Functional Characterization of a Novel Heterozygous Mutation in the Glucokinase Gene That Causes MODY2 in Chinese Pedigrees.

Glucokinase (GCK) plays a central role in glucose regulation. The heterozygous mutations of GCK can cause a monogenic form of diabetes, maturity-onset diabetes of the young (MODY) directly. In our study, we aimed to explore the mechanism of the novel mutation GCK p.Ala259Thr leading to glucokinase deficiency and hyperglycemia. Thirty early-onset diabetes pedigrees were referred to whole exome sequencing for novel mutations identification. Purified wild-type and mutant GCK proteins were obtained from E.coli systems and then subjected to the kinetic and thermal stability analysis to test the effects on GCK activity. One novel missense mutation GCK p.Ala259Thr was identified and co-segregated with diabetes in a Chinese MODY2 pedigree. The kinetic analysis showed that this mutation result in a decreased affinity and catalytic capability for glucose. The thermal stability analysis also indicated that the mutant protein presented dramatically decreased activity at the same temperature. Our study firstly identified a novel MODY2 mutation p.Ala259Thr in Chinese diabetes pedigrees. The kinetic and thermal stability analysis confirmed that this mutation caused hyperglycemia through severely damaging the enzyme activities and protein stability.

Jiang F ，Yan J ，Zhang R ，Ma X ，Bao Y ，Gu Y ，Hu C ... -  《Frontiers in Endocrinology》

Insights into pathogenesis of five novel GCK mutations identified in Chinese MODY patients.

Heterozygous inactivating mutations in GCK are associated with defects in pancreatic insulin secretion and/or hepatic glycogen synthesis leading to mild chronic hyperglycaemia of maturity onset diabetes of young type 2 (MODY2). However, the effect of naturally occurring GCK mutations on the pathogenesis for MODY2 hyperglycaemia remains largely unclear, especially in the Asian population. The aim of this study is to explore the potential pathogenicity of novel GCK mutations related to MODY2. Genetic screening for GCK mutations from 96 classical MODY families was performed, and structure-function characterization and clinical profile of identified GCK mutations were conducted. Five novel (F195S, I211T, V222D, E236G and K458R) and five known (T49N, I159V, R186X, A188T and M381T) mutations were identified and co-segregated with hyperglycaemia in their pedigrees. R186X generates non-functional truncated form and V222D and E236G fully inactivate glucokinase due to severe structure disruptions. The other seven GCK mutations exhibited marked reductions in catalytic efficiency and thermo-stability; notably, the interaction with GKRP was significantly enhanced in I211T, I159V, T49N and K458R, reduced in F195S and M381T, and completely lost with A188T. 31% (17/55) of MODY2 patients showed signs of insulin resistance. Conventional hypoglycaemia treatment did not improve the HbA1C in MODY2 patients when insulin resistance is not present. Five novel GCK mutations have been identified in Chinese MODY. The defects in enzymatic activity and protein stability, together with alteration of GKRP binding on GCK mutants may synergistically contribute to the development of MODY2 hyperglycaemia. No treatment should be prescribed to MODY2 patients when insulin resistance is not present.

Liu L ，Liu Y ，Ge X ，Liu X ，Chen C ，Wang Y ，Li M ，Yin J ，Zhang J ，Chen Y ，Zhang R ，Jiang Y ，Zhao W ，Yang D ，Zheng T ，Lu M ，Zhuang L ，Jiang M ... -  《-》

Insight into the biochemical characteristics of a novel glucokinase gene mutation.

Glucokinase (GCK) acts as a glucose sensor and regulates β-cell insulin secretion. The heterozygous mutations in the gene encoding GCK cause a reduction of the enzyme activity, which results in a monogenic form of diabetes, maturity-onset diabetes of the young. In the present study, we identified and functionally characterized a novel missense mutation in the GCK gene, which results in a protein mutation Glu(339)→Lys (E339K), from a Chinese family with hyperglycemia. The same GCK mutation that co-segregated with diabetes phenotype was identified in five members of this family but was not found in 200 healthy control individuals. We expressed and affinity-purified the GCK proteins from bacterial expression system that carries mutation (E339K) and fused to glutathione S-transferase. The expressed GCK protein was subjected to the measurement of its biochemical effects of the missense mutation on GCK activity. Our results showed that the mutation reduced the GCK protein yield. The enzymatic kinetics and the thermal stability analysis on the recombinant GCK proteins revealed that the mutation inactivates enzyme kinetics and severely impaired the GCK protein stability.

Shen Y ，Cai M ，Liang H ，Wang H ，Weng J ... -  《-》

GCK mutations in Chinese MODY2 patients: a family pedigree report and review of Chinese literature.

Ping Xiao Y ，Hua Xu X ，Lan Fang Y ，Jiang L ，Chen C ，Liang L ，Lin Wang C ... -  《-》

Effects of novel maturity-onset diabetes of the young (MODY)-associated mutations on glucokinase activity and protein stability.

Galán M ，Vincent O ，Roncero I ，Azriel S ，Boix-Pallares P ，Delgado-Alvarez E ，Díaz-Cadórniga F ，Blázquez E ，Navas MA ... -  《-》