References of "Gabelica, Valérie"
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See detailElectrochemical study of two tris-O-substituted calix[4]arenes: 25,27-dipropoxy-26-hydroxy-28-benzoyloxycalix[4]arene(partial cone) and 25,27-dibenzyl-26-hydroxy-28-benzoyloxy-calix[4]-arene (partial cone). Electro synthesis of the corresponding calix[4]arene-monoquinones
Louati, Alain; Spraula, Julien; Gabelica, Valérie ULg et al

in Electrochemistry Communications (2006), 8(5), 761-766

The anodic oxidation of 25,27-dipropoxy-26-hydroxy-28-benzoyloxycalix[4]arene 1 and 25,27-dibenzyl-26-hydroxy-28-benzoyloxycalix[4]arene 2 in dichloromethane was investigated by electrochemical and ... [more ▼]

The anodic oxidation of 25,27-dipropoxy-26-hydroxy-28-benzoyloxycalix[4]arene 1 and 25,27-dibenzyl-26-hydroxy-28-benzoyloxycalix[4]arene 2 in dichloromethane was investigated by electrochemical and spectroclectrochemical techniques. For both, the overall reaction is a two-electron oxidation of the phenolic group according to an ECE mechanism resulting in the ultimate formation of an observable phenoxylium cation. After reaction of the latter with traces of water and subsequent internal electron transfer, the corresponding calix[4]-monoquinones are formed. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailAscididemin and meridine stabilise G-quadruplexes and inhibit telomerase in vitro
Guittat, Lionel; De Cian, Anne; Rosu, Frédéric ULg et al

in Biochimica et Biophysica Acta - General Subjects (2005), 1724(3), 375-384

Ascididemin and Meridine are two marine compounds with pyridoacridine skeletons known to exhibit interesting antitumour activities. These molecules have been reported to behave like DNA intercalators. In ... [more ▼]

Ascididemin and Meridine are two marine compounds with pyridoacridine skeletons known to exhibit interesting antitumour activities. These molecules have been reported to behave like DNA intercalators. In this study, dialysis competition assay and mass spectrometry experiments were used to determine the affinity of ascididemin and meridine for DNA structures among duplexes, triplexes, quadruplexes and single-strands. Our data confirm that ascididemin and meridine interact with DNA but also recognize triplex and quadruplex structures. These molecules exhibit a significant preference for quadruplexes over duplexes or single-strands. Meridine is a stronger quadruplex ligand and therefore a stronger telomerase inhibitor than ascididemin (IC50= 11 and > 80 mu M, respectively in a standard TRAP assay). (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailFast gas-phase hydrogen/deuterium exchange observed for a DNA G-quadruplex
Gabelica, Valérie ULg; Rosu, Frédéric ULg; Witt, Matthias et al

in Rapid Communications in Mass Spectrometry : RCM (2005), 19(2), 201-208

The gas-phase hydrogen/deuterium (H/D) exchange kinetics of DNA G-quadruplexes has been investigated using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). The quadruplex [(TGGGGT)(4 ... [more ▼]

The gas-phase hydrogen/deuterium (H/D) exchange kinetics of DNA G-quadruplexes has been investigated using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). The quadruplex [(TGGGGT)(4).3NH(4)(+)] undergoes very fast H/D exchange, in both the positive and in the negative ion modes, compared to DNA duplexes and other quadruplexes tested, and compared to the corresponding single-stranded TGGGGT. Substitution of NH4+ for K+ did not alter this fast H/D exchange, indicating that the hydrogens of the ammonium ions are not those exchanged. However, stripping of the interior cations of the quadruplex by source collision-induced dissociation (CID) in the positive ion mode showed that the presence of the inner cations is essential for the fast exchange to be possible. Molecular dynamics simulations show that the G-quadruplex is very rigid in the gas phase with NH4+ ions inside the tetrads. We suggest that the fast H/D exchange is favored by this rigid quadruplex conformation. This example illustrates that the concept that compact DNA structures exchange H for D slower than unfolded ones is a misconception. Copyright (C) 2004 John Wiley Sons, Ltd. [less ▲]

