We describe the metal-dependent self-assembly of symmetrical protein homooligomers from protein building blocks that feature appropriately engineered metal-chelating motifs on their surfaces. Crystallographic studies indicate that the same four-helix-bundle protein construct, MBPC-1, can self-assemble into C-2 and C-3 symmetrical assemblies dictated by Cu-II and Ni-II coordination, respectively. The symmetry inherent in metal coordination can thus be directly applied to biological self-assembly.