As seen in the inset of Figure , there is a size difference between the 15+ and 21+ at a cone voltage of 10 V that suggests the 15+ is more expanded, perhaps cyclic, while the 21+ is indeed globular. When the 15+ complex undergoes isCA at a cone voltage of 160 V, the CCS decreases to a range that matches the CCS for the globular 21+. One possible reason for this match is that isCA caused the 15+ to collapse from a ring-like structure to a globular structure, similar to that possessed by the 21+. We note that in comparison to the CCS values published by the Robinson lab in 2005, our CCS values for TRAP are smaller by about 9%. This could be due to the advancement that traveling wave ion mobility has experienced since 2005, especially in terms of better understanding of its physical implementation, theoretical underpinnings, 72 application, and improved experimental CCS calibration. Experiment Type: isCA-IM-ECD To explain why we observed these SID trends as a function of isCA, we find it helpful to think about the subunit interfaces within the protein complexes. Previous work from our lab showed that SID will cause native-like protein complexes to dissociate along their weakest subunit interfaces. By this we mean the interfaces with the lowest interface area, fewest salt bridges, fewest hydrogen bonds, and hydrophobic surface area. When the protein's quaternary structure is disrupted by isCA, it is very likely that the subunit interfacial areas, salt bridges, and hydrogen bonds were disrupted along the way to low energy, non-native-like structures. These rearranged interfaces and interactions then influenced subsequent SID pathways.