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Issue 19, 2014
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Desalting protein ions in native mass spectrometry using supercharging reagents

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Abstract

Effects of the supercharging reagents m-NBA and sulfolane on sodium ion adduction to protein ions formed using native mass spectrometry were investigated. There is extensive sodium adduction on protein ions formed by electrospray ionization from aqueous solutions containing millimolar concentrations of NaCl, which can lower sensitivity by distributing the signal of a given charge state over multiple adducted ions and can reduce mass measuring accuracy for large proteins and non-covalent complexes for which individual adducts cannot be resolved. The average number of sodium ions adducted to the most abundant ion formed from ten small (8.6–29 kDa) proteins for which adducts can be resolved is reduced by 58% or 80% on average, respectively, when 1.5% m-NBA or 2.5% sulfolane are added to aqueous solutions containing sodium compared to without the supercharging reagent. Sulfolane is more effective than m-NBA at reducing sodium ion adduction and at preserving non-covalent protein–ligand and protein–protein interactions. Desalting with 2.5% sulfolane enables detection of several glycosylated forms of 79.7 kDa holo-transferrin and NADH bound to the 146 kDa homotetramer LDH, which are otherwise unresolved due to peak broadening from extensive sodium adduction. Although sulfolane is more effective than m-NBA at protein ion desalting, m-NBA reduces salt clusters at high m/z and can increase the signal-to-noise ratios of protein ions by reducing chemical noise. Desalting is likely a result of these supercharging reagents binding sodium ions in solution, thereby reducing the sodium available to adduct to protein ions.

Graphical abstract: Desalting protein ions in native mass spectrometry using supercharging reagents

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Publication details

The article was received on 16 Jun 2014, accepted on 30 Jul 2014 and first published on 30 Jul 2014


Article type: Paper
DOI: 10.1039/C4AN01085J
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Analyst, 2014,139, 4810-4819

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    Desalting protein ions in native mass spectrometry using supercharging reagents

    C. A. Cassou and E. R. Williams, Analyst, 2014, 139, 4810
    DOI: 10.1039/C4AN01085J

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