Structures of mammalian and bacterial fructose-1,6-bisphosphatase reveal the basis for synergism in AMP/fructose 2,6-bisphosphate inhibition.
Fructose-1,6-bisphosphatase (FBPase) operates at a control point in mammalian gluconeogenesis, being inhibited synergistically by fructose 2,6-bisphosphate (Fru-2,6-P(2)) and AMP. AMP and Fru-2,6-P(2) bind to allosteric and active sites, respectively, but the mechanism responsible for AMP/Fru-2,6-P(2) synergy is unclear. Demonstrated here for the first time is a global conformational change in porcine FBPase induced by Fru-2,6-P(2) in the absence of AMP. The Fru-2,6-P(2) complex exhibits a subunit pair rotation of 13 degrees from the R-state (compared with the 15 degrees 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-P(2) drives a conformational change to a T-like intermediate state can account for AMP/Fru-2,6-P(2) synergism in mammalian FBPases. AMP and Fru-2,6-P(2) 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-P(2) 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-P(2) 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-P(2) ligation.
Hines
Justin K
JK
Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa 50011, USA.
Chen
Xiaoming
X
Nix
Jay C
JC
Fromm
Herbert J
HJ
Honzatko
Richard B
RB
D000249:Adenosine Monophosphate / Q000819:agonists / Q000737:chemistry*; D000495:Allosteric Site / Q000502:physiology; D000818:Animals; D004926:Escherichia coli / Q000201:enzymology*; D006597:Fructose-Bisphosphatase / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D005635:Fructosediphosphates / Q000819:agonists / Q000737:chemistry*; D005943:Gluconeogenesis / Q000502:physiology; D008956:Models, Chemical; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013552:Swine / Q000378:metabolism*; D013816:Thermodynamics
D005635:Fructosediphosphates; D000249:Adenosine Monophosphate; C027652:fructose 2,6-diphosphate; D006597:Fructose-Bisphosphatase