1
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Subramanian G, Manchanda K, Mo Y, Sathe RY, Bharatam PV. Monovalent cation binding to model systems and the macrocyclic depsipeptide, emodepside. J Comput Chem 2024; 45:2409-2423. [PMID: 38924119 DOI: 10.1002/jcc.27451] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Revised: 05/13/2024] [Accepted: 06/09/2024] [Indexed: 06/28/2024]
Abstract
This study focuses on the systematic exploration of the emodepside conformations bound to monovalent K+ ion using quantum mechanical density functional theory (DFT) calculations at the M06-2X/6-31+G(d,p) level of theory. Nine conformers of emodepside and their complexes with K+ ion were characterized as stationary points on the potential energy surface. The conformational isomers were examined for their 3D structures, bonding, energetics, and interactions with the cation. A cavitand-like structure (CC) is identified to be the energetically most stable arrangement. To arrive at a better understanding of the K+ ion binding, calculations were initially performed on complexes formed by the K+ and Na+ ions with model ligands (methyl ester and N,N-dimethyl acetamide). Both the natural bond orbital (NBO) method and the block-localized wavefunction (BLW) energy decomposition approach was employed to assess the bonding and energetic contributions stabilizing the ion-bound model complexes. Finally, the solvent effect was evaluated through complete geometry optimizations and energy minimizations for the model ion-ligand complexes and the emodepside-K+ bound complexes using an implicit solvent model mimicking water and DMSO.
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Affiliation(s)
| | - Kanika Manchanda
- Department of Pharmacoinformatics, National Institute of Pharmaceutical Education and Research (NIPER), S.A.S Nagar (Mohali), Punjab, India
| | - Yirong Mo
- Department of Nanoscience, Joint School of Nanoscience and Nanoengineering, University of North Carolina at Greensboro, Greensboro, North Carolina, USA
| | - Rohit Y Sathe
- Department of Biological Sciences and Biotechnology, Institute of Chemical Technology, Mumbai, Maharashtra, India
| | - Prasad V Bharatam
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER), S.A.S Nagar (Mohali), Punjab, India
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2
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Hirano M, Yokoo H, Ohoka N, Ito T, Misawa T, Oba M, Inoue T, Demizu Y. Rational Design of Amphipathic Antimicrobial Peptides with Alternating L-/D-Amino Acids That Form Helical Structures. Chem Pharm Bull (Tokyo) 2024; 72:149-154. [PMID: 38296556 DOI: 10.1248/cpb.c23-00465] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2024]
Abstract
Antimicrobial peptides (AMPs) are promising therapeutic agents against bacteria. We have previously reported an amphipathic AMP Stripe composed of cationic L-Lys and hydrophobic L-Leu/L-Ala residues, and Stripe exhibited potent antimicrobial activity against Gram-positive and Gram-negative bacteria. Gramicidin A (GA), composed of repeating sequences of L- and D-amino acids, has a unique β6.3-helix structure and exhibits broad antimicrobial activity. Inspired by the structural properties and antimicrobial activities of LD-alternating peptides such as GA, in this study, we designed Stripe derivatives with LD-alternating sequences. We found that simply alternating L- and D-amino acids in the Stripe sequence to give StripeLD caused a reduction in antimicrobial activity. In contrast, AltStripeLD, with cationic and hydrophobic amino acids rearranged to yield an amphipathic distribution when the peptide adopts a β6.3-helix, displayed higher antimicrobial activity than AltStripe. These results suggest that alternating L-/D-cationic and L-/D-hydrophobic amino acids in accordance with the helical structure of an AMP may be a useful way to improve antimicrobial activity and develop new AMP drugs.
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Affiliation(s)
- Motoharu Hirano
- National Institute of Health Sciences
- Graduate School of Medical Life Science, Yokohama City University
| | - Hidetomo Yokoo
- National Institute of Health Sciences
- Medical Chemistry, Graduate School of Medical Science, Kyoto Prefectural University of Medicine
| | | | - Takahito Ito
- National Institute of Health Sciences
- Graduate School of Medical Life Science, Yokohama City University
| | | | - Makoto Oba
- Medical Chemistry, Graduate School of Medical Science, Kyoto Prefectural University of Medicine
| | | | - Yosuke Demizu
- National Institute of Health Sciences
- Graduate School of Medical Life Science, Yokohama City University
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3
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Maione S, del Valle LJ, Pérez-Madrigal MM, Cativiela C, Puiggalí J, Alemán C. Electrospray loading and release of hydrophobic gramicidin in polyester microparticles. RSC Adv 2016. [DOI: 10.1039/c6ra11056h] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Gramicidin, a pentadecapeptide with well-known antimicrobial properties and recently identified therapeutic activity against different carcinomas, has been loaded by electrospraying in biodegradable and biocompatible poly(tetramethylene succinate).
