The Nudix hydrolase CDP-chase, a CDP-choline pyrophosphatase, is an asymmetric dimer with two distinct enzymatic activities.

A Nudix enzyme from Bacillus cereus (NCBI RefSeq accession no. NP_831800) catalyzes the hydrolysis of CDP-choline to produce CMP and phosphocholine. Here, we show that in addition, the enzyme has a 3'→5' RNA exonuclease activity. The structure of the free enzyme, determined to a 1.8-Šresolution, shows that the enzyme is an asymmetric dimer. Each monomer consists of two domains, an N-terminal helical domain and a C-terminal Nudix domain. The N-terminal domain is placed relative to the C-terminal domain such as to result in an overall asymmetric arrangement with two distinct catalytic sites: one with an "enclosed" Nudix pyrophosphatase site and the other with a more open, less-defined cavity. Residues that may be important for determining the asymmetry are conserved among a group of uncharacterized Nudix enzymes from Gram-positive bacteria. Our data support a model where CDP-choline hydrolysis is catalyzed by the enclosed Nudix site and RNA exonuclease activity is catalyzed by the open site. CDP-Chase is the first identified member of a novel Nudix family in which structural asymmetry has a profound effect on the recognition of substrates.

Structural studies of the Nudix GDP-mannose hydrolase from E. coli reveals a new motif for mannose recognition.

The Nudix hydrolase superfamily, characterized by the presence of the signature sequence GX(5)EX(7)REUXEEXGU (where U is I, L, or V), is a well-studied family in which relations have been established between primary sequence and substrate specificity for many members. For example, enzymes that hydrolyze the diphosphate linkage of ADP-ribose are characterized by having a proline 15 amino acids C-terminal of the Nudix signature sequence. GDPMK is a Nudix enzyme that conserves this characteristic proline but uses GDP-mannose as the preferred substrate. By investigating the structure of the GDPMK alone, bound to magnesium, and bound to substrate, the structural basis for this divergent substrate specificity and a new rule was identified by which ADP-ribose pyrophosphatases can be distinguished from purine-DP-mannose pyrophosphatases from primary sequence alone. Kinetic and mutagenesis studies showed that GDPMK hydrolysis does not rely on a single glutamate as the catalytic base. Instead, catalysis is dependent on residues that coordinate the magnesium ions and residues that position the substrate properly for catalysis. GDPMK was thought to play a role in biofilm formation because of its upregulation in response to RcsC signaling; however, GDPMK knockout strains show no defect in their capacity of forming biofilms.

Structure and function of the E. coli dihydroneopterin triphosphate pyrophosphatase: a Nudix enzyme involved in folate biosynthesis.

Nudix hydrolases are a superfamily of pyrophosphatases, most of which are involved in clearing the cell of potentially deleterious metabolites and in preventing the accumulation of metabolic intermediates. We determined that the product of the orf17 gene of Escherichia coli, a Nudix NTP hydrolase, catalyzes the hydrolytic release of pyrophosphate from dihydroneopterin triphosphate, the committed step of folate synthesis in bacteria. That this dihydroneopterin hydrolase (DHNTPase) is indeed a key enzyme in the folate pathway was confirmed in vivo: knockout of this gene in E. coli leads to a marked reduction in folate synthesis that is completely restored by a plasmid carrying the gene. We also determined the crystal structure of this enzyme using data to 1.8 A resolution and studied the kinetics of the reaction. These results provide insight into the structural bases for catalysis and substrate specificity in this enzyme and allow the definition of the dihydroneopterin triphosphate pyrophosphatase family of Nudix enzymes.

Structural studies of the Nudix hydrolase DR1025 from Deinococcus radiodurans and its ligand complexes.

We have determined the crystal structure, at 1.4A, of the Nudix hydrolase DR1025 from the extremely radiation resistant bacterium Deinococcus radiodurans. The protein forms an intertwined homodimer by exchanging N-terminal segments between chains. We have identified additional conserved elements of the Nudix fold, including the metal-binding motif, a kinked beta-strand characterized by a proline two positions upstream of the Nudix consensus sequence, and participation of the N-terminal extension in the formation of the substrate-binding pocket. Crystal structures were also solved of DR1025 crystallized in the presence of magnesium and either a GTP analog or Ap(4)A (both at 1.6A resolution). In the Ap(4)A co-crystal, the electron density indicated that the product of asymmetric hydrolysis, ATP, was bound to the enzyme. The GTP analog bound structure showed that GTP was bound almost identically as ATP. Neither nucleoside triphosphate was further cleaved.

A UDP-X diphosphatase from Streptococcus pneumoniae hydrolyzes precursors of peptidoglycan biosynthesis.

