Gas-phase protein assemblies: Unfolding landscapes and preserving native-like structures using noncovalent adducts

Mass spectrometry is a rapidly emerging technology for characterising the native structures of protein complexes. One challenge in interpreting results from mass spectrometry experiments is that the structures of protein complexes in the gas phase may differ from those in solution. As such, there is great interest in using small molecules to stabilise the structure of large proteins and their complexes in the gas-phase. Here, we investigate the stabilisation properties of trisH+, a cationic non-volatile electrospray buffer component, by experimentally characterising the unfolding and dissociation of three gas-phase tetrameric protein complexes. We find that trisH+ preferentially stabilises the compact native-like state of the complexes studied here. We put these results in context, and look beyond the water-soluble complexes studied here to discuss the mechanistic implications of this work on the stabilisation of membrane protein complexes during electrospray ionisation.