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Jayawant ES, Hutchinson J, Gašparíková D, Lockey C, Pruñonosa Lara L, Guy C, Brooks RL, Dixon AM. Molecular Basis of Selectivity and Activity for the Antimicrobial Peptide Lynronne-1 Informs Rational Design of Peptide with Improved Activity. Chembiochem 2021; 22:2430-2439. [PMID: 34028161 PMCID: PMC8362026 DOI: 10.1002/cbic.202100151] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 05/13/2021] [Indexed: 11/24/2022]
Abstract
Antibiotic resistance is a significant threat to human health, with natural products remaining the best source for new antimicrobial compounds. Antimicrobial peptides (AMPs) are natural products with great potential for clinical use as they are small, amenable to customization, and show broad-spectrum activities. Lynronne-1 is a promising AMP identified in the rumen microbiome that shows broad-spectrum activity against pathogens such as methicillin-resistant Staphylococcus aureus and Acinetobacter baumannii. Here we investigated the structure of Lynronne-1 using solution NMR spectroscopy and identified a 13-residue amphipathic helix containing all six cationic residues. We used biophysical approaches to observe folding, membrane partitioning and membrane lysis selective to the presence of anionic lipids. We translated our understanding of Lynronne-1 structure to design peptides which varied in the size of their hydrophobic helical face. These peptides displayed the predicted continuum of membrane-lysis activities in vitro and in vivo, and yielded a new AMP with 4-fold improved activity against A. baumannii and 32-fold improved activity against S. aureus.
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Affiliation(s)
- Eleanor S. Jayawant
- Department of ChemistryUniversity of WarwickGibbett Hill RoadCoventryCV4 7ALUK
| | - Jack Hutchinson
- Department of ChemistryUniversity of WarwickGibbett Hill RoadCoventryCV4 7ALUK
| | - Dorota Gašparíková
- Department of ChemistryUniversity of WarwickGibbett Hill RoadCoventryCV4 7ALUK
| | - Christine Lockey
- Department of ChemistryUniversity of WarwickGibbett Hill RoadCoventryCV4 7ALUK
| | | | - Ciaran Guy
- SynBio Doctoral Training CentreUniversity of WarwickGibbet Hill RoadCoventryCV4 7ALUK
| | - Rhiannon L. Brooks
- MAS Centre for Doctoral TrainingUniversity of WarwickGibbet Hill RoadCoventryCV4 7ALUK
| | - Ann M. Dixon
- Department of ChemistryUniversity of WarwickGibbett Hill RoadCoventryCV4 7ALUK
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2
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Effect of Benzheterazoles on the Micellar Behavior of Sodium Dodecylsulfate in Dimethylsulfoxide: A Conductometric and Spectroscopic Approach. J SURFACTANTS DETERG 2019. [DOI: 10.1002/jsde.12358] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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3
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Ross EE, Hoag B, Joslin I, Johnston T. Measurements of Ion Binding to Lipid-Hosted Ionophores by Affinity Chromatography. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:9410-9421. [PMID: 31282163 DOI: 10.1021/acs.langmuir.9b01301] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The binding affinity between antibiotic ionophores and alkali ions within supported lipid bilayers was evaluated using affinity chromatography. We used zonal elution and frontal analysis methods in nanovolume liquid chromatography to characterize the binding selectivity of the carrier and channel ionophores valinomycin and gramicidin A within different phosphatidylcholine bilayers. Distinct binding sensitivity to the lipid phase, both in affinity and selectivity, is observed for valinomycin, whereas gramicidin is less sensitive to changes in a membrane environment, behavior that is consistent with ion binding occurring within the interior of an established channel. There is good agreement between the chromatographic retention and the reported binding selectivity measured by other techniques. Surface potential near the binding site affects ion retention and the apparent association binding constants, but not the binding selectivity or enthalpy measurements. A model accounting for the surface potential contributions of retained ions during frontal analyses yields values close to intrinsic binding constants for gramicidin A (KA for K+ between 70 and 120 M-1) using reasonable estimates of the initial potential that is postulated to arise from the underlying silica.
