Virtuelle (Nano) Welten: PDB Molecule of the Month 26: Nitrogenase

The Nitrogen-splitting Anvil

At the heart of nitrogenase is an unusual complex of iron, sulfur and a molybdenum ion, which is thought to perform the nitrogen-fixing reaction. A string of cofactors feed electrons to this MoFe-cluster. As seen in the illustration on the left, electrons start at a pair of ATP molecules (two at each end of the dimeric complex), flow inwards into the iron-sulfur cluster, then to the P-cluster, and finally to the MoFe-cluster. The three metal clusters are shown in the close-up figure at right. The MoFe-cluster is at the bottom, with the molybdenum atom in bright red. A homocitrate molecule, shown with white carbon atoms and pink oxygen atoms, helps to stabilize this unusual metal ion. The P-cluster is in the middle and the iron-sulfur cluster of the Fe protein is at the top. In spite of the detailed knowledge provided by the beautiful structures of nitrogenase (1n2c is shown here), the actual binding site for nitrogen gas is still a subject of controversy and intense study.