Figure 1.

Comparison of similar active sites. (a) Synechocystis sp. PCC 6803 structure (PDB entry 3rpl, yellow) shown with key active-site residues shown as sticks (Asp33, Glu57, Glu100, Thr102, Tyr131, Lys134, Arg176, Arg178, Asp198, Asp200 and Glu225). (b) T. elongatus structure (PDB entry 5a5l, purple) bound with sedoheptulose-7-phosphate (lavender) with equivalent active-site residues shown as sticks (Asp33, Glu57, Glu100, Thr102, Tyr131, Lys134, Arg176, Arg178, Asp198, Asp200 and Glu225). Magnesium ions are shown as spheres. The phosphate (PO₄) of the suggested product complex is clearly visible. Ligand OMIT map difference density is shown for the S7P ligand and phosphate (lavender mesh) using a 4σ contour level. Active-site residues and metals are in the same conformation; selectivity between the sugars is not the result of large-scale conformational change.