Steve Ealick's Research Group
Human Adenosine Kinase
PDB file: 1BX4
Adenosine kinase (AK), the most abundant nucleoside kinase in mammals, catalyzes the phosphorylation of ribofurnosyl-containing nucleoside analogues at the 5′-hydroxyl using ATP or GTP as the phosphate donor. We determined the structure of human adenosine kinase by X-ray crystallography using MAD phasing techniques and refined the structure to 1.5 Å resolution. The overall structure is similar to the recently reported structure of ribokinase from Escherichia coli (Sigrell et al. (1998) Structure 6, 183-193).
The enzyme is a monomer whose structure consists of one large α/β domain with nine β-strands, eight α-helices, and one small α/β-domain with five β-strands and two α-helices. Two molecules of adenosine are present in the AK crystal structure.
The active site is formed along the edge of the β-sheet in the large domain while the small domain acts as a lid to cover the upper face of the active site. One adenosine molecule is located in a site that matches the ribose site in ribokinase and probably represents the binding site for the nucleoside undergoing phosphorylation. As shown in this schematic diagram, a Mg2+ ion binding site is observed in a trough between the two adenosine sites. The structure of the active site is consistent with the observed substrate specificity. The active-site model suggests that Asp300 is an important catalytic residue involved in the deprotonation of the 5′-hydroxyl during the phosphate transfer. The second adenosine site probably represents the ATP/ADP binding site. The bisubstrate analogue, P1,P4-(didenosine 5′)-tetraphosphate (Ap4A) is a potent inhibitor of adenosine kinase, and was used to help delineate the pathway for phosphoryl transfer.
Mathews, II, Erion, MD, and Ealick SE. Structure of Human Adenosine Kinase at 1.5 Å Resolution. Biochemistry 37:15607-15620 (1998).