The gene for a Nudix enzyme (SP_1669) was found to code for a UDP-X diphosphatase. The SP_1669 gene is localized among genes encoding proteins that participate in cell division in Streptococcus pneumoniae. One of these genes, MurF, encodes an enzyme that catalyzes the last step of the Mur pathway of peptidoglycan biosynthesis. Mur pathway substrates are all derived from UDP-glucosamine and all are potential Nudix substrates. We showed that UDP-X diphosphatase can hydrolyze the Mur pathway substrates UDP-N-acetylmuramic acid and UDP-N-acetylmuramoyl-L-alanine. The 1.39 Å resolution crystal structure of this enzyme shows that it folds as an asymmetric homodimer with two distinct active sites, each containing elements of the conserved Nudix box sequence. In addition to its Nudix catalytic activity, the enzyme has a 3'5' RNA exonuclease activity. We propose that the structural asymmetry in UDP-X diphosphatase facilitates the recognition of these two distinct classes of substrates, Nudix substrates and RNA. UDP-X diphosphatase is a prototype of a new family of Nudix enzymes with unique structural characteristics: two monomers, each consisting of an N-terminal helix bundle domain and a C-terminal Nudix domain, form an asymmetric dimer with two distinct active sites. These enzymes function to hydrolyze bacterial cell wall precursors and degrade RNA.

Three new Nudix hydrolases from Escherichia coli.

Three members of the Nudix (nucleoside diphosphate X) hydrolase superfamily have been cloned from Escherichia coli MG1655 and expressed. The proteins have been purified and identified as enzymes active on nucleoside diphosphate derivatives with the following specificities. Orf141 (yfaO) is a nucleoside triphosphatase preferring pyrimidine deoxynucleoside triphosphates. Orf153 (ymfB) is a nonspecific nucleoside tri- and diphosphatase and atypically releases inorganic orthophosphate from triphosphates instead of pyrophosphate. Orf191 (yffH) is a highly active GDP-mannose pyrophosphatase. All three enzymes require a divalent cation for activity and are optimally active at alkaline pH, characteristic of the Nudix hydrolase superfamily. The question of whether or not Orf1.9 (wcaH) is a bona fide member of the Nudix hydrolase superfamily is discussed.

The pnhA gene of Pasteurella multocida encodes a dinucleoside oligophosphate pyrophosphatase member of the Nudix hydrolase superfamily.

The pnhA gene of Pasteurella multocida encodes PnhA, which is a member of the Nudix hydrolase subfamily of dinucleoside oligophosphate pyrophosphatases. PnhA hydrolyzes diadenosine tetra-, penta-, and hexaphosphates with a preference for diadenosine pentaphosphate, from which it forms ATP and ADP. PnhA requires a divalent metal cation, Mg(2+) or Mn(2+), and prefers an alkaline pH of 8 for optimal activity. A P. multocida strain that lacked a functional pnhA gene, ACP13, was constructed to further characterize the function of PnhA. The cellular size of ACP13 was found to be 60% less than that of wild-type P. multocida, but the growth rate of ACP13 and its sensitivity to heat shock conditions were similar to those of the wild type, and the wild-type cell size was restored in the presence of a functional pnhA gene. Wild-type and ACP13 strains were tested for virulence by using the chicken embryo lethality model, and ACP13 was found to be up to 1,000-fold less virulent than the wild-type strain. This is the first study to use an animal model in assessing the virulence of a bacterial strain that lacked a dinucleoside oligophosphate pyrophosphatase and suggests that the pyrophosphatase PnhA, catalyzing the hydrolysis of diadenosine pentaphosphates, may also play a role in facilitating P. multocida pathogenicity in the host.

Legionella pneumophila NudA Is a Nudix hydrolase and virulence factor.

We studied the identity and function of the 528-bp gene immediately upstream of Legionella pneumophila F2310 ptsP (enzyme I(Ntr)). This gene, nudA, encoded for a Nudix hydrolase based on the inferred protein sequence. NudA had hydrolytic activity typical of other Nudix hydrolases, such as Escherichia coli YgdP, in that Ap(n)A's, in particular diadenosine pentaphosphate (Ap(5)A), were the preferred substrates. NudA hydrolyzed Ap(5)A to ATP plus ADP. Both ptsP and nudA were cotranscribed. Bacterial two-hybrid analysis showed no PtsP-NudA interactions. Gene nudA was present in 19 of 20 different L. pneumophila strains tested and in 5 of 10 different Legionella spp. other than L. pneumophila. An in-frame nudA mutation was made in L. pneumophila F2310 to determine the phenotype. The nudA mutant was an auxotroph that grew slowly in liquid and on solid media and had a smaller colony size than its parent. In addition, the mutant was more salt resistant than its parent and grew very poorly at 25 degrees C; all of these characteristics, as well as auxotrophy and slow-growth rate, were reversed by transcomplementation with nudA. The nudA mutant was outcompeted by about fourfold by the parent in competition studies in macrophages; transcomplementation almost completely restored this defect. Competition studies in guinea pigs with L. pneumophila pneumonia showed that the nudA mutant was outcompeted by its parent in both lung and spleen. NudA is of major importance for resisting stress in L. pneumophila and is a virulence factor.

Gene ytkD of Bacillus subtilis encodes an atypical nucleoside triphosphatase member of the Nudix hydrolase superfamily.

