Vibrational Signatures of S-Nitrosoglutathione as Gaseous, Protonated Species

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• 作者：Barbara Gregori ; Leonardo Guidoni ; Barbara Chiavarino ; Debora Scuderi ; Edith Nicol ; Gilles Frison ; Simonetta Fornarini ; Maria Elisa Crestoni
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：October 30, 2014
• 年：2014
• 卷：118
• 期：43
• 页码：12371-12382
• 全文大小：446K
• ISSN：1520-5207

文摘

Gas-phase ions of protonated l-glutathione as native species, [GSH + H]⁺, and S-nitroso derivative, [GSNO + H]⁺, have been generated by electrospray ionization and probed via infrared multiple photon dissociation (IRMPD) action spectroscopy. Insight into the conformational landscape is gained from interpretation of the IR spectra aided by high-level theoretical calculations, which enables structural assignment disclosing both the site of protonation and the intramolecular hydrogen-bond network. Calculations yield the low-energy structures of [GSNO + H]⁺. A admixture of the four most stable ones (SN1, AN1, SN2, and AN2) is apt to account for the experimental IRMPD spectra obtained in both the 1000鈥?000 and the 3100鈥?700 cm^鈥? spectral ranges. The most stable form of [GSNO + H]⁺, SN1, protonated at the amino group, presents a syn conformation at the S鈥揘 (partial) double bond and all peptidic carbonyls involved in (strong) C鈺怬路路路H鈥揘 hydrogen bonds, so allowing closure of a C5 (尾-strand), two C7 (纬-turn), and one C9-membered rings. An appreciable barrier to rotation of 43 kJ mol^鈥? about the S鈥揘 bond is found to separate SN1 from the analogous anti isomer AN1, which lies only 0.70 kJ mol^鈥? higher in free energy. Conformers obtained for [GSH + H]⁺ are very similar to the [GSNO + H]⁺ counterparts, indicating that the S-nitrosation motif does not affect significantly the geometry of the peptide. The observed 谓(NO) signatures at 1622 and 1690 cm^鈥?, merged with other absorptions, are revealed by their sensitivity to ¹⁵NO isotope labeling and by comparison with the IRMPD spectrum of native [GSH + H]⁺, providing a diagnostic probe for the S-nitrosation feature in natural peptides.