Negative Ions Enhance Survival of Membrane Protein Complexes.
Membrane protein complexes are commonly introduced to the mass spectrometer solubilized in detergent micelles. The collisional activation used to remove the detergent, however, often causes protein unfolding and dissociation. As in the case for soluble proteins, electrospray in the positive ion mode is most commonly used for the study of membrane proteins. Here we show several distinct advantages of employing the negative ion mode. Negative polarity can yield lower average charge states for membrane proteins solubilized in saccharide detergents, with enhanced peak resolution and reduced adduct formation. Most importantly, we demonstrate that negative ion mode electrospray ionization (ESI) minimizes subunit dissociation in the gas phase, allowing access to biologically relevant oligomeric states. Together, these properties mean that intact membrane protein ions can be generated in a greater range of solubilizing detergents. The formation of negative ions, therefore, greatly expands the possibilities of using mass spectrometry on this intractable class of protein. Graphical Abstract ᅟ.
Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 5QY, UK.
Idlir
I
Liko
Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 5QY, UK.
Jonathan T S
JT
Hopper
Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 5QY, UK.
Timothy M
TM
Allison
Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 5QY, UK.
Justin L P
JL
Benesch
Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 5QY, UK. carol.robinson@chem.ox.ac.uk.
Carol V
CV
Robinson
D003902:Detergents / Q000737:chemistry; D007477:Ions; D008565:Membrane Proteins / Q000737:chemistry*; D008823:Micelles; D021241:Spectrometry, Mass, Electrospray Ionization
D003902:Detergents; D007477:Ions; D008565:Membrane Proteins; D008823:Micelles
Membrane proteins; Negative polarity; Structural biology