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Affiliation(s)
- Silvana Maione
- Department of Chemical Engineering
- ETSEIB
- Universitat Politècnica de Catalunya
- Barcelona 08028
- Spain
| | - Luis J. del Valle
- Department of Chemical Engineering
- ETSEIB
- Universitat Politècnica de Catalunya
- Barcelona 08028
- Spain
| | - Maria M. Pérez-Madrigal
- Department of Chemical Engineering
- ETSEIB
- Universitat Politècnica de Catalunya
- Barcelona 08028
- Spain
| | - Carlos Cativiela
- Departamento de Química Orgánica
- Instituto de Síntesis Química y Catálisis Homogénea-ISQCH
- CSIC-Universidad de Zaragoza
- 50009 Zaragoza
- Spain
| | - Jordi Puiggalí
- Department of Chemical Engineering
- ETSEIB
- Universitat Politècnica de Catalunya
- Barcelona 08028
- Spain
| | - Carlos Alemán
- Department of Chemical Engineering
- ETSEIB
- Universitat Politècnica de Catalunya
- Barcelona 08028
- Spain
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4
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Jadhav KB, Lichtenecker RJ, Bullach A, Mandal B, Arndt HD. Dynamic Combinatorial Enrichment of PolyconformationalD-/L-Peptide Dimers. Chemistry 2015; 21:5898-908. [DOI: 10.1002/chem.201405413] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Indexed: 01/19/2023]
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5
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Mao J, Kuranaga T, Hamamoto H, Sekimizu K, Inoue M. Rational Design, Synthesis, and Biological Evaluation of Lactam-Bridged Gramicidin A Analogues: Discovery of a Low-Hemolytic Antibacterial Peptide. ChemMedChem 2014; 10:540-5. [DOI: 10.1002/cmdc.201402473] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Indexed: 11/09/2022]
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6
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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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7
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Itoh H, Inoue M. Chemical construction and structural permutation of potent cytotoxin polytheonamide B: discovery of artificial peptides with distinct functions. Acc Chem Res 2013; 46:1567-78. [PMID: 23488446 DOI: 10.1021/ar300315p] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Polytheonamide B (1), isolated from the marine sponge Theonella swinhoei, is a posttranslationally modified ribosomal peptide (MW 5030 Da) that displays extraordinary cytotoxicity. Among its 48 amino acid residues, this peptide includes a variety D- and L-amino acids that do not occur in proteins, and the chiralities of these amino acids alternate in sequence. These structural features induce the formation of a stable β6.3-helix, giving rise to a tubular structure of over 4 nm in length. In the biological setting, this fold is believed to transport cations across the lipid bilayer through a pore, thereby acting as an ion channel. In this Account, we discuss the construction and structural permutations of this potent cytotoxin. First we describe the 161-step chemical construction of this unusual peptide 1. By developing a synthetic route to 1, we established the chemical basis for subsequent SAR studies to pinpoint the proteinogenic and nonproteinogenic building blocks within the molecule that confer its toxicity and channel function. Using fully synthetic 1, we generated seven analogues with point mutations, and studies of their activity revealed the importance of the N-terminal moiety. Next, we simplified the structure of 1 by substituting six amino acid residues of 1 to design a more synthetically accessible analogue 9. This dansylated polytheonamide mimic 9 was synthesized in 127 total steps, and we evaluated its function to show that it can emulate the toxic and ion channel activities of 1 despite its multiple structural modifications. Finally, we applied a highly automated synthetic route to 48-mer 9 to generate 13 substructures of 27-39-mers. The 37-mer 12 exhibited nanomolar level toxicity through a potentially distinct mode of action from 1 and 9. The SAR studies of polytheonamide B and the 21 artificial analogues have deepened our understanding of the precise structural requirements for the biological functions of 1. They have also led to the discovery of artificial molecules with various toxicities and channel functions. These achievements demonstrate the benefits of total synthesis and the importance of efficient construction of complex molecules. The knowledge accumulated through these studies will be useful for the rational design of new tailor-made channel peptides and cytotoxic molecules with desired functions.
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Affiliation(s)
- Hiroaki Itoh
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Masayuki Inoue
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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8
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Itoh H, Matsuoka S, Kreir M, Inoue M. Design, Synthesis and Functional Analysis of Dansylated Polytheonamide Mimic: An Artificial Peptide Ion Channel. J Am Chem Soc 2012; 134:14011-8. [DOI: 10.1021/ja303831a] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- Hiroaki Itoh
- Graduate School of Pharmaceutical
Sciences, The University of Tokyo, Hongo,
Bunkyo-ku, Tokyo 113-0033, Japan
| | - Shigeru Matsuoka
- Graduate School of Pharmaceutical
Sciences, The University of Tokyo, Hongo,
Bunkyo-ku, Tokyo 113-0033, Japan
| | - Mohamed Kreir
- Nanion Technologies GmbH, Gabrielenstrasse 9, D-80636 Munich, Germany
| | - Masayuki Inoue
- Graduate School of Pharmaceutical
Sciences, The University of Tokyo, Hongo,
Bunkyo-ku, Tokyo 113-0033, Japan
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9
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Wu G, Zhu J. NMR studies of alkali metal ions in organic and biological solids. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2012; 61:1-70. [PMID: 22340207 DOI: 10.1016/j.pnmrs.2011.06.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2010] [Accepted: 05/31/2011] [Indexed: 05/31/2023]
Affiliation(s)
- Gang Wu
- Department of Chemistry, Queen's University, 90 Bader Lane, Kingston, Ontario, Canada.
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10
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Höfer N, Aragão D, Lyons JA, Caffrey M. Membrane Protein Crystallization in Lipidic Mesophases. Hosting lipid affects on the crystallization and structure of a transmembrane peptide. CRYSTAL GROWTH & DESIGN 2011; 11:1182-1192. [PMID: 22933857 PMCID: PMC3427940 DOI: 10.1021/cg101384p] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Gramicidin is an apolar pentadecapeptide antibiotic consisting of alternating D-and L-amino acids. It functions, in part, by creating pores in membranes of susceptible cells rendering them leaky to monovalent cations. The peptide should be able to traverse the host membrane either as a double stranded, intertwined double helix (DSDH) or as a head-to-head single stranded helix (HHSH). Current structure models are based on macromolecular X-ray crystallography (MX) and nuclear magnetic resonance (NMR). However, the HHSH form has only been observed by NMR. The shape and size of the different gramicidin conformations differ. We speculated therefore that reconstituting it into a lipidic mesophase with bilayers of different microstructures would preferentially stabilize one form over the other. By using such mesophases for in meso crystallogenesis the expectation was that at least one would generate crystals of gramicidin in the HHSH form for structure determination by MX. This was tested using commercial and in-house synthesised lipids that support in meso crystallogenesis. Lipid acyl chain lengths were varied from 14 to 18 carbons to provide mesophases with a range of bilayer thicknesses. Unexpectedly, all lipids produced high quality, structure-grade crystals with gramicidin only in the DSDH conformation.
