street, Chicago, Illinois 60637, USA
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38
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Patrick JW, Gamez RC, Russell DH. Elucidation of Conformer Preferences for a Hydrophobic Antimicrobial Peptide by Vesicle Capture-Freeze-Drying: A Preparatory Method Coupled to Ion Mobility-Mass Spectrometry. Anal Chem 2014; 87:578-83. [DOI: 10.1021/ac503163g] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- John W. Patrick
- The Laboratory for Biological Mass Spectrometry, Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
| | - Roberto C. Gamez
- The Laboratory for Biological Mass Spectrometry, Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
| | - David H. Russell
- The Laboratory for Biological Mass Spectrometry, Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
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Nelson JW, Zhou Z, Breaker RR. Gramicidin D enhances the antibacterial activity of fluoride. Bioorg Med Chem Lett 2014; 24:2969-2971. [PMID: 24857543 PMCID: PMC4048840 DOI: 10.1016/j.bmcl.2014.03.061] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Revised: 03/18/2014] [Accepted: 03/19/2014] [Indexed: 11/20/2022]
Abstract
Fluoride is a toxic anion found in many natural environments. One of the major bacterial defenses against fluoride is the cell envelope, which limits passage of the membrane-impermeant fluoride anion. Accordingly, compounds that enhance the permeability of bacterial membranes to fluoride should also enhance fluoride toxicity. In this study, we demonstrate that the pore-forming antibiotic gramicidin D increases fluoride uptake in Bacillus subtilis and that the antibacterial activity of this compound is potentiated by fluoride. Polymyxin B, another membrane-targeting antibiotic with a different mechanism of action, shows no such improvement. These results, along with previous findings, indicate that certain compounds that destabilize bacterial cell envelopes can enhance the toxicity of fluoride.
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Affiliation(s)
- James W. Nelson
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, CT 06520, USA
| | - Zhiyuan Zhou
- Department of Molecular, Cellular and Developmental Biology, Yale University, P.O. Box 208103, New Haven, CT 06520, USA
| | - Ronald R. Breaker
- Department of Molecular, Cellular and Developmental Biology, Yale University, P.O. Box 208103, New Haven, CT 06520, USA
- Department of Molecular Biophysics and Biochemistry, Yale University, P.O. Box 208103, New Haven, CT 06520, USA
- Howard Hughes Medical Institute
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40
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Cross TA, Ekanayake V, Paulino J, Wright A. Solid state NMR: The essential technology for helical membrane protein structural characterization. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 239:100-9. [PMID: 24412099 PMCID: PMC3957465 DOI: 10.1016/j.jmr.2013.12.006] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Revised: 12/03/2013] [Accepted: 12/09/2013] [Indexed: 05/21/2023]
Abstract
NMR spectroscopy of helical membrane proteins has been very challenging on multiple fronts. The expression and purification of these proteins while maintaining functionality has consumed countless graduate student hours. Sample preparations have depended on whether solution or solid-state NMR spectroscopy was to be performed - neither have been easy. In recent years it has become increasingly apparent that membrane mimic environments influence the structural result. Indeed, in these recent years we have rediscovered that Nobel laureate, Christian Anfinsen, did not say that protein structure was exclusively dictated by the amino acid sequence, but rather by the sequence in a given environment (Anfinsen, 1973) [106]. The environment matters, molecular interactions with the membrane environment are significant and many examples of distorted, non-native membrane protein structures have recently been documented in the literature. However, solid-state NMR structures of helical membrane proteins in proteoliposomes and bilayers are proving to be native structures that permit a high resolution characterization of their functional states. Indeed, solid-state NMR is uniquely able to characterize helical membrane protein structures in lipid environments without detergents. Recent progress in expression, purification, reconstitution, sample preparation and in the solid-state NMR spectroscopy of both oriented samples and magic angle spinning samples has demonstrated that helical membrane protein structures can be achieved in a timely fashion. Indeed, this is a spectacular opportunity for the NMR community to have a major impact on biomedical research through the solid-state NMR spectroscopy of these proteins.
