Collaborative use of neutron and X-ray for determination of drug target proteins

Kuroki, Ryota; Tamada, Taro; Kurihara, Kazuo; Ohara, Takashi   ; Adachi, Motoyasu

Crystallography enables us to obtain accurate atomic positions within proteins. High resolution X-ray crystallography provides information for most of the atoms comprising a protein, with the exception of hydrogens. Neutron diffraction data can provide information of the location of hydrogen atoms to the structural information determined by X-ray crystallography. Here, we show the recent result of the structural determination of drug-target proteins, porcine pancreatic elastase and human immuno-deficiency virus type-1 protease by both X-ray and neutron diffraction. The structure of porcine pancreatic elastase with its potent inhibitor was determined at room temperature to 1.2 resolution by X-ray diffraction and 1.65 resolution by neutron diffraction. The structure of HIV-PR with its potent inhibitor was also determined to 1.4 resolution by X-ray diffraction and 1.9 resolution by neutron diffraction. Ultra-high resolution structures of both proteins (0.94 and 0.93 , respectively) were also determined by X-ray diffraction at 100 K. The ionization state and the location of hydrogen atoms of the catalytic residue in these enzymes were determined by neutron diffraction. Furthermore, collaborative use of both X-ray and neutron to identify the location of ambiguous hydrogen atoms will be shown.