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Billah MM, Ahmed M, Islam MZ, Yamazaki M. Processes and mechanisms underlying burst of giant unilamellar vesicles induced by antimicrobial peptides and compounds. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2024; 1866:184330. [PMID: 38679311 DOI: 10.1016/j.bbamem.2024.184330] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Revised: 04/05/2024] [Accepted: 04/23/2024] [Indexed: 05/01/2024]
Abstract
To clarify the damage of lipid bilayer region in bacterial cell membrane caused by antimicrobial peptides (AMPs) and antimicrobial compounds (AMCs), their interactions with giant unilamellar vesicles (GUVs) of various lipid compositions have been examined. The findings revealed two main causes for the leakage: nanopore formation in the membrane and burst of GUVs. Although GUV burst has been explained previously based on the carpet model, the supporting evidence is limited. In this review, to better clarify the mechanism of GUV burst by AMPs, AMCs, and other membrane-active peptides, we described current knowledge of the conditions, characteristics, and detailed processes of GUV burst and the changes in the shape of the GUVs during burst. We identified several physical factors that affect GUV burst, such as membrane tension, electrostatic interaction, structural changes of GUV membrane such as membrane folding, and oil in the membrane. We also clarified one of the physical mechanisms underlying the instability of lipid bilayers that are associated with leakage in the carpet model. Based on these results, we propose a mechanism underlying some types of GUV burst induced by these substances: the growth of a nanopore to a micropore, resulting in GUV burst.
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Affiliation(s)
- Md Masum Billah
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka 422-8529, Japan; Department of Physics, Jashore University and Science and Technology, Jashore 7408, Bangladesh
| | - Marzuk Ahmed
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka 422-8529, Japan
| | - Md Zahidul Islam
- Nanomaterials Research Division, Research Institute of Electronics, Shizuoka University, Shizuoka 422-8529, Japan
| | - Masahito Yamazaki
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka 422-8529, Japan; Nanomaterials Research Division, Research Institute of Electronics, Shizuoka University, Shizuoka 422-8529, Japan; Department of Physics, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan.
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2
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Jeddi I, Saiz L. Computational design of single-stranded DNA hairpin aptamers immobilized on a biosensor substrate. Sci Rep 2021; 11:10984. [PMID: 34040012 PMCID: PMC8155018 DOI: 10.1038/s41598-021-88796-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2020] [Accepted: 04/14/2021] [Indexed: 11/09/2022] Open
Abstract
Aptamer interactions with a surface of attachment are central to the design and performance of aptamer-based biosensors. We have developed a computational modeling approach to study different system designs-including different aptamer-attachment ends, aptamer surface densities, aptamer orientations, and solvent solutions-and applied it to an anti MUC1 aptamer tethered to a silica biosensor substrate. Amongst all the system designs explored, we found that attaching the anti MUC1 aptamer through the 5' terminal end, in a high surface density configuration, and solvated in a 0.8 M NaCl solution provided the best exposure of the aptamer MUC1 binding regions and resulted in the least amount of aptamer backbone fluctuations. Many of the other designs led to non-functional systems, with the aptamer collapsing onto the surface. The computational approach we have developed and the resulting analysis techniques can be employed for the rational design of aptamer-based biosensors and provide a valuable tool for improving biosensor performance and repeatability.
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Affiliation(s)
- Iman Jeddi
- Modeling of Biological Networks and Systems Therapeutics Laboratory, Department of Biomedical Engineering, University of California, 451 East Health Sciences Drive, Davis, CA, 95616, USA
| | - Leonor Saiz
- Modeling of Biological Networks and Systems Therapeutics Laboratory, Department of Biomedical Engineering, University of California, 451 East Health Sciences Drive, Davis, CA, 95616, USA.