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Affiliation(s)
- Nicole Höfer
- Membrane Structural and Functional Biology Group, School of Biochemistry and Immunology, and School of Medicine, Trinity College, Dublin
- Department of Chemical and Environmental Sciences, University of Limerick, Limerick, Ireland
| | - David Aragão
- Membrane Structural and Functional Biology Group, School of Biochemistry and Immunology, and School of Medicine, Trinity College, Dublin
| | - Joseph A. Lyons
- Membrane Structural and Functional Biology Group, School of Biochemistry and Immunology, and School of Medicine, Trinity College, Dublin
- Department of Chemical and Environmental Sciences, University of Limerick, Limerick, Ireland
| | - Martin Caffrey
- Membrane Structural and Functional Biology Group, School of Biochemistry and Immunology, and School of Medicine, Trinity College, Dublin
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11
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Dzikovski BG, Borbat PP, Freed JH. Channel and nonchannel forms of spin-labeled gramicidin in membranes and their equilibria. J Phys Chem B 2011; 115:176-85. [PMID: 21142163 PMCID: PMC3076037 DOI: 10.1021/jp108105k] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Channel and nonchannel forms of gramicidin A (GA) were studied by ESR in various lipid environments using new mono- and double-spin-labeled compounds. For GA channels, we demonstrate here how pulse dipolar ESR can be used to determine the orientation of the membrane-traversing molecule relative to the membrane normal and to study subtle effects of lipid environment on the interspin distance in the spin-labeled gramicidin channel. To study nonchannel forms of gramicidin, pulse dipolar ESR was used first to determine interspin distances corresponding to monomers and double-helical dimers of spin-labeled GA molecules in the organic solvents trifluoroethanol and octanol. The same distances were then observed in membranes. Since detection of nonchannel forms in the membrane is complicated by aggregation, we suppressed any dipolar spectra from intermolecular interspin distances arising from the aggregates by using double-labeled GA in a mixture with excess unlabeled GA. In hydrophobic mismatching lipids (L(β) phase of DPPC), gramicidin channels dissociate into free monomers. The backbone structure of the monomeric form is similar to a monomeric unit of the channel dimer. In addition to channels and monomers, the double-helical conformation of gramicidin is present in some membrane environments. In the gel phase of saturated phosphatidylcholines, the fraction of double helices increases in the following order: DLPC < DMPC < DSPC < DPPC. The equilibrium DHD/monomer ratio in DPPC was determined. In membranes, the double-helical form is present only in aggregates. In addition, we studied the effect of N-terminal substitution in the GA molecule upon channel formation. This work demonstrates how pulsed dipolar ESR may be utilized to study complex equilibria of peptides in membranes.
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Affiliation(s)
- Boris G Dzikovski
- National Biomedical Center for Advanced ESR Technology, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA
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12
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Dittrich C, Meier W. Solid Peptide Nanoparticles - Structural Characterization and Quantification of Cargo Encapsulation. Macromol Biosci 2010; 10:1406-15. [DOI: 10.1002/mabi.201000221] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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13
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Olczak A, Główka ML, Szczesio M, Bojarska J, Wawrzak Z, Duax WL. The first crystal structure of a gramicidin complex with sodium: high-resolution study of a nonstoichiometric gramicidin D-NaI complex. ACTA CRYSTALLOGRAPHICA SECTION D: BIOLOGICAL CRYSTALLOGRAPHY 2010; 66:874-80. [PMID: 20693686 DOI: 10.1107/s0907444910019876] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2010] [Accepted: 05/26/2010] [Indexed: 05/26/2023]
Abstract
The crystal structure of the nonstoichiometric complex of gramicidin D with NaI has been studied using synchrotron radiation at 100 K. The limiting resolution was 1.25 A and the R factor was 16% for 19 883 observed reflections. The general architecture of the antiparallel two-stranded gramicidin dimers in the studied crystal was a right-handed antiparallel double-stranded form that closely resembles the structures of other right-handed species published to date. However, there were several surprising observations. In addition to the significantly different composition of linear gramicidins identified in the crystal structure, including the absence of the gramicidin C form, only two cationic sites were found in each of the two independent dimers (channels), which were partially occupied by sodium, compared with the seven sites found in the RbCl complex of gramicidin. The sum of the partial occupancies of Na(+) was only 1.26 per two dimers and was confirmed by the similar content of iodine ions (1.21 ions distributed over seven sites), which was easily visible from their anomalous signal. Another surprising observation was the significant asymmetry of the distributions and occupancies of cations in the gramicidin dimers, which was in contrast to those observed in the high-resolution structures of the complexes of heavier alkali metals with gramicidin D, especially that of rubidium.
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Affiliation(s)
- A Olczak
- Institute of General and Ecological Chemistry, Technical University of Łódź, Zeromskiego 116, 90-924 Łódź, Poland.
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14
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Mahalakshmi R, Sengupta A, Raghothama S, Shamala N, Balaram P. Tryptophan rich peptides: influence of indole rings on backbone conformation. Biopolymers 2007; 88:36-54. [PMID: 17091496 DOI: 10.1002/bip.20625] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Synthetic peptides with defined secondary structure scaffolds, namely hairpins and helices, containing tryptophan residues, have been investigated in this study to probe the influence of a large number of aromatic amino acids on backbone conformations. Solution NMR investigations of Boc-W-L-W-(D)P-G-W-L-W-OMe (peptide 1), designed to form a well-folded hairpin, clearly indicates the influence of flanking aromatic residues at the (D)Pro-Gly region on both turn nucleation and strand propagation. Indole-pyrrolidine interactions in this peptide lead to the formation of the less-frequent type I' turn at the (D)Pro-Gly segment and frayed strand regions, with the strand residues adopting local helical conformations. An analog of peptide 1 with an Aib-Gly turn-nucleated hairpin (Boc-W-L-W-U-G-W-L-W-OMe (peptide 2)) shows a preference for helical structures in solution, in both chloroform and methanol. Peptides with either one (Boc-W-L-W-U-W-L-W-OMe (peptide 3)) or two (Boc-U-W-L-W-U-W-L-W-OMe (peptide 4)) helix-nucleating Aib residues give rise to the well-folded helical conformations in the chloroform solution. The results are indicative of a preference for helical folding in peptides containing a large number of Trp residues. Investigation of a tetrapeptide analog of peptide 2, Boc-W-U-G-W-OMe (peptide 5), in solution and in the crystal state (by X-ray diffraction), also indicates a preference for a helical fold. Additionally, peptide 5 is stabilized in crystals by both aromatic interactions and an array of weak interactions. Examination of Trp-rich sequences in protein structures, however, reveals no secondary structure preference, suggesting that other stabilizing interactions in a well-folded protein may offset the influence of indole rings on backbone conformations.
