InterPro domain: IPR000086

The Nudix superfamily is widespread among eukaryotes, bacteria, archaea and viruses and consists mainly of pyrophosphohydrolases that act upon substrates of general structure NUcleoside DIphosphate linked to another moiety, X (NDP-X) to yield NMP plus P-X. Such substrates include (d)NTPs (both canonical and oxidised derivatives), nucleotide sugars and alcohols, dinucleoside polyphosphates (NpnN), dinucleotide coenzymes and capped RNAs. However, phosphohydrolase activity, including activity towards NDPs themselves, and non-nucleotide substrates such as diphosphoinositol polyphosphates (DIPs), 5-phosphoribosyl 1-pyrophosphate (PRPP), thiamine pyrophosphate (TPP) and dihydroneopterin triphosphate (DHNTP) have also been described. Some superfamily members, such as Escherichia coli mutT, have the ability to degrade potentially mutagenic, oxidised nucleotides while others control the levels of metabolic intermediates and signalling compounds. In procaryotes and simple eucaryotes, the number of Nudix genes varies from 0 to over 30, reflecting the metabolic complexity and adaptability of the organism. Nudix hydrolases are typically small proteins, larger ones having additional domains with interactive or other catalytic functions [ 1 ].

The Nudix domain formed by two beta-sheets packed between alpha-helices [ 2 , 3 ]. It can accomodate sequences of different lengths in the connecting loops and in the amtiparallel beta-sheet. Catalysis depends on the conserved 23-amino acid Nudix motif (Nudix box), G-x(5)-E-x(5)-[UA]-x-R-E-x(2)-E-E-x-G-U, where U is an aliphatic, hydrophobic residue. This sequence is located in a loop-helix-loop structural motif and the Glu residues in the core of the motif, R-E-x(2)-E-E, play an important role in binding essential divalent cations [ 4 ]. The substrate specificity is determined by other residues outside the Nudix box. For example, CoA pyrophosphatases share the NuCoA motif L-L-T-x-R-[SA]-x(3)-R-x(3)-G-x(3)-F-P-G-G that is located N-terminal of the Nudix box and is involved in CoA recognition [ 4 ].

1. The Nudix hydrolase superfamily. Cell. Mol. Life Sci. 63, 123-43
2. The MutT proteins or "Nudix" hydrolases, a family of versatile, widely distributed, "housecleaning" enzymes. J. Biol. Chem. 271, 25059-62
3. Structure and function of the E. coli dihydroneopterin triphosphate pyrophosphatase: a Nudix enzyme involved in folate biosynthesis. Structure 15, 1014-22
4. Biochemical and physiological characterization of Arabidopsis thaliana AtCoAse: a Nudix CoA hydrolyzing protein that improves plant development. Physiol Plant 135, 365-78