The Active Form of Chlamydia trachomatis Ribonucleotide Reductase R2 Protein Contains a Heterodinuclear Mn(IV)/Fe(III) Cluster with S = 1 Ground State

Abstract

The class I ribonucleotide reductase from Chlamydia trachomatis uses a stable MnIV/FeIII cofactor to initiate nucleotide reduction by a free-radical mechanism. The enzyme provides the first example both of a Mn-dependent ribonucleotide reductase and of a Mn/Fe redox cofactor. In this work, we have used variable-field Mossbauer spectroscopy to demonstrate that the active cofactor has an S = 1 ground state due to antiferromagnetic coupling between the MnIV (SMn = 3/2) and high-spin FeIII (SFe = 5/2) sites.