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15
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Mahalakshmi R, Sengupta A, Raghothama S, Shamala N, Balaram P. Tryptophan-containing peptide helices: interactions involving the indole side chain. ACTA ACUST UNITED AC 2006; 66:277-96. [PMID: 16218995 DOI: 10.1111/j.1399-3011.2005.00301.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Two designed peptide sequences containing Trp residues at positions i and i + 5 (Boc-Leu-Trp-Val-Ala-Aib-Leu-Trp-Val-OMe, 1) as well as i and i + 6 (Boc-Leu-Trp-Val-Aib-Ala-Aib-Leu-Trp-Val-OMe, 2) containing one and two centrally positioned Aib residues, respectively, for helix nucleation, have been shown to form stable helices in chloroform solutions. Structures derived from nuclear magnetic resonance (NMR) data reveal six and seven intramolecularly hydrogen-bonded NH groups in peptides 1 and 2, respectively. The helical conformation of octapeptide 1 has also been established in the solid state by X-ray diffraction. The crystal structure reveals an interesting packing motif in which helical columns are stabilized by side chain-backbone hydrogen bonding involving the indole Nepsilon1H of Trp(2) as donor, and an acceptor C=O group from Leu(6) of a neighboring molecule. Helical columns also associate laterally, and strong interactions are observed between the Trp(2) and Trp(7) residues on neighboring molecules. The edge-to-face aromatic interactions between the indoles suggest a potential C-H...pi interaction involving the Czeta3H of Trp(2). Concentration dependence of NMR chemical shifts provides evidence for peptide association in solution involving the Trp(2) Nepsilon1H protons, presumably in a manner similar to that observed in the crystal.
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Affiliation(s)
- R Mahalakshmi
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
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16
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Zhang J, Thurbide KB. Direct analysis of gramicidin double helices using packed column supercritical fluid chromatography. J Chromatogr A 2006; 1101:286-92. [PMID: 16239008 DOI: 10.1016/j.chroma.2005.10.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2005] [Revised: 09/30/2005] [Accepted: 10/05/2005] [Indexed: 11/25/2022]
Abstract
Direct analysis of the monomeric and four double helical dimeric conformations of gramicidin has been achieved using packed column supercritical fluid chromatography (pSFC). Using a PRP-1 polymeric column and typical conditions of 40 degrees C column temperature, 25 MPa column pressure, and 35% n-pentanol modifier addition, all of the gramicidin conformers were readily separated. To evaluate the method, the dynamic characteristics of the monomer and dimer species were monitored as a function of solvent type, incubation time, solvent temperature, and initial concentration. The findings agree with those previously obtained by other methods but also yield new information about the relative amounts of two closely related dimers (species 1 and 2) as well as the simultaneous changes in the full dimer/monomer distribution. Results indicate that the developed pSFC method can be an informative complimentary tool for readily monitoring changes in the full profile of gramicidin species present in different environments.
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Affiliation(s)
- Jianmin Zhang
- Department of Chemistry, University of Calgary, 2500 University Drive, N.W., Calgary, Alta., Canada T2N 1N4
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17
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Jagannadham MV, Nagaraj R. Conformation of gramicidin a in water: Inference from analysis of hydrogen/deuterium exchange behavior by matrix assisted laser desorption ionization mass spectrometry. Biopolymers 2005; 80:708-13. [PMID: 15887265 DOI: 10.1002/bip.20293] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Gramicidin A (the major component of gramicidin D) is a highly hydrophobic peptide with very little solubility in water. Hence, the conformation of this peptide has been extensively investigated in organic solvents and model membranes, but not in water. The peptide adopts a beta6.3-helical conformation in the monomeric and dimeric forms. We have investigated the conformation of gramicidin A in water by monitoring hydrogen-deuterium exchange by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. Our results indicate that gramicidin A is monomeric and exists in a highly folded conformation. The metal ion bound forms are clearly discernible in the monomers. The presence of the dimeric form is not observed. It is unlikely this is due to the operating conditions or the method used, as both hetero- and homodimers in gramicidin D are detected when methanol is used as a solvent. The present study also establishes that the linear gramicidins retain a history of solvent environment when ions are generated by matrix-assisted laser desorption ionization and analyzed by time-of-flight.
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Affiliation(s)
- M V Jagannadham
- Centre for Cellular and Molecular Biology,Uppal Road,Hyderabad 500 007, India.
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18
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Mo Y, Cross TA, Nerdal W. Structural restraints and heterogeneous orientation of the gramicidin A channel closed state in lipid bilayers. Biophys J 2004; 86:2837-45. [PMID: 15111401 PMCID: PMC1304153 DOI: 10.1016/s0006-3495(04)74336-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Although there have been several decades of literature illustrating the opening and closing of the monovalent cation selective gramicidin A channel through single channel conductance, the closed conformation has remained poorly characterized. In sharp contrast, the open-state dimer is one of the highest resolution structures yet characterized in a lipid environment. To shift the open/closed equilibrium dramatically toward the closed state, a lower peptide/lipid molar ratio and, most importantly, long-chain lipids have been used. For the first time, structural evidence for a monomeric state has been observed for the native gramicidin A peptide. Solid-state NMR spectroscopy of single-site (15)N-labeled gramicidin in uniformly aligned bilayers in the L(alpha) phase have been observed. The results suggest a kinked structure with considerable orientational heterogeneity. The C-terminal domain is well structured, has a well-defined orientation in the bilayer, and appears to be in the bilayer interfacial region. On the other hand, the N-terminal domain, although appearing to be well structured and in the hydrophobic core of the bilayer, has a broad range of orientations relative to the bilayer normal. The structure is not just half of the open-state dimer, and neither is the structure restricted to the surface of the bilayer. Consequently, the monomeric or closed state appears to be a hybrid of these two models from the literature.
