Electrospray ionization mass spectrometry (ESI-MS) is gentle enough to preserve non-covalent interactions, enabling direct and accurate measurements of protein stoichiometries. This is particularly powerful for analysing highly polydisperse samples with lowly populated assembly states. Whereas many biophysical techniques report only ensemble averages and struggle to resolve rare species, mass spectrometry provides per-state resolution and captures the relative abundances of all assemblies within the sample. 

A biologically relevant example is the oligomers formed by amyloidogenic species during aggregation in diseases such as Alzheimer’s and Parkinson’s diseases. These transient intermediates are among the most toxic species in the aggregation pathway but are exceptionally difficult to study: they are rare, structurally heterogeneous, and unstable, making them hard to analyse or purify in solution.

To address this, the Pagel group employs a mass-spectrometry-based strategy that separates aggregates according to their stoichiometries. Coupling to ion mobility spectrometry (IMS) introduces an additional separation by molecular shape and provides insight into assembly pathways, while integration with gas-phase infrared (IR) spectroscopy enables direct probing of secondary structure. Together, this multidimensional “gas-phase purification” approach offers unique access to the structural landscape of polydisperse protein samples.

The Pagel group investigates amyloid formation using both gas-phase and solution-state spectroscopy. As part of the DFG-funded International Research Training Group 2662 “Charging into the Future” we specifically study interactions between amyloidogenic proteins and glycosaminoglycans (GAGs), highly charged glycans expressed on cell surfaces.

Figure: ESI-MS distinguished between stable magic number multimers (A), transient polydisperse oligomers populated during amyloid aggregation (B), and the absence of oligomers in non-aggregating peptide systems (C). Peaks annotated by their oligomeric state/charge state (n/z) ratio.

Related Publications

• Gas-phase purification enables structural studies of amyloid intermediates
  Horlebein, J.; Moon, E.; Szekeres, G.P.; von Helden, G.; Österlund, N. & Pagel, K. Trends Chem. 2025
• Mass spectrometry detects folding intermediates populated during urea-induced protein denaturation
  Österlund, N.; Jordan, J.S.; Renzi, E.; Szekeres, G.P. & Pagel, K. Chem. Sci. 2025
• NFGAIL amyloid oligomers: the onset of beta-sheet formation and the mechanism for fibril formation
  Hoffmann, W.; Folmert, K.; Moschner, J.; Huang, X.; von Berlepsch, H.; Koksch, B.; Bowers. M.T.; von Helden, G. & Pagel, K. J. Am. Chem. Soc. 2017
• An infrared spectroscopy approach to follow β-sheet formation in peptide amyloid assemblies
  Seo, J.; Hoffmann, W.; Warnke, S.; Huang, X.; Gewinner, S.; Schöllkopf, W.; Bowers. M.T.; von Helden, G. & Pagel, K. Nat. Chem. 2016
• Retention of native protein structures in the absence of solvent: a coupled ion mobility and spectroscopic study
  Seo, J.; Hoffmann, W.; Warnke, S.; Bowers, M.T.; Pagel, K. & von Helden, G. Angew. Chem. Int. Ed. 2016