Theoretical study on the magnetic interactions of active site in hemerythrin

The active site structure of hemerythrin are μ-(hydro)oxo bridged diiron cores and are universal in many non-hem proteins. The magnitudes of antiferromagnetic interactions in the binuclear iron center are largely different in each oxidization states. To clarify the magnetic interactions and electronic structures in oxy-hemerythrin(Hr), deoxy-Hr and met-Hr, hybrid density-functional theory were performed in the broken symmetry way. Effective-exchange interactions are calculated by B2LYP method and they are in good agreement with experimental values. Natural orbital analyses are utilized to clarify their magnetic interactions between the iron spin sites. It is found that there are five magnetic interactions of σ, π₁, π₂, δ₁, and δ₂. Former three interactions are stronger interactions through μ-oxo. The latter two δ interactions are weaker interactions through carboxyl groups. Magnetic interaction of π₁ type is most significantly changed by dioxygen bonding, where the magnetic interaction pathway is through p orbital parallel to hydrogen atom of μ-hydroxo. At dioxygen bonding state of oxy-Hr, orbital interactions between diiron spin sites and dioxygen are discussed.