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Affiliation(s)
- Y Mo
- Department of Chemistry and Biochemistry and Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, USA
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19
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Wimley WC, White SH. Reversible unfolding of beta-sheets in membranes: a calorimetric study. J Mol Biol 2004; 342:703-11. [PMID: 15342231 PMCID: PMC2935845 DOI: 10.1016/j.jmb.2004.06.093] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2004] [Revised: 06/21/2004] [Accepted: 06/23/2004] [Indexed: 12/14/2022]
Abstract
The hexapeptide acetyl-Trp-Leu(5) (AcWL(5)) has the remarkable ability to assemble reversibly and spontaneously into beta-sheets on lipid membranes as a result of monomer partitioning followed by cooperative assembly. This system provides a unique opportunity to study the thermodynamics of protein folding in membranes, which we have done using isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). The results, which may represent the first example of reversible thermal unfolding of peptides in membranes, help to define the contribution of hydrogen bonding to the extreme thermal stability of membrane proteins. ITC revealed that the enthalpy change for partitioning of monomeric, unstructured AcWL(5) from water into membranes was zero within experimental error over the temperature range of 5 degrees C to 75 degrees C. DSC showed that the beta-sheet aggregates underwent a reversible, endothermic, and very asymmetric thermal transition with a concentration-dependent transition temperature (T(m)) in the range of 60 degrees C to 80 degrees C. A numerical model of nucleation and growth-dependent assembly of oligomeric beta-sheets, proposed earlier to describe beta-sheet formation in membranes, recreated remarkably well the unusual shape and concentration-dependence of the transition peaks. The enthalpy for thermal unfolding of AcWL(5) beta-sheets in the membrane was found to be about 8(+/-1)kcal mol(-1), or about 1.3(+/-0.2)kcal mol(-1) per residue.
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Affiliation(s)
- William C Wimley
- Department of Biochemistry SL43, Tulane University Health Sciences Center, New Orleans, LA 70112-2699, USA.
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20
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Abstract
Although most antibiotics do not need metal ions for their biological activities, there are a number of antibiotics that require metal ions to function properly, such as bleomycin (BLM), streptonigrin (SN), and bacitracin. The coordinated metal ions in these antibiotics play an important role in maintaining proper structure and/or function of these antibiotics. Removal of the metal ions from these antibiotics can cause changes in structure and/or function of these antibiotics. Similar to the case of "metalloproteins," these antibiotics are dubbed "metalloantibiotics" which are the title subjects of this review. Metalloantibiotics can interact with several different kinds of biomolecules, including DNA, RNA, proteins, receptors, and lipids, rendering their unique and specific bioactivities. In addition to the microbial-originated metalloantibiotics, many metalloantibiotic derivatives and metal complexes of synthetic ligands also show antibacterial, antiviral, and anti-neoplastic activities which are also briefly discussed to provide a broad sense of the term "metalloantibiotics."
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Affiliation(s)
- Li-June Ming
- Department of Chemistry and Institute for Biomolecular Science, University of South Florida, Tampa, Florida 33620-5250, USA.
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Stroud RM, Nollert P, Miercke L. The glycerol facilitator GlpF its aquaporin family of channels, and their selectivity. ADVANCES IN PROTEIN CHEMISTRY 2003; 63:291-316. [PMID: 12629974 DOI: 10.1016/s0065-3233(03)63011-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Robert M Stroud
- Department of Biochemistry and Biophysics, School of Medicine, University of California, San Francisco, California 94143, USA
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Shobini J, Mishra AK, Chandra N. Conformation of gramicidin-A in CTAB micellar media. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY. B, BIOLOGY 2003; 70:117-24. [PMID: 12849702 DOI: 10.1016/s1011-1344(03)00055-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Gramicidin A (gA) is a linear pentadecapeptide, which exhibits various conformations depending on the environment. The conformational behavior of gA in spherical and rod-shaped cationic micelles formed by cetyltrimethylammonium bromide (CTAB) surfactant has been studied using circular dichroism (CD) and fluorescence spectroscopy, and a probable structure of gramicidin A in CTAB media has been proposed. A CD study shows that gramicidin A assumes beta(6.3) helical structure in cationic spherical as well as rod-shaped CTAB micellar media. Modeling studies show the flexibility of the side chain conformation particularly in tryptophan-9. Study of intrinsic fluorescence of tryptophans in gramicidin A indicates three distinct environments for the four-tryptophan residues in CTAB media.
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Affiliation(s)
- J Shobini
- Department of Chemistry, Indian Institute of Technology--Madras, Chennai 600 036, India
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23
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Duax WL, Pletnev V, Burkhart BM. Mechanism of ion transport and gating in gramicidin nanotubes. J Mol Struct 2003. [DOI: 10.1016/s0022-2860(02)00522-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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24
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Nollert P, Harries WE, Fu D, Miercke LJ, Stroud RM. Atomic structure of a glycerol channel and implications for substrate permeation in aqua(glycero)porins. FEBS Lett 2001; 504:112-7. [PMID: 11532442 DOI: 10.1016/s0014-5793(01)02710-7] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The structure of a glycerol channel from Escherichia coli at 2.2 A resolution serves as a basis for the understanding of selective transmembrane substrate permeation. In the course of permeation, glycerol molecules diffuse through a tripathic channel with their alkyl backbone wedged against a hydrophobic corner, such that OH groups become acceptors and donors of hydrogen bonds at the same time. The structure of the channel explains the preferential permeability for linear carbohydrates and absolute exclusion of ions and charged solutes. Its gene-duplicated sequence has a structural counterpart in a pseudo two-fold symmetry within the monomeric channel protein.
