MTH1 hydrolyzes oxidized nucleotide triphosphates, thereby preventing them from 
being incorporated into DNA. We here present the structures of human MTH1 (1.9Å) 
and its complex with the product 8-oxo-dGMP (1.8Å). Unexpectedly MTH1 binds the 
nucleotide in the anti conformation with no direct interaction between the 8-oxo 
group and the protein. We suggest that the specificity depends on the 
stabilization of an enol tautomer of the 8-oxo form of dGTP. The binding of the 
product induces no major structural changes. The structures reveal the mode of 
nucleotide binding in MTH1 and provide the structural basis for inhibitor 
design.