Preliminary neutron diffraction analysis of challenging human manganese superoxide dismutase crystals

Superoxide dismutases (SODs) are enzymes that protect against oxidative stress by dismutation of superoxide into oxygen and hydrogen peroxide through cyclic reduction and oxidation of the active-site metal. The complete enzymatic mechanisms of SODs are unknown since data on the positions of hydrogen are limited. Here, methods are presented for large crystal growth and neutron data collection of human manganese SOD (MnSOD) using perdeuteration and the MaNDi beamline at Oak Ridge National Laboratory. The crystal from which the human MnSOD data set was obtained is the crystal with the largest unit-cell edge (240 Å) from which data have been collected via neutron diffraction to sufficient resolution (2.30 Å) where hydrogen positions can be observed.The growth of crystals of perdeuterated human manganese superoxide dismutase with a unit-cell edge of 240 was optimized for neutron data collection. Data were collected to 2.30 Å resolution from a 0.26 mm³ crystal. This is the crystal with the largest unit-cell edge from which data have been collected via neutron diffraction to sufficient resolution where hydrogen positions can be observed.