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See detailInternal energy and fragmentation of ions produced in electrospray sources
Gabelica, Valérie ULg; De Pauw, Edwin ULg

in Mass Spectrometry Reviews (2005), 24(4), 566-587

This review addresses the determination of the internal energy of ions produced by electrospray ionization (ESI) sources, and the influence of the internal energy on analyte fragmentation. A control of ... [more ▼]

This review addresses the determination of the internal energy of ions produced by electrospray ionization (ESI) sources, and the influence of the internal energy on analyte fragmentation. A control of the analyte internal energy is crucial for several applications of electrospray mass spectrometry, like structural studies, construction of reproducible and exportable spectral libraries, analysis of non-covalent complexes. Sections II and III summarize the Electrospray mechanisms and source design considerations which are relevant to the problem of internal energy, and Section IV gives an overview of the interrelationships between ion internal energy, reaction time scale, and analyte fragmentation. In these three sections we tried to make the most important theoretical elements understandable by all ESI users, and their understanding requires a minimal background in physical chemistry. We then present the different approaches used to experimentally determine the ion internal energy, as well as various attempts in modeling the internal energy uptake in electrospray sources. Finally, a tentative comparison between electrospray and other ionization sources is made. As the reader will see, although many reports appeared on the subject, the knowledge in the field of internal energy of ions produced by soft ionization sources is still scarce, because of the complexity of the system, and this is what makes this area of research so interesting. The last section presents some perspectives for future research. [less ▲]

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See detailFormation of upper rim acylated calix[4]arenes using a sacrifici al zinc anode
Louati, Alain; Vataj, Rame; Gabelica, Valérie ULg et al

in Tetrahedron Letters (2005), 46(44), 7499-7502

A straightforward electrosynthetic method is described, which allows upper rim acylation of non-p-halogenated calix[4]-arenes. For example, a solution of tetrapropoxycalix[4]arene 4 was electrolysed in ... [more ▼]

A straightforward electrosynthetic method is described, which allows upper rim acylation of non-p-halogenated calix[4]-arenes. For example, a solution of tetrapropoxycalix[4]arene 4 was electrolysed in the presence of ZnBr2, in an undivided cell fitted with a sacrificial zinc anode using pure acetonitrile as solvent, yielding an organozinc species, which was then treated with acetyl chloride in the presence of a palladium catalyst to afford 5,11-diacety1-25,26,27,28-tetrapropoxycalix[4]arene 5 in ca. 35% yield after workup. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailInternal energy build-up in matrix-assisted laser desorption/ionization
Gabelica, Valérie ULg; Schulz, Eric; Karas, Michael

in Journal of Mass Spectrometry [=JMS] (2004), 39(6), 579-593

This paper reports detailed studies on the internal energy of ions formed in matrix-assisted laser desorption/ionization (MALDI) using delayed extraction MALDI-time-of-flight (TOF) and atmospheric ... [more ▼]

This paper reports detailed studies on the internal energy of ions formed in matrix-assisted laser desorption/ionization (MALDI) using delayed extraction MALDI-time-of-flight (TOF) and atmospheric pressure (AP) MALDI mass spectrometric (MS) methods. We use benzylpyridinium cations as internal energy probes. Our study reveals three distinct contributions to internal energy build-up in vacuum-MALDI (classical MALDI-TOF), each having different effects on ion fragmentation. Some fragments are formed before ion extraction (i.e. no more than 100 ns after the laser impact), and they are therefore well resolved and recorded as sharp signals in the MALDI-TOFMS scan. This prompt fragmentation can have two origins: (i) in-plume thermal activation, presumably always present, and (ii) in-plume chemical activation, in the course of reactions with hydrogen radicals. In addition to early internal energy build-up associated with these well-resolved promptly formed fragments, a broad peak slightly offset to higher masses could be detected corresponding to fragments formed after the extraction has started. This second signal corresponds to a third source of internal energy in MALDI ions, (iii) the extraction-induced collisional activation of the ions with the neutral components of the plume. These three contributions are difficult to quantify in vacuum-MALDI, because of the combined influence of several parameters (nature of the matrix, spot-to-spot variability, total laser exposure, delay time, acceleration voltage) on extraction-induced fragmentation. AP-MALDI, on the other hand, has two advantages for comparative studies of analyte fragmentation. First, extraction-induced fragmentation is absent, and only the contributions of early plume activation remain. Second, the reproducibility is far better than in vacuum-MALDI. AP-MALDI is therefore expected to shed new light on the early steps of the MALDI process. Copyright (C) 2004 John Wiley Sons, Ltd. [less ▲]

