3Fe4SCluster

The 3Fe4S cluster, commonly written as [3Fe-4S], is a type of iron-sulfur cluster that contains three iron atoms and four inorganic sulfide ligands. It is one of several iron-sulfur motifs found in a range of proteins and synthetic systems. In proteins, the cluster is typically coordinated by cysteine thiolate ligands, and may also involve other protein ligands, all converging to position the cluster for electron transfer or catalysis.

Structure and topology: The geometry of the [3Fe-4S] cluster is often described as a truncated form of the [4Fe-4S] cubane, lacking one iron center, which yields a three-iron core connected by sulfide bridges. The exact arrangement can vary among proteins, with different bridge patterns and ligand sets giving rise to subtle structural differences that influence redox properties and stability.

Redox properties and function: [3Fe-4S] clusters are redox-active and can undergo changes in oxidation state during biological processes. They participate in one-electron transfers and can couple electron transfer to substrate transformation or to other cofactors within a metabolic pathway. The redox potentials of these clusters are tuned by the surrounding protein environment, enabling participation in diverse catalytic and regulatory roles.

Occurrence and significance: [3Fe-4S] clusters are found in a subset of ferredoxins and other iron-sulfur proteins, including enzymes where the cluster arrangement provides specific redox and structural requirements not met by other motifs. They also appear in synthetic models used to study Fe-S chemistry and electron-transfer processes.

Laboratory and model systems: In vitro reconstitution of apo-proteins with [3Fe-4S] clusters and spectroscopic characterization (EPR, Mössbauer, UV-Vis) help reveal oxidation states, ligand effects, and assembly pathways. These studies advance understanding of iron-sulfur chemistry and potential bioelectronic applications.