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Affiliation(s)
- Eric E Ross
- Department of Chemistry & Biochemistry , Gonzaga University , Spokane , Washington 99258 , United States
| | - Bridget Hoag
- Department of Chemistry & Biochemistry , Gonzaga University , Spokane , Washington 99258 , United States
| | - Ian Joslin
- Department of Chemistry & Biochemistry , Gonzaga University , Spokane , Washington 99258 , United States
| | - Taylor Johnston
- Department of Chemistry & Biochemistry , Gonzaga University , Spokane , Washington 99258 , United States
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4
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McKay MJ, Afrose F, Koeppe RE, Greathouse DV. Helix formation and stability in membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:2108-2117. [PMID: 29447916 DOI: 10.1016/j.bbamem.2018.02.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 02/06/2018] [Accepted: 02/07/2018] [Indexed: 01/05/2023]
Abstract
In this article we review current understanding of basic principles for the folding of membrane proteins, focusing on the more abundant alpha-helical class. Membrane proteins, vital to many biological functions and implicated in numerous diseases, fold into their active conformations in the complex environment of the cell bilayer membrane. While many membrane proteins rely on the translocon and chaperone proteins to fold correctly, others can achieve their functional form in the absence of any translation apparatus or other aides. Nevertheless, the spontaneous folding process is not well understood at the molecular level. Recent findings suggest that helix fraying and loop formation may be important for overall structure, dynamics and regulation of function. Several types of membrane helices with ionizable amino acids change their topology with pH. Additionally we note that some peptides, including many that are rich in arginine, and a particular analogue of gramicidin, are able passively to translocate across cell membranes. The findings indicate that a final protein structure in a lipid-bilayer membrane is sequence-based, with lipids contributing to stability and regulation. While much progress has been made toward understanding the folding process for alpha-helical membrane proteins, it remains a work in progress. This article is part of a Special Issue entitled: Emergence of Complex Behavior in Biomembranes edited by Marjorie Longo.
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Affiliation(s)
- Matthew J McKay
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA
| | - Fahmida Afrose
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA
| | - Roger E Koeppe
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA
| | - Denise V Greathouse
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA.
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5
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Teng P, Ma N, Cerrato DC, She F, Odom T, Wang X, Ming LJ, van der Vaart A, Wojtas L, Xu H, Cai J. Right-Handed Helical Foldamers Consisting of De Novo d-AApeptides. J Am Chem Soc 2017; 139:7363-7369. [PMID: 28480699 PMCID: PMC5885761 DOI: 10.1021/jacs.7b03007] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
New types of foldamer scaffolds are formidably challenging to design and synthesize, yet highly desirable as structural mimics of peptides/proteins with a wide repertoire of functions. In particular, the development of peptidomimetic helical foldamers holds promise for new biomaterials, catalysts, and drug molecules. Unnatural l-sulfono-γ-AApeptides were recently developed and shown to have potential applications in both biomedical and material sciences. However, d-sulfono-γ-AApeptides, the enantiomers of l-sulfono-γ-AApeptides, have never been studied due to the lack of high-resolution three-dimensional structures to guide structure-based design. Herein, we report the first synthesis and X-ray crystal structures of a series of 2:1 l-amino acid/d-sulfono-γ-AApeptide hybrid foldamers, and elucidate their folded conformation at the atomic level. Single-crystal X-ray crystallography indicates that this class of oligomers folds into well-defined right-handed helices with unique helical parameters. The helical structures were consistent with data obtained from solution 2D NMR, CD studies, and molecular dynamics simulations. Our findings are expected to inspire the structure-based design of this type of unique folding biopolymers for biomaterials and biomedical applications.