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See detailInvestigation of non-covalent interactions between paramagnetic complexes and human serum albumin by electrospray mass spectrometry
Henrotte, Virginie; Laurent, Sophie ULg; Gabelica, Valérie ULg et al

in Rapid Communications in Mass Spectrometry : RCM (2004), 18(17), 1919-1924

Stable gadolinium(III) chelates are nowadays routinely used as contrast agents for magnetic resonance imaging (MRI). Their non-covalent binding to human serum albumin (HSA) has shown to improve their ... [more ▼]

Stable gadolinium(III) chelates are nowadays routinely used as contrast agents for magnetic resonance imaging (MRI). Their non-covalent binding to human serum albumin (HSA) has shown to improve their efficacy. Non-covalent interactions lead to complex formation that can be quantified by several techniques that are mostly tedious and time-consuming. In this study, electrospray ionization mass spectrometry (ESI-MS) was used to investigate the interaction between HSA and several gadolinium(III) complexes. The results were compared with those obtained in the liquid phase. Four gadolinium complexes were investigated: Gd-DTPA 1, Gd-C4Me-DTPA 2, Gd-EOB-DTPA 3, and MP-2269 4. Relaxometry studies show that complexes 1 and 2 have no significant affinity for HSA, while complexes 3 and 4 have increasing affinities for the protein. 1:1 and 1:2 complexes between HSA and MP-2269 were detected by ESI-MS for a twofold excess of the contrast agent, whereas a ligand/protein molar ratio of 4:1 was necessary to observe a 1:1 stoichiometry for Gd-EOB-DTPA, an observation that is in good agreement with the known weaker affinity of the contrast agent for the protein. At a fourfold molar excess, no supramolecular complex was observed for Gd-DTPA I and Gd-C4Me-DTPA 2; a tenfold molar excess was necessary to detect a 1:1 complex, confirming the very weak affinity of these contrast agents for HSA. [less ▲]

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See detailInfluence of the capillary temperature and the source pressure on the internal energy distribution of electrosprayed ions
Gabelica, Valérie ULg; De Pauw, Edwin ULg; Karas, Michael

in International Journal of Mass Spectrometry (2004), 231(2-3), 189-195

The internal energy distributions in a heated capillary nano-electrospray source have been determined using the "survival yield" method. At low capillary temperatures, the internal energy distribution is ... [more ▼]

The internal energy distributions in a heated capillary nano-electrospray source have been determined using the "survival yield" method. At low capillary temperatures, the internal energy distribution is characterized by a low-energy tail, which can be attributed to a fraction of ions not fully desolvated in the heated capillary. This low-energy tais is shown to disappear when the source pressure is increased. This explains why increased source pressure is favorable in the case of highly hydrophilic compounds or non-covalent complexes in order to achieve sufficient desolvation without fragmentation. It is also shown that "high temperature-low voltage" are not equivalent to "low temperature-high voltage" source conditions. These observations are important for fundamental issues as well as for source-CID mass spectral library searching applications. [less ▲]

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See detailCalibration of ion effective temperatures achieved by resonant activation in a quadrupole ion trap
Gabelica, Valérie ULg; Karas, Michael; De Pauw, Edwin ULg

in Analytical Chemistry (2003), 75(19), 5152-5159

The present paper describes a calibration of the ion effective temperatures as a function of the resonant activation amplitude in a quadrupole ion trap mass spectrometer. MS/MS experiments are performed ... [more ▼]

