Influence of solvent composition and capillary temperature on the conformations of electrosprayed ions: unfolding of compact ubiquitin conformers from pseudonative and denatured solutions

High-resolution ion mobility/mass spectrometry methods have been used to ex amine the influence of solvent composition and capillary temperature on the gas-phase conformations of ubiquitin ions (+6 to +13) formed during electr ospray ionization. Three general conformer types are observed: compact form s (favored for the +6 and +7 charge states); partially folded conformers (f avored for the +8 and +9 ions); and, unfolded conformers (favored for the 10 to +13 charge states). The populations of different conformers are highl y sensitive to solvent composition and capillary temperature used for elect rospray ionization. Electrospray of "pseudonative" solutions leads to forma tion of some conformers that are more compact than those observed for "dena tured" solutions. Studies as a function of capillary temperature show that as the capillary temperature is increased, compact and partially folded sta tes undergo unfolding transitions. Compact states from pseudonative solutio ns unfold at higher temperatures than compact states from denatured solutio ns. The products of unfolding transitions have similar cross sections for b oth solution types. (Int J Mass Spectrom 185/186/187 (1999) 37-47) (C) 1999 Elsevier Science B.V.