On the maximum charge state and proton transfer reactivity of peptide and protein ions formed by electrospray ionization

A relatively simple model for calculation of the energetics of gas-phase proton transfer reactions and the maximum charge state of multiply protonated ions formed by electrospray ionization is presented. This model is based on estimates of the intrinsic proton transfer reactivity of sites of protonation and point charge Coulomb interactions. From this model, apparent gas-phase basicities (GBapp) of multiply protonated ions are calculated. Comparison of this value to the gas-phase basicity of the solvent from which an ion is formed enables a maximum charge state to be calculated. For 13 commonly electrosprayed proteins, our calculated maximum charge states are within an average of 6% of the experimental values reported in the literature. This indicates that the maximum charge state for proteins is determined by their gas-phase reactivity. Similar results are observed for peptides with many basic residues. For peptides with few basic residues, we find that the maximum charge state is better correlated to the charge state in solution. For low charge state ions, we find that the most basic sites Arg, Lys, and His are preferentially protonated. A significant fraction of the less basic residues Pro, Trp, and Gln are protonated in high charge state ions. The calculated GBapp of individual protonation sites varies dramatically in the high charge state ions. From these values, we calculate a reduced cross section for proton transfer reactivity that is significantly lower than the Langevin collision frequency when the GBapp of the ion is approximately equal to the GB of the neutral base.

[1]  M. Mann,et al.  Electrospray ionization for mass spectrometry of large biomolecules. , 1989, Science.

[2]  F. Röllgen,et al.  Desolvation of ions and molecules in thermospray mass spectrometry , 1989 .

[3]  K. Siu,et al.  Electrospray Mass Spectrometric Study of Protein-Ketone Equilibria in Solution , 1994 .

[4]  Richard D. Smith,et al.  Investigation of the Gas-Phase Structure of Electrosprayed Proteins Using Ion-Molecule Reactions , 1994, Journal of the American Society for Mass Spectrometry.

[5]  P. Kebarle,et al.  Dependence of ion intensity in electrospray mass spectrometry on the concentration of the analytes in the electrosprayed solution , 1993 .

[6]  R. C. Weast.  CRC Handbook of Chemistry and Physics , 1973 .

[7]  C. Beddell,et al.  Mechanism of production of ions in electrospray mass spectrometry , 1993 .

[8]  V. Katta,et al.  Conformational changes in proteins probed by hydrogen-exchange electrospray-ionization mass spectrometry. , 1991, Rapid communications in mass spectrometry : RCM.

[9]  J. V. Iribarne,et al.  On the evaporation of small ions from charged droplets , 1976 .

[10]  Joel F. Liebman,et al.  Evaluated Gas Phase Basicities and Proton Affinities of Molecules; Heats of Formation of Protonated Molecules , 1984 .

[11]  Richard D. Smith,et al.  Proton transfer reactions of multiply charged peptide and protein cations and anions , 1995 .

[12]  Richard D. Smith,et al.  Principles and practice of electrospray ionization—mass spectrometry for large polypeptides and proteins , 1991 .

[13]  Richard D. Smith,et al.  Proton transfer reaction studies of multiply charged proteins in a high mass-to-charge ratio quadrupole mass spectrometer , 1994, Journal of the American Society for Mass Spectrometry.

[14]  P. Kebarle,et al.  An ion source with which ions produced by electrospray can be subjected to ion/molecule reactions at intermediate pressures (10–100 Torr). Deprotonation of polyprotonated peptides , 1992 .

[15]  C. G. Edmonds,et al.  Solvent-induced conformational changes of polypeptides probed by electrospray-ionization mass spectrometry. , 1991, Rapid communications in mass spectrometry : RCM.

[16]  P. Kebarle,et al.  From ions in solution to ions in the gas phase - the mechanism of electrospray mass spectrometry , 1993 .

[17]  K. Siu,et al.  Electrospray mass spectra of protein cations formed in basic solutions , 1994 .

[18]  C. Fenselau,et al.  Proton affinity of arginine measured by the kinetic approach , 1992 .

[19]  B. Chait,et al.  Heat-induced conformational changes in proteins studied by electrospray ionization mass spectrometry. , 1993, Analytical chemistry.

[20]  R. Smith,et al.  Protein structural effects in gas phase ion/molecule reactions with diethylamine. , 1992, Rapid communications in mass spectrometry : RCM.

[21]  J. Henion,et al.  The determination of protein, oligonucleotide and peptide molecular weights by ion-spray mass spectrometry. , 1988, Rapid communications in mass spectrometry : RCM.

[22]  Francis M. Wampler,et al.  Coexisting stable conformations of gaseous protein ions. , 1993, Proceedings of the National Academy of Sciences of the United States of America.

[23]  R. Cooks,et al.  Conformer selection of protein ions by ion mobility in a triple quadrupole mass spectrometer , 1994, Journal of the American Society for Mass Spectrometry.

