Soft X-ray spectroscopy as a probe for gas-phase protein structure: Electron impact ionization from within

Sadia Bari, Dmitrii Egorov, Thomas L.c. Jansen, Rebecca Boll, Ronnie Hoekstra, Simone Techert, Vicente Zamudio-bayer, Christine Bülow, Rebecka Lindblad, Georg Leistner, Arkadiusz Ławicki, Konstantin Hirsch, Piter S. Miedema, Bernd Von Issendorf, Tobias Lau, Thomas Schlathölter

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Abstract

Preservation of protein conformation upon transfer into the gas-phase is keyfor structure determination of free single molecules, e.g. using X-ray free-electron lasers. In the gasphase, the helicity of melittin decreases strongly as the protein’s protonation state increases. We demonstrate the sensitivity of soft X-ray spectroscopy to the gas phase conformation of melittin cations ([melittin+qH]q+, q=2-4) in a cryogenic linear radiofrequency ion trap. With increasing helicity we observe a decrease of the dominating carbon 1s-* transition in the amide C=O bonds for non-dissociative single ionization and an increase for non-dissociative double ionization. As the underlying mechanism we identify inelastic electron scattering.Using an independent atom model we show that the more compact nature of the helical protein conformation substantially increases the probability for off-site intramolecular ionization by inelastic Auger electron scattering.
Original languageEnglish
Pages (from-to)7631-7636
JournalChemistry
Volume24
Issue number30
Early online date10-Apr-2018
DOIs
Publication statusPublished - 28-May-2018

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