| Popis: |
Protein neutron crystallography is a powerful technique to determine the positions of hydrogen atoms, providing crucial biochemical information such as the protonation states of catalytic groups and the geometry of hydrogen bonds. Recently, we determined the crystal structure of a bacterial copper amine oxidase by joint refinement using X-ray and neutron diffraction data sets at resolutions of 1.14 A and 1.72 A, respectively (Murakawa, T. et al. (2020). Proc. Natl Acad. Sci. USA, 117, 10818?10824). While the joint refinement is effective for determination of the accurate positions of heavy atoms on the basis of the electron density, the structural information of light atoms (hydrogen and deuterium) derived from the neutron diffraction data might be affected by the X-ray data. To unravel the information included in the neutron diffraction data, we conducted the structure determination again using only the neutron diffraction data at a 1.72 A resolution and compared the results with those obtained by the previous study. Most hydrogen and deuterium atoms were identified at essentially the same positions in both the neutron-only and X-ray/neutron joint refinements. Nevertheless, the neutron-only refinement was found to be less effective than the joint refinement in providing very accurate heavy atom coordinates that lead to significant improvement of the neutron scattering length density map, especially for the active-site cofactor. Consequently, we have confirmed that the X-ray/neutron joint refinement is crucial for determination of the real chemical structure of the catalytic site of the enzyme. |