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3
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Kucukkal TG, Alsaiari F, Stuart SJ. Modeling ion permeation in wild-type and mutant human α7 nachr ion channels. JOURNAL OF THEORETICAL & COMPUTATIONAL CHEMISTRY 2018. [DOI: 10.1142/s0219633618500451] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Molecular dynamics simulations of wild type and two mutant (T248F and L251T) human [Formula: see text]7 nicotinic acetylcholine receptors (nAChR) have been performed. The channel transmembrane domains were modeled from the closed channel structure from torpedo ray (PDB ID 2BG9) and embedded in DPPC lipid bilayers, surrounded by physiological saline solution. An external electric field was used to obtain stable open channel structures. The adaptive biasing force (ABF) method was used to obtain potential of mean force (PMF) profiles for Na[Formula: see text] ion translocation through the wild type and mutant receptors. Based on the geometry and PMF profiles, the channel gate was found to be at one of the two hydrophobic conserved regions (V249-L251) near the lower end of the channel. The L251T mutation reduced the energetic barrier by 1.9[Formula: see text]kcal/mol, consistent with a slight increase in the channel radius in the bottleneck region. On the other hand, the T248F mutation caused a significant decrease in the channel radius (0.4 Å) and a substantial increase of 3.9[Formula: see text]kcal/mol in the energetic barrier. Ion permeation in all three structures was compared and found to be consistent with barrier height values. Using an external field in an incrementally increasing manner was found to be an effective way to obtain stable open, conducting channel structures.
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Affiliation(s)
- Tugba G Kucukkal
- Department of Science, Technology and Mathematics, Gallaudet University, 800 Florida Ave North East Washington, District of Columbia 20002, USA
| | - Feras Alsaiari
- Park View High School, 400 West Laurel Avenue, Sterling, Virginia 20164, USA
| | - Steven J Stuart
- Department of Chemistry, Clemson University, Clemson, South Carolina 29634, USA
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4
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Maltsev S, Hudson SM, Sahu ID, Liu L, Lorigan GA. Solid-state NMR (31)P paramagnetic relaxation enhancement membrane protein immersion depth measurements. J Phys Chem B 2014; 118:4370-7. [PMID: 24689497 PMCID: PMC4002136 DOI: 10.1021/jp500267y] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Revised: 04/01/2014] [Indexed: 11/29/2022]
Abstract
Paramagnetic relaxation enhancement (PRE) is a widely used approach for measuring long-range distance constraints in biomolecular solution NMR spectroscopy. In this paper, we show that (31)P PRE solid-state NMR spectroscopy can be utilized to determine the immersion depth of spin-labeled membrane peptides and proteins. Changes in the (31)P NMR PRE times coupled with modeling studies can be used to describe the spin-label position/amino acid within the lipid bilayer and the corresponding helical tilt. This method provides valuable insight on protein-lipid interactions and membrane protein structural topology. Solid-state (31)P NMR data on the 23 amino acid α-helical nicotinic acetylcholine receptor nAChR M2δ transmembrane domain model peptide followed predicted behavior of (31)P PRE rates of the phospholipid headgroup as the spin-label moves from the membrane surface toward the center of the membrane. Residue 11 showed the smallest changes in (31)P PRE (center of the membrane), while residue 22 shows the largest (31)P PRE change (near the membrane surface), when compared to the diamagnetic control M2δ sample. This PRE SS-NMR technique can be used as a molecular ruler to measure membrane immersion depth.
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Affiliation(s)
- Sergey Maltsev
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Stephen M. Hudson
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Indra D. Sahu
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Lishan Liu
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Gary A. Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
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5
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Ashby JA, McGonigle IV, Price KL, Cohen N, Comitani F, Dougherty DA, Molteni C, Lummis SCR. GABA binding to an insect GABA receptor: a molecular dynamics and mutagenesis study. Biophys J 2012. [PMID: 23200041 DOI: 10.1016/j.bpj.2012.10.016] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
RDL receptors are GABA-activated inhibitory Cys-loop receptors found throughout the insect CNS. They are a key target for insecticides. Here, we characterize the GABA binding site in RDL receptors using computational and electrophysiological techniques. A homology model of the extracellular domain of RDL was generated and GABA docked into the binding site. Molecular dynamics simulations predicted critical GABA binding interactions with aromatic residues F206, Y254, and Y109 and hydrophilic residues E204, S176, R111, R166, S176, and T251. These residues were mutated, expressed in Xenopus oocytes, and their functions assessed using electrophysiology. The data support the binding mechanism provided by the simulations, which predict that GABA forms many interactions with binding site residues, the most significant of which are cation-π interactions with F206 and Y254, H-bonds with E204, S205, R111, S176, T251, and ionic interactions with R111 and E204. These findings clarify the roles of a range of residues in binding GABA in the RDL receptor, and also show that molecular dynamics simulations are a useful tool to identify specific interactions in Cys-loop receptors.
