Fig. 1: Reaction schemes for the allomorphic activation of βPGM and differences in the interdomain hinge closure angle for βPGM structures.

a, b Reaction schemes for the phosphorylation of βPGM using either F16BP or βG16BP as allomorphic activators. Substrate-free βPGM exists as two conformers with different activities that result from cis-trans isomerisation of the K145-P146 peptide bond¹³. The fully active form is cis-P βPGM. a Both cis-P βPGM and trans-P βPGM are phosphorylated by F16BP (as βF16BP) generating cis-P βPGM^P and trans-P βPGM^P, together with the release of either β-fructose 1-phosphate (βF1P) or fructose 6-phosphate (F6P). A pronounced lag phase is observed in catalytic activity until the population of cis-P βPGM^P dominates. b The βG16BP reaction intermediate is able to couple the conformational switch and the phosphorylation step, resulting in the rapid generation of cis-P βPGM^P along with either βG1P or G6P as products. A linear, fast initial rate is observed in kinetic profiles. Although the trans-P βPGM to trans-P βPGM^P phosphorylation reaction (long dotted arrow) is possible, it has not been observed experimentally. Hydrolysis reactions, liberating inorganic phosphate (P_i), yield short lifetimes for both cis-P βPGM^P and trans-P βPGM^P (~30 s in vitro²⁵). c–e Differences in the interdomain hinge closure angle for βPGM. Core domain superposition of the open substrate-free conformation (pale grey ribbon, cis-P βPGM_WT, PDB 2WHE²⁶) with either (c) the NAC I conformation (gold ribbon, cis-P βPGM_WT:BeF₃:G6P complex, PDB 2WF9²⁷), (d) the NAC III conformation (pink ribbon, cis-P βPGM_D10N:βG16BP complex, PDB 5OK1²⁹) or (e) the fully closed near-transition state conformation (blue ribbon, cis-P βPGM_WT:MgF₃:G6P complex, PDB 2WF5²⁶). Mg_cat is depicted as a green sphere, G6P is shown as purple sticks, βG16BP is shown as teal sticks, and the BeF₃^– and MgF₃^– moieties are illustrated as green and pale blue sticks.