LAUSR

The accurate replication, transcription, and maintenance of genetic material requires housekeeping enzymes that prevent the spontaneous mutagenesis of DNA by catalyzing the removal of oxidized deoxynucleoside triphosphates (dNTPs). These include the Nudix hydrolase superfamily member human Mut1 homolog (MTH1, human NUDT1), which catalyzes the removal of a variety of oxidized dNTPs such as 8-oxo-dGTP, 2-oxo-dATP, and 8-oxo-dATP (1, 2). The Nudix hydrolases are divalent cation (Mg 2 + /Mn 2 + ) dependent enzymes that have protective, regulatory, and signaling func-tions across all domains of life and share a Nudix box motif GX 5 EX 7 REUXEEXGU (U is a bulky hydrophobic residue and X is any amino acid other than the essential glutamates) that forms the active site (1, 2). In addition to its role in DNA maintenance, MTH1 is up-regulated in many tumors and is a chemothera-peutic target. Thus, the architecture and catalytic mechanism of MTH1 have been of considerable interest. The most exten-sively characterized Nudix enzyme is Escherichia coli pyrophos-phohydrolase MutT, a homolog of MTH1 that ef fi ciently catalyzes the excision of an oxidatively damaged 8-oxo-dGTP to sanitize the nucleotide pool and avoid misincorporation of 8-oxo-G opposite dA during DNA replication (1). The reaction occurs via a nucleophilic attack at the β -phosphorus to convert 8-oxo-dGTP to a nucleotide monophosphate (NMP) and inor-ganic pyrophosphate. Kinetic and static structural studies of MutT show that the hydrolytic reaction may proceed via a two-metal-ion mechanism (1, 3 – 7).