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Affiliation(s)
- Timothy A Cross
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA; Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA; Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA.
| | - Vindana Ekanayake
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA; Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA
| | - Joana Paulino
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA; Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
| | - Anna Wright
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA; Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
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41
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Alejo JL, Blanchard SC, Andersen OS. Small-molecule photostabilizing agents are modifiers of lipid bilayer properties. Biophys J 2014; 104:2410-8. [PMID: 23746513 DOI: 10.1016/j.bpj.2013.04.039] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2012] [Revised: 04/09/2013] [Accepted: 04/11/2013] [Indexed: 10/26/2022] Open
Abstract
Small-molecule photostabilizing or protective agents (PAs) provide essential support for the stability demands on fluorescent dyes in single-molecule spectroscopy and fluorescence microscopy. These agents are employed also in studies of cell membranes and model systems mimicking lipid bilayer environments, but there is little information about their possible effects on membrane structure and physical properties. Given the impact of amphipathic small molecules on bilayer properties such as elasticity and intrinsic curvature, we investigated the effects of six commonly used PAs--cyclooctatetraene (COT), para-nitrobenzyl alcohol (NBA), Trolox (TX), 1,4-diazabicyclo[2.2.2]octane (DABCO), para-nitrobenzoic acid (pNBA), and n-propyl gallate (nPG)--on bilayer properties using a gramicidin A (gA)-based fluorescence quench assay to probe for PA-induced changes in the gramicidin monomer↔dimer equilibrium. The experiments were done using fluorophore-loaded large unilamellar vesicles that had been doped with gA, and changes in the gA monomer↔dimer equilibrium were assayed using a gA channel-permeable fluorescence quencher (Tl⁺). Changes in bilayer properties caused by, e.g., PA adsorption at the bilayer/solution interface that alter the equilibrium constant for gA channel formation, and thus the number of conducting gA channels in the large unilamellar vesicle membrane, will be detectable as changes in the rate of Tl⁺ influx-the fluorescence quench rate. Over the experimentally relevant millimolar concentration range, TX, NBA, and pNBA, caused comparable increases in gA channel activity. COT, also in the millimolar range, caused a slight decrease in gA channel activity. nPG increased channel activity at submillimolar concentrations. DABCO did not alter gA activity. Five of the six tested PAs thus alter lipid bilayer properties at experimentally relevant concentrations, which becomes important for the design and analysis of fluorescence studies in cells and model membrane systems. We therefore tested combinations of COT, NBA, and TX; the combinations altered the fluorescence quench rate less than would be predicted assuming their effects on bilayer properties were additive. The combination of equimolar concentrations of COT and NBA caused minimal changes in the fluorescence quench rate.
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Affiliation(s)
- Jose L Alejo
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY, USA
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42
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Ion channel stability of Gramicidin A in lipid bilayers: Effect of hydrophobic mismatch. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:328-38. [DOI: 10.1016/j.bbamem.2013.10.005] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Revised: 09/20/2013] [Accepted: 10/03/2013] [Indexed: 11/18/2022]
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43
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Todorović M, Bowler DR, Gillan MJ, Miyazaki T. Density-functional theory study of gramicidin A ion channel geometry and electronic properties. J R Soc Interface 2013; 10:20130547. [PMID: 24068174 PMCID: PMC3808544 DOI: 10.1098/rsif.2013.0547] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2013] [Accepted: 09/03/2013] [Indexed: 01/29/2023] Open
Abstract
Understanding the mechanisms underlying ion channel function from the atomic-scale requires accurate ab initio modelling as well as careful experiments. Here, we present a density functional theory (DFT) study of the ion channel gramicidin A (gA), whose inner pore conducts only monovalent cations and whose conductance has been shown to depend on the side chains of the amino acids in the channel. We investigate the ground state geometry and electronic properties of the channel in vacuum, focusing on their dependence on the side chains of the amino acids. We find that the side chains affect the ground state geometry, while the electrostatic potential of the pore is independent of the side chains. This study is also in preparation for a full, linear scaling DFT study of gA in a lipid bilayer with surrounding water. We demonstrate that linear scaling DFT methods can accurately model the system with reasonable computational cost. Linear scaling DFT allows ab initio calculations with 10,000-100,000 atoms and beyond, and will be an important new tool for biomolecular simulations.
