Structural Interrogation of Electrosprayed Peptide Ions by Gas-Phase H/D Exchange and Electron Capture Dissociation Mass Spectrometry

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<p>The structural characterization of gaseous biomolecular ions remains a challenging task. Here, we employ a combination of gas-phase hydrogen–deuterium exchange (HDX) and electron capture dissociation (ECD) mass spectrometry for gaining insights into the properties of two electrosprayed peptides: RA9K and RG9K. Mass analysis of ECD fragments provides spatially resolved labeling information. ND3-mediated HDX at peptide termini and amino acid side chains goes to completion within 1 s. Backbone amide labeling occurs more slowly, and proceeds in a structurally sensitive fashion. HDX is more extensive for RG9K than for RA9K, suggesting a more “open” conformation for the former. Residues 7–10 in RA9K are strongly protected, which indicates the presence of stable backbone hydrogen bonds at these sites. Our findings are consistent with the results of previous ion mobility measurements and computational investigations. Overall, it appears that the combination of gas-phase HDX and ECD represents a viable approach for uncovering structural features of biomolecular ions in the gas phase.</p>