Conformational studies of ?-conotoxins using electrospray mass spectrometry

Abstract

MVIIA and MVIIB ω‐conotoxins were chosen to investigate the effect of experimental conditions on their conformations, because of the presence of three disulfide bridges in these toxins. There were no significant effects of ion‐source temperature, cone voltage, pH and percentage of cosolvent. We show that charge state distributions (CSDs) observed in their electrospray mass spectra are not a true reflection of the behaviour in the bulk solution because of electrostatic effects during the ion‐evaporation process in the ion source. As a result it is not possible to deduce from the observed CSDs that some basic amino acids are hidden in the core of the peptide structure. This is important in view of the complementary finding that nearly all labile hydrogens are rapidly exchanged in deuterated solvents. The mass spectrometry results can be reconciled with results of NMR experiments and molecular calculations from the literature. Copyright © 2000 John Wiley & Sons, Ltd.

Conformational study of a new SGTx1 neurotoxin from the spider Scodra griseipes using mass spectrometry

“…CSD and H/D exchange give complementary information. The present results, similar to those already reported for similar peptides,40,, 41 seem to be characteristic of the rigid basic bridged structure of the peptide. Thus, it is difficult to make reliable predictions of CSDs for such peptides.…”

“…However, the maximum charge state observed at pH 7 was found to be higher than the predicted value (+4 against +2). It has already been demonstrated for similar rigid and basic peptides, ω‐conotoxin40 and α‐dendrotoxin,41 that the maximum charge states observed in the ES mass spectra (gas‐phase ions) do not reflect the charges in solution. Presumably, this discrepancy arises during the desolvation (ion evaporation) process.…”

“…Based on several previous studies37–41 on proteins analyzed by ES‐MS, we assumed that the CSD observed reflects to some degree the distribution of protein net charge. Numerous parameters can influence this CSD such as the pH, the presence of organic solvent, the temperature, the protein concentration, and also the presence of intramolecular covalent linkages (i.e.…”

Conformational changes in β‐endorphin as studied by electrospray ionization mass spectrometry

“…This approach has been used for over two decades to investigate peptide and protein structures 5,. 6,, 10,, 11,, 13–21 The specific amide hydrogen exchange rate has allowed conformational analysis of small, soluble proteins by NMR 5,. 6,, 21 The underlying basis of this approach is that a considerably lower number of hydrogens are available for exchange in a tightly folded conformer than in the open structure, where labile hydrogens are exposed to the solvent and free to exchange more rapidly.…”

Trifluoroethanol-induced conformational changes in α- and β-neoendorphins monitored using hydrogen/deuterium exchange mass spectrometry and circular dichroism spectroscopy

“…The time-resolved HX experiments further support the existence of secondary structures for neoendorphins in the presence of TFE. In water, all of the labile hydrogens were exchanged within 30 s. This type of fast HX behavior is a common phenomenon for several other peptides [28][29][30][31][32][33][34][35]. The HX rates were relatively slower in 50% and 80% solvent systems.…”