The solution dependence of gas-phase unfolding for ubiquitin [M+7H]7+ ions has been studied by ion mobility spectrometry-mass spectrometry (IMS-MS). Different acidic water:methanol solutions are used to favor the native (N), more helical (A), or unfolded (U) solution states of ubiquitin. Unfolding of gas-phase ubiquitin ions is achieved by collisional heating and newly formed structures are examined by IMS. With an activation voltage of 100 V, a selected distribution of compact structures unfolds, forming three resolvable elongated states (E1-E3). The relative populations of these elongated structures depend strongly on the solution composition. Activation of compact ions from aqueous solutions known to favor N-state ubiquitin produces mostly the E1 type elongated state, whereas, activation of compact ions from methanol containing solutions that populate A-state ubiquitin favors the E3 elongated state. Presumably, this difference arises because of differences in precursor ion structures emerging from solution. Thus, it appears that information about solution populations can be retained after ionization, selection, and activation to produce the elongated states. These data as well as others are discussed.

Ion mobility/mass spectrometry techniques are used to study the chiral preferences of small proline clusters (containing 2 to 23 proline monomers) produced by electrospray ionization. By varying the composition of the electrospray solution from enantiomerically pure (100% L or 100% D) to racemic (50:50 L:D), it is possible to delineate which cluster sizes prefer homochiral (resolved) or heterochiral (antiresolved) compositions. The results show a remarkable oscillation in chiral preference. Singly protonated clusters, [xPro+H](+) (where x corresponds to the number of prolines), favor homochiral assemblies (for x = 4, 6, 11 and 12); heterochiral structures are preferred (although the preferences are not as strong) for x = 5 and 7. Larger, doubly protonated clusters [xPro+2H](2+) favor homochiral assemblies for x = 18, 19, and 23 and heterochiral structures for x = 14, 16, 17, 20, 21, and 22. Some of the variations that are observed can be rationalized through simple structures that would lead to especially stable geometries. It is suggested that some antiresolved clusters, such as [22Pro+2H](2+), may be comprised of resolved D- and L-proline domains.

Hydrogen/deuterium (H/D) exchange reactions between different elongated conformations of [M+11H]11+ ions of ubiquitin and D2O are studied by a combination of ion mobility spectrometry (IMS) and mass spectrometry techniques. Three conformers (B, C, and D), resolved in the IMS separation, each exchange ~27 hydrogens upon exposure to 0.06 torr of D2O vapor for ~35 to 40 ms. However, a region of the IMS spectrum that appears between the C and D states (corresponding to ions that undergo a structural transition during the mobility separation) undergoes substantially more exchanges (~39 total sites, 44% more than the B, C, and D states). Selection and activation of the individual B, C, and D states reveals that the increased H/D exchange occurs during the transition between structures. Overall, these studies suggest a key process in establishing the maximum exchange levels involves structural transitions, which allow protected sites to be exposed for some fraction of the reaction time. Analysis of changes in exchange levels upon structural transitions can provide insight about common regions of structure that exist in the B, C, and D conformations.

Development and application of an ELISA method for the analysis of protein-based binding media of artworks.