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Forbes MW, Jockusch RA. Gas-phase fluorescence excitation and emission spectroscopy of three xanthene dyes (rhodamine 575, rhodamine 590 and rhodamine 6G) in a quadrupole ion trap mass spectrometer. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2011; 22:93-109. [PMID: 21472548 DOI: 10.1007/s13361-010-0017-4] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2010] [Revised: 09/01/2010] [Accepted: 09/07/2010] [Indexed: 05/30/2023]
Abstract
The gas-phase fluorescence excitation, emission and photodissociation characteristics of three xanthene dyes (rhodamine 575, rhodamine 590, and rhodamine 6G) have been investigated in a quadrupole ion trap mass spectrometer. Measured gas-phase excitation and dispersed emission spectra are compared with solution-phase spectra and computations. The excitation and emission maxima for all three protonated dyes lie at higher energy in the gas phase than in solution. The measured Stokes shifts are significantly smaller for the isolated gaseous ions than the solvated ions. Laser power-dependence measurements indicate that absorption of multiple photons is required for photodissociation. Redshifts and broadening of the dispersed fluorescence spectra at high excitation laser power provide evidence of gradual heating of the ion population, pointing to a mechanism of sequential multiple-photon activation through absorption/emission cycling. The relative brightness in the gas phase follows the order R575(1.00) < R590(1.15) < R6G(1.29). Fluorescence emission from several mass-selected product ions has been measured.
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Braz VA, Barkley MD, Jockusch RA, Wintrode PL. Efavirenz binding site in HIV-1 reverse transcriptase monomers. Biochemistry 2010; 49:10565-73. [PMID: 21090588 DOI: 10.1021/bi101480z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Efavirenz (EFV) is a potent nonnucleoside reverse transcriptase inhibitor (NNRTI) used in the treatment of AIDS. NNRTIs bind in a hydrophobic pocket located in the p66 subunit of reverse transcriptase (RT), which is not present in crystal structures of RT without an inhibitor. Recent studies showed that monomeric forms of the p66 and p51 subunits bind efavirenz with micromolar affinity. The effect of efavirenz on the solution conformations of p66 and p51 monomers was studied by hydrogen-deuterium exchange mass spectrometry (HXMS) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). HXMS data reveal that five peptides, four of which contain efavirenz contact residues seen in the crystal structure of the RT-EFV complex, exhibit a reduced level of exchange in monomer-EFV complexes. Moreover, peptide 232-246 undergoes slow cooperative unfolding-refolding in the bound monomers, but at a rate much slower than that observed in the p66 subunit of the RT heterodimer [Seckler, J. M., Howard, K. J., Barkley, M. D., and Wintrode, P. L. (2009) Biochemistry 48, 7646-7655]. These results suggest that the efavirenz binding site on p66 and p51 monomers is similar to the NNRTI binding pocket in the p66 subunit of RT. Nanoelectrospray ionization FT-ICR mass spectra indicate that the intact monomers each have (at least) two different conformations. In the presence of efavirenz, the mass spectra change significantly and suggest that p51 adopts a single, more compact conformation, whereas p66 undergoes facile, electrospray-induced cleavage. The population shift is consistent with a selected-fit binding mechanism.
