Glucokinase regulatory protein is essential for the proper subcellular localisation of liver glucokinase

Glucokinase (GK), a key enzyme in the glucose homeostatic responses of the liver, changes its intracellular localisation depending on the metabolic st atus of the cell. Rat liver GK and Xenopus laevis GK, fused to the green fl uorescent protein (GFP), concentrated in the nucleus of cultured rat hepato cytes at low glucose and translocated to the cytoplasm at high glucose. Thr ee mutant forms of Xenopus GK with reduced affinity for GK regulatory prote in (GKRP) did not concentrate in the hepatocyte nuclei, even at low glucose . In COS-1 and HeLa cells, a blue fluorescent protein (BFP)-tagged version of rat liver GK was only able to accumulate in the nucleus when it was co-e xpressed with GKRP-GFP. At low glucose, both proteins concentrated in the n uclear compartment and at high glucose, BFP-GK translocated to the cytosol while GKRP-GFP remained in the nucleus. These findings indicate that the pr esence of and binding to GKRP are necessary and sufficient for the proper i ntracellular localisation of CX and directly involve GKRP in the control of the GK subcellular distribution. (C) 1999 Federation of European Biochemic al Societies.