Increasing: Charge While Preserving Noncovalent Protein Complexes for ESI-MS

Increased multiple charging of native proteins and noncovalent protein complexes is observed in electrospray ionization (EST) mass spectra obtained from nondenaturing protein solutions containing up to 1% (vol/vol) m-nitrobenzyl alcohol (m-NBA). The increases in charge ranged from 8% for the 690 kDa alpha(7)beta(7)beta(7)alpha(7) 20S proteasome complex to 48% additional charge for the zinc-bound 29 kDa carbonic anhydrase-II protein. No dissociation of the noncovalently bound ligands/subunits was observed upon the addition of m-NBA. It is not clear if the enhanced charging is related to altered surface tension as proposed in the supercharging model of Iavarone and Williams (Iavarone, A. T.; Williams, E. R. J. Am. Chem. Soc. 2003, 125, 2319-2327). However, more highly charged noncovalent protein complexes have utility in relaxing slightly the mass-to-charge (m/z) requirements of the mass spectrometer for detection and will be effective for enhancing the efficiency for tandem mass spectrometry studies of protein complexes. (J Am Soc Mass Spectrom 2009, 20, 593-596) (C) 2009 Published by Elsevier Inc. on behalf of American Society for Mass Spectrometry