Figure 3.
Quantifying charge regulation associated with lysine acylation using protein charge ladders and CE. a and b, electrospray ionization mass spectra of unmodified (a) and pyromellitylated (b) WT apo-SOD1 proteins (denoted as WT-PM(1.22)) used in amyloid assays. Mass spectra for all other acyl modifications are shown in supplemental Figs. S1 and S2. c and d, CE electropherograms of protein charge ladders of WT apo-SOD1 with acyl groups with ΔZformal = −4 (c) and acyl groups with ΔZformal = −2 (d) for the purpose of measuring ΔZ of acylation. e and f, average values of measured ΔZ (ΔZCE) for all modifications with ΔZformal = −4 (e) and all modifications with ΔZformal = −2 (f). The number of acyl modifications in CE electropherograms refers to the number of modifications per SOD1 dimer, whereas the number of acyl modifications in mass spectra refers to modifications per monomer (electrospray ionization leads to dissociation of SOD1 dimer). ΔZCE values in e and f are average values for each type of modification. The values of ΔZCE for each acyl group are listed in Fig. 2.