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Affiliation(s)
- Milica Todorović
- National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
| | - David R. Bowler
- International Centre for Materials Nanoarchitectonics (MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
- London Centre for Nanotechnology, UCL, 17–19 Gordon Street, London WC1H 0AH, UK
- Thomas Young Centre, Department of Physics and Astronomy, UCL, Gower Street, London WC1E 6BT, UK
| | - Michael J. Gillan
- London Centre for Nanotechnology, UCL, 17–19 Gordon Street, London WC1H 0AH, UK
- Thomas Young Centre, Department of Physics and Astronomy, UCL, Gower Street, London WC1E 6BT, UK
| | - Tsuyoshi Miyazaki
- National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
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Demizu Y, Yamashita H, Yamazaki N, Sato Y, Doi M, Tanaka M, Kurihara M. Oligopeptides with Equal Amounts of l- and d-Amino Acids May Prefer a Helix Screw Sense. J Org Chem 2013; 78:12106-13. [DOI: 10.1021/jo402133e] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Yosuke Demizu
- Division
of Organic Chemistry, National Institute of Health Sciences, Tokyo 158-8501, Japan
| | - Hiroko Yamashita
- Division
of Organic Chemistry, National Institute of Health Sciences, Tokyo 158-8501, Japan
- Graduate
School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama 226-8501, Japan
| | - Norikazu Yamazaki
- Division
of Organic Chemistry, National Institute of Health Sciences, Tokyo 158-8501, Japan
| | - Yukiko Sato
- Division
of Organic Chemistry, National Institute of Health Sciences, Tokyo 158-8501, Japan
| | - Mitsunobu Doi
- Osaka
University of Pharmaceutical Sciences, Osaka 569-1094, Japan
| | - Masakazu Tanaka
- Graduate
School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8521, Japan
| | - Masaaki Kurihara
- Division
of Organic Chemistry, National Institute of Health Sciences, Tokyo 158-8501, Japan
- Graduate
School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama 226-8501, Japan
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Jensen MØ, Jogini V, Eastwood MP, Shaw DE. Atomic-level simulation of current-voltage relationships in single-file ion channels. ACTA ACUST UNITED AC 2013; 141:619-32. [PMID: 23589581 PMCID: PMC3639580 DOI: 10.1085/jgp.201210820] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The difficulty in characterizing ion conduction through membrane channels at the level of individual permeation events has made it challenging to elucidate the mechanistic principles underpinning this fundamental physiological process. Using long, all-atom simulations enabled by special-purpose hardware, we studied K+ permeation across the KV1.2/2.1 voltage-gated potassium channel. At experimentally accessible voltages, which include the physiological range, the simulated permeation rate was substantially lower than the experimentally observed rate. The current–voltage relationship was also nonlinear but became linear at much higher voltages. We observed permeation consistent with a “knock-on” mechanism at all voltages. At high voltages, the permeation rate was in accordance with our previously reported KV1.2 pore-only simulations, after the simulated voltages from the previous study were recalculated using the correct method, new insight into which is provided here. Including the voltage-sensing domains in the simulated channel brought the linear current–voltage regime closer to the experimentally accessible voltages. The simulated permeation rate, however, still underestimated the experimental rate, because formation of the knock-on intermediate occurred too infrequently. Reducing the interaction strength between the ion and the selectivity filter did not increase conductance. In complementary simulations of gramicidin A, similar changes in interaction strength did increase the observed permeation rate. Permeation nevertheless remained substantially below the experimental value, largely because of infrequent ion recruitment into the pore lumen. Despite the need to apply large voltages to simulate the permeation process, the apparent voltage insensitivity of the permeation mechanism suggests that the direct simulation of permeation at the single-ion level can provide fundamental physiological insight into ion channel function. Notably, our simulations suggest that the knock-on permeation mechanisms in KV1.2 and KcsA may be different.