The present paper describes a calibration of the ion effective temperatures as a function of the resonant activation amplitude in a quadrupole ion trap mass spectrometer. MS/MS experiments are performed on leucine enkephalin (M + H)(+), bradykinin (M + H)(+), (M + 2H)(2+), and (M + 3H)(3+), and ubiquitin (M + 11H)(11+). For each amplitude, the effective temperature is calculated as the temperature that would give the same dissociation rate constant as the one observed and is calculated using published Arrhenius parameters. The effective temperature is found to be linearly dependent on the activation amplitude on the range investigated. The dependence of the slope and of the intercept of the T-eff = f (amplitude) functions on the parent ion m/z is examined and an equation is derived to calibrate the ion effective temperature between 365 and 600 K Below 365 K, a deviation from linearity is expected. Above 600 1 the validity of the equation will depend on whether the rapid energy exchange limit is still reached. Calculating backward, the Arrhenius parameters from the measured dissociation rates using this calibration show excellent agreement with the published values. The calibration can therefore be used to determine Arrhenius activation parameters from dissociation kinetics under resonant activation in quadrupole ion trap mass spectrometers. [less ▲]

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See detailInteractions of cryptolepine and neocryptolepine with unusual DNA structures
Guittat, Lionel; Alberti, Patrizia; Rosu, Frédéric ULg et al

in Biochimie (2003), 85(5), 535-547

Cryptolepine, the main alkaloid present in the roots of Cryptolepis sanguinolenta, presents a large spectrum of biological properties. It has been reported to behave like a DNA intercalator with a ... [more ▼]

Cryptolepine, the main alkaloid present in the roots of Cryptolepis sanguinolenta, presents a large spectrum of biological properties. It has been reported to behave like a DNA intercalator with a preference for GC-rich sequences. In this study, dialysis competition assay and mass spectrometry experiments were used to determine the affinity of cryptolepine and neocryptolepine for DNA structures among duplexes, triplexes, quadruplexes and single strands. Our data confirm that cryptolepine and neocryptolepine prefer GC over AT-rich duplex sequences, but also recognize triplex and quadruplex structures. These compounds are weak telomerase inhibitors and exhibit a significant preference for triplexes over quadruplexes or duplexes. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Societe francaise de biochimie et biologic moleculaire. All rights reserved. [less ▲]

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See detailInfluence of response factors on determining equilibrium association constants of non-covalent complexes by electrospray ionization mass spectrometry
Gabelica, Valérie ULg; Galic, Nives; Rosu, Frédéric ULg et al

in Journal of Mass Spectrometry [=JMS] (2003), 38(5), 491-501

A method for determining the equilibrium association constant of a complexation reaction A + B <=> AB by electrospray ionization mass spectrometry is described. The method consists in measuring the ... [more ▼]

A method for determining the equilibrium association constant of a complexation reaction A + B <=> AB by electrospray ionization mass spectrometry is described. The method consists in measuring the relative intensities of the peaks corresponding to A and to AB in equimolar A–B solutions at different concentrations C0. The results are fitted by a non-linear least-squares procedure, with the two variable parameters being the equilibrium association constant Ka and a factor R, defined by I(AB)/I.A/ = R× [AB]/[A]. The factor R is the ratio between the response factors of AB and A, and corrects for the relative electrospray responses of the complex and the free substrate A, mass discrimination of instrumental origin and/or moderate in-source dissociation. The method is illustrated with the following two systems: complexes between a double-stranded 12-base pair oligonucleotide and minor groove binders, and cyclodextrin complexeswith a,!-dicarboxylic acids. For the oligonucleotide complexes, it is found that the response of the complex is not dramatically different to the response of the free oligonucleotide duplex, as the double helix conformation is disturbed by the drug only to a minor extent. In the case of cyclodextrin complexes, these complexes were found to have a much higher response than free cyclodextrin. This may be due to the fact that cyclodextrin is neutral in solution, whereas the complex is charged, but it can also stem from the fact that a significant proportion of the complex is in a non-inclusion geometry. The present method requires the exact determination of the concentrations of the reactants and is applicable to 1 : 1 complexes. [less ▲]

