Figure 3.

Various observed products of gas-phase protein complex dissociation are shown. This figure is color coded to correspond with techniques requiring either high (red) or low (blue) ion activation energies to access the product ions depicted. Protein complex ions activated using energetic collisions (CID, solid arrows) typically fragment via a pathway that leads to charge-reduced, monomer-stripped complexes and unfolded monomer ions (a). In references [27] and [191], exceptions to these general observations were reported (b). Electron capture dissociation (ECD, large dashed arrow) can result in the cleavage of peptide bonds within the complex and sequence-informative fragment ions as observed in reference [192] (c). Surface induced dissociation (SID, small dashed arrow) of protein complexes at higher effective energies can lead to the ejection of subcomplexes from the assembly, as observed in reference [138] (d). Charge manipulation is required to access other protein complex fragmentation pathways. Charge reduction of protein complex precursor ions, followed by collisional activation, results in either the ejection of compact protein subunits (e) or covalent fragmentation of the peptide backbone without the ejection of any protein subunits from the assembly, as observed in reference [131] (f). Charge amplification, followed by high-energy CID can lead to the ejection of large subunits from the assembly as observed in reference [193] (g), or the dissociation of protein subunits from the complex that then fragment into peptide ions as observed in reference [130] (h).