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Mustafa I, Elkamel A, Chen P, Ibrahim G, Elnashaie S. Effect of cholineacetyltransferase activity and choline recycle ratio on diffusion-reaction modeling, bifurcation and chaotic behavior of acetylcholine neurocycle and their relation to Alzheimer's and Parkinson's diseases. Chem Eng Sci 2012. [DOI: 10.1016/j.ces.2011.08.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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7
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SHILLCOCK JULIAN, LIPOWSKY REINHARD. VISUALIZING SOFT MATTER: MESOSCOPIC SIMULATIONS OF MEMBRANES, VESICLES AND NANOPARTICLES. ACTA ACUST UNITED AC 2011. [DOI: 10.1142/s1793048007000428] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Biological membranes have properties and behavior that emerge from the propagation of the molecular characteristics of their components across many scales. Artificial smart materials, such as drug delivery vehicles and nanoparticles, often rely on modifying naturally-occurring soft matter, such as polymers and lipid vesicles, so that they possess useful behavior. Mesoscopic simulations allow in silico experiments to be easily and cheaply performed on complex, soft materials requiring as input only the molecular structure of the constituents at a coarse-grained level. They can therefore act as a guide to experimenters prior to performing costly assays. Additionally, mesoscopic simulations provide the only currently feasible window on the length and time scales relevant to important biophysical processes such as vesicle fusion. We describe here recent work using Dissipative Particle Dynamics simulations to explore the structure and behavior of amphiphilic membranes, the fusion of vesicles, and the interactions between rigid nanoparticles and soft surfaces.
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Affiliation(s)
- JULIAN SHILLCOCK
- Theory Department, Max Planck Institute of Colloids and Interfaces, 14424 Potsdam, Germany
| | - REINHARD LIPOWSKY
- Theory Department, Max Planck Institute of Colloids and Interfaces, 14424 Potsdam, Germany
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8
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Nusair NA, Mayo DJ, Dorozenski TD, Cardon TB, Inbaraj JJ, Karp ES, Newstadt JP, Grosser SM, Lorigan GA. Time-resolved EPR immersion depth studies of a transmembrane peptide incorporated into bicelles. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:821-8. [PMID: 22100865 DOI: 10.1016/j.bbamem.2011.11.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2011] [Revised: 10/31/2011] [Accepted: 11/02/2011] [Indexed: 11/25/2022]
Abstract
The reduction in EPR signal intensity of nitroxide spin-labels by ascorbic acid has been measured as a function of time to investigate the immersion depth of the spin-labeled M2δ AChR peptide incorporated into a bicelle system utilizing EPR spectroscopy. The corresponding decay curves of n-DSA (n=5, 7, 12, and 16) EPR signals have been used to (1) calibrate the depth of the bicelle membrane and (2) establish a calibration curve for measuring the depth of spin-labeled transmembrane peptides. The kinetic EPR data of CLS, n-DSA (n=5, 7, 12, and 16), and M2δ AChR peptide spin-labeled at Glu-1 and Ala-12 revealed excellent exponential and linear fits. For a model M2δ AChR peptide, the depth of immersion was calculated to be 5.8Å and 3Å for Glu-1, and 21.7Å and 19Å for Ala-12 in the gel-phase (298K) and L(α)-phases (318K), respectively. The immersion depth values are consistent with the pitch of an α-helix and the structural model of M2δ AChR incorporated into the bicelle system is in a good agreement with previous studies. Therefore, this EPR time-resolved kinetic technique provides a new reliable method to determine the immersion depth of membrane-bound peptides, as well as, explore the structural characteristics of the M2δ AChR peptide.
