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Lycklama A Nijeholt JA, Wu ZC, Driessen AJM. Conformational dynamics of the plug domain of the SecYEG protein-conducting channel. J Biol Chem 2011; 286:43881-43890. [PMID: 22033919 PMCID: PMC3243504 DOI: 10.1074/jbc.m111.297507] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Revised: 10/20/2011] [Indexed: 11/06/2022] Open
Abstract
The central pore of the SecYEG preprotein-conducting channel is closed at the periplasmic face of the membrane by a plug domain. To study its conformational dynamics, the plug was labeled site-specifically with an environment-sensitive fluorophore. In the presence of a stable preprotein translocation inter-mediate, the SecY plug showed an enhanced solvent exposure consistent with a displacement from the hydrophobic central pore region. In contrast, binding and insertion of a ribosome-bound nascent membrane protein did not alter the plug conformation. These data indicate different plug dynamics depending on the ligand bound state of the SecYEG channel.
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Affiliation(s)
- Jelger A Lycklama A Nijeholt
- Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology institute, and the Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Zht Cheng Wu
- Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology institute, and the Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Arnold J M Driessen
- Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology institute, and the Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands.
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2
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Pillman HA, Blanchard GJ. Effects of Energy Dissipation on Motional Dynamics in Unilamellar Vesicles. J Phys Chem B 2010; 114:13703-9. [DOI: 10.1021/jp1045723] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Heather A. Pillman
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824-1322, United States
| | - G. J. Blanchard
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824-1322, United States
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3
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Wang Y, Clark TB, Goodson T. Two-photon and time-resolved fluorescence conformational studies of aggregation in amyloid peptides. J Phys Chem B 2010; 114:7112-20. [PMID: 20429591 DOI: 10.1021/jp101496y] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The conformational changes associated with the aggregation of proteins are critical to the understanding of fundamental molecular events involved in early processes of neurodegenerative diseases. A detailed investigation of these processes requires the development of new approaches that allow for sensitive measurements of protein interactions. In this paper, we applied two-photon spectroscopy coupled with time-resolved fluorescence measurements to analyze amyloid peptide interactions through aggregation-dependent concentration effects. Labeled amyloid-beta peptide (TAMRA-Abeta1-42) was used in our investigation, and measurements of two-photon-excited fluorescence of the free and covalently conjugated peptide structure were carried out. The peptide secondary structure was correlated with a short fluorescence lifetime component, and this was associated with intramolecular interactions. Comparison of the fractional occupancy of the fluorescence lifetime measured at different excitation modes demonstrates the high sensitivity of the two-photon method in comparison to one-photon excitation (OPE). These results give strong justification for the development of fluorescence-lifetime-based multiphoton imaging and assays.
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Affiliation(s)
- Ying Wang
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA
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4
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Oberts BP, Blanchard GJ. Strategies for the growth of self-assembled phospholipid adlayers. Bioelectrochemistry 2010; 80:10-6. [PMID: 20452837 DOI: 10.1016/j.bioelechem.2010.03.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2010] [Revised: 03/22/2010] [Accepted: 03/23/2010] [Indexed: 11/25/2022]
Abstract
The creation of robust phospholipid adlayers is an important step in the development of biomimetic systems that contain and utilize trans-membrane proteins. The present methods for the creation of lipid bilayer structures, either by vesicle fusion or Langmuir-Blodgett/Langmuir-Schaefer deposition, produce lipid bilayer structures that are not bound strongly to the support on which they are deposited. While fluidity is an important property of lipid adlayer structures, the ability to form physically robust adlayers requires that some interaction more energetically favorable than physisorption be used to bind lipid adlayers. We have developed a means to bind lipid adlayers to interfaces through their phospholipid headgroups, utilizing metal ion complexation, with the strength of interaction and resulting quality of the monolayer being dependent on the identity of both the phospholipid and the metal ion used.
