The novel GCK variant p.Val455Leu associated with hyperinsulinism is susceptible to allosteric activation and is conducive to weight gain and the development of diabetes

Abstract

Aims/hypothesis The mammalian enzyme glucokinase (GK), expressed predominantly in liver and pancreas, plays an essential role in carbohydrate metabolism. Monogenic GK disorders emphasise the role of GK in determining the blood glucose set point. Methods A family with congenital hyperinsulinism (CHI) was examined for GCK gene variants by Sanger sequencing. A combined approach, involving kinetic analysis (also using GK activators and inhibitors), intracellular translocation assays, insulin secretion measurements and structural modelling, was used to investigate the novel variant compared with known variants. Results We report on the novel gain-of-function GCK variant p.Val455Leu (V455L), inherited as an autosomal dominant trait in a German family with CHI and concomitant obesity (fasting blood glucose 2.1 mmol/l, BMI 45.0 kg/m2, HOMA-IR 1.5 in an adult female family member); one male family member developed type 2 diabetes until age 35 years (with fasting glucose 2.8–3.7 mmol/l, BMI 38.9 kg/m2, HOMA-IR 4.6). Kinetic characterisation of the V455L variant revealed a significant increase in glucose affinity (glucose concentration at which reaction rate is half its maximum rate [S0.5]: mutant 2.4 ± 0.3 mmol/l vs wild-type 7.6 ± 1.0 mmol/l), accompanied by a distinct additive susceptibility to both the endogenous activator fructose 2,6-bisphosphatase and the synthetic allosteric activator RO-28-1675. The effect of RO-28-1675 was more pronounced when compared with the previously known GK variants V455M and V455E. Binding to the inhibitor glucokinase regulatory protein was unimpaired for V455L and V455E but was reduced for V455M, whereas mannoheptulose inhibited all GK variants and the wild-type enzyme. Structural analyses suggested a role for residue 455 in rearrangements between the inactive and active conformations of GK and also in allosteric activation. Comparison with V455M and V455E and an overview of activating GK variants provided a context for the novel sequence aberration in terms of altered GK enzyme characteristics caused by single amino acid changes. Conclusion/interpretation We provide new knowledge on the structure–function relationship of GK, with special emphasis on enzyme activation, potentially yielding fresh strategic insights into breaking the vicious circle of fluctuating blood glucose levels and the attendant risk of long-lasting metabolic changes in both CHI and type 2 diabetes. Graphical abstract

Stem Cell Based Models in Congenital Hyperinsulinism – Perspective on Practicalities and Possibilities

“…Huopio and colleagues established that, in addition to causing hypoglycemia in infancy (65), dominant K ATP HI mutations predispose to T2DM later in life (66), providing clinical evidence for the detrimental consequences of long-term beta cell hyperactivity. Similar T2DM predisposing effect has been discovered in carriers of activating glucokinase mutations (GCK-HI) (67,68).…”

Rare variant association analysis in 51,256 type 2 diabetes cases and 370,487 controls informs the spectrum of pathogenicity of monogenic diabetes genes

“…For example, the GCK p.Val455Glu is located in the same position as a GCK activating mutation (p.Val455M) causing familial hyperinsulinism 48 . It has been reported previously in individuals with impaired glucose tolerance or fasting hyperglycemia 49 , and two independent studies have demonstrated that the variant is kinetically inactivating consistent with loss of function 50,51 . Identifying carriers of GCK inactivating mutations is important, not only because these carriers may not need treatment, but also because of possible complications in pregnancy if the risk allele is not inherited by the fetus of carrier mothers, resulting in hyperglycemia and excessive growth in the fetus 52 .…”

Whole-exome sequencing reveals novel variants of monogenic diabetes in Tunisia: impact on diagnosis and healthcare management

“…Given the role of glucokinase in the development of maturity-onset diabetes of the young GCK_MODY or MODY_2 (MIM # 125851), mutations in GCKR have been considered to be associated with MODY_2 (The et al, 2001). A recent study showed an association between GCKR mutations and high FPG levels, triglyceride measurement, and obesity (Langer et al, 2021). Previous studies reported that a common genetic variant in GCKR (rs1260326) was associated with varying metabolic characteristics (Goodman et al, 2020;Zahedi et al, 2021).…”