[24]  L. Pedersen,et al.  The barrier to proton transfer from multiply protonated molecules: A quantum mechanical approach , 1992 .

[25]  Brian T. Chait,et al.  Probing conformational changes in proteins by mass spectrometry , 1990 .

[26]  J. Fenn,et al.  Ion formation from charged droplets: Roles of geometry, energy, and time , 1993, Journal of the American Society for Mass Spectrometry.

[27]  C. Lebrilla,et al.  Gas-phase basicities and sites of protonation of glycine oligomers (GLYn; n = 1-5) , 1993 .

[28]  D. Bohme,et al.  Proton transfer from a fullerene dication. Bracketing the gas-phase acidity of C[sub 60]H[sup [center dot]2+] , 1993 .

[29]  C. D. Gelatt,et al.  Optimization by Simulated Annealing , 1983, Science.

[30]  R. Cooks,et al.  Proton affinities from dissociations of proton-bound dimers , 1981 .

[31]  P. Schnier,et al.  ELECTROSTATIC FORCES AND DIELECTRIC POLARIZABILITY OF MULTIPLY PROTONATED GAS-PHASE CYTOCHROME C IONS PROBED BY ION/MOLECULE CHEMISTRY , 1995 .

[32]  I. Amster,et al.  Gas-phase basicity measurements of dipeptides that contain valine , 1993 .

[33]  Richard D. Smith,et al.  Coulombic effects in the dissociation of large highly charged ions , 1991 .

[34]  D. S. Gross,et al.  Experimental Measurement of Coulomb Energy and Intrinsic Dielectric Polarizability of a Multiply Protonated Peptide Ion Using Electrospray Ionization Fourier-Transform Mass Spectrometry , 1995 .

[35]  Wan Ahmad Tajuddin.  Seeking Global Minima , 1994 .

[36]  C. Dobson,et al.  A partially folded state of hen egg white lysozyme in trifluoroethanol: structural characterization and implications for protein folding. , 1993, Biochemistry.

[37]  C. G. Edmonds,et al.  Effect of reducing disulfide-containing proteins on electrospray ionization mass spectra. , 1990, Analytical chemistry.

[38]  F. McLafferty,et al.  Improved fourier-transform ion-cyclotron-resonance mass spectrometry of large biomolecules , 1993, Journal of the American Society for Mass Spectrometry.

[39]  C. Lebrilla,et al.  Intrinsic basicity of oligomeric peptides that contain glycine, alanine, and valine—The effects of the alkyl side chain on proton transfer reactions , 1995, Journal of the American Society for Mass Spectrometry.

[40]  D. S. Gross,et al.  MEASUREMENT OF COULOMB ENERGY AND DIELECTRIC POLARIZABILITY OF GAS-PHASE DIPROTONATED DIAMINOALKANES , 1995 .

[41]  D. Bohme,et al.  Gas-phase reactions of the buckminsterfullerene cations C[sub 60][sup [center dot]+], C[sub 60][sup 2+], and C[sub 60][sup [center dot]3+] with water, alcohols, and ethers , 1993 .

[42]  C. Fenselau,et al.  Proton affinities of polyglycines assessed by using the kinetic method , 1992, Journal of the American Society for Mass Spectrometry.

[43]  C. Fenselau,et al.  Electrospray analysis of proteins: A comparison of positive-ion and negative-ion mass spectra at high and low pH , 1992 .

[44]  J. Fenn,et al.  Electrospray mass spectrometry of poly(ethylene glycols) with molecular weights up to five million , 1992 .

[45]  F. McLafferty,et al.  Gas-phase folding and unfolding of cytochrome c cations. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[46]  G. Glish,et al.  Reactions of Dimethylamine with Multiply Charged Ions of Cytochrome c , 1990 .

[47]  D. J. Douglas,et al.  Collision cross sections for protein ions , 1993, Journal of the American Society for Mass Spectrometry.

[48]  C. Fenselau,et al.  Structural Determinants of Gas Phase Basicities of Peptides , 1993 .

[49]  R. Cooks,et al.  Gas‐phase basicities and proton affinities of lysine and histidine measured from the dissociation of proton‐bound dimers , 1994 .

[50]  K. Siu,et al.  Are the electrospray mass spectra of proteins related to their aqueous solution chemistry? , 1992, Journal of the American Society for Mass Spectrometry.

[51]  R. C. Mobley,et al.  Molecular Beams of Macroions , 1968 .

[52]  R. Cole,et al.  Disparity between solution‐phase equilibria and charge state distributions in positive‐ion electrospray mass spectrometry , 1994 .

[53]  G. Kruppa,et al.  Deprotonation reactions of multiply protonated ubiquitin ions. , 1994, Rapid communications in mass spectrometry : RCM.

[54]  M. Bowers.  Gas phase ion chemistry , 1979 .