The Do Lab published their research “Cytotoxicity of α-Helical, Staphylococcus aureus PSMα3 Investigated by Post-Ion-Mobility Dissociation Mass Spectrometry” in Analytical Chemistry.
Staphylococcus aureus, a major bacterial human pathogen, secretes phenol-soluble modulin (PSM) peptides to stimulate inflammatory responses and kill human cells. PSMα3 is the prominent member of the PSM family and exerts its toxic function via the formation of cross-α fibrils. The fibril structure of PSMα3 resembles the eukaryotic amyloid fibrils found in the brain of Alzheimer’s disease patient, but each unit is an α-helix peptide and not a β-strand.
In this study, the Do Lab investigated how oligomeric structures and interactions with cell membrane mimetics could determine peptide cytotoxicity. To overcome the dynamic nature of interaction and aggregation process, they use ion mobility spectrometry mass spectrometry (IMS-MS) to measure the molecular shapes of the oligomeric species.
Due to the weakly-bound nature of these oligomers, it is possible for them to dissociate within the mass spectrometer. This phenomenon, called post-ion mobility dissociation, has been well documented in the past but has not been considered in previous biomolecular self-assembly studies.
The Do Lab took advantage of this typically undesired phenomenon to elucidate the molecular structures of the oligomers and determine the number of detergent molecules (which mimic the lipids in cell membrane) required to stabilize the complexes.
Consequently, the most toxic PSMα3 variant was shown to preserve its α-helical signature and required the smallest number of detergent molecules, indicating that a key virulence factor of toxic PSMα3 lies in its ability to quickly insert into the cell membrane. The same approach can be applied to similar peptide systems. Amber Gray, first author and graduate student said, “Ultimately, our study highlights the ambiguity previously present in IMS-MS data and sheds new insight into the interpretation of such data in biomolecular self-assembly studies.”