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Affiliation(s)
- B P Oberts
- Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
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5
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Hay CE, Marken F, Blanchard GJ. Solvent-Dependent Changes in Molecular Reorientation Dynamics: The Role of Solvent−Solvent Interactions. J Phys Chem A 2010; 114:4957-62. [DOI: 10.1021/jp912217r] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Christine E. Hay
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824, and University of Bath, Department of Chemistry, Claverton Down, Bath BA2 7AY, United Kingdom
| | - Frank Marken
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824, and University of Bath, Department of Chemistry, Claverton Down, Bath BA2 7AY, United Kingdom
| | - G. J. Blanchard
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824, and University of Bath, Department of Chemistry, Claverton Down, Bath BA2 7AY, United Kingdom
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6
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Oberts BP, Blanchard GJ. Headgroup-dependent lipid self-assembly on zirconium phosphate-terminated interfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:13918-13925. [PMID: 19459589 DOI: 10.1021/la900507w] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We report on the self-assembly of selected phospholipids on a Zr phosphate-terminated thiol self-assembled monolayer (SAM) formed on a planar Au surface. The gold substrates were first reacted with 6-mercapto-1-hexanol and then treated with POCl(3) and ZrOCl(2)(aq) prior to exposure to phospholipids. The phospholipids used for adlayer formation were 1,2-dimyristoyl-sn-glycero-3-phosphatidic acid (DMPA), 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC), 1,2-dimyristoyl-sn-glycero-3-phosphatidylethanolamine (DMPE), 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DMPG), and 1,2-dimyristoyl-sn-glycero-3-[phospho-L-serine] (DMPS), and deposition was accomplished through vesicle fusion. The resulting interfaces were characterized using optical ellipsometry and water contact angle measurements, and cyclic voltammetry was used to interrogate the quality of the phospholipid adlayers. Our data indicate that the strongest lipid-interface interaction is with DMPA, whereas DMPC produces a slightly less organized adlayer. Phospholipids DMPE, DMPG, and DMPS were all found to interact relatively weakly with the zirconated interface, and we understand these results in the context of steric and hydrogen bonding effects in the adlayer that are dominated by the phospholipid headgroup.
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Affiliation(s)
- B P Oberts
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824-1322, USA
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7
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Oberts BP, Blanchard GJ. Ionic binding of phospholipids to interfaces: dependence on metal ion identity. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:13025-13033. [PMID: 19572493 DOI: 10.1021/la901922m] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We report on the deposition of 1,2-dimyristoyl-sn-glycero-3-phosphatidic acid (DMPA) on selected metal-phosphate-terminated self-assembled monolayers (SAMs) constructed on Au. The phosphate-terminated SAMs were reacted with Zr(4+), Cu(+), Cu(2+), Fe(3+), Zn(2+), Ni(2+), Ca(2+), and Mg(2+), with subsequent exposure of the resulting interface to DMPA unilamellar vesicles. The resulting interface was characterized using X-ray photoelectron spectroscopy (XPS), optical ellipsometry, water contact angle measurements, and cyclic voltammetry (CV). The strongest lipid-metal ion interfacial interactions are with Zr(4+) and Fe(3+), with Ca(2+), Cu(+), Ni(2+), Zn(2+), and Mg(2+) producing somewhat less well organized adlayers. Cu(2+) did not bind strongly to the interfacial phosphate moiety, yielding a lipid bilayer structure. These results can be understood in the context of the strength of the metal bisphosphate complex that forms between the phospholipid and the chemically modified interface.
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Affiliation(s)
- B P Oberts
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824-1322, USA
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Oberts BP, Blanchard GJ. Formation of air-stable supported lipid monolayers and bilayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:2962-2970. [PMID: 19437768 DOI: 10.1021/la803486g] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We have devised a means of depositing planar, air-stable supported lipid adlayers on modified Au substrates. Using the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), we form planar supported adlayer structures by vesicle fusion. Lipid bilayer formation proceeds on a hydroxythiol-terminated Au surface. Phospholipid monolayers form on hydroxythiol-terminated gold surfaces that have been treated with POCl3 and ZrOCl2(aq) prior to lipid deposition, providing an interface that interacts strongly with the DMPC phosphocholine headgroup. We use FTIR, cyclic voltammetry, optical ellipsometry, and water contact angle measurements to confirm the presence of lipid bilayers or monolayers on the modified Au substrates. For the zirconated surface, we observe the conversion of an initial partial lipid bilayer to a lipid monolayer, over a ca. 20 min time period, on the basis on ellipsometric thickness and contact angle data. 31P NMR measurements show the complexation of the phospholipid headgroup to a Zr-phosphate surface.
