Crystal Structures of T. b. rhodesiense Adenosine Kinase Complexed with Inhibitor and Activator: Implications for Catalysis and Hyperactivation

Background: The essential purine salvage pathway of Trypanosoma
brucei bears interesting catalytic enzymes for chemotherapeutic
intervention of Human African Trypanosomiasis. Unlike mammalian
cells, trypanosomes lack de novo purine synthesis and completely
rely on salvage from their hosts. One of the key enzymes is
adenosine kinase which catalyzes the phosphorylation of ingested
adenosine to form adenosine monophosphate (AMP) utilizing adenosine
triphosphate (ATP) as the preferred phosphoryl donor. Methods and
Findings: Here, we present the first structures of Trypanosoma
brucei rhodesiense adenosine kinase (TbrAK): lthe structure of
TbrAK in complex with the bisubstrate inhibitor
P(1),P(5)-di(adenosine-5')-pentaphosphate (AP5A) at 1.55 angstrom,
and TbrAK complexed with the recently discovered activator
4-5-(4-phenoxyphenyl)-2H-pyrazol-3-yl]morpholine (compound 1) at
2.8 angstrom resolution. Conclusions: The structural details and
their comparison give new insights into substrate and activator
binding to TbrAK at the molecular level. Further structure-activity
relationship analyses of a series of derivatives of compound 1
support the observed binding mode of the activator and provide a
possible mechanism of action with respect to their activating
effect towards TbrAK.