Figure 4. Ubl₃ proteins oligomerize in the presence of Ca²⁺.

(a-c) SEC-MALS analysis of E. coli Ubl₃ (a), M. brachiatum Ubl₃ (b), and Citrobacter Ubl₃ (d) in the absence of divalent cations. Black lines indicate dRI (change in refractive index; left Y axis) and red dots indicate measured molar mass (right Y axis; shown in logarithmic scale). The expected molar mass of a monomer species is shown as a dotted line. (d-f) SEC-MALS analysis of E. coli Ubl₃ (d), M. brachiatum Ubl₃ (e), and Citrobacter Ubl₃ (f) in the presence of 5 mM MgCl₂. The expected molar mass of monomer and dimer species are shown as dotted lines. (g-i) SEC-MALS analysis of E. coli Ubl₃ in the presence of 50 µM CaCl₂ (g), M. brachiatum Ubl₃ in the presence of 5 mM CaCl₂ (h), and Citrobacter Ubl₃ in the presence of 5 mM CaCl₂ (i).