Neutron structure analysis of electron transfer proteins

Hirano, Yu; Kurihara, Kazuo; Tamada, Taro; Kusaka, Katsuhiro*; Miki, Kunio*

Many electron transfer proteins possess prosthetic groups, such as heme, flavin and iron-sulfur cluster. The electron transfer reaction is associated with the movement of hydrogen atoms or outer electrons of the prosthetic groups. We have determined high-resolution neutron structure of both high-potential iron-sulfur protein (HiPIP) and NADH cytochrome reductase (b5R). We have collected neutron diffraction data of HiPIP and b5R at iBIX beamline of J-PARC, and diffraction data sets were obtained at 1.1 resolution (HiPIP) and 1.4 resolution (b5R). X-ray diffraction data sets of HiPIP and b5R were also collected using the same crystals used for the neutron diffraction experiment. We have performed X-ray and neutron joint refinement, and we determined protonation states of amino acid residues and orientation of water molecules on the surface of the proteins.