Additive activation of glucokinase by the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase and the chemical activator LY2121260.
The glucose phosphorylating enzyme glucokinase plays a crucial role in stimulus-secretion coupling in pancreatic beta cells and in glucose metabolism in liver. Glucose mediates a shift of the enzyme's conformational equilibrium towards the closed conformation with high glucokinase activity. Further activation of glucokinase is endogenously mediated by interaction with the bisphosphatase domain (FBPase-2) of the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2) and can be achieved also by a new class of glucokinase activators (GKA), chemical compounds that might be suited for type 2 diabetes therapy. While FBPase-2 increased only the phosphorylating capacity of glucokinase, the GKA LY2121260 augmented in addition the affinity of glucokinase for glucose. PFK-2/FBPase-2 but not LY2121260 antagonized glucokinase inhibition by the competitive glucokinase inhibitor mannoheptulose at increasing glucose concentrations. Interestingly, an additive activation of glucokinase was observed by use of recombinant FBPase-2 together with LY2121260. This new crucial observation could be confirmed with cellular extracts containing the glucokinase and PFK-2/FBPase-2 proteins. Addition of LY2121260 resulted in a further significant increase in glucokinase activity. Because the glucokinase-PFK-2/FBPase-2 complex was conserved under LY2121260 treatment as shown by size exclusion chromatography a concerted action of both activators towards the closed active glucokinase conformation can be anticipated. Thus, as a result of the additive effect of both activators on glucokinase activity, the largest increase of glucose-induced insulin secretion was observed in the combined presence of PFK-2/FBPase-2 and LY2121260.
Institute of Clinical Biochemistry, Hannover Medical School, Hannover, Germany. simone.baltrusch@med.uni-rostock.de
Simone
S
Baltrusch
Heike
H
Schmitt
Anke
A
Brix
Sara
S
Langer
Sigurd
S
Lenzen
D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005941:Glucokinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006539:Heptoses / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D008356:Mannoheptulose / Q000494:pharmacology; D025481:Phosphofructokinase-2 / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013450:Sulfones / Q000494:pharmacology*; D013844:Thiazoles / Q000494:pharmacology*
C503863:2-cyclohexyl-1-(4-methanesulfonylphenyl)cyclopropanecarboxylic acid thiazol-2-ylamide; D004791:Enzyme Inhibitors; D006539:Heptoses; D007328:Insulin; D011994:Recombinant Proteins; D013450:Sulfones; D013844:Thiazoles; C025642:perseitol; D008356:Mannoheptulose; D025481:Phosphofructokinase-2; D005941:Glucokinase; D005947:Glucose