Submicrometer Emitter ESI Tips for Native Mass Spectrometry of Membrane Proteins in Ionic and Nonionic Detergents
Native mass spectrometry (native-MS) of membrane proteins typically requires a detergent screening protocol, protein solubilization in the preferred detergent, followed by protein liberation from the micelle by collisional activation. Here, submicrometer nano-ESI emitter tips are used for native-MS of membrane proteins solubilized in both nonionic and ionic detergent solutions. With the submicrometer nano-ESI emitter tips, resolved charge-state distributions of membrane protein ions are obtained from a 150 mM NaCl, 25 mM Tris-HCl with 1.1% octyl glucoside solution. The relative abundances of NaCl and detergent cluster ions at high m /z are significantly reduced with the submicrometer emitters compared with larger nano-ESI emitters that are commonly used. This technique is beneficial for significantly decreasing the abundances (by two to three orders of magnitude compared with the larger tip size: 1.6 μm) of detergent cluster ions formed from aqueous ammonium acetate solutions containing detergents that can overlap with the membrane protein ion signal. Resolved charge-state distributions of membrane protein ions from aqueous ammonium acetate solutions containing ionic detergents were obtained with the submicrometer nano-ESI emitters; this is the first report of native-MS of membrane proteins solubilized by ionic detergents.
KeywordsMembrane protein Native MS Detergents Desalting Ionic detergents Submicron Tips ESI Bacteriorhodopsin Aquaporin Z
The authors are grateful for financial support from the National Institutes of Health (R01GM097357 to E.R.W. and R01GM103479 to J.A.L.) and for funds to acquire the Synapt G2Si (S10OD020062) used in these experiments. The authors thank Drs. Ryan Leib and Anthony Iavarone for helpful discussions, Drs. Nicholas Woodall and James U. Bowie (UCLA) for the generous gift of the bacteriorhodopsin T47A mutant, and Dr. Pascal Egea (UCLA) for preparation and gift of Aquaporin Z.
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