The Trajectory Taken by Dimeric Cu/Zn Superoxide Dismutase Through the Protein Unfolding and Dissociation Landscape Is Modulated by Salt-Bridge Formation

17 September 2019, Version 2
This content is a preprint and has not undergone peer review at the time of posting.


Native mass spectrometry (MS) is a powerful means for studying macromolecular protein assemblies, including accessing activated states. However, much remains to be understood about what governs which regions of the protein (un)folding funnel are explored by activation of protein ions in vacuum. Here we examine the trajectory that dimeric Cu/Zn superoxide dismutase (SOD1) dimers take over the unfolding and dissociation free energy landscape in vacuum. We examined wild-type SOD1 and six disease-related point-mutants by using tandem MS and ion-mobility MS (MS/MS-IMMS) coupled with increasing collisional activation potentials. For six of the seven SOD1 variants, increasing activation promoted dimers to transition through two unfolding events to access three gas-phase conformers before dissociating symmetrically into monomers with (as near as possible) equal charges. The exception was G37R, which proceeded only through the first unfolding transition, and displayed a much higher abundance of asymmetric products. We localise this effect to the formation of a new salt-bridge in the first activated conformation. To examine the data quantitatively, we generated a model of SOD1 gas phase unfolding and dissociation, and applied Arrhenius-type analysis to estimate the barriers on the corresponding free energy landscape. This reveals an increase in the barrier height to unfolding in G37R to be >5 kJ/mol-1 higher than for the other variants, consistent with expectations for the strength of a salt-bridge. Our work demonstrates the importance of bond formation during the unfolding of proteins in vacuum, and provides a framework for comparing quantitatively the free energy landscape they explore upon activation.


Native Mass Spectrometry
Gas Phase Protein Unfolding
Gas Phase Protein Dissociation

Supplementary materials

Supplementary Information


Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.