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Issue 12, 2017
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Re-configurable, multi-mode contained-electrospray ionization for protein folding and unfolding on the millisecond time scale

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Abstract

A new reconfigurable contained-electrospray (ES) ion source is described that can be operated in three unique modes (Types I, II and III) and was applied to control the charge state of proteins for subsequent online characterization by mass spectrometry. Using this device, proteins prepared in 100% water were highly charged after exposure to hydrochloric acid vapor. For myoglobin, the shift to a higher charge state occurred faster than the heme cofactor could escape the unfolding protein. This effect reflected in the detection of highly charged holo-myoglobin intermediates (+26), which suggests the modification process occurred on a millisecond time scale (Type I mode). By introducing a cavity in the contained-ES emitter (Type II mode), increased protein denaturation was observed where only apo-myoglobin ions were detected. A similar increase in the charge effect was observed for less pH sensitive proteins such as ubiquitin and cytochrome c. In a third type of experiment, acidified aqueous-based droplets containing unfolded proteins were briefly exposed to aqueous ammonium acetate/triethylammonium acetate solution mixtures to increase the droplet pH and to induce protein folding during electrospray ionization. Charge-state distributions showed protein folding occurred, including the appearance of charged reduced species that were not observed when sprayed in pure water. The three operational modes of contained-electrospray allow online modification of an analyte during charge droplet formation using both vapor and non-volatile liquid reagents, without a direct addition of the modifying reagent to the analyte solution.

Graphical abstract: Re-configurable, multi-mode contained-electrospray ionization for protein folding and unfolding on the millisecond time scale

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Publication details

The article was received on 01 Mar 2017, accepted on 02 May 2017 and first published on 02 May 2017


Article type: Paper
DOI: 10.1039/C7AN00362E
Citation: Analyst, 2017,142, 2152-2160
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    Re-configurable, multi-mode contained-electrospray ionization for protein folding and unfolding on the millisecond time scale

    C. F. Miller, D. S. Kulyk, J. W. Kim and A. K. Badu-Tawiah, Analyst, 2017, 142, 2152
    DOI: 10.1039/C7AN00362E

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