Using Proteins, Interfaces, Structures and Assemblies (PISA) (), an interface analysis was performed on PDB 1SWB, the SA tetramer. Identified interfacial residues are located within SA's anti-parallel β-sheet. In Figures and these residues are highlighted in tan. The residues between the highlighted regions belong to the β-sheet's hairpin turns and were not included as interfacial residues by PISA. Returning to Figures and, a cone voltage of 20 V resulted in 24% sequence coverage, not including internal fragments. The sequence coverage was 53% at a cone voltage of 160 V. Since the SID data indicate that isCA clearly rearranges the quaternary structure, possibly by causing monomer subunits to elongate, the uptick in sequence coverage was unsurprising. Next, we should note that the increased sequence coverage came from the N-terminus, and the interface between subunits, especially between residues 75 -120. This strongly suggests that isCA disrupted protein tertiary structure by elongating the N-terminal domain and rearranged the quaternary structure along the strong monomer-monomer interfacial areas. This evidence validates our conclusion that the SID results in Figure reflect interfacial changes between subunits, which was also suggested by the increase in average monomer charge state.