Multiple Electron Ejection from Proteins Resulting from Single-Photon Excitation in the Valence Shell

One-photon multiple ionization is a signature of dynamical electron correlations in atoms and small molecules, as observed in the Auger process when Auger electron emission follows core–shell ionization. In such a process, the high energy needed to remove several electrons is due to the strong Coulombic attraction between the last departing electron(s) and the ionic core. Multiply negatively charged molecules offer the possibility to overcome the Coulombic attraction, opening the way for multielectron photodetachment following valence shell excitation. Here photodetachment studies have been performed on electrosprayed protein polyanions using vacuum ultraviolet synchrotron radiation coupled to a radiofrequency ion trap. Double, triple, and quadruple electron emissions from protein polyanions resulting from single-photon excitation in the valence shell were observed with ionization thresholds below 20 eV photon energy. This suggests the existence of large electronic correlations in proteins between weakly bound electrons standing on distant sites. Besides, the resulting multiradical polyanions appear to be remarkably stable, an important issue in radiobiology

Lysozyme tertiary structure (PDB:1AKI).

<p>(a) CELAAAMK is shown in yellow, GTDVQAWIR in green, HGLDNYR in white, GYSLGNWVCAAK in blue, FESNFNTQATNR in pink and WWCNDGR in red. (b) 180° degree rotation around y-axis.</p

Workflow of the analytical method.

<p>Workflow of the analytical method.</p

Summary of the data for observed peptides analyzed by SRM.

<p>Summary of the data for observed peptides analyzed by SRM.</p

Characteristic doses t₁ and t₂ for observed peptides from native and reduced-alkylated form of lysozyme.

<p>CV stands for coefficient of variation.</p

Sequence of the chicken lysozyme with, highlighted in blue, the detected peptides.

<p>Sequence of the chicken lysozyme with, highlighted in blue, the detected peptides.</p

Evolution of the signal of the CELAAAMK peptide (a, b) and oxidized CELAAA<i>M</i>K peptide (c, d).

<p>CELAAAMK peptide (3 transitions) irradiated in the native (a) and reduced-alkylated form (b) Oxidized CELAAA<i><u>M</u></i>K peptide (3 transitions) irradiated in the native (c) and reduced-alkylated form (d).</p

Summary of backbone and side-chain root mean square deviation (RMSD) data for each observed peptide from the native and reduced-alkylated lysozyme.

<p>The results of the two molecular simulation runs are presented separately.</p

Half-life irradiation doses (D₅₀) and saturating intensity (I_sat) measured for each observed peptide from native and reduced-alkylated form of lysozyme.

<p>CV stands for coefficient of variation.</p

Analysis of the reduced-alkylated lysozyme irradiated with a dose at 1000 Gy.

<p>(a) TIC chromatogram, (b) CID spectrum of the CELAAAMK ion <i>m/z</i> 447.2 detected between 8.8 and 9.9 min and (c) CID spectrum of the CELAAA<i><u>M</u></i>K ion <i>m/z</i> 455.2 detected between 6.8 and 7.2 min.</p