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Affiliation(s)
- Peng Teng
- Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, United States
| | - Ning Ma
- Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, United States
| | - Darrell Cole Cerrato
- Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, United States
| | - Fengyu She
- Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, United States
| | - Timothy Odom
- Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, United States
| | - Xiang Wang
- College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan 410083, China
| | - Li-June Ming
- Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, United States
| | - Arjan van der Vaart
- Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, United States
| | - Lukasz Wojtas
- Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, United States
| | - Hai Xu
- College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan 410083, China
| | - Jianfeng Cai
- Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, United States
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Sarkar P, Chattopadhyay A. Micellar dipole potential is sensitive to sphere-to-rod transition. Chem Phys Lipids 2015; 195:34-8. [PMID: 26616562 DOI: 10.1016/j.chemphyslip.2015.11.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2015] [Revised: 11/16/2015] [Accepted: 11/17/2015] [Indexed: 12/31/2022]
Abstract
Structural transitions involving shape changes play an important role in cellular physiology. Charged micelles offer a convenient model system in which structural transitions can be suitably induced by increasing the ionic strength of the medium. In this paper, we have explored sphere-to-rod transition in charged micelles of SDS and CTAB by monitoring micellar dipole potential using the dual wavelength ratiometric approach utilizing the potential-sensitive membrane probe di-8-ANEPPS. Our results show that micellar dipole potential is sensitive to sphere-to-rod transition in charged micelles. Micellar dipole potential exhibited increase with increasing ionic strength (salt), irrespective of the nature of micellar charge, implying considerable dipolar reorganization underlying structural transitions. We interpret the increase in dipole potential due to sphere-to-rod transition because of an increase in the population of confined (nonrandom) dipoles induced by micellar organizational change. This is due to the fact that dipole potential arises due to the nonrandom arrangement of micellar dipoles and water molecules at the micelle interface. Our results constitute one of the first reports describing drastic dipolar reorganization due to micellar shape (and size) change. We envision that dipole potential measurements could provide novel insights into micellar processes that are associated with dipolar reorganization.
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Affiliation(s)
- Parijat Sarkar
- CSIR-Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
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7
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Dipolar rearrangement during micellization explored using a potential-sensitive fluorescent probe. Chem Phys Lipids 2015; 191:91-5. [PMID: 26327331 DOI: 10.1016/j.chemphyslip.2015.08.016] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2015] [Revised: 08/22/2015] [Accepted: 08/24/2015] [Indexed: 02/07/2023]
Abstract
Dipole potential is the potential difference within the membrane bilayer, which originates due to the nonrandom arrangement of lipid dipoles and water molecules at the membrane interface. Although dipole potential is generally used in the context of bilayer membranes, the nonrandom arrangement of amphiphiles and water dipoles would also contribute to dipole potential in organized molecular assemblies such as micelles. In this work, we show that the process of micelle formation from monomers for a representative variety of detergents is associated with dipolar rearrangement. We monitor the dipolar reorganization upon micellization as a change in dipole potential, measured by the dual wavelength ratiometric approach utilizing the potential-sensitive membrane probe di-8-ANEPPS. We further utilized this phenomenon to estimate the critical micelle concentration (CMC) of a variety of detergents. CMC determined by this method are in overall agreement with the literature values of CMC for these detergents. To the best of our knowledge, these results constitute the first report showing dipolar reorientation during micellization. We conclude that dipole potential measurements could provide a novel approach to explore micellar organization.
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8
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Chen L, Chen SH, Russell DH. An experimental study of the solvent-dependent self-assembly/disassembly and conformer preferences of gramicidin A. Anal Chem 2013; 85:7826-33. [PMID: 23855712 DOI: 10.1021/ac401370t] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The solvent dependence of self-assembly/disassembly kinetics and conformer preferences of the gramicidin A (GA) dimer is investigated using a combination of techniques, viz., electrospray ionization-ion mobility-mass spectrometry (IM-MS), collision-induced dissociation (CID), and hydrogen/deuterium exchange (HDX)-MS. IM-MS measurements reveal that there are possibly three distinct GA dimeric species, detected as sodium ion adduct ions [2GA + 2Na](2+), and these are assigned as the parallel β-helix, antiparallel β-helix, and head-to-head dimer. The monomerization kinetics and equilibrium abundances of the dimer ions depend upon solvent polarity. The antiparallel β-helix was the thermodynamically preferred species in less polar solvents. HDX measurements and collision-induced dissociation (CID) of the intermediate complex confirm the well-protected dimer geometry with strong intermolecular hydrogen bonds. This combined IM-HDX-CID methodology provides a comprehensive view of GA self-assembly/disassembly in low dielectric solutions, showing its potential utility in solving solution-phase protein self-assembly/disassembly kinetics and providing structural information of the multimers at the same time.