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Herrera AI, Al-Rawi A, Cook GA, Gao J, Iwamoto T, Prakash O, Tomich JM, Chen J. Structural characterization of two pore-forming peptides: consequences of introducing a C-terminal tryptophan. Proteins 2010; 78:2238-50. [PMID: 20544961 PMCID: PMC2909830 DOI: 10.1002/prot.22736] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Synthetic channel-forming peptides that can restore chloride conductance across epithelial membranes could provide a novel treatment of channelopathies such as cystic fibrosis. Among a series of 22-residue peptides derived from the second transmembrane segment of the glycine receptor alpha(1)-subunit (M2GlyR), p22-S22W (KKKKP ARVGL GITTV LTMTT QW) is particularly promising with robust membrane insertion and assembly. The concentration to reach one-half maximal short circuit current is reduced to 45 +/- 6 microM from that of 210 +/- 70 microM of peptide p22 (KKKKP ARVGL GITTV LTMTT QS). However, this is accompanied with nearly 50% reduction in conductance. Toward obtaining a molecular level understanding of the channel activities, we combine information from solution NMR, existing biophysical data, and molecular modeling to construct atomistic models of the putative pentameric channels of p22 and p22-S22W. Simulations in membrane bilayers demonstrate that these structural models, even though highly flexible, are stable and remain adequately open for ion conductance. The membrane-anchoring tryptophan residues not only rigidify the whole channel, suggesting increased stability, but also lead to global changes in the pore profile. Specifically, the p22-S22W pore has a smaller opening on average, consistent with lower measured conductance. Direct observation of several incidences of chloride transport suggests several qualitative features of how these channels might selectively conduct anions. The current study thus helps to rationalize the functional consequences of introducing a single C-terminal tryptophan. Availability of these structural models also paves the way for future work to rationally modify and improve M2GlyR-derived peptides toward potential peptide-based channel replacement therapy.
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Affiliation(s)
| | | | | | - Jian Gao
- Department of Biochemistry, Kansas State University, Manhattan KS 66506, USA
| | - Takeo Iwamoto
- Department of Biochemistry, Kansas State University, Manhattan KS 66506, USA
| | - Om Prakash
- Department of Biochemistry, Kansas State University, Manhattan KS 66506, USA
| | - John M. Tomich
- Department of Biochemistry, Kansas State University, Manhattan KS 66506, USA
| | - Jianhan Chen
- Department of Biochemistry, Kansas State University, Manhattan KS 66506, USA
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10
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Bordag N, Keller S. α-Helical transmembrane peptides: A “Divide and Conquer” approach to membrane proteins. Chem Phys Lipids 2010; 163:1-26. [PMID: 19682979 DOI: 10.1016/j.chemphyslip.2009.07.009] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2009] [Revised: 07/21/2009] [Accepted: 07/21/2009] [Indexed: 11/26/2022]
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11
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Antollini SS, Xu Y, Jiang H, Barrantes FJ. Fluorescence and molecular dynamics studies of the acetylcholine receptor γM4 transmembrane peptide in reconstituted systems. Mol Membr Biol 2009; 22:471-83. [PMID: 16373319 DOI: 10.1080/09687860500367915] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
A combination of fluorescence spectroscopy and molecular dynamics (MD) is applied to assess the conformational dynamics of a peptide making up the outermost ring of the nicotinic acetylcholine receptor (AChR) transmembrane region and the effect of membrane thickness and cholesterol on the hydrophobic matching of this peptide. The fluorescence studies exploit the intrinsic fluorescence of the only tryptophan residue in a synthetic peptide corresponding to the fourth transmembrane domain of the AChR gamma subunit (gammaM4-Trp(6)) reconstituted in lipid bilayers of varying thickness, and combine this information with quenching studies using depth-sensitive phosphatidylcholine spin-labeled probes and acrylamide, polarization of fluorescence, and generalized polarization of Laurdan. A direct correlation was found between bilayer width and the depth of insertion of Trp(6). We further extend our recent MD study of the conformational dynamics of the AChR channel to focus on the crosstalk between M4 and the lipid-belt region. The isolated gammaM4 peptide is shown to possess considerable orientational flexibility while maintaining a linear alpha-helical structure, and to vary its tilt depending on bilayer width and cholesterol (Chol) content. MD studies also show that gammaM4 also establishes contacts with the other TM peptides on its inner face, stabilizing a shorter TM length that is still highly sensitive to the lipid environment. In the native membrane the topology of the M4 ring is likely to exhibit a similar behavior, dynamically modifying its tilt to match the hydrophobic thickness of the bilayer.
