Figure 3

Stereo views of the active site. (A) Active site of subunit A of SuhB, with metal sites (beige) and inositol-1-phosphate (coloured by atom type, carbons in light grey) modelled based on superimposition with the structures of bovine (PDB:2BJI, [17]) and human IMPase (PDB:1IMA, [29]). Residues in contact with metal sites and substrate in the modelled complex are shown as sticks and numbered according to the SuhB sequence. Secondary structure elements are coloured as in Figure 2A. The loop in violet indicates the approximate position of the α1-α2 loop, based on the superposition with PDB:1IMA [29]. (B) Bias-free difference density map of the β9-α6 loop in SuhB, calculated after simulated annealing of the model with residues 178–188 deleted and contoured at 2σ. The density is superimposed with apo SuhB (blue sticks) and human IMPase in complex with inositol-1-phosphate (light green, PDB:1IMA, [29]). Putative (grey) and experimental (red) contact distances with substrate are indicated. (C) Active site of subunit C of SuhB with σ_A-weighted Fo-Fc map contoured at 3σ, showing unexplained density around the putative substrate position and metal site 1.