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See detailThermometer ions for matrix-enhanced laser desorption/ionization internal energy calibration
Greisch, Jean-François ULg; Gabelica, Valérie ULg; Remacle, Françoise ULg et al

in Rapid Communications in Mass Spectrometry : RCM (2003), 17(16), 1847-1854

This work describes a method to use relative fragmentation yields to characterize the internal energy distribution of ions produced by matrix-enhanced laser desorption/ionization mass spectrometry (MELDI ... [more ▼]

This work describes a method to use relative fragmentation yields to characterize the internal energy distribution of ions produced by matrix-enhanced laser desorption/ionization mass spectrometry (MELDI-MS, see: Wright LG, Cooks RG, Wood KL. Biomed. Mass Spectrom. 1985; 12:153162). Assuming that the fragmentation proceeds statistically and that the collisions in the source lead to a Boltzmann-like distribution of the internal energy, a characteristic parameter, the effective temperature, is introduced to describe the internal energy distribution of the ions observed. The hypotheses, advantages and drawbacks of the implementation of the method that uses substituted benzylpyridinium salts as thermometer ions are discussed. Use is made of two matrices that produce no matrix cations in MELDI and are suitable for small cationic salts. The actual value of this effective temperature significantly depends on an accurate determination of the threshold dissociation energies and on the time spent in the source, in addition to the statistical hypothesis itself. The method could be applied to normalize spectra in order to compare results issued from different instruments. [less ▲]

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See detailTelomestatin-induced stabilization of the human telomeric DNA quadruplex monitored by electrospray mass spectrometry
Rosu, Frédéric ULg; Gabelica, Valérie ULg; Shin-ya, Kazuo et al

in Chemical Communications (2003), (21), 2702-2703

Electrospray mass spectrometry (ESI-MS) was used to monitor the kinetics of duplex formation between the human telomeric DNA quadruplex and its complementary strand; the complexation of telomestatin to ... [more ▼]

Electrospray mass spectrometry (ESI-MS) was used to monitor the kinetics of duplex formation between the human telomeric DNA quadruplex and its complementary strand; the complexation of telomestatin to the G-quadruplex delays the unwinding of the quadruplex structure and formation of the duplex. [less ▲]

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See detailAspects quantitatifs de la spectrométrie de masse des biomolécules
De Pauw, Edwin ULg; Gabelica, Valérie ULg; Gillet, Marie-Claire ULg et al

Conference (2002, March)

Spectrométrie de masse en 2002 : plus haut, plus vite… mais jusqu’où et pourquoi faire ?

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See detailA study of noncovalent interactions by electrospray mass spectrometry
Gabelica, Valérie ULg

Doctoral thesis (2002)

This work describes a study of noncovalent interactions by electrospray mass spectrometry (ES-MS). In particular, we studied DNA duplexes, DNA complexes with drugs and cyclodextrin complexes with ... [more ▼]

This work describes a study of noncovalent interactions by electrospray mass spectrometry (ES-MS). In particular, we studied DNA duplexes, DNA complexes with drugs and cyclodextrin complexes with aliphatic acids. ES-MS experiments were performed on a hybrid quadrupole-TOF instrument and on an ion trap instrument. Basically two kinds of information can be obtained on the complexes. First, the full scan mass spectra give information on the composition of the solution that is injected, and therefore on the solution-phase stability of the complexes. We compare the ESMS data with the solution-phase data, and discuss the specificity of the observed complexes. The problem of nonspecific aggregation was encountered for the hydrophobic cyclodextrin complexes. We developed a new method for determining simultaneously the equilibrium association constant of [1:1] complexes and the ratio between the electrospray response factors of the complex and the free substrate. A change in the substrate conformation upon ligand binding can be detected by measuring the response factors of the complex and the free host. Second, the collision-induced dissociation of the complexes in the gas phase and the measurement of the amounts of fragments resulting from this dissociation give information on the gas phase kinetic stability of the complexes. It is shown that different collision regimes allow the system to fragment via different pathways, and that fast activation conditions favor the noncovalent dissociation of the complex because this process is entropy favored. The gas-phase kinetic stability measurements on series of homologous complexes suggest that intermolecular interactions like hydrogen bonding, electrostatic interactions, and stacking are conserved in the gas phase. Finally, on the basis of the results obtained on DNA duplexes, we propose a general multistep mechanism for the dissociation of noncovalent complexes. [less ▲]