Gene ytkD of Bacillus subtilis, a member of the Nudix hydrolase superfamily, has been cloned and expressed in Escherichia coli. The purified protein has been characterized as a nucleoside triphosphatase active on all of the canonical ribo- and deoxyribonucleoside triphosphates. Whereas all other nucleoside triphosphatase members of the superfamily release inorganic pyrophosphate and the cognate nucleoside monophosphate, YtkD hydrolyses nucleoside triphosphates in a stepwise fashion through the diphosphate to the monophosphate, releasing two molecules of inorganic orthophosphate. Contrary to a previous report, our enzymological and genetic studies indicate that ytkD is not an orthologue of E. coli mutT.

The gene e.1 (nudE.1) of T4 bacteriophage designates a new member of the Nudix hydrolase superfamily active on flavin adenine dinucleotide, adenosine 5'-triphospho-5'-adenosine, and ADP-ribose.

The T4 bacteriophage gene e.1 was cloned into an expression vector and expressed in Escherichia coli, and the purified protein was identified as a Nudix hydrolase active on FAD, adenosine 5'-triphospho-5'-adenosine (Ap(3)A), and ADP-ribose. Typical of members of the Nudix hydrolases, the enzyme has an alkaline pH optimum (pH 8) and requires a divalent cation for activity that can be satisfied by Mg(2+) or Mn(2+). For all substrates, AMP is one of the products, and unlike most of the other enzymes active on Ap(3)A, the T4 enzyme hydrolyzes higher homologues including Ap(4-6)A. This is the first member of the Nudix hydrolase gene superfamily identified in bacterial viruses and the only one present in T4. Although the protein was predicted to be orthologous to E. coli MutT on the basis of a sequence homology search, the properties of the gene and of the purified protein do not support this notion because of the following. (a) The purified enzyme hydrolyzes substrates not acted upon by MutT, and it does not hydrolyze canonical MutT substrates. (b) The e.1 gene does not complement mutT1 in vivo. (c) The deletion of e.1 does not increase the spontaneous mutation frequency of T4 phage. The properties of the enzyme most closely resemble those of Orf186 of E. coli, the product of the nudE gene, and we therefore propose the mnemonic nudE.1 for the T4 phage orthologue.

The 26 Nudix hydrolases of Bacillus cereus, a close relative of Bacillus anthracis.

The genome of Bacillus cereus contains 26 Nudix hydrolase genes, second only to its closest relative, Bacillus anthracis which has 30. All 26 genes have been cloned, 25 have been expressed, and 21 produced soluble proteins suitable for analysis. Substrates for 16 of the enzymes were identified; these included ADP-ribose, diadenosine polyphosphates, sugar nucleotides, and deoxynucleoside triphosphates. One of the enzymes was a CDP-choline pyrophosphatase, the first Nudix hydrolase active on this substrate. Furthermore, as a result of this and previous work we have identified a new sub-family of the Nudix hydrolase superfamily recognizable by a specific amino acid motif outside of the Nudix box.

A new subfamily of the Nudix hydrolase superfamily active on 5-methyl-UTP (ribo-TTP) and UTP.

A new subfamily of the Nudix hydrolases, identified by conserved amino acids upstream and downstream of the Nudix box, has been characterized. The cloned, expressed, and purified orthologous enzymes have major activities on the non-canonical nucleoside triphosphate 5-methyl-UTP (ribo-TTP) and the canonical nucleotide UTP. In addition to their homologous signature sequences and their similar substrate specificities, the members of the subfamily are inhabitants of or are related to the bacterial rhizosphere. We propose the acronym and mnemonic, utp, for the gene designating this unique UTPase.

The Rickettsia prowazekii invasion gene homolog (invA) encodes a Nudix hydrolase active on adenosine (5')-pentaphospho-(5')-adenosine.

The genomic sequence of Rickettsia prowazekii, the obligate intracellular bacterium responsible for epidemic typhus, reveals an uncharacterized invasion gene homolog (invA). The deduced protein of 18,752 Da contains a Nudix signature, the specific motif found in the Nudix hydrolase family. To characterize the function of InvA, the gene was cloned and overexpressed in Escherichia coli. The expressed protein was purified to near homogeneity and subsequently tested for its enzymatic activity against a series of nucleoside diphosphate derivatives. The purified InvA exhibits hydrolytic activity toward dinucleoside oligophosphates (Np(n)N; n > or = 5), a group of cellular signaling molecules. At optimal pH 8.5, the enzyme actively degrades adenosine (5')-pentaphospho-(5')-adenosine into ATP and ADP with a K(m) of 0.1 mM and k(cat) of 1.9 s(-1). Guanosine (5')-pentaphospho-(5')-guanosine and adenosine-(5')-hexaphospho (5')-adenosine are also substrates. Similar to other Nudix hydrolases, InvA requires a divalent metal cation, Mg(2+) or Zn(2+), for optimal activity. These data suggest that the rickettsial invasion protein likely plays a role in controlling the concentration of stress-induced dinucleoside oligophosphates following bacterial invasion.