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Szolnoki É, Hetényi A, Mándity IM, Fülöp F, Martinek TA. Foldameric β-H18/20PMixed Helix Stabilized by Head-to-Tail Contacts: A Way to Higher-Order Structures. European J Org Chem 2013. [DOI: 10.1002/ejoc.201201633] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Panahi A, Feig M. Dynamic Heterogeneous Dielectric Generalized Born (DHDGB): An implicit membrane model with a dynamically varying bilayer thickness. J Chem Theory Comput 2013; 9:1709-1719. [PMID: 23585740 PMCID: PMC3622271 DOI: 10.1021/ct300975k] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
An extension to the heterogeneous dielectric generalized Born (HDGB) implicit membrane formalism is presented to allow dynamic membrane deformations in response to membrane-inserted biomolecules during molecular dynamic simulations. The flexible membrane is implemented through additional degrees of freedom that represent the membrane deformation at the contact points of a membrane-inserted solute with the membrane. The extra degrees of freedom determine the dielectric and non-polar solvation free energy profiles that are used to obtain the solvation free energy in the presence of the membrane and are used to calculate membrane deformation free energies according to an elastic membrane model. With the dynamic HDGB (DHDGB) model the membrane is able to deform in response to the insertion of charged molecules thereby avoiding the overestimation of insertion free energies with static membrane models. The DHDGB model also allows the membrane to respond to the insertion of membrane-spanning solutes with hydrophobic mismatch. The model is tested with the membrane insertion of amino acid side chain analogs, arginine-containing helices, the WALP23 peptide, and the gramicidin A channel.
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Affiliation(s)
- Afra Panahi
- Department of Chemistry, Michigan State University, East Lansing, MI, 48824
| | - Michael Feig
- Department of Chemistry, Michigan State University, East Lansing, MI, 48824
- Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, MI, 48824
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48
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Lee KI, Pastor RW, Andersen OS, Im W. Assessing smectic liquid-crystal continuum models for elastic bilayer deformations. Chem Phys Lipids 2013; 169:19-26. [PMID: 23348553 DOI: 10.1016/j.chemphyslip.2013.01.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2012] [Revised: 01/08/2013] [Accepted: 01/10/2013] [Indexed: 10/27/2022]
Abstract
For four decades, since W. Helfrich's pioneering study of smectic A liquid crystals in 1973, continuum elastic models (CEMs) have been employed as tools to understand the energetics of protein-induced lipid bilayer deformations. Among the assumptions underlying this use is that all relevant protein-lipid interactions can be included in the continuum representation of the protein-bilayer interactions through the physical parameters determined for protein-free bilayers and the choice of boundary conditions at the protein/bilayer interface. To better understand this assumption, we review the general structure of CEMs, examine how different choices of boundary conditions and physical moduli profiles alter the predicted bilayer thickness profiles around gramicidin A (gA) and mitochondrial voltage-dependent anion channels (VDAC), respectively, and compare these profiles with those obtained from all-atom molecular dynamics simulations. We find that the profiles differ qualitatively in the first lipid shell around the channels, indicating that the CEMs do not capture accurately the consequences of the protein-induced local changes in lipid bilayer dynamics. Therefore, one needs to be careful when interpreting the results of CEM-based analyses of lipid bilayer-membrane protein interactions.
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Affiliation(s)
- Kyu Ii Lee
- Department of Molecular Biosciences and Center for Bioinformatics, The University of Kansas, Lawrence, KS 66047, USA
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Yoo J, Cui Q. Three-dimensional stress field around a membrane protein: atomistic and coarse-grained simulation analysis of gramicidin A. Biophys J 2013; 104:117-27. [PMID: 23332064 PMCID: PMC3540266 DOI: 10.1016/j.bpj.2012.11.3812] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2012] [Revised: 10/29/2012] [Accepted: 11/21/2012] [Indexed: 01/25/2023] Open
Abstract
Using both atomistic and coarse-grained (CG) models, we compute the three-dimensional stress field around a gramicidin A (gA) dimer in lipid bilayers that feature different degrees of negative hydrophobic mismatch. The general trends in the computed stress field are similar at the atomistic and CG levels, supporting the use of the CG model for analyzing the mechanical features of protein/lipid/water interfaces. The calculations reveal that the stress field near the protein-lipid interface exhibits a layered structure with both significant repulsive and attractive regions, with the magnitude of the stress reaching 1000 bar in certain regions. Analysis of density profiles and stress field distributions helps highlight the Trp residues at the protein/membrane/water interface as mechanical anchors, suggesting that similar analysis is useful for identifying tension sensors in other membrane proteins, especially membrane proteins involved in mechanosensation. This work fosters a connection between microscopic and continuum mechanics models for proteins in complex environments and makes it possible to test the validity of assumptions commonly made in continuum mechanics models for membrane mediated processes. For example, using the calculated stress field, we estimate the free energy of membrane deformation induced by the hydrophobic mismatch, and the results for regions beyond the annular lipids are in general consistent with relevant experimental data and previous theoretical estimates using elasticity theory. On the other hand, the assumptions of homogeneous material properties for the membrane and a bilayer thickness at the protein/lipid interface being independent of lipid type (e.g., tail length) appear to be oversimplified, highlighting the importance of annular lipids of membrane proteins. Finally, the stress field analysis makes it clear that the effect of even rather severe hydrophobic mismatch propagates to only about two to three lipid layers, thus putting a limit on the range of cooperativity between membrane proteins in crowded cellular membranes.
