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 examine the influence of solvent composition and capillary temperature on the gas-phase conformations of ubiquitin ions (+6 to +13) formed during electrospray ionization. Three general conformer types are observed: compact forms (favored for the +6 and +7 charge states); partially folded conformers (favored for the +8 and +9 ions); and, unfolded conformers (favored for the +10 to +13 charge states). The populations of different conformers are highly sensitive to solvent composition and capillary temperature used for electrospray ionization. Electrospray of "pseudonative" solutions leads to formation of some conformers that are more compact than those observed for "denatured" solutions. Studies as a function of capillary temperature show that as the capillary temperature is increased, compact and partially folded states undergo unfolding transitions. Compact states from pseudonative solutions unfold at higher temperatures than compact states from denatured solutions. The products of unfolding transitions have similar cross sections for both solution types. (Int J Mass Spectrom 185/186/187 (1999) 37-47) (C) 1999 Elsevier Science B.V.