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Protein conformation and supercharging with DMSO from aqueous solution.
Harry J Sterling1, James S Prell, Catherine A Cassou
1Department of Chemistry, University of California, Berkeley, CA 94720-1460, USA.
Journal of the American Society for Mass Spectrometry
|September 29, 2011
Summary
Dimethyl sulfoxide (DMSO) acts as a protein supercharging reagent in electrospray ionization. Higher DMSO concentrations cause protein unfolding and increased ion charge, driven by denaturation in the ESI droplet.
Area of Science:
- Analytical Chemistry
- Biochemistry
- Physical Chemistry
Background:
- Electrospray ionization (ESI) is a crucial technique for analyzing proteins.
- Supercharging reagents enhance protein ion detection in ESI-MS.
- Understanding the mechanism of supercharging is vital for optimizing protein analysis.
Purpose of the Study:
- To investigate the efficacy of dimethyl sulfoxide (DMSO) as a supercharging reagent.
- To elucidate the mechanism behind DMSO-mediated protein supercharging in ESI.
- To compare DMSO's properties with other supercharging reagents.
Main Methods:
- Electrospray ionization mass spectrometry (ESI-MS) was used to analyze protein ions.
- Near-UV circular dichroism (CD) spectroscopy assessed protein structure.
- Solution-phase hydrogen/deuterium exchange mass spectrometry (HDX-MS) probed structural changes.
- Computational methods calculated proton affinity and gas-phase basicity.
Main Results:
- Low DMSO concentrations compacted protein structures; higher concentrations caused unfolding.
- Significant protein unfolding occurred at ~63% DMSO for lysozyme and ~43% for myoglobin.
- Supercharging onset correlated with protein denaturation, not solely proton transfer.
Conclusions:
- DMSO supercharging arises from chemical/thermal denaturation within the ESI droplet.
- Preferential evaporation of water concentrates DMSO, driving denaturation.
- Proton transfer reactivity is not the primary driver of charge enhancement in DMSO-assisted ESI-MS.
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