From clinicogenetic studies of maturity-onset diabetes of the young to unraveling complex mechanisms of glucokinase regulation.
Glucokinase functions as a glucose sensor in pancreatic beta-cells and regulates hepatic glucose metabolism. A total of 83 probands were referred for a diagnostic screening of mutations in the glucokinase (GCK) gene. We found 11 different mutations (V62A, G72R, L146R, A208T, M210K, Y215X, S263P, E339G, R377C, S453L, and IVS5 + 1G>C) in 14 probands. Functional characterization of recombinant glutathionyl S-transferase-G72R glucokinase showed slightly increased activity, whereas S263P and G264S had near-normal activity. The other point mutations were inactivating. S263P showed marked thermal instability, whereas the stability of G72R and G264S differed only slightly from that of wild type. G72R and M210K did not respond to an allosteric glucokinase activator (GKA) or the hepatic glucokinase regulatory protein (GKRP). Mutation analysis of the role of glycine at position 72 by substituting E, F, K, M, S, or Q showed that G is unique since all these mutants had very low or no activity and were refractory to GKRP and GKA. Structural analysis provided plausible explanations for the drug resistance of G72R and M210K. Our study provides further evidence that protein instability in combination with loss of control by a putative endogenous activator and GKRP could be involved in the development of hyperglycemia in maturity-onset diabetes of the young, type 2. Furthermore, based on data obtained on G264S, we propose that other and still unknown mechanisms participate in the regulation of glucokinase.
Sagen
Jørn V
JV
Section for Pediatrics, Department of Clinical Medicine, University of Bergen, Bergen, Norway.
Odili
Stella
S
Bjørkhaug
Lise
L
Zelent
Dorothy
D
Buettger
Carol
C
Kwagh
Jae
J
Stanley
Charles
C
Dahl-Jørgensen
Knut
K
de Beaufort
Carine
C
Bell
Graeme I
GI
Han
Yi
Y
Grimsby
Joseph
J
Taub
Rebecca
R
Molven
Anders
A
Søvik
Oddmund
O
Njølstad
Pål R
PR
Matschinsky
Franz M
FM
D001665:Binding Sites; D001786:Blood Glucose / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D018360:Crystallography, X-Ray; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000473:pathology* / Q000517:prevention & control; D004795:Enzyme Stability / Q000187:drug effects; D005820:Genetic Testing; D005941:Glucokinase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D006943:Hyperglycemia / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism*; D009154:Mutation; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
D001786:Blood Glucose; D002352:Carrier Proteins; D050505:Mutant Proteins; C080906:glucokinase regulatory protein; D005941:Glucokinase; D005947:Glucose