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McQueen PD, Sagoo S, Yao H, Jockusch RA. On the Intrinsic Photophysics of Fluorescein. Angew Chem Int Ed Engl 2010. [DOI: 10.1002/ange.201004366] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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McQueen PD, Sagoo S, Yao H, Jockusch RA. On the Intrinsic Photophysics of Fluorescein. Angew Chem Int Ed Engl 2010; 49:9193-6. [DOI: 10.1002/anie.201004366] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Talbot FO, Rullo A, Yao H, Jockusch RA. Fluorescence Resonance Energy Transfer in Gaseous, Mass-Selected Polyproline Peptides. J Am Chem Soc 2010; 132:16156-64. [DOI: 10.1021/ja1067405] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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Bian Q, Forbes MW, Talbot FO, Jockusch RA. Gas-phase fluorescence excitation and emission spectroscopy of mass-selected trapped molecular ions. Phys Chem Chem Phys 2010; 12:2590-8. [DOI: 10.1039/b921076h] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Schnier PD, Price WD, Jockusch RA, Williams ER. Blackbody infrared radiative dissociation of bradykinin and its analogues: energetics, dynamics, and evidence for salt-bridge structures in the gas phase. J Am Chem Soc 2009; 118:7178-89. [PMID: 16525512 PMCID: PMC1393282 DOI: 10.1021/ja9609157] [Citation(s) in RCA: 361] [Impact Index Per Article: 24.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Blackbody infrared radiative dissociation (BIRD) spectra of singly and doubly protonated bradykinin and its analogues are measured in a Fourier-transform mass spectrometer. Rate constants for dissociation are measured as a function of temperature with reaction delays up to 600 s. From these data, Arrhenius activation parameters in the zero-pressure limit are obtained. The activation parameters and dissociation products for the singly protonated ions are highly sensitive to small changes in ion structure. The Arrhenius activation energy (E(a)) and pre-exponential (or frequency factor, A) of the singly protonated ions investigated here range from 0.6 to 1.4 eV and 10(5) to 10(12) s(-1), respectively. For bradykinin and its analogues differing by modification of the residues between the two arginine groups on either end of the molecule, the singly and doubly protonated ions have average activation energies of 1.2 and 0.8 eV, respectively, and average A values of 10(8) and 10(12) s(-1), respectively, i.e., the presence of a second charge reduces the activation energy by 0.4 eV and decreases the A value by a factor of 10(4). This demonstrates that the presence of a second charge can dramatically influence the dissociation dynamics of these ions. The doubly protonated methyl ester of bradykinin has an E(a) of 0.82 eV, comparable to the value of 0.84 eV for bradykinin itself. However, this value is 0.21 +/- 0.08 eV greater than that of singly protonated methyl ester of bradykinin, indicating that the Coulomb repulsion is not the most significant factor in the activation energy of this ion. Both singly and doubly protonated Lys-bradykinin ions have higher activation energies than the corresponding bradykinin ions indicating that the addition of a basic residue stabilizes these ions with respect to dissociation. Methylation of the carboxylic acid group of the C-terminus reduces the E(a) of bradykinin from 1.3 to 0.6 eV and the A factor from 1012 to 105 s(-1). This modification also dramatically changes the dissociation products. Similar results are observed for [Ala(6)]-bradykinin and its methyl ester. These results, in combination with others presented here, provide experimental evidence that the most stable form of singly protonated bradykinin is a salt-bridge structure.
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Rodriguez-Cruz SE, Jockusch RA, Williams ER. Hydration energies of divalent metal ions, Ca2+ (H2O)n (N = 5-7) and Ni2+ (H2O)m (N = 6-8), obtained by blackbody infrared radiative dissociation. J Am Chem Soc 2009; 120:5842-3. [PMID: 16479268 PMCID: PMC1364451 DOI: 10.1021/ja980716i] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Rodriguez-Cruz SE, Jockusch RA, Williams ER. Binding energies of hexahydrated alkaline earth metal ions, M2+(H2O)6, M = Mg, Ca, Sr, Ba: evidence of isomeric structures for magnesium. J Am Chem Soc 2009; 121:1986-7. [PMID: 16429613 PMCID: PMC1325213 DOI: 10.1021/ja983232v] [Citation(s) in RCA: 100] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Price WD, Jockusch RA, Williams ER. Binding energies of protonated betaine complexes: a probe of zwitterion structure in the gas phase. J Am Chem Soc 2009; 120:3474-84. [PMID: 16543945 PMCID: PMC1403153 DOI: 10.1021/ja972527q] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The dissociation kinetics of proton-bound dimers of betaine with molecules of comparable gas-phase basicity were investigated using blackbody infrared radiative dissociation (BIRD). Threshold dissociation energies were obtained from these data using master equation modeling. For bases that have comparable or higher gas-phase basicity, the binding energy of the protonated base.betaine complex is approximately 1.4 eV. For molecules that are approximately 2 kcal/mol or more less basic, the dissociation energy of the complexes is approximately 1.2 eV. The higher binding energy of the former is attributed to an ion-zwitterion structure which has a much larger ion-dipole interaction. The lower binding energy for molecules that are approximately 2 kcal/mol or more less basic indicates that an ion-molecule structure is more favored. Semiempirical calculations at both the AM1 and PM3 levels indicate the most stable ion-molecule structure is one in which the base interacts with the charged quaternary ammonium end of betaine. These results indicate that the measurement of binding energies of neutral molecules to biological ions could provide a useful probe for the presence of zwitterions and salt bridges in the gas phase. From the BIRD data, the gas-phase basicity of betaine obtained from the kinetic method is found to be 239.2 +/- 1.0 kcal/mol. This value is in excellent agreement with the value of 239.3 kcal/mol (298 K) from ab initio calculations at the MP2/6-31+g** level. The measured value is slightly higher than those reported previously. This difference is attributed to entropy effects. The lower ion internal energy and longer time frame of BIRD experiments should provide values closer to those at standard temperature.