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Affiliation(s)
- P Nollert
- Department of Biochemistry and Biophysics, School of Medicine, University of California, San Francisco, CA94143-0448, USA
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25
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Mondal S, Ghosh S. Gramicidin A and its complexes with Cs+ and Tl+ ions in organic solvents. A study by steady state and time resolved emission spectroscopy. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY. B, BIOLOGY 2001; 60:12-24. [PMID: 11386676 DOI: 10.1016/s1011-1344(00)00138-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Gramicidin A (gr A), a linear pentadecapeptide containing four trp residues has been studied using steady state and time resolved fluorescence (at 298 K) and phosphorescence (at 77 K) in methanol (CH3OH), ethanol (C2H5OH), dimethyl sulfoxide (DMSO), 1,4-dioxane, 2-methyl tetrahydrofuran (2-MeTHF), ethanol/benzene (C2H5OH/C6H6) mixed solvent. Similar studies have also been carried out in CH3OH containing monovalent cations K+, Cs+, Tl+ and divalent cation Ca2+. Lambda(max) of fluorescence is found to be a good signature of the different forms having double helical structure [dh (1) to dh (4)] (J. Struct. Biol. 121 (1998) 123-141). Steady state and time resolved quenching studies of gr A by KI in CH3OH and DMSO and life time of the emitting singlet states of gr A support that gr A exists as a mixture of different forms of double helical (dh) structure [dh (1) to dh (4)] in CH3OH and as a random coil structure in DMSO. This study further indicates that emitting trp residue in DMSO is better shielded than that in CH3OH. Phosphorescence spectra of gr A at 77 K in CH3OH glass suggests that gr A retains a particular conformation dh (3) in this matrix. The phosphorescence spectra of gr A [conformation dh (4)] in 2-MeTHF at 77 K is further red shifted indicating that among all the dh forms, dh (4) has the emitting trp residue in most hydrophobic environment. The hydrophobicity of the emitting tryptophan environment is thus found to be in the order: dh (1)<dh (3)<dh (4). Since 2-MeTHF forms a clear glass at low temperature, it is thus possible to study the side chain arrangement of gr A dh (4) as a function of temperature. The phosphorescence spectra in different alcohol glassy matrix are in conformity with the observation of different side chain arrangement of gr A as one changes the polarity of alcohol. Steady state and time resolved quenching studies of gr A using Cs+ ion in CH3OH at 298 K clearly demonstrate the two binding sites for the metal ions and provide the value of equilibrium constant of the 'non-emitting' complex of gr A with Cs+ ion in the ground state. The observation of distinct red shift of the (0,0) band of the phosphorescence spectra of the complexes of gr A with K+, Cs+ and Tl+ ions at 77 K compared to that in CH3OH glass confirms the metal ion induced change of conformation in dh (3). The result also suggests that the emitting trp residues in the complexes are in somewhat more hydrophobic environment compared with that in the free gr A in CH3OH glass. The triplet state life time of these complexes indicate that the heavy metal ions Cs+ and Tl+ are within a Van der Waal's distance of emitting trp residue in gr A in CH3OH glass at 77 K so that they are capable of inducing increased spin-orbit coupling due to a heavy atom effect.
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Affiliation(s)
- S Mondal
- Department of Chemistry, Presidency College, Calcutta, India
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Greathouse DV, Koeppe RE, Providence LL, Shobana S, Andersen OS. Design and characterization of gramicidin channels. Methods Enzymol 2001; 294:525-50. [PMID: 9916247 DOI: 10.1016/s0076-6879(99)94031-4] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
This article summarizes methods for the chemical synthesis and biophysical characterization of gramicidins with varying sequences and labels. The family of gramicidin channels has developed into a powerful model system for understanding fundamental properties, interactions, and dynamics of proteins and lipids generally, and ion channels specifically, in biological membranes.
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Affiliation(s)
- D V Greathouse
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville 72701, USA
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27
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28
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Metzler DE, Metzler CM, Sauke DJ. Lipids, Membranes, and Cell Coats. Biochemistry 2001. [DOI: 10.1016/b978-012492543-4/50011-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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30
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Fu D, Libson A, Miercke LJ, Weitzman C, Nollert P, Krucinski J, Stroud RM. Structure of a glycerol-conducting channel and the basis for its selectivity. Science 2000; 290:481-6. [PMID: 11039922 DOI: 10.1126/science.290.5491.481] [Citation(s) in RCA: 814] [Impact Index Per Article: 33.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Membrane channel proteins of the aquaporin family are highly selective for permeation of specific small molecules, with absolute exclusion of ions and charged solutes and without dissipation of the electrochemical potential across the cell membrane. We report the crystal structure of the Escherichia coli glycerol facilitator (GlpF) with its primary permeant substrate glycerol at 2.2 angstrom resolution. Glycerol molecules line up in an amphipathic channel in single file. In the narrow selectivity filter of the channel the glycerol alkyl backbone is wedged against a hydrophobic corner, and successive hydroxyl groups form hydrogen bonds with a pair of acceptor, and donor atoms. Two conserved aspartic acid-proline-alanine motifs form a key interface between two gene-duplicated segments that each encode three-and-one-half membrane-spanning helices around the channel. This structure elucidates the mechanism of selective permeability for linear carbohydrates and suggests how ions and water are excluded.
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Affiliation(s)
- D Fu
- Department of Biochemistry and Biophysics, School of Medicine, University of California, San Francisco, CA 94143-0448, USA
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31
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Abstract
This review compares and contrasts the structures of several different types of ion channels with known three-dimensional structures, including gramicidin and the family of peptaibol channels, as well as the Streptomyces lividans potassium channel, to reveal common features in their structures that relate to their functional roles in ion binding and transport across membranes. Specifically, the locations of aromatic amino acids, the dimensions of the molecules, the multimeric nature of the channels and the roles of hydrogen bonds in stabilising such structures, the means by which the channels open and close, and the chemical nature of the groups which make up the channel lumen are discussed. The emphasis is on the commonality of features found in model channels, which may ultimately be found in other biological channel structures.
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Affiliation(s)
- B A Wallace
- Department of Crystallography, Birkbeck College, University of London, London WC1E 7HX, UK.
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32
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33
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Abstract
The linear pentadecapeptide antibiotic, gramicidin D, a heterogeneous mixture of six components, is a naturally occurring product of Bacillus brevis known to form ion channels in synthetic and natural membranes. The conformation of gramicidin A in the solid state, in organic solvents, and in planar lipid bilayers and the relationship between the composition and the conformation of gramicidin and its selective transport of ions across membranes has been the subject of intense investigation for over 50 years. The x-ray crystal structure and nmr solution spectroscopy agree fully with one another and reveal that entirely different conformations of gramicidin are present in uncomplexed and ion complexed forms. Precise refinements of the three-dimensional structures of naturally occurring gramicidin D in crystals obtained from methanol, ethanol, and n-propanol demonstrate the unexpected presence of stable left-handed antiparallel double-helical heterodimers that vary with the crystallization solvent. The side chains of Trp residues in the three structures exhibit sequence-specific patterns of conformational preference. Tyr substitution for Trp at position 11 appears to favor beta ribbon formation and stabilization of the antiparallel double helix. This conformation acts as a template for gramicidin folding and nucleation of the different crystal forms. The fact that a minor component in a heterogeneous mixture influences aggregation and crystal nucleation has potential applications to other systems in which anomalous behavior is exhibited by aggregation of apparently homogeneous materials, such as the enigmatic behavior of prion proteins. The crystallographically determined structures of cesium, potassium, rubidium, and hydronium ion complexes of gramicidin A are in excellent agreement with the nmr structure determination of the cesium ion gramicidin complex in a methanol chloroform mixture (50 : 50). The right-handed antiparallel double stranded double helical structures (DSDHR) also exhibit geometric features compatible with the solid-state 15N and 2H nmr data recorded for gramicidin in planar lipid bilayers and attributed to the active form of gramicidin A. The DSDHR crystal structures reveal an ion channel with a single partially solvated cation distributed over three ion binding sites. The channel lumen is relatively smooth and electrostatically negative as required for cation passage, while the exterior is electrostatically neutral, a requirement for membrane insertion. The "coordination" of the Cs+ ion is achieved by interaction with the pi orbitals of the carbonyls which do not point toward the ions. The K+ binding sites, which are similar in position to Cs+ binding sites, are shifted off center slightly toward the wall of the channel.
