Probing the substrate recognition mechanism of the human MTH1 protein by nucleotide analogs

To examine the substrate recognition mechanism of the human MTH1 protein, which hydrolyzes 2-hydroxy-dATP, 8-hydroxy-dATP, and 8-hydroxy-dGTP, ten nucleotide analogs (8-bromo-dATP, 8-bromo-dGTP, deoxyisoinosine triphosphate, 8-hydroxy-dITP, 2-aminopurine-deoxyriboside triphosphate, 2-amino-dATP, deoxyxanthosine triphosphate, deoxyoxanosine triphosphate, dITP, and dUTP) were incubated with the MTH1 protein. Of these, the former five nucleotides were hydrolyzed with various efficiencies. The fact that the syn-oriented brominated nucleotides were hydrolyzed suggests that the MTH1 protein binds to deoxynucleotides adopting the syn-conformation. However, 8-hydroxy-dITP, which lacks the 2-amino group of 8-hydroxy-dGTP, was degraded with tenfold less efficiency as compared with 8-hydroxy-dGTP. In addition, deoxyisoinosine triphosphate, lacking the 6-amino group of 2-hydroxy-dATP, was hydrolyzed as efficiently as 8-hydroxy-dGTP, but less efficiently than 2-hydroxy-dATP. These results clarify the effects of the anti/syn conformation and the functional groups on the 2 and 6 positions of the purine ring on the recognition by the human MTH1 protein.