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Forbes MW, Jockusch RA. Deactivation Pathways of an Isolated Green Fluorescent Protein Model Chromophore Studied by Electronic Action Spectroscopy. J Am Chem Soc 2009; 131:17038-9. [DOI: 10.1021/ja9066404] [Citation(s) in RCA: 117] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Forbes MW, Jockusch RA, Young AB, Harrison AG. Fragmentation of protonated dipeptides containing arginine. Effect of activation method. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2007; 18:1959-66. [PMID: 17869129 DOI: 10.1016/j.jasms.2007.08.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2007] [Revised: 08/07/2007] [Accepted: 08/07/2007] [Indexed: 05/17/2023]
Abstract
The fragmentation reactions of the protonated dipeptides Gly-Arg and Arg-Gly have been studied using collision-induced dissociation (CID) in a quadrupole ion trap, by in-source CID in a single-quadrupole mass spectrometer and by CID in the quadrupole cell of a QqTOF mass spectrometer. In agreement with earlier quadrupole ion trap studies (Farrugia, J. M.; O'Hair, R. A. J., Int. J. Mass Spectrom., 2003, 222, 229), the CID mass spectra obtained with the ion trap for the MH(+) ions and major fragment ions are very similar for the two isomers indicating rearrangement to a common structure before fragmentation. In contrast, in-source CID of the MH(+) ions and QqTOF CID of the MH(+), [MH - NH(3)](+) and [MH <23 HN = C(NH(2))(2)](+) ions provide distinctly different spectra for the isomeric dipeptides, indicating that rearrangement to a common structure has not occurred to a significant extent under these conditions even near the threshold for fragmentation in the QqTOF instrument. Clearly, under normal operating conditions significantly different fragmentation behavior is observed in the ion trap and beam-type experiments. This different behavior probably can be attributed to the shorter observation times and concomitant higher excitation energies in the in-source and QqTOF experiments compared to the long observation times and lower excitation energies relevant to the ion trap experiments. Based largely on elemental compositions derived from accurate mass measurements in QqTOF studies fragmentation schemes are proposed for the MH(+), [MH - NH(3)](+), and [MH - (HN = C(NH(2))(2))](+) ions.
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Forbes MW, Bush MF, Polfer NC, Oomens J, Dunbar RC, Williams ER, Jockusch RA. Infrared Spectroscopy of Arginine Cation Complexes: Direct Observation of Gas-Phase Zwitterions. J Phys Chem A 2007; 111:11759-70. [DOI: 10.1021/jp074859f] [Citation(s) in RCA: 164] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Bush MF, Forbes MW, Jockusch RA, Oomens J, Polfer NC, Saykally RJ, Williams ER. Infrared Spectroscopy of Cationized Lysine and ε-N-methyllysine in the Gas Phase: Effects of Alkali-Metal Ion Size and Proton Affinity on Zwitterion Stability. J Phys Chem A 2007; 111:7753-60. [PMID: 17636967 DOI: 10.1021/jp071902q] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The gas-phase structures of protonated and alkali-metal-cationized lysine (Lys) and epsilon-N-methyllysine (Lys(Me)) are investigated using infrared multiple photon dissociation (IRMPD) spectroscopy utilizing light generated by a free electron laser, in conjunction with ab initio calculations. IRMPD spectra of Lys.Li(+) and Lys.Na(+) are similar, but the spectrum for Lys.K(+) is different, indicating that the structure of lysine in these complexes depends on the metal ion size. The carbonyl stretch of a carboxylic acid group is clearly observed in each of these spectra, indicating that lysine is nonzwitterionic in these complexes. A detailed comparison of these spectra to those calculated for candidate low-energy structures indicates that the bonding motif for the metal ion changes from tricoordinated for Li and Na to dicoordinated for K, clearly revealing the increased importance of hydrogen-bonding relative to metal ion solvation with increasing metal ion size. Spectra for Lys(Me).M(+) show that Lys(Me), an analogue of lysine whose side chain contains a secondary amine, is nonzwitterionic with Li and zwitterionic with K and both forms are present for Na. The proton affinity of Lys(Me) is 16 kJ/mol higher than that of Lys; the higher proton affinity of a secondary amine can result in its preferential protonation and stabilization of the zwitterionic form.
