Table 2.

Calculated relative energies for the binding of different combinations of Mn^II and Fe^II to the reduced structures of GkR2loxI and class Ia E. coli R2 (EcR2)

Protein	Protein metal site	Solvated ions	Relative energy, kcal/mol
GkR2loxI	FeII/FeII	MnII, MnII	0.0
	MnII/FeII	MnII, FeII	1.3
	FeII/MnII	MnII, FeII	3.7
	MnII/MnII	FeII, FeII	6.9
Class Ia EcR2	FeII/FeII	MnII, MnII	0.0
	MnII/FeII	MnII, FeII	4.3
	FeII/MnII	MnII, FeII	3.2
	MnII/MnII	FeII, FeII	7.2

The relative energy values are obtained by combining the DFT energy of the active site with a particular combination of the two metal ions with the DFT energy of the remaining two metal ions coordinated by six water molecules in a continuum water solvent. All energy values are relative to the system with the lowest energy (the Fe^II/Fe^II-bound protein), which is set to zero. Positive values represent a higher relative energy and thus a less favorable assembly.