could play a role in protecting the proteins from unfolding in the gas phase. Study 14.6 also shows that
A8-35-solubilized MPs are transferred to the gas phase along with bound lipids, thus permitting
MP/lipid interactions to be explored by ESI-IM-MS. In a broad study of the holotranslocon from
E. coli, lipids were extracted by chloroform/methanol from the A8-35-trapped translocon before being
analyzed by liquid chromatography-ESI-MS (Botte et al. 2016).
In Study 14.7 (Watkinson et al. 2015), a systematic study was carried out of the transfer from
solution to vacuum of three β-barrel MPs, OmpT, tOmpA, and PagP (Fig. 14.11, top), using as the
Fig. 14.11 ESI-MS spectra of OmpT (left), tOmpA (center), and PagP (right) kept in DDM solution or
transferred to A8-35, A8-75, SAPol, A34-35, A34-75, or NAPol, as indicated. The tOmpA/A34-35
spectrum was acquired following purification by SEC. All other spectra shown were obtained without
prior SEC. Collision voltages in the trap (PagP and OmpT ¼ 100–150 V; tOmpA ¼ 50–100 V) and
transfer (50–100 V) regions prior to and immediately following the drift cell, respectively, were varied to
optimize liberation of each OMP with minimal impact on its structure. Origin of the crystal structures:
OmpT, PDB file 1I78; tOmpA, PDB file 1QJP; PagP, PDB file 1THQ (Adapted from Watkinson et al.
2015. https://doi.org/10.1016/j.ijms.2015.06.017, article available under the terms of the Creative
Commons Attribution License (CC BY)).
14.3 Electrospray Ionization-Mass Spectrometry Studies
639
A8-35-solubilized MPs are transferred to the gas phase along with bound lipids, thus permitting
MP/lipid interactions to be explored by ESI-IM-MS. In a broad study of the holotranslocon from
E. coli, lipids were extracted by chloroform/methanol from the A8-35-trapped translocon before being
analyzed by liquid chromatography-ESI-MS (Botte et al. 2016).
In Study 14.7 (Watkinson et al. 2015), a systematic study was carried out of the transfer from
solution to vacuum of three β-barrel MPs, OmpT, tOmpA, and PagP (Fig. 14.11, top), using as the
Fig. 14.11 ESI-MS spectra of OmpT (left), tOmpA (center), and PagP (right) kept in DDM solution or
transferred to A8-35, A8-75, SAPol, A34-35, A34-75, or NAPol, as indicated. The tOmpA/A34-35
spectrum was acquired following purification by SEC. All other spectra shown were obtained without
prior SEC. Collision voltages in the trap (PagP and OmpT ¼ 100–150 V; tOmpA ¼ 50–100 V) and
transfer (50–100 V) regions prior to and immediately following the drift cell, respectively, were varied to
optimize liberation of each OMP with minimal impact on its structure. Origin of the crystal structures:
OmpT, PDB file 1I78; tOmpA, PDB file 1QJP; PagP, PDB file 1THQ (Adapted from Watkinson et al.
2015. https://doi.org/10.1016/j.ijms.2015.06.017, article available under the terms of the Creative
Commons Attribution License (CC BY)).
14.3 Electrospray Ionization-Mass Spectrometry Studies
639