Elongated conformers of charge states +11 to +15 of bovine ubiquitin studied using ESI-FAIMS-MS

Recent advancements in high-field asymmetric waveform ion mobility spectrom etry (FAIMS) have led to significant improvements in the application of thi s technology to the study of protein conformers. Compared with previous wor k, the maximum value of the separation voltage (i.e., the dispersion voltag e) has increased, thereby enabling multiple, elongated conformers of indivi dual charge states of bovine ubiquitin to be separated in the gas phase (e. g., four conformers of each of the +11 and +12 charge states were separated ). The use of a carrier gas mixture of 40% nitrogen and 60% helium changed the separation selectivity compared with pure nitrogen and enhanced the sig nal intensity, especially for the +14 and +15 charge states (the latter was not detected in a nitrogen carrier gas). Conformer cross sections were det ermined using the FAIMS/energy-loss method and found to be similar within a given charge state. The cross sections for conformers of charge states +13 , +14, and +15 plateau at about 2000 Angstrom (2) suggesting that the struc ture of bovine ubiquitin is essentially unfolded after the addition of the 13th proton. (C) 2001 American Society for Mass Spectrometry.