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Affiliation(s)
- B M Burkhart
- Hauptman-Woodward Medical Research Institute, Inc., 73 High Street, Buffalo, New York 14203-1196, USA
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34
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Kovacs F, Quine J, Cross TA. Validation of the single-stranded channel conformation of gramicidin A by solid-state NMR. Proc Natl Acad Sci U S A 1999; 96:7910-5. [PMID: 10393921 PMCID: PMC22161 DOI: 10.1073/pnas.96.14.7910] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The monovalent cation selective channel formed by a dimer of the polypeptide gramicidin A has a single-stranded, right-handed helical motif with 6.5 residues per turn forming a 4-A diameter pore. The structure has been refined to high resolution against 120 orientational constraints obtained from samples in a liquid-crystalline phase lipid bilayer. These structural constraints from solid-state NMR reflect the orientation of spin interaction tensors with respect to a unique molecular axis. Because these tensors are fixed in the molecular frame and because the samples are uniformly aligned with respect to the magnetic field of the NMR spectrometer, each constraint restricts the orientation of internuclear vectors with respect to the laboratory frame of reference. The structural motif of this channel has been validated, and the high-resolution structure has led to precise models for cation binding, cation selectivity, and cation conductance efficiency. The structure is consistent with the electrophysiological data and numerous biophysical studies. Contrary to a recent claim [Burkhart, B. M., Li, N., Langs, D. A., Pangborn, W. A. & Duax, W. L. (1998) Proc. Natl. Acad. Sci. USA 95, 12950-12955], the solid-state NMR constraints for gramicidin A in a lipid bilayer are not consistent with an x-ray crystallographic structure for gramicidin having a double-stranded, right-handed helix with 7.2 residues per turn.
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Affiliation(s)
- F Kovacs
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32306-4005, USA
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35
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Abstract
We have used molecular dynamics simulations, corresponding to a total simulation time of 11 ns, to investigate the effective short-time local diffusion coefficient of potassium and chloride ions in a series of model ion channels. These models, which include channels formed by the fungal peptide alamethicin, by a synthetic leucine-serine peptide, and by the pore-lining M2 helix bundle of the nicotinic acetylcholine receptor, have a range of different secondary structures, diameters and hydrophobicities. We find that the diffusion coefficients of both ions are appreciably reduced in the narrower channels, the extent of the reduction being similar for both the anionic and cationic species. This suggests that a difference in mobility cannot be the source of the ion selectivity exhibited by some of the channels (for example, the leucine-serine peptide). We find no evidence for a reduction in mobility of either ion in the nAChR model. These results are broadly in line with a previous similar study of Na+ ions, and may be useful in Poisson-Nernst-Planck, Eyring rate theory or Brownian dynamics calculations of channel conductance.
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Affiliation(s)
- G R Smith
- Department of Biochemistry, University of Oxford, UK.
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36
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Smith GR, Sansom MS. Dynamic properties of Na+ ions in models of ion channels: a molecular dynamics study. Biophys J 1998; 75:2767-82. [PMID: 9826599 PMCID: PMC1299950 DOI: 10.1016/s0006-3495(98)77720-3] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023] Open
Abstract
We present simulation results for the effective diffusion coefficients of a sodium ion in a series of model ion channels of different diameters and hydrophobicities, including models of alamethicin, a leucine-serine peptide, and the M2 helix bundle of the nicotinic acetylcholine receptor. The diffusion coefficient, which in the simulations has a value of 0.15(2) A2ps-1 in bulk water, is found to be reduced to as little as 0.02(1) A2ps-1 in the narrower channels, and to about 0.10(5) A2ps-1 in wider channels such as the nicotinic acetylcholine receptor. It is anticipated that this work will be useful in connection with calculations of channel conductivity using such techniques as the Poisson-Nernst-Planck equation, Eyring rate theory, or Brownian dynamics.
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Affiliation(s)
- G R Smith
- Laboratory of Molecular Biophysics, University of Oxford, Oxford OX1 3QU, United Kingdom
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37
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Abstract
Non-lamellar-forming lipids play an important role in determining the physical properties of membranes. They affect the activity of membrane proteins and peptides. In addition, peptides which lyse membranes as well as those which promote membrane fusion facilitate the formation of non-lamellar phases, either micelles, cubic or hexagonal phases. The relationship of these diverse effects on membrane curvature is discussed in relation to the function of certain peptides and proteins. Specific examples of ionophoric peptides, cytotoxic peptides and viral fusion peptides are given. In addition, we compare the modulation of the rate of photoisomerisation of an integral membrane protein, rhodopsin, by non-lamellar-forming lipids with the effects of these lipids on an amphitropic protein, protein kinase C. Among these diverse systems it is frequently observed that the modulation of biological activity can be described in terms of the effect of the peptide or protein on the relative stability of lamellar and non-lamellar structures.
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Affiliation(s)
- R M Epand
- Department of Biochemistry, McMaster University Health Sciences Centre, Hamilton, Ont. L8N 3Z5, Canada.
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Burkhart BM, Gassman RM, Langs DA, Pangborn WA, Duax WL. Heterodimer formation and crystal nucleation of gramicidin D. Biophys J 1998; 75:2135-46. [PMID: 9788907 PMCID: PMC1299886 DOI: 10.1016/s0006-3495(98)77656-8] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The linear pentadecapeptide antibiotic gramicidin D is a heterogeneous mixture of six components. Precise refinements of three-dimensional structures of naturally occurring gramicidin D in crystals obtained from methanol, ethanol, and n-propanol demonstrate the unexpected presence of stable left-handed antiparallel double-helical heterodimers that vary with the crystallization solvent. The side chains of Trp residues in the three structures exhibit sequence-specific patterns of conformational preference. Tyr substitution for Trp at position 11 appears to favor beta ribbon formation and stabilization of the antiparallel double helix that acts as a template for gramicidin folding and nucleation of different crystal forms. The fact that a minor component in a heterogeneous mixture influences aggregation and crystal nucleation has potential applications to other systems in which anomalous behavior is exhibited by aggregation of apparently homogeneous materials, such as the enigmatic behavior of prion proteins.
