title: Microheterogeneity within conformational states of ubiquitin revealed by high resolution trapped ion mobility spectrometry.
abstract: The present work employs trapped ion mobility spectrometry (TIMS) for the analysis of ubiquitin ions known to display a multitude of previously unresolved interchangeable conformations upon electrospray ionization. The conformational distributions of ubiquitin [M + 6H](6+) through [M + 13H](13+) ions observed by TIMS are nearly identical to numerous drift tube ion mobility spectrometry studies reported in the literature. At an experimental resolving power up to ∼300, many of the congested conformations within the well-known compact, partially folded, and elongated [M + 7H](7+) states are separated. Minimizing the voltages (RF and DC) in the entrance funnel results in exclusive observation of compact [M + 7H](7+) conformers. However, under these conditions, the mobility-dependent pseudopotential coefficient may discriminate against ions having larger collision cross sections-a universal effect for all RF ion guides, funnels, and traps operating in the presence of a gas. The data presented underscore the complications associated with direct comparison of collision cross section values that represent an ensemble average of multiple underlying conformations. As illustrated herein, the microheterogeneity within a particular conformational family and the relative state-to-state abundance can be altered by solvent memory, energetic, and kinetic effects.
authors.affiliation: Bruker Daltonics, 40 Manning Road, Billerica, Massachusetts 01821, USA. melvin.park@bruker.com.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Ridgeway
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Silveira
authors.forename: Jacob E
authors.initials: JE
authors.lastname: Meier
authors.forename: Melvin A
authors.initials: MA
authors.lastname: Park
mesh_terms: D007700:Kinetics; D013058:Mass Spectrometry; D011487:Protein Conformation; D013816:Thermodynamics; D025801:Ubiquitin / Q000737:chemistry*
chemical_list: D025801:Ubiquitin