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Affiliation(s)
- Silvia S Antollini
- Instituto de Investigaciones Bioquímicas de Bahía Blanca and UNESCO Chair of Biophysics & Molecular Neurobiology, Argentina
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12
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Behavioral differences between phosphatidic acid and phosphatidylcholine in the presence of the nicotinic acetylcholine receptor. Biophys J 2008; 95:5637-47. [PMID: 18835908 DOI: 10.1529/biophysj.108.136895] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
It has been found experimentally that negatively charged phosphatidic acid (PA) lipids and cholesterol molecules stabilize the nicotinic acetylcholine receptor (nAChR) in a functional resting state that can participate in an agonist-induced conformational change. In this study, we compare phosphatidylcholine (PC) and PA lipid behavior in the presence of the nAChR to determine why PC lipids do not support a functional nAChR. For lipids that are located within 1.0 nm of the protein, both PC and PA lipids have very similar order-parameter and bilayer-thickness values, which indicate that the annular lipid properties are protein-dependent. The most significant difference between the PC and PA bilayers is the formation of a lipid domain around the protein, which is visible in the PA bilayer but not the PC bilayer. This suggests that the PA domain may help stabilize the nAChR resting state. The PA lipids in the microdomain have a decreased order compared to a homogeneous PA bilayer and the lipids near the protein attempt to increase the free space in their vicinity by residing in multiple lateral planes.
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13
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Wells GB. Structural answers and persistent questions about how nicotinic receptors work. FRONTIERS IN BIOSCIENCE : A JOURNAL AND VIRTUAL LIBRARY 2008; 13:5479-510. [PMID: 18508600 PMCID: PMC2430769 DOI: 10.2741/3094] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The electron diffraction structure of nicotinic acetylcholine receptor (nAChR) from Torpedo marmorata and the X-ray crystallographic structure of acetylcholine binding protein (AChBP) are providing new answers to persistent questions about how nAChRs function as biophysical machines and as participants in cellular and systems physiology. New high-resolution information about nAChR structures might come from advances in crystallography and NMR, from extracellular domain nAChRs as high fidelity models, and from prokaryotic nicotinoid proteins. At the level of biophysics, structures of different nAChRs with different pharmacological profiles and kinetics will help describe how agonists and antagonists bind to orthosteric binding sites, how allosteric modulators affect function by binding outside these sites, how nAChRs control ion flow, and how large cytoplasmic domains affect function. At the level of cellular and systems physiology, structures of nAChRs will help characterize interactions with other cellular components, including lipids and trafficking and signaling proteins, and contribute to understanding the roles of nAChRs in addiction, neurodegeneration, and mental illness. Understanding nAChRs at an atomic level will be important for designing interventions for these pathologies.
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Affiliation(s)
- Gregg B Wells
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Science Center, College Station, TX 77843-1114, USA.
