Abstract
The ability of 18-crown-6 (18C6) to form noncovalent complexes with cationic groups in the gas phase has been leveraged in numerous, largely orthogonal mass spectrometry-based applications. Although the fundamental interaction between 18C6 and a charged group in the gas phase is quite strong, the strength of attachment of 18C6 to large molecules is more difficult to predict because intramolecular binding of the cation can be competitive. Herein, we demonstrate in experiments with model peptides that 18C6 adducts are not strongly attached to flexible molecules with numerous potential hydrogen bonding sites. 18C6 adduct stability is increased if intramolecular charge complexation is inhibited by sterics or competitive binding. It is demonstrated with molecular mechanics that significant structural changes occur upon loss of 18C6 in model peptides. Examination of the loss of 18C6 adducts from proteins following collisional activation reveals that lower charge states lose the most 18C6. The degree of 18C6 adduct stability may reflect the degree of structural reorganization that occurs following collisional activation, suggesting that lower charge states represent structures that are not similar to gas phase idealized states. In this regard, 18C6 may serve the function of protecting solution phase protein structure. Collisional activation of holomyoglobin with 18C6 adducts attached reveals that heme loss occurs primarily after 18C6 loss, further supporting the notion that 18C6 protects native structure by solvating charged sites.
Similar content being viewed by others
References
Gokel, G.W., Leevy, W.M., Weber, M.E.: Crown ethers: sensors for ions and molecular scaffolds for materials and biological models. Chem. Rev. 104, 2723–2750 (2004)
Landini, D., Montanar, F., Pirisi, F.M.: Crown ethers as phase-transfer catalysts in 2-phase reactions. J. Chem. Soc. Chem. Commun. 21, 879–880 (1974)
De Silva, A.P., Desilva, S.A.: Fluorescent signaling crown ethers-switching on of fluorescence by alkali-metal ion recognition and binding in situ. J. Chem. Soc. Chem. Commun. 23, 1709–1710 (1986)
Kuhn, R., Stoecklin, F., Erni, F.: Chiral separations by host–guest complexation with cyclodextrin and crown-ether in capillary zone electrophoresis. Chromatographia 33, 32–36 (1992)
Maleknia, S., Brodbelt, J.: Gas-phase selectivities of crown ethers for alkali–metal ion complexation. J. Am. Chem. Soc. 114, 4295–4298 (1992)
Chu, I.H., Zhang, H., Dearden, D.V.: Macrocyclic chemistry in the gas-phase—intrinsic cation affinities and complexation rates for alkali–metal cation complexes of crown-ethers and glymes. J. Am. Chem. Soc. 115, 5736–5744 (1993)
More, M.B., Ray, D., Armentrout, P.B.: Intrinsic affinities of alkali cations for 15-crown-5 and 18-crown-6: bond dissociation energies of gas-phase M+−crown ether complexes. J. Am. Chem. Soc. 121, 417–423 (1999)
Julian, R.R., Beauchamp, J.L.: Site specific sequestering and stabilization of charge in peptides by supramolecular adduct formation with 18-crown-6 ether by way of electrospray ionization. Int. J. Mass Spectrom. 210, 613–623 (2001)
Lee, S.W., Lee, H.N., Kim, H.S., Beauchamp, J.L.: Selective binding of crown ethers to protonated peptides can be used to probe mechanisms of H/D exchange and collision-induced dissociation reactions in the gas phase. J. Am. Chem. Soc. 120, 5800–5805 (1998)
Ly, T., Julian, R.R.: Using ESI-MS to probe protein structure by site-specific noncovalent attachment of 18-crown-6. J. Am. Soc. Mass Spectrom. 17, 1209–1215 (2006)
Sun, Q.Y., Nelson, H., Ly, T., Stoltz, B.M., Julian, R.R.: Side chain chemistry mediates backbone fragmentation in hydrogen deficient peptide radicals. J. Proteome Res. 8, 958–966 (2009)
