Mammalian Nudt15 hydrolytic and binding activity on methylated guanosine mononucleotides

The Nudt15 enzyme of the NUDIX protein family is the subject of extensive study due to its action on thiopurine drugs used in the treatment of cancer and inflammatory diseases. In addition to thiopurines, Nudt15 is enzymatically active in vitro on several nucleotide substrates. It has also been suggested that this enzyme may play a role in 5'RNA turnover by hydrolyzing m⁷GDP, a product of mRNA decapping. However, no detailed studies on this substrate with Nudt15 are available. Here, we analyzed the enzymatic activity of Nudt15 with m⁷GDP, its triphosphate form m⁷GTP, and the trimethylated counterparts (m₃^2,2,7GDP and m₃^2,2,7GTP). Kinetic data revealed a moderate activity of Nudt15 toward these methylated mononucleotides compared to the dGTP substrate. However m⁷GDP and m₃^2,2,7GDP showed a distinct stabilization of Nudt15 upon ligand binding, in the same range as dGTP, and thus these two mononucleotides may be used as leading structures in the design of small molecule binders of Nudt15.