Allosteric regulation of hepatic fructose-1,6-bisphosphatase: Insights from E. coli
Date
2022-12
Authors
Kruesel, Claire Elizabeth
Major Professor
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Honzatko, Richard B
Nelson, Scott W
Coffman, Clark R
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Abstract
Fructose-1,6-bisphosphatase (FBP) catalyzes an irreversible hydrolysis in gluconeogenesis. The reciprocal glycolytic reaction by phosphofructokinase consumes ATP, necessitating coordinate regulation of both enzymes to avoid futile cycling. A homotetramer, FBP exhibits a quaternary shift from active (R-) to inactive (T-) state upon ligation by AMP. Hepatic FPB is further modulated by competitive inhibitor fructose-2,6-bisphosphatase (Fru-2,6-P2), the dynamic levels of which are controlled by insulin and glucagon. Despite binding at the active site at least 28 Å removed from the AMP site, Fru-2,6-P2 exhibits synergy with AMP and thus defines a regulatory scheme responsive to shifting metabolic needs. This potential for governing hepatic glucose levels positions FBP as a logical diabetes drug target. Failed attempts to map Fru-2,6-P2•AMP synergy encouraged examination of Escherichia coli, which requires FBP to grow on gluconeogenic substrates but lacks endogenous Fru-2,6-P2. Without Fru-2,6-P2•AMP synergy, how does E. coli avoid futile cycling and what might this reveal about the mammalian system? Described herein is a crystal structure of E. coli FBP complexed with AMP and glucose-6-phosphate (Glc-6-P), a downstream metabolite shown to partially inhibit FBP. Glc-6-P also assists AMP binding in a manner analogous to hepatic Fru-2,6-P2•AMP synergy, a similarity suggesting Glc-6-P•AMP synergy as evolutionary predecessor. In light of FBP’s importance as diabetes drug target, its emerging multipronged roles in cancer progression, and the need to identify novel targets in pathogens, characterizing E. coli FBP structure-function relationships has the potential to lay groundwork for truly impactful human health interventions.
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