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Careful transfer of ions into the gas-phase permits the measurement of protein structures, with ion mobility-mass spectrometry, which provides shape and stoichiometry information. Collision cross sections (CCS) can be obtained from measurements made of the proteins mobility through a given gas, and such structural information once obtained should also permit inter-lab comparisons. However, until recently there was not a recommended standard form for the reporting of such meas-urements. In this study we explore the use of collision cross section distributions to allow comparisons of IM-MS data for proteins on different instruments. We present measurements on seven standard proteins across three IM-MS configurations, namely an Agilent 6560 IMQToF, a Waters Synapt G2 possessing a TWIMS cell and a modified Synapt G2 possessing an RF confining linear field drift cell. Mobility measurements were taken using both He and N2 as the drift gases. To aid comparability across instruments and best assess the corresponding gas-phase conformational landscapes of the protein 'standards', we present the data in the form of averaged collision cross section distributions. For experiments carried out in N2, CCS values for the most compact ion conformations have an inter-instrument variability of ≤ 3%, and the total CCS distributions are generally similar across platforms. For experiments carried out in He, we observe the total CCS distributions to follow the same trend as observed in N2, whilst CCS for the most compact ion conformations sampled on the 6560 are systematically smaller by up to 10% than those observed on the G2. From this study, we observe the applied protein calibration procedure (for TWIMS) to yield TWCCS for native-like proteins which are largely similar to those obtained on DTIMS instruments. However, when considering the ease by which unintentional protein structural activation in vacuo can occur and the broad range of DTCCS within the literature from which to calibrate drift times against, we advise caution when calibrating sample protein drift times against protein 'standards' in order to obtain CCS values and thus recommend the use of CCS distributions.
This article was published in the following journal.
Name: Analytical chemistry
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