Phenotypic heterogeneity of glucokinase-diabetes mutations: Studies of structure, function and regulatory mechanisms leading to treatment

Glucokinase (GK) is the major glucose sensor in the pancreatic beta-cell where it catalyses the first step of glycolysis. Mutations in human GK (hGK) can be inactivating or activating. Heterozygous inactivating mutations lead to a mild form of diabetes, M ODY2, while homozygous inactivating mutations cause a severe type of diabetes manifesting the first day of life (permanent neonatal diabetes). Activating mutations, however, result in the opposite phenotype, i.e. hypoglycaemia due to hyperinsulinism. This broad spectrum of phenotypes of the GK mutations demonstrates the essential role of hGK in glucose homeostasis. Characterisation of recombinant GK mutations, as seen in MODY2, in terms of catalytic activity and glucose/MgATP binding affinity, has shown that some of the mutants demonstrate wild-type (wt) characteristics, indicating that other mechanisms have to be revealed in order to explain the metabolic phenotypes of the diabetic disease. The current project will focus on alternative mechanisms for th e regulation of the catalytic activity and the in vitro/in vivo stability of beta-cell hGK and its MODY2-associated mutant forms. Complementary in vitro and in vivo studies are expected to reveal novel information on the mechanisms involved in the regulat ion of hGK at the cellular level, and thus prove important for the detailed characterisation of its mutant phenotypes. The project is an interdisciplinary collaboration between (1) The Diabetes Research Group, with long experience within clinical, molec ular genetic and functional studies of diabetes, and (2) the research group of Prof. Flatmark, who has a broad experience in biochemical/biophysicalmethods in the study of recombinant enzymes/proteins. The project is expected to reveal novel mechanisms fo r the regulation of hGK at the cellular level, which may prove important for the detailed characterization of its mutant phenotypesand thus for the treatment of the individual patients.