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14
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Szarecka A, Xu Y, Tang P. Dynamics of heteropentameric nicotinic acetylcholine receptor: implications of the gating mechanism. Proteins 2007; 68:948-60. [PMID: 17546671 DOI: 10.1002/prot.21462] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The dynamics characteristics of the currently available structure of Torpedo nicotinic acetylcholine receptor (nAChR), including the extracellular, transmembrane, and intracellular domains (ICDs), were analyzed using the Gaussian Network Model (GNM) and Anisotropic Network Model (ANM). We found that a symmetric quaternary twist motion, reported previously in the literature in a homopentameric receptor (Cheng et al. J Mol Biol 2006;355:310-324; Taly et al. Biophys J 2005;88:3954-3965), occurred also in the heteropentameric Torpedo nAChR. We believe, however, that the symmetric twist alone is not sufficient to explain a large body of experimental data indicating asymmetry and subunit nonequivalence during gating. Here we report our results supporting the hypothesis that a combination of symmetric and asymmetric motions opens the gate. We show that the asymmetric motion involves tilting of the TM2 helices. Furthermore, our study reveals three additional aspects of channel dynamics: (1) loop A serves as an allosteric mediator between the ligand binding loops and those at the domain interface, particularly the linker between TM2 and TM3; (2) the ICD can modulate the pore dynamics and thus should not be neglected in gating studies; and (3) the F loops, which are peculiarly longer and poorly-conserved in non-alpha-subunits, have important dynamical implications.
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Affiliation(s)
- Agnieszka Szarecka
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
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15
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Cheng X, Ivanov I, Wang H, Sine SM, McCammon JA. Nanosecond-timescale conformational dynamics of the human alpha7 nicotinic acetylcholine receptor. Biophys J 2007; 93:2622-34. [PMID: 17573436 PMCID: PMC1989720 DOI: 10.1529/biophysj.107.109843] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We explore the conformational dynamics of a homology model of the human alpha7 nicotinic acetylcholine receptor using molecular dynamics simulation and analyses of root mean-square fluctuations, block partitioning of segmental motion, and principal component analysis. The results reveal flexible regions and concerted global motions of the subunits encompassing extracellular and transmembrane domains of the subunits. The most relevant motions comprise a bending, hinged at the beta10-M1 region, accompanied by concerted tilting of the M2 helices that widens the intracellular end of the channel. Despite the nanosecond timescale, the observations suggest that tilting of the M2 helices may initiate opening of the pore. The results also reveal direct coupling between a twisting motion of the extracellular domain and dynamic changes of M2. Covariance analysis of interresidue motions shows that this coupling arises through a network of residues within the Cys and M2-M3 loops where Phe135 is stabilized within a hydrophobic pocket formed by Leu270 and Ile271. The resulting concerted motion causes a downward shift of the M2 helices that disrupts a hydrophobic girdle formed by 9' and 13' residues.
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Affiliation(s)
- Xiaolin Cheng
- Howard Hughes Medical Institute, National Science Foundation Center for Theoretical Biophysics, Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA.
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16
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Ivanov I, Cheng X, Sine SM, McCammon JA. Barriers to Ion Translocation in Cationic and Anionic Receptors from the Cys-Loop Family. J Am Chem Soc 2007; 129:8217-24. [PMID: 17552523 DOI: 10.1021/ja070778l] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Understanding the mechanisms of gating and ion permeation in biological channels and receptors has been a long-standing challenge in biophysics. Recent advances in structural biology have revealed the architecture of a number of transmembrane channels and allowed detailed, molecular-level insight into these systems. Herein, we have examined the barriers to ion conductance and origins of ion selectivity in models of the cationic human alpha7 nicotinic acetylcholine receptor (nAChR) and the anionic alpha1 glycine receptor (GlyR), based on the structure of Torpedo nAChR. Molecular dynamics simulations were used to determine water density profiles along the channel length, and they established that both receptor pores were fully hydrated. The very low water density in the middle of the nAChR pore indicated the existence of a hydrophobic constriction. By contrast, the pore of GlyR was lined with hydrophilic residues and remained well-hydrated throughout. Adaptive biasing force simulations allowed us to reconstruct potentials of mean force (PMFs) for chloride and sodium ions in the two receptors. For the nicotinic receptor we observed barriers to ion translocation associated with rings of hydrophobic residues-Val13' and Leu9'-in the middle of the transmembrane domain. This finding further substantiates the hydrophobic gating hypothesis for nAChR. The PMF revealed no significant hydrophobic barrier for chloride translocation in GlyR. For both receptors nonpermeant ions displayed considerable barriers. Thus, the overall electrostatics and the presence of rings of charged residues at the entrance and exit of the channels were sufficient to explain the experimentally observed anion and cation selectivity.
