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Filipe HAL, Moreno MJ, Loura LMS. The Secret Lives of Fluorescent Membrane Probes as Revealed by Molecular Dynamics Simulations. Molecules 2020; 25:E3424. [PMID: 32731549 PMCID: PMC7435664 DOI: 10.3390/molecules25153424] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Revised: 07/23/2020] [Accepted: 07/25/2020] [Indexed: 12/15/2022] Open
Abstract
Fluorescent probes have been employed for more than half a century to study the structure and dynamics of model and biological membranes, using spectroscopic and/or microscopic experimental approaches. While their utilization has led to tremendous progress in our knowledge of membrane biophysics and physiology, in some respects the behavior of bilayer-inserted membrane probes has long remained inscrutable. The location, orientation and interaction of fluorophores with lipid and/or water molecules are often not well known, and they are crucial for understanding what the probe is actually reporting. Moreover, because the probe is an extraneous inclusion, it may perturb the properties of the host membrane system, altering the very properties it is supposed to measure. For these reasons, the need for independent methodologies to assess the behavior of bilayer-inserted fluorescence probes has been recognized for a long time. Because of recent improvements in computational tools, molecular dynamics (MD) simulations have become a popular means of obtaining this important information. The present review addresses MD studies of all major classes of fluorescent membrane probes, focusing in the period between 2011 and 2020, during which such work has undergone a dramatic surge in both the number of studies and the variety of probes and properties accessed.
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Affiliation(s)
- Hugo A. L. Filipe
- Chemistry Department, Coimbra Chemistry Center, Faculty of Sciences and Technology, University of Coimbra, 3004-535 Coimbra, Portugal;
| | - Maria João Moreno
- Coimbra Chemistry Center and CNC—Center for Neuroscience and Cell Biology, Chemistry Department, Faculty of Sciences and Technology, University of Coimbra, 3004-535 Coimbra, Portugal;
| | - Luís M. S. Loura
- Coimbra Chemistry Center and CNC—Center for Neuroscience and Cell Biology, Faculty of Pharmacy, University of Coimbra, 3000-548 Coimbra, Portugal
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2
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Filipe HAL, Pokorná Š, Hof M, Amaro M, Loura LMS. Orientation of nitro-group governs the fluorescence lifetime of nitrobenzoxadiazole (NBD)-labeled lipids in lipid bilayers. Phys Chem Chem Phys 2019; 21:1682-1688. [PMID: 30418442 DOI: 10.1039/c8cp06064a] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Nitrobenzoxadiazole (NBD) labeled lipids are popular fluorescent probes of membrane structure and dynamics, and have been widely used in both model systems and living cells. Irrespective of attachment to the lipid head group or hydrocarbon chains, the NBD fluorophore generally adopts a transverse bilayer location near the host lipid carbonyl/glycerol moieties. Still, considerable variability is observed in the measured fluorescence lifetimes, indicating that overall fluorophore location is not the determinant of NBD fluorescence properties. Combining fluorescence experiments and molecular dynamics simulations, we show that for two almost identical NBD probes, significant differences in fluorophore orientation and fluorescence lifetime are observed. Integrating these findings with literature data, we demonstrate a correlation between NBD orientation and fluorescence lifetime. The latter is longer when the NBD nitro group is predominantly oriented towards the bilayer interior, compared to probes for which it points to the water medium.
