nucleotide-binding domain (NBD) of type IV hexokinase from metazoan hexokinase (HK) domain family
Hexokinase (EC 2.7.1.1) possesses the ability to transfer an inorganic phosphate group from ATP to a substrate. It catalyzes the ATP-dependent phosphorylation of aldo- and keto-hexose sugars to the hexose-6-phosphate (H6P). It can catalyze this reaction on glucose, fructose, sorbitol and glucosamine, and as such is the first step in a number of metabolic pathways. Hexokinase contains two structurally similar domains. Some members of the family have two copies of each of these domains. For example, members from vertebrates contain four hexokinase isozymes, designated I to IV, where types I to III contain a duplication of the two-domain yeast-type hexokinases. Both the N- and C-terminal halves bind hexose and H6P. In types I and III only the C-terminal half supports catalysis. Their N-terminal half is the regulatory region. In type II, both halves support catalysis. Type IV hexokinase is similar to the yeast enzyme in containing only the two domains and is sometimes incorrectly referred to as glucokinase. Whereas types I to III can phosphorylate a variety of hexose sugars and are inhibited by glucose-6-phosphate (G6P), type IV is specific for glucose and shows no G6P inhibition. The model corresponds to type IV hexokinase. It is found in the liver and pancreatic beta-cells, where it is controlled by insulin (activation) and glucagon (inhibition). In pancreatic beta-cells, type IV enzyme acts as a glucose sensor to modify insulin secretion. Mutations in type IV hexokinase have been associated with diabetes mellitus.
Feature 1: catalytic site [active site], 3 residue positions
Conserved feature residue pattern:D T D
Evidence:
Comment:It has been proposed that the first Asp coordinates and positions the MgATP, and (in concert with the Mg2+) stabilizes the ADP leaving group during the phospho transfer. The second Asp would act as a general base during catalysis, assisting the removal of a proton from the attacking hydroxyl group. The Thr could stabilize the transition state.
Jiyao W et al.(2023). "The conserved domain database in 2023.",