Neutron structure of low-potential [4Fe-4S] BtFd
(A) Overall neutron structure of BtFd. BtFd polypeptides are colored in rainbow colors from blue (N-terminus) to red (C-terminus). The [4Fe-4S] cluster and water molecules are shown as a space-filling model. White and cyan balls indicate hydrogen (deuterium) and oxygen atoms, respectively. The figure on the right is the left one rotated approximately 90°. (B) The 2Fo–Fc (1.0 sigma: blue cage) and Fo–Fc (3.0 sigma: green cage) neutron-scattering length density map around the [4Fe-4S] cluster and the structural model. The 2Fo–Fc map is shown within 1 Å around the [4Fe-4S] cluster for clarity. (C) X-ray electron density map of the corresponding region of (B). 2Fo–Fc (5.0 sigma) and Fo–Fc (3.0 sigma) maps are shown in blue and green, respectively. (D) Hydrogen bond with the [4Fe-4S] cluster and its ligand Sγ atoms of cysteines. The hydrogen (deuterium), oxygen, carbon, and nitrogen atoms are shown in white, red, cyan, and blue, respectively. The hydrogen bonds indicate pink broken lines and the distance between the amide hydrogen and sulfur atoms is shown in angstroms. (E) The distances and angles of the hydrogen bonds. The distance/angle between the hydrogen and the sulfur are shown on the left and the center columns, and the distance between nitrogen/oxygen and sulfur are shown on the right column. (F) Hydrogen bond between Thr63-OH and the main chain –CO of Thr10.