Cyanide Binding to [FeFe]‐Hydrogenase Stabilizes the Alternative Configuration of the Proton Transfer Pathway
Jifu Duan, Anja Hemschemeier, David J. Burr, Sven T. Stripp, Eckhard Hofmann, Thomas Happe
Abstract
Abstract Hydrogenases are H 2 converting enzymes that harbor catalytic cofactors in which iron (Fe) ions are coordinated by biologically unusual carbon monoxide (CO) and cyanide (CN − ) ligands. Extrinsic CO and CN − , however, inhibit hydrogenases. The mechanism by which CN − binds to [FeFe]‐hydrogenases is not known. Here, we obtained crystal structures of the CN − ‐treated [FeFe]‐hydrogenase CpI from Clostridium pasteurianum . The high resolution of 1.39 Å allowed us to distinguish intrinsic CN − and CO ligands and to show that extrinsic CN − binds to the open coordination site of the cofactor where CO is known to bind. In contrast to other inhibitors, CN − treated crystals show conformational changes of conserved residues within the proton transfer pathway which could allow a direct proton transfer between E279 and S319. This configuration has been proposed to be vital for efficient proton transfer, but has never been observed structurally.