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Affiliation(s)
- Hugo A L Filipe
- Coimbra Chemistry Center, University of Coimbra, P-3004-535 Coimbra, Portugal
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3
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Kyrychenko A, Rodnin MV, Ghatak C, Ladokhin AS. Joint refinement of FRET measurements using spectroscopic and computational tools. Anal Biochem 2017; 522:1-9. [PMID: 28108168 DOI: 10.1016/j.ab.2017.01.011] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2016] [Revised: 01/12/2017] [Accepted: 01/16/2017] [Indexed: 12/28/2022]
Abstract
The variability of the orientation factor is a long-standing challenge in converting FRET efficiency measurements into donor-acceptor distances. We propose the use of molecular dynamics (MD) simulations to characterize orientation distributions and thus improve the accuracy of distance measurements. Here, we test this approach by comparing experimental and simulated FRET efficiencies for a model donor-acceptor pair of enhanced cyan and enhanced yellow FPs connected by a flexible linker. Several spectroscopic techniques were used to characterize FRET in solution. In addition, a series of atomistic MD simulations of a total length of 1.5 μs were carried out to calculate the distances and the orientation factor in the FRET-pair. The resulting MD-based and experimentally measured FRET efficiency histograms coincided with each other, allowing for direct comparison of distance distributions. Despite the fact that the calculated average orientation factor was close to 2/3, the application of the average κ2 to the entire histogram of FRET efficiencies resulted in a substantial artificial broadening of the calculated distribution of apparent donor-acceptor distances. By combining single pair-FRET measurements with computational tools, we demonstrate that accounting for the donor and acceptor orientation heterogeneity is critical for accurate representation of the donor-acceptor distance distribution from FRET measurements.
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Affiliation(s)
- Alexander Kyrychenko
- Institute of Chemistry and School of Chemistry, V. N. Karazin Kharkiv National University, 4 Svobody Square, Kharkiv 61022, Ukraine; Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS 66160-7421, USA.
| | - Mykola V Rodnin
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS 66160-7421, USA
| | - Chiranjib Ghatak
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS 66160-7421, USA
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS 66160-7421, USA.
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4
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Amaro M, Filipe HAL, Prates Ramalho JP, Hof M, Loura LMS. Fluorescence of nitrobenzoxadiazole (NBD)-labeled lipids in model membranes is connected not to lipid mobility but to probe location. Phys Chem Chem Phys 2016; 18:7042-54. [PMID: 26727975 DOI: 10.1039/c5cp05238f] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Nitrobenzoxadiazole (NBD)-labeled lipids are popular fluorescent membrane probes. However, the understanding of important aspects of the photophysics of NBD remains incomplete, including the observed shift in the emission spectrum of NBD-lipids to longer wavelengths following excitation at the red edge of the absorption spectrum (red-edge excitation shift or REES). REES of NBD-lipids in membrane environments has been previously interpreted as reflecting restricted mobility of solvent surrounding the fluorophore. However, this requires a large change in the dipole moment (Δμ) of NBD upon excitation. Previous calculations of the value of Δμ of NBD in the literature have been carried out using outdated semi-empirical methods, leading to conflicting values. Using up-to-date density functional theory methods, we recalculated the value of Δμ and verified that it is rather small (∼2 D). Fluorescence measurements confirmed that the value of REES is ∼16 nm for 1,2-dioleoyl-sn-glycero-3-phospho-l-serine-N-(NBD) (NBD-PS) in dioleoylphosphatidylcholine vesicles. However, the observed shift is independent of both the temperature and the presence of cholesterol and is therefore insensitive to the mobility and hydration of the membrane. Moreover, red-edge excitation leads to an increased contribution of the decay component with a shorter lifetime, whereas time-resolved emission spectra of NBD-PS displayed an atypical blue shift following excitation. This excludes restrictions to solvent relaxation as the cause of the measured REES and TRES of NBD, pointing instead to the heterogeneous transverse location of probes as the origin of these effects. The latter hypothesis was confirmed by molecular dynamics simulations, from which the calculated heterogeneity of the hydration and location of NBD correlated with the measured fluorescence lifetimes/REES. Globally, our combination of theoretical and experiment-based techniques has led to a considerably improved understanding of the photophysics of NBD and a reinterpretation of its REES in particular.
