Catalytically important damage-free structures of a copper nitrite reductase obtained by femtosecond X-ray laser and room-temperature neutron crystallography.

Copper-containing nitrite reductases (CuNiRs) that convert NO to NO via a Cu-His-Cys-Cu proton-coupled redox system are of central importance in nitrogen-based energy metabolism. These metalloenzymes, like all redox enzymes, are very susceptible to radiation damage from the intense synchrotron-radiation X-rays that are used to obtain structures at high resolution. Understanding the chemistry that underpins the enzyme mechanisms in these systems requires resolutions of better than 2 Å.

An unprecedented dioxygen species revealed by serial femtosecond rotation crystallography in copper nitrite reductase.

Synchrotron-based X-ray structural studies of ligand-bound enzymes are powerful tools to further our understanding of reaction mechanisms. For redox enzymes, it is necessary to study both the oxidized and reduced active sites to fully elucidate the reaction, an objective that is complicated by potential X-ray photoreduction. In the presence of the substrate, this can be exploited to construct a structural movie of the events associated with catalysis.