New Publication – Page 2

Apr. 2013May. 2013

New Publications: Electron Transfer Dissociation of Photolabeled Peptides

hydrazine_loos Gas-phase conformations and electron transfer dissociations of pentapeptide ions containing the photo-Leu residue (L*) were studied. Exhaustive conformational search including molecular dynamics force-field, semi-empirical, ab initio, and density functional theory calculations established that the photo-Leu residue did not alter the gas-phase conformations of (GL*GGK + 2H)²⁺ and (GL*GGK-NH₂ + H)⁺ ions, which showed the same conformer energy ranking as the unmodified Leu-containing ions. This finding is significant in that it simplifies conformational analysis of photo-labeled peptide ions. Electron transfer dissociation mass spectra of (GL*GGK + 2H)²⁺, (GL*GGK-NH₂ + 2H)²⁺,(GL*GGKK + 2H)²⁺, (GL*GLK + 2H)²⁺, and (GL*LGK + 2H)²⁺ showed 16 %–21 % fragment ions originating by radical rearrangements and cleavages in the diazirine ring. These side-chain dissociations resulted in eliminations of N₂H₃, N₂H₄, [N₂H₅], and [NH₄O] neutral fragments and were particularly abundant in long-lived charge-reduced cation-radicals. Deuterium labeling established that the neutral hydrazine molecules mainly contained two exchangeable and two nonexchangeable hydrogen atoms from the peptide and underwent further H/D exchange in an ion–molecule complex. Electron structure calculations on the charge-reduced ions indicated that the unpaired electron was delocalized between the diazirine and amide π* electronic systems in the low electronic states of the cation-radicals. The diazirine moiety in GL*GGK-NH₂was calculated to have an intrinsic electron affinity of 1.5 eV, which was further increased by the Coulomb effect of the peptide positive charge. Mechanisms are proposed for the unusual elimination of hydrazine from the photo-labeled peptide ions.

Electron Transfer Dissociation of Photolabeled Peptides. Backbone Cleavages Compete with Diazirine Ring Rearrangements Aleš Marek, Robert Pepin, Bo Peng, Kenneth J. Laszlo, Matthew F. Bush, František Tureček. J. Am. Soc. Mass Spectrom. 2013, DOI:10.1007/s13361-013-0630-0. (Link|PUBMED)

Aug. 2012Sep. 2012

New Publication: Ion Mobility of Peptide Ions

One difficulty in using ion mobility (IM) mass spectrometry (MS) to improve the specificity of peptide ion assignments is that IM separations are performed using a range of pressures, gas compositions, temperatures, and modes of separation, which makes it challenging to rapidly extract accurate shape parameters. We report collision cross section values (Ω) in both He and N₂ gases for 113 peptide ions determined directly from drift times measured in a low-pressure, ambient temperature drift cell with radio-frequency (rf) ion confinement. These peptide ions have masses ranging from 231 to 2969 Da, Ω_He of 89–616 Å², and Ω_N₂ of 151–801 Å²; thus, they are ideal for calibrating results from proteomics experiments. These results were used to quantify the errors associated with traveling-wave Ω measurements of peptide ions and the errors concomitant with using drift times measured in N₂ gas to estimate Ω_He. More broadly, these results enable the rapid and accurate determination of calibrated Ω for peptide ions, which could be used as an additional parameter to increase the specificity of assignments in proteomics experiments.

Ion Mobility Mass Spectrometry of Peptide Ions: Effects of Drift Gas and Calibration Strategies Matthew F. Bush, Iain D. G. Campuzano, Carol V. Robinson. Anal. Chem. 2012, 84, 7124–7130.

Dec. 2011Sep. 2012

New Article in Analytical Chemistry

Collision cross sections (CCS) for a set of drug-like molecules were measured using RF-confining drift tube ion mobility experiments in both helium and nitrogen gases. These results enabled accurate calibrated CCS using traveling-wave ion mobility experiments and improved accuracy CCS calculations for ions in nitrogen gas. These experiments demonstrate that ion mobility is sensitive to very subtle differences in molecular structure, including differentiation of the diastereomers betamethasone (left) and dexamethasone (right).

Structural Characterization of Drug-like Compounds by Ion Mobility Mass Spectrometry: Comparison of Theoretical and Experimentally Derived Nitrogen Collision Cross-sections Iain Campuzano, Matthew F. Bush, Carol V. Robinson, Claire Beaumont, Keith Richardson, Hyungjun Kim, Hugh I. Kim. Anal. Chem. 2012, 84, 1026-1033.

Dec. 2011Sep. 2012

New Frontiers Article in Chemical Physics Letters

One challenge in interpreting results from mass spectrometry experiments is that the structures of protein complexes in the gas phase may differ from those in solution. Here, we investigate the stabilization properties of trisH+, a non-volatile electrospray buffer component, by experimentally characterizing the unfolding and dissociation of three gas-phase tetrameric protein complexes. We find that trisH+ preferentially stabilizes the compact native-like state of these protein complexes.

Gas-Phase Protein Assemblies: Unfolding Landscapes and Preserving Native-Like Structures Using Noncovalent Adducts Joanna Freekea, Matthew F. Bush, Carol V. Robinson, Brandon T. Ruotolo. Chem. Phys. Lett. 2012, 524, 1-9.