Donor Micah T, Mroz Austin M, Prell James S
Department of Chemistry and Biochemistry , 1253 University of Oregon , Eugene , OR 97403-1253 , USA.
Materials Science Institute , University of Oregon , 1252 University of Oregon , Eugene , OR 97403-1252 , USA . Email:
Chem Sci. 2019 Mar 6;10(14):4097-4106. doi: 10.1039/c9sc00644c. eCollection 2019 Apr 14.
Recent advances in native mass spectrometry have enabled its use to probe the structure of and interactions within biomolecular complexes. Surface-induced dissociation, in which inter- and intramolecular interactions are disrupted following an energetic ion-surface collision, is a method that can directly interrogate the topology of protein complexes. However, a quantitative relationship between the ion kinetic energy at the moment of surface collision and the internal energy deposited into the ion has not yet been established for proteins. The factors affecting energy deposition in surface-induced unfolding (SIU) of protein monomers were investigated and a calibration relating laboratory-frame kinetic energy to internal energy developed. Protein monomers were unfolded by SIU and by collision-induced unfolding (CIU). CIU and SIU cause proteins to undergo the same unfolding transitions at different values of laboratory-frame kinetic energy. There is a strong correlation between the SIU and CIU energies, demonstrating that SIU, like CIU, can largely be understood as a thermal process. The change in internal energy in CIU was modeled using a Monte Carlo approach and theory. Computed values of the overall efficiency were found to be approximately 25% and used to rescale the CIU energy axis and relate nominal SIU energies to internal energy. The energy deposition efficiency in SIU increases with mass and kinetic energy from a low of ∼20% to a high of ∼68%, indicating that the effective mass of the surface increases along with the mass of the ion. The effect of ion structure on energy deposition was probed using multiple stages of ion activation. Energy deposition in SIU strongly depends on structure, decreasing as the protein is elongated, due to decreased effective protein-surface collisional cross section and increased transfer to rotational modes.
近年来，基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）技术取得了显著进展，使其能够用于探究生物分子复合物的结构及其内部相互作用。表面诱导解离（Surface-Induced Dissociation，SID）是一种能够直接研究蛋白质复合物拓扑结构的方法，在高能离子与表面碰撞后，分子间和分子内的相互作用会被破坏。然而，目前尚未建立蛋白质表面碰撞瞬间离子动能与沉积到离子中的内能之间的定量关系。本研究对影响蛋白质单体表面诱导解折叠（Surface-Induced Unfolding，SIU）能量沉积的因素进行了研究，并建立了实验室坐标系动能与内能之间的校准关系。通过SIU和碰撞诱导解折叠（Collision-Induced Unfolding，CIU）对蛋白质单体进行解折叠。CIU和SIU使蛋白质在不同的实验室坐标系动能值下经历相同的解折叠转变。SIU和CIU能量之间存在很强的相关性，这表明SIU与CIU一样，在很大程度上可以被理解为一个热过程。使用蒙特卡罗方法和理论对CIU中的内能变化进行了建模。计算得到的总效率值约为25%，并用于重新标定CIU能量轴，将名义SIU能量与内能联系起来。SIU中的能量沉积效率随着质量和动能的增加而增加，从约20%的低值增加到约68%的高值，这表明表面的有效质量随着离子质量的增加而增加。使用多阶段离子活化来探究离子结构对能量沉积的影响。SIU中的能量沉积强烈依赖于结构，随着蛋白质的拉长而降低，这是由于有效蛋白质-表面碰撞截面减小以及向旋转模式的转移增加所致。