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Affiliation(s)
- Jejoong Yoo
- Graduate Program in Biophysics, University of Wisconsin, Madison, Wisconsin
| | - Qiang Cui
- Graduate Program in Biophysics, University of Wisconsin, Madison, Wisconsin
- Department of Chemistry and Theoretical Chemistry Institute, University of Wisconsin, Madison, Wisconsin
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50
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Bruno MJ, Rusinova R, Gleason NJ, Koeppe RE, Andersen OS. Interactions of drugs and amphiphiles with membranes: modulation of lipid bilayer elastic properties by changes in acyl chain unsaturation and protonation. Faraday Discuss 2013; 161:461-80; discussion 563-89. [PMID: 23805753 PMCID: PMC3703894 DOI: 10.1039/c2fd20092a] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/05/2023]
Abstract
Poly-unsaturated fatty acids (PUFAs) alter the function of many membrane proteins, whereas monounsatured fatty acids generally are inert. We previously showed that docosahexaenoic acid (DHA) at pH 7 decreases the bilayer stiffness, consistent with an amphiphile-induced increase in elasticity, but not with a negative change in curvature; oleic acid (OA) was inert (Bruno, Koeppe and Andersen, Proc. Natl. Acad. Sci., 2007, 104, 9638-9643). To further explore how PUFAs and other amphiphiles may alter lipid bilayer properties, and thus membrane protein function, we examined how changes in acyl chain unsaturation and head group charge and size alter bilayer properties, as sensed by bilayer-spanning gramicidin A (gA) channels of different lengths. Compared to DHA, the neutral DHA-methyl ester has reduced effects on bilayer properties and 1-palmitoyl-2-docosahexaenoyl-phosphatidylcholine (PDPC) forms bilayers that are softer than dioleoylphosphatidylcholine (DOPC). The changes in channel function are larger for the short gA channels, indicating that changes in elasticity dominate over changes in curvature. We altered the fatty acid protonation by titration: docosahexaenoic acid (DHA) is more potent at pH 9 (relative to pH 7) and is inert at pH 4; OA, which was inert at pH 7, becomes a potent modifier of bilayer properties at pH 9. At both pH 7 and 9, DHA and OA produced larger changes in the lifetimes of the short gA channels, demonstrating that they increase lipid bilayer elasticity when deprotonated--though OA promotes the formation of inverted hexagonal phases at pH 7. The positively charged oleylamine (OAm), which has a small head-group and therefore should be a negative curvature promoter, inhibited gA channel function with similar reductions in the lifetimes of the short and long gA channels, indicating a curvature-dominated effect. Monitoring the single-channel conductance, we find that the negatively charged fatty acids increase the conductance by increasing the local negative charge around the channel, whereas the positively charged OAm has no effect. These results suggest that deprotonated fatty acids increase bilayer elasticity by reversibly adsorbing at the bilayer/solution interface.
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Affiliation(s)
- Michael J. Bruno
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York 10065, USA
- Department of Chemistry, Guilford College, Greensboro, NC 27410, USA
| | - Radda Rusinova
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York 10065, USA
| | - Nicholas J. Gleason
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - Roger E. Koeppe
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - Olaf S. Andersen
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York 10065, USA
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