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Affiliation(s)
- Ivaylo Ivanov
- Department of Chemistry and Biochemistry, University of California-San Diego, La Jolla, CA 92093-0365, USA.
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17
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Cheng X, Wang H, Grant B, Sine SM, McCammon JA. Targeted molecular dynamics study of C-loop closure and channel gating in nicotinic receptors. PLoS Comput Biol 2006; 2:e134. [PMID: 17009865 PMCID: PMC1584325 DOI: 10.1371/journal.pcbi.0020134] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2006] [Accepted: 08/23/2006] [Indexed: 11/24/2022] Open
Abstract
The initial coupling between ligand binding and channel gating in the human α7 nicotinic acetylcholine receptor (nAChR) has been investigated with targeted molecular dynamics (TMD) simulation. During the simulation, eight residues at the tip of the C-loop in two alternating subunits were forced to move toward a ligand-bound conformation as captured in the crystallographic structure of acetylcholine binding protein (AChBP) in complex with carbamoylcholine. Comparison of apo- and ligand-bound AChBP structures shows only minor rearrangements distal from the ligand-binding site. In contrast, comparison of apo and TMD simulation structures of the nAChR reveals significant changes toward the bottom of the ligand-binding domain. These structural rearrangements are subsequently translated to the pore domain, leading to a partly open channel within 4 ns of TMD simulation. Furthermore, we confirmed that two highly conserved residue pairs, one located near the ligand-binding pocket (Lys145 and Tyr188), and the other located toward the bottom of the ligand-binding domain (Arg206 and Glu45), are likely to play important roles in coupling agonist binding to channel gating. Overall, our simulations suggest that gating movements of the α7 receptor may involve relatively small structural changes within the ligand-binding domain, implying that the gating transition is energy-efficient and can be easily modulated by agonist binding/unbinding. Nicotinic acetylcholine receptors are ligand-gated ion channels responsible for neurotransmitter-mediated signal transduction at synapses throughout the central and peripheral nervous systems. Binding of neurotransmitter molecules to subunit interfaces in the N-terminal extracellular domain induces structural rearrangements of the membrane-spanning domain permitting the influx of cations. A full understanding of how the conformational changes propagate from the ligand-binding site to the pore domain is of great interest to biologists, yet remains to be established. Using a special simulation technique known as targeted molecular dynamics, Cheng and colleagues probed the early stages of ligand-induced conformational rearrangements that may lead to channel opening. During the simulation, Cheng et al. observed a sequence of conformational changes that stem from the ligand-binding site to the transmembrane domain resulting in a wider channel. From these results, they suggest that gating movements may entail only small structural changes in the ligand-binding domain, implying that channel gating is energy-efficient and can readily be modulated by the binding/unbinding of agonist molecules.
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Affiliation(s)
- Xiaolin Cheng
- Howard Hughes Medical Institute, University of California San Diego, La Jolla, California, United States of America.
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Vemparala S, Saiz L, Eckenhoff RG, Klein ML. Partitioning of anesthetics into a lipid bilayer and their interaction with membrane-bound peptide bundles. Biophys J 2006; 91:2815-25. [PMID: 16877515 PMCID: PMC1578482 DOI: 10.1529/biophysj.106.085324] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Molecular dynamics simulations have been performed to investigate the partitioning of the volatile anesthetic halothane from an aqueous phase into a coexisting hydrated bilayer, composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipids, with embedded alpha-helical peptide bundles based on the membrane-bound portions of the alpha- and delta-subunits, respectively, of nicotinic acetylcholine receptor. In the molecular dynamics simulations halothane molecules spontaneously partitioned into the DOPC bilayer and then preferentially occupied regions close to lipid headgroups. A single halothane molecule was observed to bind to tyrosine (Tyr-277) residue in the alpha-subunit, an experimentally identified specific binding site. The binding of halothane attenuated the local loop dynamics of alpha-subunit and significantly influenced global concerted motions suggesting anesthetic action in modulating protein function. Steered molecular dynamics calculations on a single halothane molecule partitioned into a DOPC lipid bilayer were performed to probe the free energy profile of halothane across the lipid-water interface and rationalize the observed spontaneous partitioning. Partitioned halothane molecules affect the hydrocarbon chains of the DOPC lipid, by lowering of the hydrocarbon tilt angles. The anesthetic molecules also caused a decrease in the number of peptide-lipid contacts. The observed local and global effects of anesthetic binding on protein motions demonstrated in this study may underlie the mechanism of action of anesthetics at a molecular level.
