Co²⁺/Co⁺ Redox Tuning in Methyltransferases Induced by a Conformational Change at the Axial Ligand

Abstract

Density functional theory and quantum mechanics/molecular mechanics computations predict cob­(I)­alamin (Co⁺Cbx), a universal B₁₂ intermediate state, to be a pentacoordinated square pyramidal complex, which is different from the most widely accepted viewpoint of its tetracoordinated square planar geometry. The square pyramidality of Co⁺Cbx is inspired by the fact that a Co⁺ ion, which has a dominant d⁸ electronic configuration, forms a distinctive Co⁺--H interaction because of the availability of appropriately oriented filled d orbitals. This uniquely H-bonded Co⁺Cbx may have catalytic relevance in the context of thermodynamically uphill Co²⁺/Co⁺ reduction that constitutes an essential component in a large variety of methyltransferases