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Affiliation(s)
- B P Oberts
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824-1322, USA
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Greenough KP, Blanchard GJ. Lipid headgroups mediate organization and dynamics in bilayers. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2009; 71:2050-2056. [PMID: 18805049 DOI: 10.1016/j.saa.2008.08.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2008] [Revised: 08/02/2008] [Accepted: 08/04/2008] [Indexed: 05/26/2023]
Abstract
We report on the fluorescence lifetime and anisotropy decay dynamics of the tethered chromophore NBD in unilamellar vesicles comprised of phosphoglycerol and phosphocholine lipids with C(12) and C(18) saturated acyl chains, with or without cholesterol and/or sphingomyelin. For the phosphocholine vesicles, we use the chromophore 2-(12-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)dodecanoyl-1-hexadecanoyl-sn-glycero-3-phosphocholine (NBD-PC), and for the phosphoglycerol vesicles, we use the chromophore 2-(12-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)dodecanoyl-1-hexadecanoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (NBD-PG). The addition of cholesterol and/or sphingomyelin to the PC vesicles restricts the chromophore environment, in agreement with the known rigidizing effect of cholesterol on PC membranes. The PG systems do not exhibit an analogous effect with the addition of cholesterol and/or sphingomyelin. The motional freedom of the NBD chromophore is, in general, more restricted in the PC bilayers than it is in the PG bilayers, and we understand this behavior in the context of the role of the lipid headgroups in mediating bilayer organization.
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Affiliation(s)
- Kelly P Greenough
- Michigan State University, Department of Chemistry, East Lansing, MI 48824, United States
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Greenough KP, Blanchard GJ. Evaluating the role of chromophore side group identity in mediating solution-phase rotational motion. J Phys Chem A 2007; 111:558-66. [PMID: 17249743 DOI: 10.1021/jp065423n] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We report on the rotational diffusion dynamics of the chromophore 7-nitrobenz-2-oxa-1,3-diazole (NBD) in a series of protic and polar aprotic solvents, as a function of the identity of the side group appended to the chromophore amine functionality. The central issue we address is whether or not the side groups play a role in mediating the anisotropic reorientation dynamics of the chromophore. To understand the motional properties of the chromophores in detail, we use both one-photon and two-photon excited fluorescence anisotropy decay measurements, and from these complementary excitation methods, we extract two of the Cartesian components of the rotational diffusion constant, D. The experimental data indicate that, regardless of the functionality of the pendant side group, the reorienting moieties exhibit ratios of Dz/Dx in the range 1.8-2.0. There is a small but discernible difference between the substituted chromophores. For all of the substituted NBD chromophores, dielectric friction plays a discernible role in determining their reorientation dynamics.
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Affiliation(s)
- Kelly P Greenough
- Michigan State University, Department of Chemistry, East Lansing, Michigan 48824-1322, USA
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Kastantin M, Ananthanarayanan B, Lin B, Ressl J, Black M, Tirrell M. Increase of Fluorescence Anisotropy Upon Self-Assembly in Headgroup-Labeled Surfactants. Macromol Biosci 2007; 7:189-94. [PMID: 17295406 DOI: 10.1002/mabi.200600203] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The change in fluorescence anisotropy upon micellization in headgroup-labeled surfactants is investigated. After eliminating the likelihood of depolarizing RET, anisotropy is shown to increase upon self-assembly due to increased rotational correlation times of the fluorophore. This is shown using two surfactant-fluorophore systems. Anisotropy in NBD-labeled phospholipids is studied both in chloroform (unaggregated) and in water (unilamellar vesicles), while in tryptophan-containing peptide-amphiphiles, the variation of anisotropy with concentration leads to a reasonable measurement of CAC. Anisotropy increase is shown to be largely the product of increased rotational correlation times for the fluorophore, relative to its tau. These results serve as a basis for future work that measures the amount of depolarizing energy transfer, characterizing distances between similar fluorescent headgroups on mixed micelles.
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Affiliation(s)
- Mark Kastantin
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA.
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