Fig. 6: The formation of a metaphosphate-like reaction intermediate in AtPFA-DSP1^49–215.

a the relative positions of a catalytic water (Wat1; pink sphere) and 5-InsP₇ (stick format) in a crystal complex with AtPFA-DSP1^{49–150,C150S,151–215} (PDB accession code 7MOD); polar interactions are highlighted with broken black lines, with bond distances marked in Å. The omit Fo-Fc electron density map is contoured at 5σ and shown in green mesh. b a reaction intermediate that we designate to be a metaphosphate anion (ball and stick format; orange for phosphorus, red for oxygens). The crystal complex depicted in this panel was obtained by soaking 0.1 mM 5-InsP₇ into AtPFA-DSP1^49–215 at pH 8.0 for 2 h (7MOM; Supplementary Table 1). Broken black lines designate polar interactions with residues (stick format; blue for nitrogen, yellow for sulfur). The omit Fo-Fc electron density map is contoured at 4σ and shown in green mesh. A putative reactive water molecule (Wat2) is shown as a purple sphere. Distances are described in Å. His155 is shown in N^ε2-protonated τ tautomer state. c relative positions of Wat2 and the putative metaphosphate to illustrate distances between elements (Å); those within polar interaction distance are depicted as broken gray lines. The omit Fo-Fc electron density map is contoured at 4σ and shown in green mesh. Panel (d) is a rendering of the corresponding ligand–protein interactions created by Ligplot+. Panel (e) shows polar interactions (<3.2 Å; broken black lines) that Cys150 has with Thr157 and His149.