Bohrer, B.C., Clemmer, D.E.: Shift reagents for multidimensional ion mobility spectrometry-mass spectrometry analysis of complex peptide mixtures: evaluation of 18-Crown-6 ether complexes. Anal. Chem. 83, 5377–5385 (2011)
Pagel, K., Hyung, S.-J., Ruotolo, B.T., Robinson, C.V.: Alternate dissociation pathways identified in charge-reduced protein complex ions. Anal. Chem. 82(12), 5363–5372 (2010)
Kupser, P., Pagel, K., Oomens, J., Polfer, N., Koksch, B., Meijer, G., von Helden, G.: Amide-I and -II vibrations of the cyclic beta-sheet model peptide gramicidin S in the gas phase. J. Am. Chem. Soc. 132, 2085–2093 (2010)
Buschmann, H.J., Schollmeyer, E., Mutihac, L.: The complexation of the ammonium ion by 18-crown-6 in different solvents and by noncyclic ligands, crown ethers, and cryptands in methanol. Supramol. Sci. 5, 139–142 (1998)
Hamdy, O.M., Julian, R.R.: Reflections on charge state distributions, protein structure, and the mystical mechanism of electrospray ionization. J. Am. Soc. Mass Spectrom. 23, 1–6 (2012)
Chen, Y., Rodgers, M.T.: Structural and energetic effects in the molecular recognition of amino acids by 18-crown-6. J. Am. Chem. Soc. 134, 5863–5875 (2012)
Chen, Y., Rodgers, M.T.: Structural and energetic effects in the molecular recognition of protonated peptidomimetic bases by 18-crown-6. J. Am. Chem. Soc. 134, 2313–2324 (2012)
David, W.M., Brodbelt, J.S.: Threshold dissociation energies of protonated amine/polyether complexes in a quadrupole ion trap. J. Am. Soc. Mass Spectrom. 14(4), 383–392 (2003)
Chan, W.C., White, P.D.: Fmoc Solid Phase Peptide Synthesis, pp. 9–74. Oxford University Press, New York (2000)
McClellan, J.E., Murphy, J.P., Mulholland, J.J., Yost, R.A.: Effects of fragile ions on mass resolution and on isolation for tandem mass spectrometry in the quadrupole ion trap mass spectrometer. Anal. Chem. 74, 402–412 (2002)
Murphy, J.P., Yost, R.A.: Origin of mass shifts in the quadrupole ion trap: dissociation of fragile ions observed with a hybrid ion trap/mass filter instrument. Rapid Commun. Mass Spectrom. 14, 270–273 (2000)
Cowan, D.A., Kiman, A.T., Kubli-Garfias, C., Welchman, H.J.: Ion trap MS/MS of intact testosterone and epitestosterone conjugates—adducts, fragile ions, and the advantages of derivatization. Steroids 73, 621–628 (2008)
Huffman, C.L., Williams, M.L., Benoist, D.M., Overstreet, R.E., Jellen-McCullough, E.E.: Dependence of collision-induced dissociation energy on molecular degrees of freedom as a means to assess relative binding affinity in multivalent complexes. Rapid Commun. Mass Spectrom. 25, 2299–2306 (2011)
Brodbelt, J.S.: Shedding light on the Frontier of photodissociation. J. Am. Soc. Mass Spectrom. 22, 197–206 (2011)
Newsome, G.A., Glish, G.L.: Improving IRMPD in a quadrupole ion trap. J. Am. Soc. Mass Spectrom. 20, 1127–1131 (2009)
Uetrecht, C., Rose, R.J., van Duijn, E., Lorenzen, K., Heck, A.J.R.: Ion mobility mass spectrometry of proteins and protein assemblies. Chem. Soc. Rev. 39, 1633–1655 (2009)
Warnke, S., von Helden, G., Pagel, K.: Protein structure in the gas phase: the influence of side-chain microsolvation. J. Am. Chem. Soc. 135, 1177–1180 (2013)
Babu, K.R., Douglas, D.J.: Methanol-induced conformations of myoglobin at pH 4.0. Biochemistry 39, 14702–14710 (2000)
Acknowledgments
The authors thank NIH for funding (R01 GM084106) and John Syka and Jae Schwartz for helpful discussions.
Author information
Authors and Affiliations
Corresponding author
Electronic supplementary material
Below is the link to the electronic supplementary material.
ESM 1
(DOCX 596 kb)
Rights and permissions
About this article
Cite this article
Tao, Y., Julian, R.R. Factors that Influence Competitive Intermolecular Solvation of Protonated Groups in Peptides and Proteins in the Gas Phase. J. Am. Soc. Mass Spectrom. 24, 1634–1640 (2013). https://doi.org/10.1007/s13361-013-0684-z
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s13361-013-0684-z