Unfolding and Folding of the Three-Helix Bundle Protein KIX in the Absence of Solvent.

Moritz Schennach,Kathrin Breuker,Eva-Maria Schneeberger

doi:10.1007/s13361-016-1363-7

Moritz Schennach, Kathrin Breuker + Show 1 more

Open Access

https://doi.org/10.1007/s13361-016-1363-7

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Abstract

Electron capture dissociation was used to probe the structure, unfolding, and folding of KIX ions in the gas phase. At energies for vibrational activation that were sufficiently high to cause loss of small molecules such as NH3 and H2O by breaking of covalent bonds in about 5% of the KIX (M + nH)n+ ions with n = 7–9, only partial unfolding was observed, consistent with our previous hypothesis that salt bridges play an important role in stabilizing the native solution fold after transfer into the gas phase. Folding of the partially unfolded ions on a timescale of up to 10 s was observed only for (M + nH)n+ ions with n = 9, but not n = 7 and n = 8, which we attribute to differences in the distribution of charges within the (M + nH)n+ ions.Graphical ᅟ

Highlights

Native mass spectrometry (MS) has, over the past 25 years, developed from interpreting mass spectra from electrospray ionization (ESI) of different solutions to approaches by which the dissociation of biomolecules such as proteins and nucleic acids and their noncovalent complexes is studied, or their rotationally averaged collision cross section is probed by ion mobility MS [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]
We have recently reported that gaseous cytochrome c ions from horse and tuna heart, the fold of which is virtually identical in solution, show vastly dissimilar folding behavior, and found evidence that the formation of salt bridges is a major driving force for protein folding in the gas phase [34]
We have previously proposed that the transfer of proteins into the gas phase by electrospray ionization causes the formation of salt bridges and ionic hydrogen bonds on the protein surface, by which a native fold can be stabilized during and after the phase transition [32, 48]

Summary

Introduction

Native mass spectrometry (MS) has, over the past 25 years, developed from interpreting mass spectra from electrospray ionization (ESI) of different solutions to approaches by which the dissociation of biomolecules such as proteins and nucleic acids and their noncovalent complexes is studied, or their rotationally averaged collision cross section is probed by ion mobility MS [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]. We investigate the unfolding and folding of the threehelix bundle protein KIX, for which ECD data indicated substantial preservation of the native solution structure in the (M + 7H)7+ ions, on a timescale of at least 4 s after transfer into the gas phase, even after vibrational ion activation by 28 eV collisions with argon gas [33].

Results

Conclusion