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Affiliation(s)
- Mariana Amaro
- Department of Biophysical Chemistry, J. Heyrovský Institute of Physical Chemistry of the Academy of Sciences of the Czech Republic, v.v.i., Dolejskova 3, 182 23 Prague, Czech Republic.
| | - Hugo A L Filipe
- Centro de Química de Coimbra, Largo D. Dinis, Rua Larga, 3004-535 Coimbra, Portugal. and Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Largo D. Dinis, Rua Larga, 3004-535 Coimbra, Portugal and Centro de Neurociências e Biologia Celular, Universidade de Coimbra, 3004-504 Coimbra, Portugal
| | - J P Prates Ramalho
- Departamento de Química and Centro de Química de Évora, Escola de Ciências e Tecnologia, Universidade de Évora, Rua Romão Ramalho, 59, 7000-671 Évora, Portugal
| | - Martin Hof
- Department of Biophysical Chemistry, J. Heyrovský Institute of Physical Chemistry of the Academy of Sciences of the Czech Republic, v.v.i., Dolejskova 3, 182 23 Prague, Czech Republic.
| | - Luís M S Loura
- Centro de Química de Coimbra, Largo D. Dinis, Rua Larga, 3004-535 Coimbra, Portugal. and Centro de Neurociências e Biologia Celular, Universidade de Coimbra, 3004-504 Coimbra, Portugal and Faculdade de Farmácia, Universidade de Coimbra, Pólo das Ciências da Saúde, Azinhaga de Santa Comba, 3000-548 Coimbra, Portugal
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Filipe HAL, Bowman D, Palmeira T, Cardoso RMS, Loura LMS, Moreno MJ. Interaction of NBD-labelled fatty amines with liquid-ordered membranes: a combined molecular dynamics simulation and fluorescence spectroscopy study. Phys Chem Chem Phys 2016; 17:27534-47. [PMID: 26426766 DOI: 10.1039/c5cp04191k] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A complete homologous series of fluorescent 7-nitrobenz-2-oxa-1,3-diazol-4-yl-(NBD) labelled fatty amines of varying alkyl chain lengths, NBD-Cn, inserted in 1-palmitoyl, 2-oleoyl-sn-glycero-3-phosphocholine (POPC) or N-palmitoyl sphingomyelin (SpM) bilayers, with 50 mol% and 40 mol% cholesterol (Chol), respectively, was studied using atomistic molecular dynamics simulations. For all amphiphiles in both bilayers, the NBD fluorophore locates at the interface, in a more external position than that previously observed for pure POPC bilayers. This shallower location of the NBD group agrees with the lower fluorescent quantum yield, shorter fluorescence lifetime, and higher ionisation constants (smaller pKa) determined experimentally. The more external location is also consistent with the changes measured in steady-state fluorescence anisotropy from POPC to POPC/Chol (1 : 1) vesicles. Accordingly, the equilibrium location of the NBD group within the various bilayers is mainly dictated by bilayer compositions, and is mostly unaffected by the length of the attached alkyl chain. Similarly to the behaviour observed in POPC bilayers, the longer-chained NBD-Cn amphiphiles show significant mass density near the mixed bilayers' midplanes, and the alkyl chains of the longer derivatives, mainly NBD-C16, penetrate the opposite bilayer leaflet to some extent. However, this effect is quantitatively less pronounced in these ordered bilayers than in POPC. Similarly to POPC bilayers, the effects of these amphiphiles on the structure and dynamics of the host lipid were found to be relatively mild, in comparison with acyl-chain phospholipid analogues.
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Affiliation(s)
- Hugo A L Filipe
- Centro de Química de Coimbra, Largo D. Dinis, Rua Larga, 3004-535 Coimbra, Portugal
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Filipe HAL, Santos LS, Prates Ramalho JP, Moreno MJ, Loura LMS. Behaviour of NBD-head group labelled phosphatidylethanolamines in POPC bilayers: a molecular dynamics study. Phys Chem Chem Phys 2015; 17:20066-79. [DOI: 10.1039/c5cp01596k] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
An NBD-diC16PE/POPC bilayer with typical fluorophore inverted-snorkelling configurations, and mass density profiles across the membrane. The wide distribution of the NBD fluorophore lies at the origin of its complex emission kinetics.