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Affiliation(s)
- Liuxi Chen
- Laboratory for Biological Mass Spectrometry, Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
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9
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Chaudhuri A, Haldar S, Chattopadhyay A. Structural transition in micelles: novel insight into microenvironmental changes in polarity and dynamics. Chem Phys Lipids 2012; 165:497-504. [DOI: 10.1016/j.chemphyslip.2011.09.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Revised: 09/15/2011] [Accepted: 09/16/2011] [Indexed: 01/23/2023]
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10
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Chaudhuri A, Haldar S, Chattopadhyay A. Organization and dynamics in micellar structural transition monitored by pyrene fluorescence. Biochem Biophys Res Commun 2009; 390:728-32. [DOI: 10.1016/j.bbrc.2009.10.037] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2009] [Accepted: 10/08/2009] [Indexed: 11/28/2022]
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11
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Sun H, Greathouse DV, Andersen OS, Koeppe RE. The preference of tryptophan for membrane interfaces: insights from N-methylation of tryptophans in gramicidin channels. J Biol Chem 2008; 283:22233-43. [PMID: 18550546 PMCID: PMC2494914 DOI: 10.1074/jbc.m802074200] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2008] [Revised: 06/03/2008] [Indexed: 11/06/2022] Open
Abstract
To better understand the structural and functional roles of tryptophan at the membrane/water interface in membrane proteins, we examined the structural and functional consequences of Trp --> 1-methyl-tryptophan substitutions in membrane-spanning gramicidin A channels. Gramicidin A channels are miniproteins that are anchored to the interface by four Trps near the C terminus of each subunit in a membrane-spanning dimer. We masked the hydrogen bonding ability of individual or multiple Trps by 1-methylation of the indole ring and examined the structural and functional changes using circular dichroism spectroscopy, size exclusion chromatography, solid state (2)H NMR spectroscopy, and single channel analysis. N-Methylation causes distinct changes in the subunit conformational preference, channel-forming propensity, single channel conductance and lifetime, and average indole ring orientations within the membrane-spanning channels. The extent of the local ring dynamic wobble does not increase, and may decrease slightly, when the indole NH is replaced by the non-hydrogen-bonding and more bulky and hydrophobic N-CH(3) group. The changes in conformational preference, which are associated with a shift in the distribution of the aromatic residues across the bilayer, are similar to those observed previously with Trp --> Phe substitutions. We conclude that indole N-H hydrogen bonding is of major importance for the folding of gramicidin channels. The changes in ion permeability, however, are quite different for Trp --> Phe and Trp --> 1-methyl-tryptophan substitutions, indicating that the indole dipole moment and perhaps also ring size and are important for ion permeation through these channels.
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Affiliation(s)
- Haiyan Sun
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, USA
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12
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Liu Z, Xu Y, Tang P. Steered Molecular Dynamics Simulations of Na+ Permeation across the Gramicidin A Channel. J Phys Chem B 2006; 110:12789-95. [PMID: 16800614 DOI: 10.1021/jp060688n] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The potential of mean forces (PMF) governing Na+ permeation through gramicidin A (gA) channels with explicit water and membrane was characterized using steered molecular dynamics (SMD) simulations. Constant-force SMD with a steering force parallel to the channel axis revealed at least seven energy wells in each monomer of the channel dimer. Except at the channel dimer interface, each energy well is associated with at least three and at most four backbone carbonyl oxygens and two water oxygens in a pseudo-hexahedral or pseudo-octahedral coordination with the Na+ ion. Repeated constant-velocity SMD by dragging a Na+ ion from each energy well in opposite directions parallel to the channel axis allowed the computation of the PMF across the gA channel, revealing a global minimum corresponding to Na+ binding sites near the entrance of gA at +/-9.3 A from the geometric center of the channel. The effect of volatile anesthetics on the PMF was also analyzed in the presence of halothane molecules. Although the accuracy of the current PMF calculation from SMD simulations is not yet sufficient to quantify the PMF difference with and without anesthetics, the comparison of the overall PMF profiles nevertheless confirms that the anesthetics cause insignificant changes to the structural makeup of the free energy wells along the channel and the overall permeation barrier. On average, the PMF appears less rugged in the outer part of the channel in the presence of anesthetics, consistent with our earlier finding that halothane interaction with anchoring residues makes the gA channel more dynamic. A causal relationship was observed between the reorientation of the coordinating backbone carbonyl oxygen and Na+ transit from one energy well to another, suggesting the possibility that even minute changes in the conformation of pore-lining residues due to dynamic motion could be sufficient to trigger the ion permeation. Because some of the carbonyl oxygens contribute to Na+ coordination in two adjacent energy wells, our SMD results reveal that the atomic picture of ion "hopping" through a gA channel actually involves a Na+ ion being carried in a relay by the coordinating oxygens from one energy well to the next. Steered molecular dynamics complements other computational approaches as an attractive means for the atomistic interpretation of experimental permeation studies.
