Di-Tyrosine Cross-Link Decreases the Collisional Cross-Section of Aβ Peptide Dimers and Trimers in the Gas Phase: An Ion Mobility Study
Figure 5
Fragments of IMS-MS spectra for different charged trimer.
Selected regions of ion mobility separated mass spectra (IMS-MS) covering trimeric signals in 2D rendition (colored panels, drift time at horizontal axis and m/z at vertical axis). Lower panels show the corresponding ion mobility drift time profiles, i.e. projections of the signal group on the drift time axis. Panels showing isotopic envelopes are cross-sections at indicated (blue arrows) drift time values which correspond to a given oligomeric form, for instance TRI8+ denoting a non-covalently stabilized trimer charged 8+, whereas cTRI8+ a covalently stabilized trimer charged 8+, etc. Spectra are shown before reaction (A,C) and at 90 min of reaction (B,D). (A,B) 1854–1858 m/z region showing signals of the two structurally alternate (at 10.25 and 12.2 ms) TRI7+ forms before reaction (A), after incubation (B) accompanied by a strong new signals of cTRI7+ at smaller m/z and shorter drift time (8.36 and 7.6 ms), i.e., corresponding to covalently stabilized more compact trimeric form. (C,D) 1624–1626 m/z region with two structurally alternate non-covalently stabilized forms of 8+ charged trimer (at 10.25 and 11.03 ms) before reaction, dominated after incubation by new trimeric forms covalently stabilized by a di-Tyr (at 9.04 and 9.7 ms) and a tri-Tyr (at 7.6 ms) bond. Experiment was repeated at least three times. See also Figure S2.