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Affiliation(s)
- B M Burkhart
- Hauptman-Woodward Medical Research Institute, Inc., Buffalo, New York 14203-1196, USA
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39
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Burkhart BM, Li N, Langs DA, Pangborn WA, Duax WL. The conducting form of gramicidin A is a right-handed double-stranded double helix. Proc Natl Acad Sci U S A 1998; 95:12950-5. [PMID: 9789021 PMCID: PMC23667 DOI: 10.1073/pnas.95.22.12950] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The linear pentadecapeptide antibiotic, gramicidin D, is a naturally occurring product of Bacillus brevis known to form ion channels in synthetic and natural membranes. The x-ray crystal structures of the right-handed double-stranded double-helical dimers (DSDH) reported here agree with 15N-NMR and CD data on the functional gramicidin D channel in lipid bilayers. These structures demonstrate single-file ion transfer through the channels. The results also indicate that previous crystal structure reports of a left-handed double-stranded double-helical dimer in complex with Cs+ and K+ salts may be in error and that our evidence points to the DSDH as the major conformer responsible for ion transport in membranes.
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Affiliation(s)
- B M Burkhart
- Hauptman-Woodward Medical Research Institute, Inc., 73 High Street, Buffalo, NY 14203, USA.
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40
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41
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Doyle DA, Wallace BA. Shifting the equilibrium mixture of gramicidin double helices toward a single conformation with multivalent cationic salts. Biophys J 1998; 75:635-40. [PMID: 9675165 PMCID: PMC1299738 DOI: 10.1016/s0006-3495(98)77553-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The conformation of the polypeptide antibiotic gramicidin is greatly influenced by its environment. In methanol, it exists as an equilibrium mixture of four interwound double-helical conformers that differ in their handedness, chain orientation, and alignment. Upon the addition of multivalent cationic salts, there is a shift in the equilibrium to a single conformer, which was monitored in this study by circular dichroism spectroscopy. With increasing concentrations of multivalent cations, both the magnitude of the entire spectrum and the ratio of the 229-nm to the 210-nm peak were increased. The spectral change is not related to the charge on the cation, but appears to be related to the cationic radius, with the maximum change in ellipticity occurring for cations with a radius of approximately 1 A. The effect requires the presence of an anion whose radius is greater than that of a fluoride ion, but is otherwise not a function of anion type. It is postulated that multivalent cations interact with a binding site in one of the conformers, known as species 1 (a left-handed, parallel, no stagger double helix), stabilizing a modified form of this type of structure.
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Affiliation(s)
- D A Doyle
- Department of Crystallography, Birkbeck College, University of London, London WC1E 7HX, England
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42
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Wallace BA. Recent Advances in the High Resolution Structures of Bacterial Channels: Gramicidin A. J Struct Biol 1998; 121:123-41. [PMID: 9618340 DOI: 10.1006/jsbi.1997.3948] [Citation(s) in RCA: 123] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Gramicidin is a polypeptide antibiotic which forms dimeric channels specific for the transport of monovalent cations across membranes. It adopts several different conformations, most notably double helical (pore) and helical dimer (channels) forms, which have very different structural and functional characteristics. This review focuses on recent high resolution structure determinations of both the pore and channel forms of the molecule by X-ray crystallographic and/or NMR spectroscopic techniques. It discusses the structural consequences of binding ions and the location of ion binding sites and how the structures are related to the conductance properties of the molecule. This relatively simple molecule is probably the best characterized ion channel (both structurally and functionally) and has, to date, been the principal proving-ground for many of our ideas about the molecular nature of ion conduction in membranes. Copyright 1998 Academic Press.
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Affiliation(s)
- BA Wallace
- Department of Crystallography, Birkbeck College, University of London, London, WC1E 7HX, United Kingdom
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Girshman J, Greathouse DV, Koeppe RE, Andersen OS. Gramicidin channels in phospholipid bilayers with unsaturated acyl chains. Biophys J 1997; 73:1310-9. [PMID: 9284299 PMCID: PMC1181031 DOI: 10.1016/s0006-3495(97)78164-5] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
In organic solvents gramicidin A (gA) occurs as a mixture of slowly interconverting double-stranded dimers. Membrane-spanning gA channels, in contrast, are almost exclusively single-stranded beta(6,3)-helical dimers. Based on spectroscopic evidence, it has previously been concluded that the conformational preference of gA in phospholipid bilayers varies as a function of the degree of unsaturation of the acyl chains. Double-stranded pi pi(5,6)-helical dimers predominate (over single-stranded beta(6,3)-helical dimers) in lipid bilayer membranes with polyunsaturated acyl chains. We therefore examined the characteristics of channels formed by gA in 1-palmitoyl-2-oleoylphosphatidylcholine/n-decane, 1,2-dioleoylphosphatidylcholine/n-decane, and 1,2-dilinoleoylphosphatidylcholine/n-decane bilayers. We did not observe long-lived channels that could be conducting double-stranded pi pi(5,6)-helical dimers in any of these different membrane environments. We conclude that the single-stranded beta(6,3)-helical dimer is the only conducting species in these bilayers. Somewhat surprisingly, the average channel duration and channel-forming potency of gA are increased in dilinoleoylphosphatidylcholine/n-decane bilayers compared to 1-palmitoyl-2-oleoylphosphatidylcholine/n-decane and dioleoylphosphatidylcholine/n-decane bilayers. To test for specific interactions between the aromatic side chains of gA and the acyl chains of the bilayer, we examined the properties of channels formed by gramicidin analogues in which the four tryptophan residues were replaced with naphthylalanine (gN), tyrosine (gT), and phenylalanine (gM). The results show that all of these analogue channels experience the same relative stabilization when going from dioleoylphosphatidylcholine to dilinoleoylphosphatidylcholine bilayers.
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Affiliation(s)
- J Girshman
- Department of Physiology and Biophysics, Cornell University Medical College, New York, New York 10021, USA
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