Correia Catarina F, Clavaguera Carine, Erlekam Undine, Scuderi Debora, Ohanessian Gilles
Laboratoire des Mécanismes Réactionnels, Département de Chimie, Ecole Polytechnique, CNRS, 91128 Palaiseau Cedex, France.
Chemphyschem. 2008 Dec 1;9(17):2564-73. doi: 10.1002/cphc.200800469.
The protonated, phosphorylated dipeptide GpY+H is characterized by mid-infrared multiple-photon dissociation (IRMPD) spectroscopy and quantum-chemical calculations. The ions are generated in an external electrospray source and analyzed in a Fourier transform ion cyclotron resonance mass spectrometer, and their fragmentation is induced by resonant absorption of multiple photons emitted by a tunable free-electron laser. The IRMPD spectra are recorded in the 900-1730 cm(-1) range and compared to the absorption spectra computed for the lowest energy structures. A detailed calibration of computational levels, including B3LYP-D and coupled cluster, is carried out to obtain reliable relative energies of the low-energy conformers. It turns out that a single structure can be invoked to assign the IRMPD spectrum. Protonation at the N terminus leads to the formation of a strong ionic hydrogen bond with the phosphate P=O group in all low-energy structures. This leads to a P=O stretching frequency for GpY+H that is closer to that of pS+H than to that of pY+H and thus demonstrates the sensitivity of this mode to the phosphate environment. The COP phosphate ester stretching mode is confirmed to be an intrinsic diagnostic for identification of which type of amino acid is phosphorylated.
通过中红外多光子解离（IRMPD）光谱和量子化学计算对质子化、磷酸化二肽GpY+H进行了表征。离子在外部电喷雾源中产生，并在傅里叶变换离子回旋共振质谱仪中进行分析，其碎片化由可调谐自由电子激光发射的多光子的共振吸收诱导。IRMPD光谱在900 - 1730 cm(-1)范围内记录，并与为最低能量结构计算的吸收光谱进行比较。对包括B3LYP-D和耦合簇在内的计算水平进行了详细校准，以获得低能量构象异构体的可靠相对能量。结果表明，可以用单一结构来归属IRMPD光谱。在所有低能量结构中，N端质子化导致与磷酸根P=O基团形成强离子氢键。这使得GpY+H的P=O伸缩频率比GpY+H更接近pS+H，而不是pY+H，从而证明了该模式对磷酸根环境的敏感性。COP磷酸酯伸缩模式被确认为鉴定哪种氨基酸被磷酸化的固有诊断方法。
