A protein carboxylate coordinated oxo-centered tri-nuclear iron complex with possible implications for ferritin mineralization.

The crystal structure of an oxo-centered tri-nuclear iron complex formed on a protein surface is presented. The cluster forms when crystals of the class Ib ribonucleotide reductase R2 protein from Corynebacterium ammoniagenes are subjected to iron soaking. The tri-iron-oxo complex is coordinated by protein-derived carboxylate ligands arranged in a motif similar to the one found on the inner surface of ferritins and may mimic an early stage in the mineralization of iron in ferritins. In addition, the structure adds to the very limited data on protein-mineral interfaces.