view article

Figure 3
The practical benefits of XN refinement. Selected views of superimposed 2mFoDFc neutron scattering (blue) and electron (green) density maps calculated from the XN structure of diisopropyl fluorophosphate (DFPase; resolutions: X-ray, 1.8 Å; neutron, 2.2 Å; contoured at 1.6σ). In (a) the Nδ2 group of the Asn120 side chain scatters neutrons more strongly than X-rays, making it more easily and accurately orientated. In (b) note that the terminal amine group of the Lys151 side chain has strong neutron scattering density, whereas the methylene groups of the chain have strong electron density. In (c) the orientation of the hydroxyl group of the side chain of Thr102 is clearly indicated by the neutron scattering density. In (d)–(f) D2O molecules appear as either triangles (d), ellipsoids (e) or spheres (f) in the water structure around DFPase. The superposition of the electron-density maps provides complementary information on the location of the O atoms, greatly aiding in the interpretation of these features. In (d) the water molecule is ordered and all three atoms are seen. In (e) the O—D bond is visible with the second D invisible because of rotational disorder around this bond. In (f) the water molecules are completely rotationally disordered.

Journal logoBIOLOGICAL
ISSN: 1399-0047
Follow Acta Cryst. D
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds