Mass spectrometry of membrane transporters reveals subunit stoichiometry and interactions

Abstract
A generally applicable approach to analyze intact membrane protein complexes by mass spectrometry is reported. This method allows subunit stoichiometry, lipid binding and the effects of post-translational modifications on complex formation to be explored. We describe a general mass spectrometry approach to determine subunit stoichiometry and lipid binding in intact membrane protein complexes. By exploring conditions for preserving interactions during transmission into the gas phase and for optimally stripping away detergent, by subjecting the complex to multiple collisions, we released the intact complex largely devoid of detergent. This enabled us to characterize both subunit stoichiometry and lipid binding in 4 membrane protein complexes.