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See detailDetermination of affinity, stoichiometry and sequence selectivity of minor groove binder complexes with double-stranded oligodeoxynucleotides by electrospray ionization mass spectrometry
Rosu, Frédéric ULg; Gabelica, Valérie ULg; Houssier, Claude ULg et al

in Nucleic Acids Research (2002), 30(16), 82

Electrospray mass spectrometry was evaluated regarding the reliability of the determination of the stoichiometries and equilibrium association constants from single spectra. Complexes between minor groove ... [more ▼]

Electrospray mass spectrometry was evaluated regarding the reliability of the determination of the stoichiometries and equilibrium association constants from single spectra. Complexes between minor groove binders (Hoechst 33258, Hoechst 33342, DAPI, netropsin and berenil) and 12mer oligonucleotide duplexes with a central sequence (A/T)(4) flanked by G/C base pairs were chosen as model systems. To validate the electrospray ionization mass spectrometry (ESI-MS) method, comparisons were made with circular dichroism and fluorescence spectroscopy measurements. ESI-MS allowed the detection of minor (2 drug + DNA) species for Hoechst 33258, Hoechst 33342, DAPI and berenil with duplex d(GGGG(A/T)(4)GGGG). d(CCCC(A/T)(4)CCCC), which were undetectable with the other techniques. Assuming that the duplexes and the complexes have the same electrospray response factors, the equilbrium association constants of the 1:1 and 2:1 complexes were determined by ESI-MS, and the values show a good quantitative agreement with fluorescence determined constants for Hoechst 33258 and Hoechst 33342. It is also shown that ESI-MS can quickly give reliable information on the A/T sequence selectivity of a drug: the signal of a complex is directly related to the affinity of the drug for that particular duplex. The potential of ESI-MS as a qualitative and quantitative affinity screening method is emphasized. [less ▲]

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See detailTight binding of the antitumor drug ditercalinium to quadruplex DNA
Carrasco, Carolina; Rosu, Frédéric ULg; Gabelica, Valérie ULg et al

in Chembiochem : A European Journal of Chemical Biology (2002), 3(12), 1235-1241

The structural selectivity of the DNA-binding antitumor drug ditercalinium was investigated by competition dialysis with a series of nineteen different DNA substrates. The 7H-pyridocarbazole dimer was ... [more ▼]

The structural selectivity of the DNA-binding antitumor drug ditercalinium was investigated by competition dialysis with a series of nineteen different DNA substrates. The 7H-pyridocarbazole dimer was found to bind to double stranded DNA with a preference for GC rich species but can in addition form stable complex with triplex and quadruplex structures. The preferential interaction of the drug with four-stranded DNA structures was independantly confirmed by electrospray mass spectrometry and a detailed analysis of the binding reaction was performed by surface plasmon resonance (SPR) spectrospray. The BIAcore SPR study showed that the kinetic parameters for the interaction of ditercalinium with the human telomeric quadruplex sequence are comparable to those measured with a duplex sequence. Slow association and dissociation were observed with both the quadruplex and duplex structures. The newly discovered preferential binding of ditercalinium to the antiparallel quadruplex sequence d(AG(3)[T(2)AG(3)](3)) provides new perspective for the design of drugs that can bind to human telomeres. [less ▲]

