Ultrahigh-resolution structure of high-potential iron-sulfur protein from Thermochromatium tepidum

Crystals of the high-potential iron-sulfur protein (HiPIP) from Thermochromatium tepidum diffract X-rays to 0.80 A using synchrotron radiation at 100 K. The crystal structure of this HiPIP was refined at this ultrahigh resolution with anisotropic temperature factors for all atoms to conventional crystallographic R factors of 0.092 and 0.101 for F(o) > 4sigma(F(o)) and all reflections, respectively. The present structure provides a more precise picture than the previous 1.5 A structure and allows location of the positions of most H atoms. The structure revealed a partly hydrophobic cavity near the main hydrophobic area and a much larger inter-cluster approach distance (23.454 A, the c constant of the unit cell) in the crystal packing than other types of HiPIPs. The structural features involved in the electron-transfer reaction of HiPIP are discussed.