Weak Antiferromagnetic Coupling Via A Superexchange Interaction Between Mn(Ii)-Mn(Ii) Ions: A Qm/Mm Study Of The Active Site Of Human Cytosolic X-Propyl Aminopeptidase P

We investigate the dinuclear manganese, Mn(II)-Mn(II), active site of human cytosolic X-propyl aminopeptidase. (XPNPEP1) by employing the QM/MM method. The optimized structure supports two manganese atoms at the active site and excludes the possibility of a single Mn(II) atom or another combination of divalent metal ions, Ca(II), Fe(II), an Mg(II). A broken-symmetry solution verifies an antiferromagnetically coupled state between the Mn(II) Mn(II) pair, which is the ground state. From the energy difference between the high spin state (HS) and the broken-symmetry state (BS), we estimate the exchange coupling constant, J, to be 5.15 cm(-1). Also, we observe multiple bridges (p orbitals) from the solvent and two carboxylates linking to the Mn(II)-Mn(II), which leads to the wealdy antiferromagnetic interaction of d(5)-d(8) electrons through superexchange coupling.