Order–Disorder Transitions Govern Kinetic Cooperativity and Allostery of Monomeric Human Glucokinase

Abstract

Author SummaryGlucokinase is a key metabolic enzyme that functions as the body's principal glucose sensor. Glucokinase regulates the rate at which insulin is secreted by the pancreas by using a unique but poorly understood cooperative kinetic response to increasing glucose concentrations. The physiological importance of this enzyme is underlined by the fact that mutations in the glucokinase gene lead to maturity-onset diabetes of the young type II (MODY II), permanent neonatal diabetes mellitus (PNDM), and hypoglycemic hyperinsulinemia of infancy (HI). In this study, we use cutting-edge high-resolution nuclear magnetic resonance methods to understand how the kinetic properties of glucokinase contribute to glucose homeostasis. We also seek to understand how a class of recently discovered small-molecule drugs, which hold promise as therapeutics for type 2 diabetes, function to enhance glucokinase activity. Our results suggest that glucokinase samples a range of conformational states in the absence of glucose. However, in the presence of glucose or a small-molecule activator, the enzyme population shifts towards a more narrow, well-structured ensemble of states. Our findings provide a new model for glucokinase cooperative kinetics, which relies on a slow order–disorder transition in response to glucose concentrations. These results also reveal a universal mechanism of glucokinase activation, which may inform the development of new antidiabetic agents.