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Affiliation(s)
- Zhanwu Liu
- Department of Anesthesiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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13
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Rawat SS, Kelkar DA, Chattopadhyay A. Effect of structural transition of the host assembly on dynamics of an ion channel peptide: a fluorescence approach. Biophys J 2005; 89:3049-58. [PMID: 16100280 PMCID: PMC1366802 DOI: 10.1529/biophysj.105.060798] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Structural transition can be induced in charged micelles by increasing the ionic strength of the medium. We have monitored the organization and dynamics of the functionally important tryptophan residues of gramicidin in spherical and rod-shaped sodium dodecyl sulfate micelles utilizing a combination of wavelength-selective fluorescence and related fluorescence approaches. Our results show that tryptophans in gramicidin, present in the single-stranded beta(6.3) conformation, experience slow solvent relaxation giving rise to red edge excitation shift in spherical and rod-shaped micelles. In addition, changes in fluorescence polarization with increasing excitation or emission wavelength reinforce that the gramicidin tryptophans are localized in motionally restricted regions of these micelles. Fluorescence quenching experiments using acrylamide as a quencher of tryptophan fluorescence show that there is reduced water penetration in rod-shaped micelles. Taken together, we show that gramicidin conformation and dynamics is sensitive to the salt-induced structural transition in charged micelles. In addition, these results demonstrate that deformation of the host assembly could modulate protein conformation and dynamics.
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Affiliation(s)
- Satinder S Rawat
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
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14
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Abstract
Gramicidin channels are mini-proteins composed of two tryptophan-rich subunits. The conducting channels are formed by the transbilayer dimerization of nonconducting subunits, which are tied to the bilayer/solution interface through hydrogen bonds between the indole NH groups and the phospholipid backbone and water. The channel structure is known at atomic resolution and the channel's permeability characteristics are particularly well defined: gramicidin channels are selective for monovalent cations, with no measurable permeability to anions or polyvalent cations; ions and water move through a pore whose wall is formed by the peptide backbone; and the single-channel conductance and cation selectivity vary when the amino acid sequence is varied, even though the permeating ions make no contact with the amino acid side chains. Given the amount of experimental information that is available--for both the wild-type channels and for channels formed by amino acid-substituted gramicidin analogues--gramicidin channels provide important insights into the microphysics of ion permeation through bilayer-spanning channels. For the same reason, gramicidin channels constitute the system of choice for evaluating computational strategies for obtaining mechanistic insights into ion permeation through the complex channels formed by integral membrane proteins.
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Affiliation(s)
- Olaf S Andersen
- Weill Medical College of Cornell University, New York, NY 10021, USA.
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15
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Jordan JB, Easton PL, Hinton JF. Effects of phenylalanine substitutions in gramicidin A on the kinetics of channel formation in vesicles and channel structure in SDS micelles. Biophys J 2004; 88:224-34. [PMID: 15501932 PMCID: PMC1305000 DOI: 10.1529/biophysj.104.047456] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The common occurrence of Trp residues at the aqueous-lipid interface region of transmembrane channels is thought to be indicative of its importance for insertion and stabilization of the channel in membranes. To further investigate the effects of Trp-->Phe substitution on the structure and function of the gramicidin channel, four analogs of gramicidin A have been synthesized in which the tryptophan residues at positions 9, 11, 13, and 15 are sequentially replaced with phenylalanine. The three-dimensional structure of each viable analog has been determined using a combination of two-dimensional NMR techniques and distance geometry-simulated annealing structure calculations. These phenylalanine analogs adopt a homodimer motif, consisting of two beta6.3 helices joined by six hydrogen bonds at their NH2-termini. The replacement of the tryptophan residues does not have a significant effect on the backbone structure of the channels when compared to native gramicidin A, and only small effects are seen on side-chain conformations. Single-channel conductance measurements have shown that the conductance and lifetime of the channels are significantly affected by the replacement of the tryptophan residues (Wallace, 2000; Becker et al., 1991). The variation in conductance appears to be caused by the sequential removal of a tryptophan dipole, thereby removing the ion-dipole interaction at the channel entrance and at the ion binding site. Channel lifetime variations appear to be related to changing side chain-lipid interactions. This is supported by data relating to transport and incorporation kinetics.
