Ion mobility-mass spectrometry has emerged as a powerful tool for interrogating a wide variety of chemical systems. Collision-induced unfolding (CIU), typically performed in time-of-flight instruments, has been utilized to obtain valuable qualitative insight into protein structure and illuminate subtle differences between related species. CIU experiments can be performed relatively quickly, but unfolding energy information obtained from them has not yet been interpreted quantitatively. While several methods can determine quantitative dissociation energetics for small molecules, clusters, and peptides, these methods have rarely been applied to proteins, and never to study unfolding. Here, we present a method to rapidly determine activation energies for protein unfolding and dissociation, built on a model for energy deposition during collisional activation. The method is validated by comparing activation energies for dissociation of three complexes with those obtained using blackbody infrared radiative dissociation (BIRD); values from the two methods are in agreement. Several protein monomers were unfolded using CIU, including multiple charge states of both cations and anions, and activation energies determined. ΔH⧧ and ΔS⧧ values are found to be correlated, leading to ΔG⧧ values that lie within a narrow range (∼70-80 kJ/mol) and vary more with charge state than with protein identity. ΔG⧧ is anticorrelated with charge density, highlighting the key role of Coulombic repulsion in gas-phase unfolding. Measured ΔG⧧ values are similar to those computed for proton transfer within small peptides, suggesting that proton transfer is the rate-limiting step in gas-phase unfolding and providing evidence of a link between the Mobile Proton model and CIU.

中文翻译：

---

在Q-IM-ToF质谱仪中快速测定气相蛋白展开和解离的活化能。

离子淌度质谱已经成为询问各种化学系统的有力工具。通常在飞行时间仪器中执行的碰撞​​诱导展开（CIU）已用于获得对蛋白质结构的有价值的定性见解，并阐明相关物种之间的细微差异。CIU实验可以相对快速地进行，但是从中获得的展开的能量信息尚未得到定量的解释。尽管有几种方法可以确定小分子，簇和肽的定量解离能，但这些方法很少应用于蛋白质，也从未研究过展开。在这里，我们提出了一种快速确定蛋白质解折叠和解离的活化能的方法，建立在碰撞激活过程中能量沉积模型上。通过比较三种配合物的解离活化能与使用黑体红外辐射解离（BIRD）获得的活化能进行了验证。两种方法的值一致。使用CIU可以展开几种蛋白质单体，包括阳离子和阴离子的多个电荷状态，并确定活化能。发现ΔH⧧和ΔS值是相关的，导致ΔG⧧值在一个狭窄的范围内（约70-80kJ / mol），并且随着电荷状态的变化比与蛋白质同一性的变化更大。ΔG⧧与电荷密度反相关，突显了库仑排斥在气相展开中的关键作用。测得的ΔG⧧值类似于为小肽内的质子转移计算的值，