X-ray Crystal Structure of the Fe-Only Hydrogenase (CpI) from Clostridium pasteurianum to 1.8 Angstrom Resolution

TLDR

A three-dimensional structure for the monomeric iron-containing hydrogenase (CpI) from *Clostridium pasteurianum* was determined to 1.8 Å resolution by X‑ray crystallography using multiwavelength anomalous dispersion (MAD) phasing. CpI contains 20 iron atoms per mole organized into five Fe‑S clusters, including an H‑cluster composed of a [4Fe‑4S] cubane linked to a [2Fe] subcluster with octahedral coordination bridged by sulfide and carbonyl/cyanide, offering insights into hydrogen activation and broader implications for Fe‑S cluster biology.

Abstract

A three-dimensional structure for the monomeric iron-containing hydrogenase (CpI) from Clostridium pasteurianum was determined to 1.8 angstrom resolution by x-ray crystallography using multiwavelength anomalous dispersion (MAD) phasing. CpI, an enzyme that catalyzes the two-electron reduction of two protons to yield dihydrogen, was found to contain 20 gram atoms of iron per mole of protein, arranged into five distinct [Fe-S] clusters. The probable active-site cluster, previously termed the H-cluster, was found to be an unexpected arrangement of six iron atoms existing as a [4Fe-4S] cubane subcluster covalently bridged by a cysteinate thiol to a [2Fe] subcluster. The iron atoms of the [2Fe] subcluster both exist with an octahedral coordination geometry and are bridged to each other by three non-protein atoms, assigned as two sulfide atoms and one carbonyl or cyanide molecule. This structure provides insights into the mechanism of biological hydrogen activation and has broader implications for [Fe-S] cluster structure and function in biological systems.