CRP has a pentamer-of-monomers topology with equal interfacial areas between all subunits. This suggests that possible SID products include complementary pairs of monomer/tetramer and dimer/trimer, depending on the collision energy. At an SID energy of 765 eV, at low levels of isCA, dimer/trimer formation was the primary dissociation pathway, with monomer/tetramer also present, in line with previous reports from the Wysocki lab. This strongly suggests that the cyclic quaternary structure is intact and native-like.