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Jockusch RA, Talbot FO, Rogers PS, Simone MI, Fleet GWJ, Simons JP. Carbohydrate Amino Acids: The Intrinsic Conformational Preference for a β-Turn-Type Structure in a Carbopeptoid Building Block. J Am Chem Soc 2006; 128:16771-7. [PMID: 17177427 DOI: 10.1021/ja0607133] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Infrared ion-dip spectroscopy coupled with DFT and ab initio calculations are used to establish the intrinsic conformational preference of the basic structural unit of a peptide mimic, a cis-tetrahydrofuran-based "carbopeptoid" (amide-sugar-amide), isolated at low temperature in the gas phase. The carbopeptoid units form a beta-turn-type structure, stabilized by an intramolecular NH --> O=C hydrogen bond across the sugar ring, thus forming a 10-membered, C10 turn. Despite the clear preference for C10 beta-turn structures in the basic unit, however, the presence of multiple hydrogen-bond donating and accepting groups also generates a rich conformational landscape, and alternative structures may be populated in related molecules. Calculations on an extended, carbopeptoid dimer unit, which includes an alternating amide-sugar-amide-sugar-amide chain, identify conformers exhibiting alternative hydrogen-bonding arrangements that are somewhat more stable than the lowest-energy double beta-turn forming conformer.
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Carçabal P, Hünig I, Gamblin DP, Liu B, Jockusch RA, Kroemer RT, Snoek LC, Fairbanks AJ, Davis BG, Simons JP. Building Up Key Segments of N-Glycans in the Gas Phase: Intrinsic Structural Preferences of the α(1,3) and α(1,6) Dimannosides. J Am Chem Soc 2006; 128:1976-81. [PMID: 16464099 DOI: 10.1021/ja055891v] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The intrinsic conformer specific vibrational spectra of two important subunits of the core pentasaccharide of N-linked glycans, the alpha(1,3) and alpha(1,6) dimannosides, have been recorded in the gas phase. Coupling these measurements with a computational exploration of their conformational landscapes has enabled their conformational assignment and has identified characteristic vibrational signatures associated with particular conformational families-including those that do or do not display inter-ring hydrogen bonding across the glycosidic linkage. In addition, the IR spectra of the monosaccharide moieties provide benchmarks, through which the conformational assignments can be refined. This introduces a general concept of modularity and secondary structure in oligosaccharides--essential for the success of similar studies on larger oligosaccharides in the future.
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Carçabal P, Jockusch RA, Hünig I, Snoek LC, Kroemer RT, Davis BG, Gamblin DP, Compagnon I, Oomens J, Simons JP. Hydrogen Bonding and Cooperativity in Isolated and Hydrated Sugars: Mannose, Galactose, Glucose, and Lactose. J Am Chem Soc 2005; 127:11414-25. [PMID: 16089470 DOI: 10.1021/ja0518575] [Citation(s) in RCA: 144] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The conformation of phenyl-substituted monosaccharides (mannose, galactose, and glucose) and their singly hydrated complexes has been investigated in the gas phase by means of a combination of mass selected, conformer specific ultraviolet and infrared double resonance hole burning spectroscopy experiments, and ab initio quantum chemistry calculations. In each case, the water molecule inserts into the carbohydrate at a position where it can replace a weak intramolecular interaction by two stronger intermolecular hydrogen bonds. The insertion can produce significant changes in the conformational preferences of the carbohydrates, and there is a clear preference for structures where cooperative effects enhance the stability of the monosaccharide conformers to which the water molecule chooses to bind. The conclusions drawn from the study of monosaccharide-water complexes are extended to the disaccharide lactose and discussed in the light of the underlying mechanisms that may be involved in the binding of carbohydrate assemblies to proteins and the involvement, or not, of key structural water molecules.
