Micelles Protect Membrane Complexes from Solution to Vacuum
Nelson P. Barrera,1
Natalie Di Bartolo,2
Paula J. Booth,2
Carol V. Robinson1*
The ability to maintain interactions between soluble protein subunits in the gas phase of a mass spectrometer gives critical insight into the stoichiometry and interaction networks of protein complexes. Conversely, for membrane protein complexes in micelles, the transition into the gas phase usually leads to the disruption of interactions, particularly between cytoplasmic and membrane subunits, and a mass spectrum dominated by large aggregates of detergent molecules. We show that by applying nanoelectrospray to a micellar solution of a membrane protein complex, the heteromeric adenosine 5'-triphosphate (ATP)–binding cassette transporter BtuC2D2, we can maintain the complex intact in the gas phase of a mass spectrometer. Dissociation of either transmembrane (BtuC) or cytoplasmic (BtuD) subunits uncovers modifications to the transmembrane subunits and cooperative binding of ATP. By protecting a membrane protein complex within a n-dodecyl-β-D-maltoside micelle, we demonstrated a powerful strategy that will enable the subunit stoichiometry and ligand-binding properties of membrane complexes to be determined directly, by precise determination of the masses of intact complexes and dissociated subunits.
1 Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB21EW, UK.
2 Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK.
* To whom correspondence should be addressed. E-mail: cvr24{at}cam.ac.uk
