title: Evidence for two new solution states of ubiquitin by IMS-MS analysis.
abstract: Ion mobility spectrometry coupled with mass spectrometry (IMS-MS) is used to investigate the populations of different states for ubiquitin in water:methanol solutions. In these experiments, ubiquitin is electrosprayed from 20 water:methanol (100:0 to 5:95, pH = 2) solutions, ranging from native to denaturing conditions. With an increased percentage of methanol in solution, ubiquitin ions ([M + 7H](7+) to [M + 12H](12+)) show substantial variations in both charge state distributions and ion mobility distributions. Analysis of these data provides evidence for the existence of five ubiquitin states in solution: the native N state, favored in solutions of 100:0 to 70:30 water:methanol for the +7 and +8 charge states; the more helical A state and a new closely related A' state, favored in solutions of 70:30 to 5:95 water:methanol for the +9 to +12 charge states; the unfolded U state, populated in 40:60 to 5:95 water:methanol solutions for the +8 to +10 and +12 charge states; and a new low-abundance state termed the B state, observed for 100:0 to 70:30 water:methanol solutions in the +8 to +10 and +12 charge states. The relative abundances for different states in different solutions are determined. The analysis presented here provides insight into how solution structures evolve into anhydrous conformations and demonstrates the utility of IMS-MS methods as a means of characterizing populations of conformers for proteins in solution.
authors.affiliation: Department of Chemistry, Indiana University , 800 Kirkwood Avenue, Bloomington, Indiana 47405, United States.
authors.forename: Huilin
authors.initials: H
authors.lastname: Shi
authors.forename: David E
authors.initials: DE
authors.lastname: Clemmer
mesh_terms: D007477:Ions / Q000737:chemistry; D000432:Methanol / Q000737:chemistry; D012996:Solutions / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D025801:Ubiquitin / Q000737:chemistry* / Q000378:metabolism; D014867:Water / Q000737:chemistry
chemical_list: D007477:Ions; D012996:Solutions; D025801:Ubiquitin; D014867:Water; D000432:Methanol