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Affiliation(s)
- Satyavani Vemparala
- Department of Chemistry and Center for Molecular Modeling, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
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Shillcock JC, Lipowsky R. The computational route from bilayer membranes to vesicle fusion. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2006; 18:S1191-S1219. [PMID: 21690837 DOI: 10.1088/0953-8984/18/28/s06] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Biological membranes are examples of 'smart' materials whose properties and behaviour emerge from the propagation across many scales of the molecular characteristics of their constituents. Artificial smart materials, such as drug delivery vehicles and biosensors, often rely on modifying naturally occurring soft matter, such as polymers and lipid vesicles, so that they possess useful behaviour. However, the complexity of natural membranes, both in their static properties, exemplified in their phase behaviour, and in their dynamic properties, as in the kinetics of their formation and interactions, hinders their rational modification. Mesoscopic simulations, such as dissipative particle dynamics (DPD), allow in silico experiments to be easily and cheaply performed on complex, soft materials requiring as input only the molecular structure of the constituents at a coarse-grained level. They can therefore act as a guide to experimenters prior to performing costly assays. Additionally, mesoscopic simulations provide the only currently feasible window on the length- and timescales relevant to important biophysical processes such as vesicle fusion. We review here the development of computational models of bilayer membranes, and in particular the use of mesoscopic simulations to follow the molecular rearrangements that occur during membrane fusion.
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Affiliation(s)
- Julian C Shillcock
- Max Planck Institute of Colloids and Interfaces, 14424 Potsdam, Germanyhttp://www.mpikg.mpg.de/th
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Corry B. An energy-efficient gating mechanism in the acetylcholine receptor channel suggested by molecular and Brownian dynamics. Biophys J 2005; 90:799-810. [PMID: 16284265 PMCID: PMC1367105 DOI: 10.1529/biophysj.105.067868] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Acetylcholine receptors mediate electrical signaling between nerve and muscle by opening and closing a transmembrane ion conductive pore. Molecular and Brownian dynamics simulations are used to shed light on the location and mechanism of the channel gate. Four separate 5 ns molecular dynamics simulations are carried out on the imaged structure of the channel, a hypothetical open structure with a slightly wider pore and a mutant structure in which a central ring of hydrophobic residues is replaced by polar groups. Water is found to partially evacuate the pore during molecular simulations of the imaged structure, whereas ions face a large energy barrier and do not conduct through the channel in Brownian dynamics simulations. The pore appears to be in a closed configuration despite containing an unobstructed pathway across the membrane as a series of hydrophobic residues in the center of the channel provide an unfavorable home to water and ions. When the channel is widened slightly, water floods into the channel and ions conduct at a rate comparable to the currents measured experimentally in open channels. The pore remains permeable to ions provided the extracellular end of the pore-lining helix is restrained near the putative open configuration to mimic the presence of the ligand binding domain. Replacing some of the hydrophobic residues with polar ones decreases the barrier for ion permeation but does not result in significant currents. The channel is posited to utilize an energy efficient gating mechanism in which only minor conformational changes of the hydrophobic region of the pore are required to create macroscopic changes in conductance.
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Affiliation(s)
- Ben Corry
- Chemistry, School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, Crawley, WA 6009, Australia.
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