Cysteine (Cys) is prone to diverse post-translational modifications in proteins, including oxidation into sulfenic acid (Cys-SOH) by reactive oxygen species generated under oxidative stress. Detection of low-concentration and metastable Cys-SOH within complex biological matrices is challenging due to the dynamic concentration range of proteins in the samples. Herein, visible laser-induced dissociation (LID) implemented in a mass spectrometer was used for streamlining the detection of Cys oxidized proteins owing to proper derivatization of Cys-SOH with a chromophore tag functionalized with a cyclohexanedione group. Once grafted, peptides undergo a high fragmentation yield under LID, leading concomitantly to informative backbone ions and to a chromophore reporter ion. Seventy-nine percent of the Cys-containing tryptic peptides derived from human serum albumin and serotransferrin tracked by parallel reaction monitoring (PRM) were detected as targets subjected to oxidation. These candidates as well as Cys-containing peptides predicted by in silico trypsin digestion of five other human plasma proteins were then tracked in real plasma samples to pinpoint the endogenous Cys-SOH subpopulation. Most of the targeted peptides were detected in all plasma samples by LID-PRM, with significant differences in their relative amounts. By eliminating the signal of interfering co-eluted compounds, LID-PRM surpasses conventional HCD (higher-energy collisional dissociation)-PRM in detecting grafted Cys-SOH-containing peptides and allows now to foresee clinical applications in large human cohorts.
半胱
氨酸(Cys)在蛋白质中容易发生多种翻译后修饰,包括在氧化应激作用下被活性氧氧化成
亚硫酸(Cys-SOH)。由于样品中蛋白质的动态浓度范围较大,因此在复杂的
生物基质中检测低浓度和易变的 Cys-SOH 具有挑战性。在本文中,由于 Cys-SOH 与环己二酮基团功能化的发色团标签进行了适当的衍生,质谱仪中的可见激光诱导解离(LID)被用于简化 Cys 氧化蛋白质的检测。一旦接枝,肽就会在 LID 条件下发生高碎裂,同时产生信息骨架离子和发色团报告离子。在通过平行反应监测(PRM)跟踪的人
血清白蛋白和血清
转铁蛋白中,有 79% 的含 Cys 的胰蛋白肽被检测为氧化目标。然后在真实血浆样本中跟踪这些候选肽以及通过对其他五种人体血浆蛋白的
硅胰
蛋白酶消化预测出的含Cys肽,以确定内源性Cys-SOH亚群。LID-PRM 在所有血浆样本中都检测到了大部分目标肽,但其相对含量存在显著差异。通过消除干扰共沉淀化合物的信号,LID-PRM 在检测含 Cys-SOH 的接枝肽方面超越了传统的 HCD(高能碰撞解离)-PRM,现在可以预见其在大量人体样本中的临床应用。