Increased Coverage in the Transmembrane Domain with Activated-Ion Electron Capture Dissociation for Top-Down Fourier-Transform Mass Spectrometry of Integral Membrane Proteins

The c-subunit of ATP synthase (AtpH) is an 8 kD integral membrane protein with two transmembrane domains; we set out to demonstrate it amenable to top-down electrospray-ionization Fourier-transform mass spectrometry (FT−MS) using both collision activated and electron capture dissociation (CAD/ECD). Thermal activation concomitant with electron delivery was necessary for efficient ECD (activated-ion ECD; aiECD), yielding complementary information and greater sequence coverage in the transmembrane domains in comparison with CAD. Keywords: electrospray-ionization mass spectrometry (ESI-MS) • Fourier-transform mass spectrometry (FT−MS) • Fourier-transform ion cyclotron resonance (FTICR) • collision activated dissociation (CAD) • electron capture dissociation (ECD) • activated-ion ECD (aiECD) • infrared multiphoton dissociation (IRMPD) • thylakoid membrane • membrane protein • ATP synthase