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See detailTriplex and quadruplex DNA structures studied by electrospray mass spectrometry
Rosu, Frédéric ULg; Gabelica, Valérie ULg; Houssier, Claude ULg et al

in Rapid Communications in Mass Spectrometry : RCM (2002), 16(18), 1729-1736

DNA triplex and quadruplex structures have been successfully detected by electrospray ionization mass spectrometry (ESI-MS). Circular dichroism and UV-melting experiments show that these structures are ... [more ▼]

DNA triplex and quadruplex structures have been successfully detected by electrospray ionization mass spectrometry (ESI-MS). Circular dichroism and UV-melting experiments show that these structures are stable in 150 mM ammonium acetate at pH 7 for the quadruplexes and pH 5.5 for the triplexes. The studied quadruplexes were the tetramer [d(TGGGGT)](4), the dimer [d(GGGGTTTTGGGG)](2), and the intramolecular folded strand dGGG(TTAGGG)(3), which is an analog of the human telomeric sequence. The absence of sodium contamination allowed demonstration of the specific inclusion of n-1 ammonium cations in the quadruplex structures, where n is the number of consecutive G-tetrads. We also detected the complexes between the quadruplexes and the quadruplex-specific drug mesoporphyrin IX. MS/MS spectra of [d(TGGGGT)](4) and the complex with the drug are also reported. As the drug does not displace the ammonium cations, one can conclude that the drug binds at the exterior of the tetrads, and not between them. For the triplex structure the ESI-MS spectra show the detection of the specific triplex, at m/z values typically higher than those typically observed for duplex species. Upon MS/MS the antigene strand, which is bound into the major groove of the duplex, separates from the triplex. This is the same dissociation pathway as in solution. To our knowledge this is the first report of a triplex DNA structure by electrospray mass spectrometry. [less ▲]

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See detailAdvantages and drawbacks of nanospray for studying noncovalent protein-DNA complexes by mass spectrometry
Gabelica, Valérie ULg; Vreuls, Christelle ULg; Filée, Patrice ULg et al

in Rapid Communications in Mass Spectrometry : RCM (2002), 16(18), 1723-1728

The noncovalent complexes between the BlaI protein dimer (wild-type and GM2 mutant) and its double-stranded DNA operator were studied by nanospray mass spectrometry and tandem mass spectrometry (MS/MS ... [more ▼]

The noncovalent complexes between the BlaI protein dimer (wild-type and GM2 mutant) and its double-stranded DNA operator were studied by nanospray mass spectrometry and tandem mass spectrometry (MS/MS). Reproducibility problems in the nanospray single-stage mass spectra are emphasized. The relative intensities depend greatly on the shape of the capillary tip and on the capillary-cone distance. This results in difficulties in assessing the relative stabilities of the complexes simply from MS' spectra of protein-DNA mixtures. Competition experiments using MS/MS are a better approach to determine relative binding affinities. A competition between histidine-tagged BlaIWT (BlaIWTHis) and the GM2 mutant revealed that the two proteins have similar affinities for the DNA operator, and that they co-dimerize to form heterocomplexes. The low sample consumption of nanospray allows MS/MS spectra to be recorded at different collision energies for different charge states with 1 muL of sample. The MS/MS experiments on the dimers reveal that the GM2 dimer is more kinetically stable in the gas phase than the wild-type dimer. The MS/MS experiments on the complexes shows that the two proteins require the same collision energy to dissociate from the complex. This indicates that the rate-limiting step in the monomer loss from the protein-DNA complex arises from the breaking of the protein-DNA interface rather than the protein-protein interface. The dissociation of the protein-DNA complex proceeds by the loss of a highly charged monomer (carrying about two-thirds of the total charge and one-third of the total mass). MS/MS experiments on a heterocomplex also show that the two proteins BlaIWTHis and BlaIGM2 have slightly different charge distributions in the fragments. This emphasizes the need for better understanding the dissociation mechanisms of biomolecular complexes. [less ▲]

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