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Affiliation(s)
- Hugo A. L. Filipe
- Departamento de Química
- Faculty of Science and Technnology
- University of Coimbra
- Rua Larga
- Portugal
| | - Lennon S. Santos
- Departamento de Química
- Faculty of Science and Technnology
- University of Coimbra
- Rua Larga
- Portugal
| | - J. P. Prates Ramalho
- Departamento de Química
- Escola de Ciências e Tecnologia
- Universidade de Évora
- Rua Romão Ramalho
- Portugal
| | - Maria João Moreno
- Departamento de Química
- Faculty of Science and Technnology
- University of Coimbra
- Rua Larga
- Portugal
| | - Luís M. S. Loura
- Centro de Química de Coimbra
- Rua Larga
- Portugal
- Centro de Neurociências e Biologia Celular
- Universidade de Coimbra
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Filipe HAL, Moreno MJ, Róg T, Vattulainen I, Loura LMS. How to tackle the issues in free energy simulations of long amphiphiles interacting with lipid membranes: convergence and local membrane deformations. J Phys Chem B 2014; 118:3572-81. [PMID: 24635540 DOI: 10.1021/jp501622d] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
One of the great challenges in membrane biophysics is to find a means to foster the transport of drugs across complex membrane structures. In this spirit, we elucidate methodological challenges associated with free energy computations of complex chainlike molecules across lipid membranes. As an appropriate standard molecule to this end, we consider 7-nitrobenz-2-oxa-1,3-diazol-4-yl-labeled fatty amine, NBD-Cn, which is here dealt with as a homologous series with varying chain lengths. We found the membrane-water interface region to be highly sensitive to details in free energy computations. Despite considerable simulation times, we observed substantial hysteresis, the cause being the small frequency of insertion/desorption events of the amphiphile's alkyl chain in the membrane interface. The hysteresis was most pronounced when the amphiphile was pulled from water to the membrane and compromised the data that were not in line with experiments. The subtleties in umbrella sampling for computing distance along the transition path were also observed to be potential causes of artifacts. With the PGD (pull geometry distance) scheme, in which the distance from the molecule was computed to a reference plane determined by an average over all lipids in the membrane, we found marked deformations in membrane structure when the amphiphile was close to the membrane. The deformations were weaker with the PGC (pull geometry cylinder) method, where the reference plane is chosen based on lipids that are within a cylinder of radius 1.7 nm from the amphiphile. Importantly, the free energy results given by PGC were found to be qualitatively consistent with experimental data, while the PGD results were not. We conclude that with long amphiphiles there is reason for concern with regard to computations of their free energy profiles. The membrane-water interface is the region where the greatest care is warranted.
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Affiliation(s)
- Hugo A L Filipe
- Centro de Química de Coimbra, Largo D. Dinis, Rua Larga, 3004-535 Coimbra, Portugal
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8
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Robalo JR, Ramalho JPP, Loura LMS. NBD-Labeled Cholesterol Analogues in Phospholipid Bilayers: Insights from Molecular Dynamics. J Phys Chem B 2013; 117:13731-42. [DOI: 10.1021/jp406135a] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- João R. Robalo
- Departamento
de Química, Escola de Ciências e Tecnologia, Universidade de Évora, Rua Romão Ramalho, 59, 7000-671 Évora, Portugal
- Centro
de Química de Évora, Universidade de Évora, Rua
Romão Ramalho, 59, 7000-671 Évora, Portugal
| | - J. P. Prates Ramalho
- Departamento
de Química, Escola de Ciências e Tecnologia, Universidade de Évora, Rua Romão Ramalho, 59, 7000-671 Évora, Portugal
- Centro
de Química de Évora, Universidade de Évora, Rua
Romão Ramalho, 59, 7000-671 Évora, Portugal
| | - Luís M. S. Loura
- Faculdade
de Farmácia, Universidade de Coimbra, Pólo das Ciências da Saúde, Azinhaga de Santa Comba, 3000-548 Coimbra, Portugal
- Centro
de Química de Coimbra, Largo D. Dinis, Rua Larga, 3004-535 Coimbra, Portugal
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Filipe HAL, Coreta-Gomes FM, Velazquez-Campoy A, Almeida AR, Peixoto AF, Pereira MM, Vaz WLC, Moreno MJ. Synthesis and Characterization of a Lipidic Alpha Amino Acid: Solubility and Interaction with Serum Albumin and Lipid Bilayers. J Phys Chem B 2013; 117:3439-48. [DOI: 10.1021/jp307874v] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Hugo A. L. Filipe
- Departamento de
Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal
| | | | - Adrian Velazquez-Campoy
- Institute of Biocomputation