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Affiliation(s)
- J B Jordan
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, USA
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16
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Sobko AA, Vigasina MA, Rokitskaya TI, Kotova EA, Zakharov SD, Cramer WA, Antonenko YN. Chemical and Photochemical Modification of Colicin E1 and Gramicidin A in Bilayer Lipid Membranes. J Membr Biol 2004; 199:51-62. [PMID: 15366423 DOI: 10.1007/s00232-004-0674-y] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Chemical modification and photodynamic treatment of the colicin E1 channel-forming domain (P178) in vesicular and planar bilayer lipid membranes (BLMs) was used to elucidate the role of tryptophan residues in colicin E1 channel activity. Modification of colicin tryptophan residues by N-bromosuccinimide (NBS), as judged by the loss of tryptophan fluorescence, resulted in complete suppression of wild-type P178 channel activity in BLMs formed from fully saturated (diphytanoyl) phospholipids, both at the macroscopic-current and single-channel levels. The similar effect on both the tryptophan fluorescence and the electric current across BLM was observed also after NBS treatment of gramicidin channels. Of the single-tryptophan P178 mutants studied, W460 showed the highest sensitivity to NBS treatment, pointing to the importance of the water-exposed Trp460 in colicin channel activity. In line with previous work, the photodynamic treatment (illumination with visible light in the presence of a photosensitizer) led to suppression of P178 channel activity in diphytanoyl-phospholipid membranes concomitant with the damage to tryptophan residues detected here by a decrease in tryptophan fluorescence. The present work revealed novel effects: activation of P178 channels as a result of both NBS and photodynamic treatments was observed with BLMs formed from unsaturated (dioleoyl) phospholipids. These phenomena are ascribed to the effect of oxidative modification of double-bond-containing lipids on P178 channel formation. The pronounced stimulation of the colicin-mediated ionic current observed after both pretreatment with NBS and sensitized photomodification of the BLMs support the idea that distortion of membrane structure can facilitate channel formation.
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Affiliation(s)
- A A Sobko
- A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119992, Russia
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17
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Raghuraman H, Chattopadhyay A. Effect of micellar charge on the conformation and dynamics of melittin. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2004; 33:611-22. [PMID: 15071759 DOI: 10.1007/s00249-004-0402-7] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/24/2003] [Revised: 02/12/2004] [Accepted: 03/08/2004] [Indexed: 10/26/2022]
Abstract
Electrostatic interactions play a crucial role in modulating and stabilizing molecular interactions in membranes and membrane-mimetic systems such as micelles. We have monitored the change in the conformation and dynamics of the cationic hemolytic peptide melittin bound to micelles of various charge types, utilizing fluorescence and circular dichroism (CD) spectroscopy. The sole tryptophan of melittin displays a red-edge excitation shift (REES) of 3-6 nm when bound to anionic, nonionic, and zwitterionic micelles. This suggests that melittin is localized in a restricted environment, probably in the interfacial region of the micelles, and this region offers considerable restriction to the reorientational motion of the solvent dipoles around the excited state tryptophan in melittin. Further, the rotational mobility of melittin is considerably reduced in these micelles and is found to be dependent on the surface charge of micelles. Interestingly, our results show that melittin does not partition into cetyltrimethylammonium bromide (CTAB) micelles owing to electrostatic repulsion between melittin and CTAB micelles, both of which carry a positive charge. In addition, the fluorescence lifetime of melittin is modulated in micelles of different charge types. The lowest mean fluorescence lifetime is observed in the case of melittin bound to anionic sodium dodecyl sulfate (SDS) micelles. CD spectroscopy shows that micelles induce significant helicity to melittin, with maximum helicity being induced in the case of melittin bound to SDS micelles. Fluorescence quenching measurements using the neutral aqueous quencher acrylamide show differential accessibility of melittin in various types of micelles. Taken together, our results show that micellar surface charge can modulate the conformation and dynamics of melittin. These results could be relevant to understanding the role of the surface charge of membranes in the interaction of membrane-active, amphiphilic peptides with membranes.
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Affiliation(s)
- H Raghuraman
- Centre for Cellular and Molecular Biology, Uppal Road, 500 007 Hyderabad, India
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