Nguyen Huong T H, Shaffer Christopher J, Ledvina Aaron R, Coon Joshua J, Tureček František
Department of Chemistry, Bagley Hall, Box 351700, University of Washington, Seattle, WA, 98195-1700.
Department of Chemistry, University of Wisconsin, Madison, WI, USA.
Int J Mass Spectrom. 2015 Feb 15;378:20-30. doi: 10.1016/j.ijms.2014.06.028.
The serine residue displays specific effects on the dissociations of peptide fragment cation-radicals of the type which are produced by electron transfer dissociation. Energy-resolved collision-induced dissociation (ER-CID), time-resolved infrared multiphoton dissociation (TR-IRMPD), and single-photon UV photodissociation at 355 nm revealed several competitive dissociation pathways consisting of loss of OH radical, water, and backbone cleavages occurring at -terminal and -terminal positions relative to the serine residue. The activation modes using slow-heating and UV photon absorption resulted in different relative intensities of fragment ions. This indicated that the dissociations proceeded through several channels with different energy-dependent kinetics. The experimental data were interpreted with the help of electron structure calculations that provided fully optimized structures and relative energies for and amide isomers of the ions as well as isomerization, dissociation, and transition state energies. UV photon absorption by the ions was due to C-radical amide groups created by ETD that provided a new chromophore absorbing at 355 nm.
丝氨酸残基对通过电子转移解离产生的此类肽片段阳离子自由基的解离具有特定影响。能量分辨碰撞诱导解离（ER-CID）、时间分辨红外多光子解离（TR-IRMPD）以及355 nm处的单光子紫外光解离揭示了几种竞争性解离途径，包括相对于丝氨酸残基在α-末端和β-末端位置发生的OH自由基损失、水损失以及主链断裂。使用缓慢加热和紫外光子吸收的活化模式导致碎片离子具有不同的相对强度。这表明解离通过具有不同能量依赖动力学的多个通道进行。借助电子结构计算对实验数据进行了解释，该计算提供了离子的α-和β-酰胺异构体的完全优化结构和相对能量，以及异构化、解离和过渡态能量。离子对紫外光子的吸收归因于电子转移解离产生的C-自由基酰胺基团，该基团提供了一个在355 nm处吸收的新发色团。
