Structures of Mammalian and Bacterial Fructose-1,6-bisphosphatase Reveal the Basis for Synergism in AMP/Fructose 2,6-Bisphosphate Inhibition

• Published in: The Journal of biological chemistry 2007-12, Vol.282 (49), p.36121-36131
• Main Authors: Hines, Justin K., Chen, Xiaoming, Nix, Jay C., Fromm, Herbert J., Honzatko, Richard B.
• Format: Article
• Language: English
• Subjects: Adenosine Monophosphate - agonists; Adenosine Monophosphate - chemistry; Allosteric Site - physiology; Animals; Escherichia coli; Escherichia coli - enzymology; Fructose-Bisphosphatase - antagonists & inhibitors; Fructose-Bisphosphatase - chemistry; Fructosediphosphates - agonists; Fructosediphosphates - chemistry; Gluconeogenesis - physiology; Models, Chemical; Protein Structure, Secondary; Protein Structure, Tertiary; Swine - metabolism; Thermodynamics
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M707302200

Fructose-1,6-bisphosphatase (FBPase) operates at a control point in mammalian gluconeogenesis, being inhibited synergistically by fructose 2,6-bisphosphate (Fru-2,6-P2) and AMP. AMP and Fru-2,6-P2 bind to allosteric and active sites, respectively, but the mechanism responsible for AMP/Fru-2,6-P2 synergy is unclear. Demonstrated here for the first time is a global conformational change in porcine FBPase induced by Fru-2,6-P2 in the absence of AMP. The Fru-2,6-P2 complex exhibits a subunit pair rotation of 13° from the R-state (compared with the 15° rotation of the T-state AMP complex) with active site loops in the disengaged conformation. A three-state thermodynamic model in which Fru-2,6-P2 drives a conformational change to a T-like intermediate state can account for AMP/Fru-2,6-P2 synergism in mammalian FBPases. AMP and Fru-2,6-P2 are not synergistic inhibitors of the Type I FBPase from Escherichia coli, and consistent with that model, the complex of E. coli FBPase with Fru-2,6-P2 remains in the R-state with dynamic loops in the engaged conformation. Evidently in porcine FBPase, the actions of AMP at the allosteric site and Fru-2,6-P2 at the active site displace engaged dynamic loops by distinct mechanisms, resulting in similar quaternary end-states. Conceivably, Type I FBPases from all eukaryotes may undergo similar global conformational changes in response to Fru-2,6-P2 ligation.