Conformational heterogeneity and intrinsic disorder in enzyme regulation: Glucokinase as a case study

Many human proteins are predicted to contain intrinsically disordered regions (IDRs), yet their occurrence in enzymes is notably rare. Human pancreatic glucokinase (GCK) is one of a small, but growing number of enzymes shown to possess an IDR. In this commentary, we summarize the results of recent biophysical studies that provide evidence for a functionally significant disorder-order transition within the IDR of GCK during the enzyme's catalytic cycle. High-resolution NMR studies indicate that kinetic cooperativity in GCK results from glucose-mediated millisecond conformational dynamics within the structurally heterogeneous and partially disordered small domain of this monomeric enzyme, whereby the precise timescale of these motions is critical for the manifestation of the kinetic cooperativity effect. GCK provides an excellent case study for understanding how structural and dynamic alterations within an IDR enable novel regulatory mechanisms. These studies also establish GCK as a model system for investigating the functional consequences of disorder and conformational heterogeneity in enzymatic systems in general.