Objective: To explore the molecular mechanisms of glucokinase (GCK) E339K mutation resulting in maturity-onset diabetes of the young-2 (MODY2).
Methods: Fasting plasma glucose (FPG), oral glucose tolerance test (OGTT) overload 2 h glucose (2hPG), glycosylated hemoglobin A1c (HbA1c) and fasting insulin (FIns) level were measured, respectively. Mutant glutathione S-transferase (GST)-GCK-cDNA was constructed with site-directed mutagenesis. Wild type and mutant GCK protein expressed in E. Coli were purified with affinity chromatography. Enzymatic kinetics and thermal stability were tested with enzyme-coupled analysis.
Results: Compared with non-mutants, mutants had higher FPG [(6.92±0.95) mmol/L vs (4.70±0.35) mmol/L, P<0.001] 2hPG [(9.00±1.49) mmol/L vs (5.51±0.86) mmol/L, P<0.001], HbA1c [(6.46±0.69)% vs (4.83±0.30)%, P<0.01], and lower FIns level [(6.15±1.97) mIU/L vs (10.79±4.93) mIU/L, P<0.01], HOMA-ß (34.16±3.62 vs 172.53±76.58, P<0.001). This mutation induced lower protein yield [(12.7±1.72) mg/L vs (16.2±2.65) mg/L, P<0.01], lower appetency for glucose [S0.5: (13.96±1.89) mmol/L vs (5.92±0.99) mmol/L, P<0.001] and ATP [Km:(3.27±1.14) mmol/L vs (0.30±0.09) mmol/L, P<0.001], lower catalytic ability [Kcat: (1.62±0.35)/s vs (25.18±2.10)/s, P<0.001]. It also showed protein thermal instability.
Conclusion: Glucokinase gene E339K mutation promotes the development of MODY2 by affecting protein yield and protein stability as well as the enzymatic kinetics of GCK.