title: Discovery of a novel site regulating glucokinase activity following characterization of a new mutation causing hyperinsulinemic hypoglycemia in humans.
abstract: Type 2 diabetes is a global problem, and current ineffective therapeutic strategies pave the way for novel treatments like small molecular activators targeting glucokinase (GCK). GCK activity is fundamental to beta cell and hepatocyte glucose metabolism, and heterozygous activating and inactivating GCK mutations cause hyperinsulinemic hypoglycemia (HH) and maturity onset diabetes of the young (MODY) respectively. Over 600 naturally occurring inactivating mutations have been reported, whereas only 13 activating mutations are documented to date. We report two novel GCK HH mutations (V389L and T103S) at residues where MODY mutations also occur (V389D and T103I). Using recombinant proteins with in vitro assays, we demonstrated that both HH mutants had a greater relative activity index than wild type (6.0 for V389L, 8.4 for T103S, and 1.0 for wild type). This was driven by an increased affinity for glucose (S(0.5), 3.3 ± 0.1 and 3.5 ± 0.1 mm, respectively) versus wild type (7.5 ± 0.1 mm). Correspondingly, the V389D and T103I MODY mutants had markedly reduced relative activity indexes (<0.1). T103I had an altered affinity for glucose (S(0.5), 24.9 ± 0.6 mm), whereas V389D also exhibited a reduced affinity for ATP and decreased catalysis rate (S(0.5), 78.6 ± 4.5 mm; ATP(K(m)), 1.5 ± 0.1 mm; K(cat), 10.3 ± 1.1s(-1)) compared with wild type (ATP(K(m)), 0.4 ± <0.1; K(cat), 62.9 ± 1.2). Both Thr-103 mutants showed reduced inhibition by the endogenous hepatic inhibitor glucokinase regulatory protein. Molecular modeling demonstrated that Thr-103 maps to the allosteric activator site, whereas Val-389 is located remotely to this position and all other previously reported activating mutations, highlighting α-helix 11 as a novel region regulating GCK activity. Our data suggest that pharmacological manipulation of GCK activity at locations distal from the allosteric activator site is possible.
authors: Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford OX3 7LJ, United Kingdom.
authors: Nicola L
authors: NL
authors: Beer
authors: Martijn
authors: M
authors: van de Bunt
authors: Kevin
authors: K
authors: Colclough
authors: Christine
authors: C
authors: Lukacs
authors: Paul
authors: P
authors: Arundel
authors: Constance L
authors: CL
authors: Chik
authors: Joseph
authors: J
authors: Grimsby
authors: Sian
authors: S
authors: Ellard
authors: Anna L
authors: AL
authors: Gloyn
mesh_terms: D000494:Allosteric Regulation / Q000235:genetics; D019943:Amino Acid Substitution; D002675:Child, Preschool; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology / Q000235:genetics; D005941:Glucokinase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006946:Hyperinsulinism / Q000201:enzymology / Q000235:genetics; D007003:Hypoglycemia / Q000201:enzymology / Q000235:genetics; D007231:Infant, Newborn; D008099:Liver / Q000201:enzymology*; D008297:Male; D020125:Mutation, Missense; D017433:Protein Structure, Secondary / Q000235:genetics
chemical_list: D005941:Glucokinase