X-ray/neutron joint refinements of serine proteases

Introduction Neutron scattering is a useful technique to observe hydrogen atoms, such as polar hydrogen in polar amino acid residues and solvent water molecules in protein crystals. However, availability of neutron source and intensity of neutron beam are limited. Currently the technique needs large sizes of protein crystals and quite a long experimental time. It was reported that using of xray diffraction data with neutron data for structure refinement gave better quality of neutron scattering length density maps. Serine proteases are interesting targets to study the reaction mechanism with the neutron diffraction technique because the reaction is related with hydrogen bonds, hydrogen migration, and activation of water solvent. In this project, we deal with human bovine βtrypsin-BPTI complex, human α-thrombin-bivalirudin complex, and Achromobactor protease I. At BL-5A, 6A, AR-NE3, we were able to obtain the decent quality of xray diffraction data for those serine proteases. This report will give a quick review of the results of the x/n joint refinements.