and Physics of Complex Systems (BIFI), Universidad de Zaragoza, Unidad Asociada BIFI-IQFR, CSIC, Zaragoza,
Spain
- Fundación ARAID, Diputación General de Aragón, Spain
| | - Ana R. Almeida
- Departamento de
Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal
| | - Andreia F. Peixoto
- Departamento de
Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal
| | - Mariette M. Pereira
- Departamento de
Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal
| | - Winchil L. C. Vaz
- Departamento de
Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal
| | - Maria J. Moreno
- Departamento de
Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal
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Simple estimation of Förster Resonance Energy Transfer (FRET) orientation factor distribution in membranes. Int J Mol Sci 2012. [PMID: 23203123 PMCID: PMC3509639 DOI: 10.3390/ijms131115252] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Because of its acute sensitivity to distance in the nanometer scale, Förster resonance energy transfer (FRET) has found a large variety of applications in many fields of chemistry, physics, and biology. One important issue regarding the correct usage of FRET is its dependence on the donor-acceptor relative orientation, expressed as the orientation factor κ2. Different donor/acceptor conformations can lead to κ2 values in the 0 ≤ κ2 ≤ 4 range. Because the characteristic distance for FRET, R0, is proportional to (κ2)1/6, uncertainties in the orientation factor are reflected in the quality of information that can be retrieved from a FRET experiment. In most cases, the average value of κ2 corresponding to the dynamic isotropic limit (<κ2> = 2/3) is used for computation of R0 and hence donor-acceptor distances and acceptor concentrations. However, this can lead to significant error in unfavorable cases. This issue is more critical in membrane systems, because of their intrinsically anisotropic nature and their reduced fluidity in comparison to most common solvents. Here, a simple numerical simulation method for estimation of the probability density function of κ2 for membrane-embedded donor and acceptor fluorophores in the dynamic regime is presented. In the simplest form, the proposed procedure uses as input the most probable orientations of the donor and acceptor transition dipoles, obtained by experimental (including linear dichroism) or theoretical (such as molecular dynamics simulation) techniques. Optionally, information about the widths of the donor and/or acceptor angular distributions may be incorporated. The methodology is illustrated for special limiting cases and common membrane FRET pairs.
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Loura LMS. Lateral distribution of NBD-PC fluorescent lipid analogs in membranes probed by molecular dynamics-assisted analysis of Förster Resonance Energy Transfer (FRET) and fluorescence quenching. Int J Mol Sci 2012; 13:14545-64. [PMID: 23203080 PMCID: PMC3509596 DOI: 10.3390/ijms131114545] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Revised: 10/29/2012] [Accepted: 11/01/2012] [Indexed: 01/19/2023] Open
Abstract
Förster resonance energy transfer (FRET) is a powerful tool used for many problems in membrane biophysics, including characterization of the lateral distribution of lipid components and other species of interest. However, quantitative analysis of FRET data with a topological model requires adequate choices for the values of several input parameters, some of which are difficult to obtain experimentally in an independent manner. For this purpose, atomistic molecular dynamics (MD) simulations can be potentially useful as they provide direct detailed information on transverse probe localization, relative probe orientation, and membrane surface area, all of which are required for analysis of FRET data. This is illustrated here for the FRET pairs involving 1,6-diphenylhexatriene (DPH) as donor and either 1-palmitoyl,2-(6-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino] hexanoyl)- sn-glycero-3-phosphocholine (C6-NBD-PC) or 1-palmitoyl,2-(12-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]dodecanoyl)-sn-glycero-3-phosphocholine (C12-NBD-PC) as acceptors, in fluid vesicles of 1,2-dipalmitoyl-sn-3-glycerophosphocholine (DPPC, 50 °C). Incorporation of results from MD simulations improves the statistical quality of model fitting to the experimental FRET data. Furthermore, the decay of DPH in the presence of moderate amounts of C12-NBD-PC (>0.4 mol%) is consistent with non-random lateral distribution of the latter, at variance with C6-NBD-PC, for which aggregation is ruled out up to 2.5 mol% concentration. These conclusions are supported by analysis of NBD-PC fluorescence self-quenching. Implications regarding the relative utility of these probes in membrane studies are discussed.
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Affiliation(s)
- Luís M S Loura
- Faculty of Pharmacy, University of Coimbra, Health Sciences Campus, Azinhaga de Santa Comba, 3000-548 Coimbra, Portugal.
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12
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Loura LMS, Prieto M. Lateral Membrane Heterogeneity Probed by FRET Spectroscopy and Microscopy. SPRINGER SERIES ON FLUORESCENCE 2012. [DOI: 10.1007/4243_2012_59] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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13
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Filipe HAL, Moreno MJ, Loura LMS. Interaction of 7-nitrobenz-2-oxa-1,3-diazol-4-yl-labeled fatty amines with 1-palmitoyl, 2-oleoyl-sn-glycero-3-phosphocholine bilayers: a molecular dynamics study. J Phys Chem B 2011; 115:10109-19. [PMID: 21749140 DOI: 10.1021/jp203532c] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A complete homologous series of fluorescent 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD)-labeled fatty amines of varying alkyl chain length, NBD-C(n), inserted in 1-palmitoyl, 2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayers, was studied using atomistic molecular dynamics (MD) simulations. For all amphiphiles, the NBD fluorophore locates near the glycerol backbone/carbonyl region of POPC and establishes stable hydrogen bonding with POPC ester oxygen atoms. Small differences observed in the transverse location of the fluorophore correlate with other calculated parameters and with small discrepancies recently measured in the photophysical properties of the molecules. The longer-chained NBD-C(n) amphiphiles show significant mass density near the bilayer midplane, and the chains of these derivatives interdigitate to some extent the opposite bilayer leaflet. This phenomenon leads to a slower lateral diffusion for the longer-chained derivatives (n > 12). Effects of these amphiphiles on the structure and dynamics of the host lipid were found to be relatively mild, in comparison with acyl-chain-labeled NBD probes. The molecular details obtained by this work allow the rationalization of the nonmonotonic behavior, recently obtained experimentally, for the photophysical parameters of the amphiphiles and the kinetic and thermodynamic parameters for their interaction with the POPC membranes.
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Affiliation(s)
- Hugo A L Filipe
- Centro de Química de Coimbra, Universidade de Coimbra, Largo D. Dinis, Rua Larga, 3004-535 Coimbra, Portugal
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Loura LMS, Ramalho JPP. Recent developments in molecular dynamics simulations of fluorescent membrane probes. Molecules 2011; 16:5437-52. [PMID: 21709624 PMCID: PMC6264736 DOI: 10.3390/molecules16075437] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2011] [Revised: 06/21/2011] [Accepted: 06/22/2011] [Indexed: 01/25/2023] Open
Abstract
Due to their sensitivity and versatility, the use of fluorescence techniques in membrane biophysics is widespread. Because membrane lipids are non-fluorescent, extrinsic membrane probes are widely used. However, the behaviour of these probes when inserted in the bilayer is often poorly understood, and it can be hard to distinguish between legitimate membrane properties and perturbation resulting from probe incorporation. Atomistic molecular dynamics simulations present a convenient way to address these issues and have been increasingly used in recent years in this context. This article reviews the application of molecular dynamics to the study of fluorescent membrane probes, focusing on recent work with complex design fluorophores and ordered bilayer systems.
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Affiliation(s)
- Luís M. S. Loura
- Faculdade de Farmácia, Universidade de Coimbra, Pólo das Ciências da Saúde, Azinhaga de Santa Comba, 3000-548 Coimbra, Portugal;
- Centro de Química de Coimbra, Universidade de Coimbra, Rua Larga, 3004-535 Coimbra, Portugal
| | - J. P. Prates Ramalho
- Centro de Química de Évora e Departamento de Química, Escola de Ciências e Tecnologia, Colégio Luís Verney, Rua Romão Ramalho 59, 7002-554 Évora, Portugal
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