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Simons JP, Jockusch RA, ÇarÇabal P, Hünig I, Kroemer RT, Macleod NA, Snoek LC. Sugars in the gas phase. Spectroscopy, conformation, hydration, co-operativity and selectivity. INT REV PHYS CHEM 2005. [DOI: 10.1080/01442350500415107] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Hünig I, Painter AJ, Jockusch RA, Carçabal P, Marzluff EM, Snoek LC, Gamblin DP, Davis BG, Simons JP. Adding water to sugar: A spectroscopic and computational study of α- and β-phenylxyloside in the gas phase. Phys Chem Chem Phys 2005; 7:2474-80. [PMID: 15962032 DOI: 10.1039/b504230e] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The gas phase structures of phenyl alpha- and beta-d-xylopyranoside (alpha- and beta-pXyl) and their mono-hydrates have been investigated using a combination of resonant two-photon ionization (R2PI), ultra-violet hole-burning and resonant infrared ion dip spectroscopy, coupled with density functional theory (DFT) and ab initio computation. The hole-burning experiments indicate the population of a single conformer only, in each of the two anomers. Their experimental and calculated infrared spectra are both consistent with a conformational assignment corresponding to the computed global minimum configuration. All three OH groups are oriented towards the oxygen atom (O1) on the anomeric carbon atom to form an all trans(ttt) counter-clockwise chain of hydrogen bonds. The mono-hydrates, alpha- and beta-pXyl(H(2)O) each populate two distinct structures in the molecular beam environment, with the water molecule inserted between OH4 and OH3 or between OH3 and OH2 in alpha-pXyl(H2O), and between OH2 and O1 in either of two alternative orientations, in beta-pXyl(H2O). In all of the mono-hydrated xyloside complexes, the water molecule inserts into the weakest link of the sugar molecules' hydrogen-bonded chain of hydroxy groups, creating a single extended chain, strengthened by co-operativity. The all-trans configuration of the xylose moiety is retained and the mono-hydrate structures correspond to those calculated to lie at the lowest relative energies.
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Jockusch RA, Kroemer RT, Talbot FO, Snoek LC, Carçabal P, Simons JP, Havenith M, Bakker JM, Compagnon I, Meijer G, von Helden G. Probing the Glycosidic Linkage: UV and IR Ion-Dip Spectroscopy of a Lactoside. J Am Chem Soc 2004; 126:5709-14. [PMID: 15125663 DOI: 10.1021/ja031679k] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The beta(1-->4) glycosidic linkage found in lactose is a prevalent structural motif in many carbohydrates and glycoconjugates. Using UV and IR ion-dip spectroscopies to probe benzyl lactoside isolated in the gas phase, we find that the disaccharide unit adopts only a single, rigid structure. Its fully resolved infrared ion-dip spectrum is in excellent agreement with that of the global minimum structure computed ab initio. This has glycosidic torsion angles of phi(H) (H1-C1-O-C4') approximately 180 degrees and psi(H) (C1-O-C4'-H4') approximately 0 degrees which correspond to a rotation of approximately 150 degrees about the glycosidic bond compared to the accepted solution-phase conformation. We discuss the biological implications of this discovery and the generality of the strategies employed in making it.
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Jockusch RA, Kroemer RT, Talbot FO, Simons JP. Hydrated Sugars in the Gas Phase: Spectroscopy and Conformation of Singly Hydrated Phenyl β-d-Glucopyranoside. J Phys Chem A 2003. [DOI: 10.1021/jp0351730] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Kelley WP, Wolters AM, Sack JT, Jockusch RA, Jurchen JC, Williams ER, Sweedler JV, Gilly WF. Characterization of a novel gastropod toxin (6-bromo-2-mercaptotryptamine) that inhibits shaker K channel activity. J Biol Chem 2003; 278:34934-42. [PMID: 12815055 DOI: 10.1074/jbc.m301271200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A novel potassium channel antagonist has been purified from the defensive mucus secreted by Calliostoma canaliculatum, a marine snail found in the temperate coastal waters of the western Pacific. The toxin is expelled from the hypobranchial gland as part of a defensive response and is contained within a viscous matrix that minimizes dilution and degradation. The active compound was isolated by multistage microbore HPLC separations followed by bioactivity assays. Nuclear magnetic resonance, combined with electrospray ionization Fourier-transform ion cyclotron resonance and electrospray ionization ion trap mass spectrometry indicate that the active component is a heretofore unknown indole-derivative, a disulfide-linked dimer of 6-bromo-2-mercaptotryptamine (BrMT). Exudates from the hypobranchial glands of various marine mollusks have been sources for dye compounds such as 6-6 dibromoindigo, the ancient dye Tyrian purple. BrMT represents the first correlation of a hypobranchial gland exudate with a molecular response. Voltage clamp experiments with a number of K channel subtypes indicate that BrMT inhibits certain voltage-gated K channels of the Kv1 subfamily.
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Paech K, Jockusch RA, Williams ER. Slow Infrared Laser Dissociation of Biomolecules in the Rapid Energy Exchange Limit. J Phys Chem A 2003. [DOI: 10.1021/jp030056q] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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