Sharif Daud, Dewasurendra Vikum K, Sultana Mst Nigar, Mahmud Sultan, Banerjee Chandrima, Rahman Mohammad, Li Peng, Clemmer David E, Johnson Matthew B, Valentine Stephen J
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States.
Department of Physics, West Virginia University, Morgantown, West Virginia 26506, United States.
J Phys Chem B. 2025 Feb 6;129(5):1626-1639. doi: 10.1021/acs.jpcb.4c04842. Epub 2025 Jan 29.
Capillary vibrating sharp-edge spray ionization (cVSSI) has been used to control the droplet charging of nebulized microdroplets and monitor effects on protein ion conformation makeup as determined by mass spectrometry (MS). Here it is observed that the application of voltage results in noticeable differences to the charge state distributions (CSDs) of ubiquitin ions. The data can be described most generally in three distinct voltage regions: Under low-voltage conditions (<+200 V, LV regime), low charge states (2+ to 4+ ions) dominate the mass spectra. For midvoltage conditions (+200 to +600 V, MV regime), higher charge states (7+ to 12+ ions) are observed. For high-voltage conditions (>+600 V, HV regime), the "nano-electrospray ionization (nESI)-type distribution" is achieved in which the 6+ and 5+ species are observed as the dominant ions. Analysis of these results suggests that different pathways to progeny nanodroplet production result in the observed ions. For the LV regime, aerodynamic breakup leads to low charge progeny droplets that are selective for the native solution conformation ensemble of ubiquitin (minus multimeric species). In the MV regime, the large droplets persist for longer periods of time, leading to droplet heating and a shift in the conformation ensemble to partially unfolded species. In the HV regime, droplets access progeny nanodroplets faster, leading to native conformation ensemble sampling as indicated by the observed nESI-type CSD. The notable observation of limited multimer formation and adduct ion formation in the LV regime is hypothesized to result from droplet aero breakup resulting in protein and charge carrier partitioning in sampled progeny droplets. The tunable droplet charging afforded by cVSSI presents opportunities to study the effects of the droplet charge, droplet size, and mass spectrometer inlet temperature on the conformer ensemble sampled by the mass spectrometer. Additionally, the approach may provide a tool for rapid comparison of protein stabilities.
毛细管振动锐边喷雾电离（cVSSI）已被用于控制雾化微滴的液滴充电，并通过质谱（MS）监测对蛋白质离子构象组成的影响。在此观察到，施加电压会导致泛素离子的电荷态分布（CSD）出现明显差异。这些数据最普遍可在三个不同的电压区域进行描述：在低电压条件下（< +200 V，LV区域），低电荷态（2 +至4 +离子）在质谱中占主导。对于中电压条件（+200至+600 V，MV区域），观察到更高的电荷态（7 +至12 +离子）。对于高电压条件（> +600 V，HV区域），实现了“纳米电喷雾电离（nESI）型分布”，其中观察到6 +和5 +物种为主要离子。对这些结果的分析表明，产生子代纳米滴的不同途径导致了观察到的离子。对于LV区域，气动破碎导致低电荷子代液滴，这些液滴对泛素的天然溶液构象集合（减去多聚体物种）具有选择性。在MV区域，大液滴持续更长时间，导致液滴加热以及构象集合向部分展开的物种转变。在HV区域，液滴更快地形成子代纳米滴，导致如观察到的nESI型CSD所示的天然构象集合采样。据推测，在LV区域中观察到的有限多聚体形成和加合物离子形成是由于液滴气动破碎导致蛋白质和电荷载体在采样的子代液滴中分配。cVSSI提供的可调液滴充电为研究液滴电荷、液滴大小和质谱仪入口温度对质谱仪采样的构象集合的影响提供了机会。此外，该方法可能为快速比较蛋白质稳定性提供一种工具。
